If you remember chatting with SmarterChild back on AOL Instant Messenger back in the day, you know how far ChatGPT and Google Bard have come. But how do these so-called chatbots work—and what’s the best way to use them to our advantage?

Chatbots are AI programs that respond to questions in a way that makes them seem like real people. That sounds pretty sophisticated, right? And these bots are. But when it comes down to it, they’re doing one thing really well: predicting one word after another.

So for ChatGPT or Google Bard, these chatbots are based on what are called large language models. That’s a kind of algorithm, and it gets trained on what are basically fill-in-the-blank, Mad-Libs style questions. The result is a program that can take your prompt and spit out an answer in phrases or sentences.

But it’s important to remember that while they might appear pretty human-like, they are most definitely not—they’re only imitating us. They don’t have common sense, and they aren’t taught the rules of grammar like you or I were in school. They are also only as good as what they were schooled on—and they can also produce a lot of nonsense.

To hear all about the nuts and bolts of how chatbots work, and the potential danger (legal or otherwise) in using them, you can subscribe to PopSci+ and read the full story by Charlotte Hu, in addition to listening to our new episode of Ask Us Anything. 

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IF A PATIENT KNEW their doctor was going to give them bad information during an upcoming appointment, they’d cancel immediately. Generative artificial intelligence models such as ChatGPT, however, frequently “hallucinate”—tech industry lingo for making stuff up. So why would anyone want to use an AI for medical purposes?

Here’s the optimistic scenario: AI tools get trained on vetted medical literature, as some models in development already do, but they also scan patient records and smartwatch data. Then, like other generative AI, they produce text, photos, and even video—personalized to each user and accurate enough to be helpful. The dystopian version: Governments, insurance companies, and entrepreneurs push flawed AI to cut costs, leaving patients desperate for medical care from human clinicians. 

Right now, it’s easy to imagine things going wrong, especially because AI has already been accused of spewing harmful advice online. In late spring, the National Eating Disorders Association temporarily disabled its chatbot after a user claimed it encouraged unhealthy diet habits. But people in the US can still download apps that use AI to evaluate symptoms. And some doctors are trying to use the technology, despite its underlying problems, to communicate more sympathetically with patients. 

ChatGPT and other large language models are “very confident, they’re very articulate, and they’re very often wrong,” says Mark Dredze, a professor of computer science at Johns Hopkins University. In short, AI has a long way to go before people can trust its medical tips. 

Still, Dredze is optimistic about the technology’s future. ChatGPT already gives advice that’s comparable to the recommendations physicians offer on Reddit forums, his newly published research has found. And future generative models might complement trips to the doctor, rather than replace consults completely, says Katie Link, a machine-learning engineer who specializes in healthcare for Hugging Face, an open-source AI platform. They could more thoroughly explain treatments and conditions after visits, for example, or help prevent misunderstandings due to language barriers.

In an even rosier outlook, Oishi Banerjee, an artificial intelligence and healthcare researcher at Harvard Medical School, envisions AI systems that would weave together multiple data sources. Using photos, patient records, information from wearable sensors, and more, they could “deliver good care anywhere to anyone,” she says. Weird rash on your arm? She imagines a dermatology app able to analyze a photo and comb through your recent diet, location data, and medical history to find the right treatment for you.

As medical AI develops, the industry must keep growing amounts of patient data secure. But regulators can lay the groundwork now for responsible progress, says Marzyeh Ghassemi, who leads a machine-learning lab at MIT. Many hospitals already sell anonymized patient data to tech companies such as Google; US agencies could require them to add that information to national data sets to improve medical AI models, Ghassemi suggests. Additionally, federal audits could review the accuracy of AI tools used by hospitals and medical groups and cut off valuable Medicare and Medicaid funding for substandard software. Doctors shouldn’t just be handed AI tools, either; they should receive extensive training on how to use them.

It’s easy to see how AI companies might tempt organizations and patients to sign up for services that can’t be trusted to produce accurate results. Lawmakers, healthcare providers, tech giants, and entrepreneurs need to move ahead with caution. Lives depend on it.

Read more about life in the age of AI: 

• Why AI could be a big problem for the 2024 presidential election
• The logic behind AI chatbots is surprisingly basic
• This AI program could teach you to be better at chess
• The first AI started a 70-year debate

Or check out all of our PopSci+ stories.

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Joel Cramer was at the pool with his kids when another dad, competing in a big splash contest, got up onto the diving board. He bounced up once, and when he landed on the board for the second time, his quadriceps muscle tore. “It rolled up his leg and balled up near the top of his thigh,” says Cramer, a professor of exercise physiology at the University of Nebraska. “[It was] like rolling up a window shade.”

That’s an extreme (and extremely rare) example of a muscle strain, a common injury that happens to high school soccer stars, recreational runners, and middle-aged racquetball players alike. “Strain” is the medical term for the condition, though it’s colloquially known as a pulled muscle. The term is a catch-all that covers everything from a small twinge to a full-on rupture.

What we call a “tear” and what we coin a “pull or strain” all boil down to the same type of injury: A rip to some part of the muscle. But some are worse than others. A mild or “grade one” strain—what many people call a “pulled muscle”—happens when you tear about 5 percent of the fibers in a particular muscle. This typically feels like an uncomfortable twinge that may force you off the court for a few weeks. A moderate sprain involves a higher percentage of fibers, and might sideline you for a month or more. A full rupture severs the muscle entirely, and usually requires surgery to repair.

[Related: Why do my muscles ache the day after a big workout?]

Okay, but how exactly do these tears occur? And why do some instances result in more muscle fiber damage than others? Cramer says three major factors contribute to this muscle busting. Muscles that cover two joints, like the hamstring which extends across the hip and knee joints, are at the highest risk. That’s because having both joints moving and stretching the muscle simultaneously adds tension, which can lead to strains.

Muscles are also more likely to strain while they are contracting. At this point, muscles are shortening and lengthening at the same time. During a dumbbell curl, for example, raising the weight up towards the shoulder compresses the bicep, and lowering it back down stretches it back out again. The muscle can create and sustain much more force during the lengthening portion of the activity, says Cramer, which makes it easier for it to strain.

Finally, muscles that have a higher proportion of fast-twitch to slow-twitch fibers strain more readily. Fast-twitch fibers contract quickly and generate more power, says Cramer. For that reason, they are the ones recruited for explosive tasks like sprinting. “It’s relatively uncommon for slow twitch [muscles] to strain,” he says. “They’re used to being active all the time.”

Technically, Cramer says, it’s possible to strain any of the skeletal muscles in your body. “For some, it’s not physiologically impossible, just very highly unlikely,” he says. “You’re probably not going to strain deep muscles with very specific functions.” The muscles in the finger, for example, are probably not going to cause much trouble, since they only have one task and don’t do much heavy lifting.

[Related: How to get muscle gains: A beginner’s guide to becoming buff]

Low flexibility and range of motion are major factors at risk for muscle strain, says Cramer. Despite the popular belief that larger muscles are tighter, Cramer says greater muscle mass is actually associated with greater give. “There’s evidence to suggest that weight training done with a good range of motion increases flexibility,” he says. And even though it may not seem like it when you’re struggling to touch your toes, Cramer says most people can teach their body to be springy enough to do the splits. So, to help keep your muscle fibers intact—pick up the weights and don’t skip your stretching routine, no matter how tedious it is.

How does a pulled muscle heal?

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In 1989, Chuck Berry and Carl Sagan partied it up at one of the biggest bashes of the summer—a celebration honoring the two Voyager spacecrafts, who were about to make a dramatic exit from our solar system. 

The twin probes, Voyager 1 and Voyager 2, launched back in 1977, with only a five-year mission to take a gander at Jupiter and Saturn’s rings and moons, hauling the Golden Record containing messages and cultural snapshots from Earth (including Chuck Berry’s music). 

Obviously, the Voyager spacecrafts have persisted a lot longer than five years: 46 years, to be exact. They’re still careening through space at a distance between 12 and 14 billion miles from Earth. So how have they lasted four decades longer than expected? Much of it has to do with a bit of vintage hardware and a handful of software updates. You can find out more (and when the crafts’ expected death dates) by subscribing to PopSci+ and reading the full story by Tatyana Woodall, and by listening to our new episode of Ask Us Anything. 

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INSIDE THE Library of Congress in Washington, D.C., there’s a living time capsule. The massive storage facility, run by the Motion Picture, Broadcasting, and Recorded Sound Division, is filled with wax cylinders, record players, and other pieces of dated audiovisual equipment. Some might see it as a junkyard of outdated technology, but Stephanie Barb likes to call this place the “land of lost toys.” 

“We used to play records all the time,” says Barb, the deputy director of IT service operations at the Library of Congress. Now, owning a record player is almost a whimsy.  

When machines become obsolete, the data they hold can be lost as well. Software and hardware fade out of general use as newer products and services replace them. It’s one of the several roadblocks technicians and archivists like Barb continuously run into in their quest to store information for long-term safekeeping. Right now, experts say there is no one storage device that can save data forever. Options like magnetic tape, Blu-ray Disc, and even DNA may provide stable but relatively temporary storage banks in which data can live while better technologies are tested and brought to market. However, each of these choices has its own shortcomings, and no one method is perfect in terms of both capacity and durability, with new innovations always on the horizon. 

The Library of Congress, for example, has a digital footprint of 176,000 terabytes, with its website catalogs of books, photos, videos, and other mediums taking up 5,350 terabytes alone (the equivalent of nearly 2 billion three-minute-long MP3s). Right now, this mountain of data is growing at around 1,500 terabytes a year. Archivists are racing against time to elongate the life of important documents and media. 

“Part of the preservation process is keeping operating systems and hardware up to date,” says Natalie Buda Smith, director of digital strategy at the Library of Congress. 

Nothing lasts forever

Preserving files in older mediums, like LP records and gaming consoles that have been discontinued, takes a bit of DIY tinkering. At the library, archivists rebuild vintage media players to recover data and transfer it to a more modern form of storage. Sometimes, the team even develops specialized technologies. For example, a system called IRENE, which the library codesigned with the Lawrence Berkeley National Laboratory, reads the depths of the grooves in broken phonograph records to convert the music to a digital format. 

This is particularly important with the materials eligible for copyright, says Barb. Books can last forever if preserved properly, but items that are submitted for copyright on more corruptible materials, like DVDs, CDs, and DVRs, can degrade over time. “That puts us in a crunch to pull that data off those obsolete technologies and preserve it digitally, because we are going to lose what’s on there,” Barb explains. Since there’s a duplicate provided with every copyright submission, the Library of Congress typically adds it to the collections with the intention to update to a more modern method. 

Back up your work

When it comes to preserving data for the future, it’s important to keep the context in which the content exists. “Content says, ‘Here are the bits’; context says, ‘Here’s all the other stuff you need to understand those bits,’” notes Ethan Miller, director emeritus of the National Science Foundation’s Center for Research in Storage Systems. The extra context includes metadata, software, and hardware such as video game emulators. It’s the modern-day equivalent of a Rosetta Stone—a key that gives meaning to written languages and symbols of the past.

A lot of the data currently being collected is “born-digital content” rather than content that had to be digitized, Buda Smith says. Artifacts gathered from internet archiving are good examples. Even though the virtual-first information may ultimately end up on a physical medium like tape, it may live in a variety of other storage forms along the way. Saving multiple backups on different mediums is also good practice. 

Held together by tape

The library preserves the majority of its data on a decades-old medium that has so far stood the test of time: simple and affordable magnetic tape. The material is a Goldilocks medium prized for its density, data-writing speeds, and low cost. 

Even though tape storage has been around since the mid-1900s, it’s still constantly being improved upon to squeeze more and more bits of data onto each inch of tape. Companies like IBM are working to double capacity per cartridge (to a maximum of 45 terabytes) in newer generations while keeping the format relevant for the future. But tape is not foolproof. If the magnetic strip is damaged or overheated, the data can be wiped out. And while tape is faster to read from and write to than more novel mediums, the data it holds is not as easy to access or edit as information stored on flash drives or hard disk drives (HDDs). 

A driving force

The way you use data, and how often, will influence which storage mediums are the best fit. HDDs—the basis of cloud infrastructure—are a good starting solution for small companies with digital collections, says Shawn Brume, IBM’s storage strategist. Take movie studios, for example. 

“We are almost 25 years into [the filming of] the Star Wars prequels,” says Brume. “Disney has never moved the raw footage from filming those off of digital technology, and has stated that it will not.” That’s because keeping them on a hard drive makes cutting footage or inserting footage, whenever the filmmakers decide they want to make changes, much easier.

But HDD becomes more expensive with time and scale, Brume adds, making its use a pricey hassle with systems that continuously pump out large batches of data, like autonomous vehicles. The average driverless car system will generate upwards of 400 terabytes a year: If you have millions of cars all doing the same, then companies will easily get crushed by HDDs. Across the industry, the total cost to store a terabyte of data on HDD deep density storage (including infrastructure operations costs) ranges from approximately $0.70 to approximately $0.80 per month, according to Brume. For tape, it’s much less, at approximately $0.08 to $0.12 per month. So with this method, the information will eventually need to be migrated to tape for lower-cost, longer-term, and offline storage. “It’s a process of ingest, collate, coordinate, and copy out to tape,” Brume says. 

IBM advises companies on how to move their data from HDDs to long-term tape infrastructure if they will need to retrieve it in the future. But the drawback of tape, unlike hard drives, is that it is pretty hard to alter. You have to erase and rewrite everything even if you want to change just one detail. 

The race to make space

An often overlooked contender may soon pull ahead of tape and cloud storage in the eternal-storage race. Many experts agree that Blu-ray, or polycarbonate optical discs, shows immense promise, especially for preserving data for decades, and maybe centuries, in an untouched box. Named after the violet laser in the reader, this system has an edge over flash or hard drives, as the parts don’t wear out, Miller explains. 

It all comes down to basic mechanics. HDDs don’t read or write very well after being powered down for a spell. Similarly, flash drives have a limited lifetime. That’s because the electrons in the device’s transistors leak out with use, passing through barriers and altering the charge of the material over months and years. “That means you have to read the flash every so often and rewrite the data,” Miller says. 

That’s where Blu-ray can excel. According to Miller, the technology needed to scan the discs is relatively simple in its construction: It’s basically a motor that spins, a reader that goes in and out, and a low-power laser. Optical drives are even simpler than those used for magnetic tapes. A lower price point of $50 to $200 per drive also sweetens the deal.  

To Miller, the question of where to store data boils down to the question of what technologies will be available in 100 to 1,000 years to read it—whether from Blu-ray or more experimental forms of storage like glass and DNA.

“If you look at history, nothing has been the forever medium except for something that’s chiseled on the wall in a cave,” Brume says. But even that information corrodes. With every new invention for record-keeping—stone, paper, code—knowledge still had to be passed down and translated to the next place. “We’ve always had to manage data,” he adds. “There’s never been a forever instance of anything.”

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IN 1989, Albert Wood and Peter Dunn thought they had unlocked a critical chemical door to treating hypertension and recurring chest pain. The two British Pfizer scientists reportedly created a new drug, named sildenafil, that reacts with a specific protein in muscle cells to allow for increased blood flow to the heart. 

But a few years later, human clinical trials revealed the drug was only effective when given multiple times a day and had a poor reaction with other existing cardiac treatments. What’s more, the blood rush was going to unexpected places in the body in addition to the heart. In one study, a nurse observed that most of the male volunteers were lying on their stomachs in embarrassment. The reason? Erections. Wood and Dunn had inadvertently stumbled upon the medicine that became Viagra. The small blue pill treats millions of people each year with erectile dysfunction, and further research suggests it may prove helpful for nonsexual problems such as pulmonary hypertension and altitude sickness.

Sidenafil is one of many prescriptions that treat multiple unrelated illnesses. How a drug becomes a medicinal Swiss Army knife depends on its chemical makeup. Each dose contains compounds that lock onto specific receptors, but that could also have the ability to create or suppress other reactions in the body.

“When somebody takes a medicine, it doesn’t necessarily go to the exact organ they are trying to target,” says Evelyn Huang, an emergency medicine resident physician at Northwestern Memorial Hospital. “The drug circulates through the entire body, so if there are certain receptors found in different parts, it would also affect that organ.” With sidenafil, the drug enlarges blood vessels generally and happens to prep the penis for action specifically. 

Another pill with the potential to tackle multiple conditions is mifepristone. This medicine is approved by the US Food and Drug Administration for medically induced abortions up to 70 days after a person’s last menstrual cycle starts. It works by blocking the effects of progesterone, which is needed to prepare and sustain pregnancy. (An ongoing lawsuit in a US district court in Texas could restrict its availability in pharmacies, doctor’s offices, and more.) Completely tamping down the hormone could also help prevent pancreatic cancer and melanomas, some early research shows. Additionally, at high doses, mifepristone aids in managing a condition called Cushing’s syndrome—characterized by extremely high levels of cortisol—by plugging the receptor that stimulates the production of sex and stress hormones. 

Dosage also matters in producing different drug responses. For example, barbiturates are a type of sedative prescribed in different amounts for a range of conditions from anxiety to seizures. This class of medications enhances the activity of GABA, a neurotransmitter that can slow down brain activity. At smaller doses, barbiturates can make someone feel drowsy and relaxed. But at higher amounts, they can be used as an anesthetic for rapid loss of consciousness. 

Because of the many ways a drug can affect the body, Huang warns against off-label use—taking a prescription for a condition other than the one it’s designed for. In any case, she recommends going over proper dosing, side effects, and other safety precautions with your healthcare provider. With more clinical and real-world research, it’s possible that off-label medications will be approved to target new health issues, producing formulas that pack more than one punch. Sidenafil, with its exciting possibilities, is at the top of that list.

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How does an airplane stay in the air? Whether you’ve pondered the question while flying or not, it remains a fascinating, complex topic. Here’s a quick look at the physics involved with an airplane’s flight, as well as a glimpse at a misconception surrounding the subject, too. 

First, picture an aircraft—a commercial airliner, such as a Boeing or Airbus transport jet—cruising in steady flight through the sky. That flight involves a delicate balance of opposing forces. “Wings produce lift, and lift counters the weight of the aircraft,” says Holger Babinsky, a professor of aerodynamics at the University of Cambridge. 

“That lift [or upward] force has to be equal to, or greater than, the weight of the airplane—that’s what keeps it in the air,” says William Crossley, the head of the School of Aeronautics and Astronautics at Purdue University. 

Meanwhile, the aircraft’s engines are giving it the thrust it needs to counter the drag it experiences from the friction of the air around it. “As you’re flying forward, you have to have enough thrust to at least equal the drag—it can be higher than the drag if you’re accelerating; it can be lower than the drag if you’re slowing down—but in steady, level flight, the thrust equals drag,” Crossley notes.

[Related: How high do planes fly?]

“You can clearly feel the lift force,” Babinsky says. In this straightforward scenario, the air is hitting the bottom of your hand, being deflected downward, and in a Newtonian sense (see law three), your hand is being pushed upward. 

Follow the curve 

But a wing, of course, is not shaped like your hand, and there are additional factors to consider. Two key points to keep in mind with wings are that the front of a wing—the leading edge—is curved, and overall, they also take on a shape called an airfoil when you look at them in cross-section. 

[Related: How pilots land their planes in powerful crosswinds]

The curved leading edge of a wing is important because airflow tends to “follow a curved surface,” Babinsky says. He says he likes to demonstrate this concept by pointing a hair dryer at the rounded edge of a bucket. The airflow will attach to the bucket’s curved surface and make a turn, potentially even snuffing out a candle on the other side that’s blocked by the bucket. Here’s a charming old video that appears to demonstrate the same idea. “Once the flow attaches itself to the curved surface, it likes to stay attached—[although] it will not stay attached forever,” he notes.

With a wing—and picture it angled up somewhat, like your hand out the window of the car—what happens is that the air encounters the rounded leading edge. “On the upper surface, the air will attach itself, and bend round, and actually follow that incidence, that angle of attack, very nicely,” he says. 

Keep things low-pressure

Ultimately, what happens is that the air moving over the top of the wing attaches to the curved surface and turns, or flows downward somewhat: a low-pressure area forms, and the air also travels faster. Meanwhile, the air is hitting the underside of the wing, like the wind hits your hand as it sticks out the car window, creating a high-pressure area. Voila: the wing has a low-pressure area above it, and higher pressure below. “The difference between those two pressures gives us lift,” Babinsky says. 

This video depicts the general process well:

Babinsky notes that more work is being done by that lower pressure area above the wing than the higher pressure one below the wing. You can think of the wing as deflecting the air flow downwards on both the top and bottom. On the lower surface of the wing, the deflection of the flow “is actually smaller than the flow deflection on the upper surface,” he notes. “Most airfoils, a very, very crude rule of thumb would be that two-thirds of the lift is generated there [on the top surface], sometimes even more,” Babinksy says.

Can you bring it all together for me one last time?

Sure! Gloria Yamauchi, an aerospace engineer at NASA’s Ames Research Center, puts it this way. “So we have an airplane, flying through the air; the air approaches the wing; it is turned by the wing at the leading edge,” she says. (By “turned,” she means that it changes direction, like the way a car plowing down the road forces the air to change its direction to go around it.) “The velocity of the air changes as it goes over the wing’s surface, above and below.” 

“The velocity over the top of the wing is, in general, greater than the velocity below the wing,” she continues, “and that means the pressure above the wing is lower than the pressure below the wing, and that difference in pressure generates an upward lifting force.”

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

This story has been updated. It was originally published in July, 2022.

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THE DEVIL found his first advocate in the church. In 1587, Pope Sixtus V established the role of Advocatus Diaboli, a Vatican official whose job was to combat any biases the pontiff might hold when advancing a candidate for sainthood. The Advocatus Diaboli would present counterarguments and dissect the validity of miracles thought to have been performed by the person in question.

The role has evolved since its religious beginning into a less formal but more sinister one in our day-to-day lives. Now psychologists know that playing devil’s advocate in a public meeting or Twitter thread can prove unnecessary and, in some cases, harmful.

From the historical church to modern boardrooms, the devil’s advocate was intended to be a crusader against groupthink, a phenomenon that can hinder proper decision making, explains Jeremy Jamieson, a psychology professor at the University of Rochester. Typically—say, during a business meeting on a new marketing campaign—the person playing the role is assigned to push back on the dominant ideation. The goal is to stop the group from reaching a decision without considering unintended consequences.

But when the conflict is fabricated, it may not be helpful. The work of Charlan Nemeth, a psychology professor at the University of California, Berkeley, indicates that the devil’s advocate isn’t as persuasive as a true dissident who believes what they’re putting forth.

The role can also have adverse psychological effects on the antagonist and those being antagonized.

In a 2014 study in the Journal of Experimental Social Psychology, Jamieson and his colleagues found that those assigned to deliver negative feedback to others experienced “psychological threat” to their sense of belonging and self-esteem. This discomfiting mental state arises when the advocate feels unable to address the stressors—such as potential negative social feedback—that come from pushing back against the group. As a result, the infernal stand-ins were overly conciliatory to the people whose points of view they were attacking. The study also noted that being on the receiving end of artificial flak was even more harmful: People felt as if they were being bullied.

The researchers also saw that the person commissioned to play the devil’s advocate frequently ended up apologizing, which could be a disadvantage to the role in itself, says Jamieson. “They’ll overcompensate in future interactions with those individuals that they had to be negative towards,” he says.

When Beelzebub’s proxy appears during everyday conversations, such compassion is often lacking. In these environments, the idea of a devil’s advocate has evolved into an insidious way of airing problematic stances. This can get particularly pernicious online, whether it be in a Facebook group or the open discourse under a news article. Under a real identity or an assumed one, social media users can easily pull others into fruitless arguments, often just to serve their own interests. “Anything that involves dissent or negative commentary is typically amplified in these settings,” Jamieson says. “People are often more willing to write aggressive, critical comments online than they would be to deliver such feedback face-to-face.”

Adopting a counterintuitive persona has also become a tool to air unpopular opinions. “More recently, when people want to say something they think might offend somebody, they might add, ‘hypothetically,’ or ‘playing devil’s advocate,’” Jamieson explains. But this doesn’t align with the proper definition of the role. Rather than exploring counterarguments, these impersonators might be trying to couch disagreements in hypotheticals or get others to accept the bigoted or generally unacceptable points of view they actually hold.

For instance, in conversations about racism, hiding behind the devil’s advocate’s mask can allow someone to undermine the experience of a person of color. Or, worse, gaslight someone about their lived experience.

Maya Rupert, a political strategist, wrote about such an incident in a 2017 Slate article. After she presented at a conference, a member of the audience told Rupert, who is Black, that she’d gotten into law school because of affirmative action. Later, one of Rupert’s white friends put on his horns and asked her to consider that person’s perspective. Maybe she hadn’t earned her spot in her law school, the friend said, but he justified his claim as a counterargument, not his point of view.

Rupert shut this down by letting her friend know that her school hadn’t used race-based admissions since 1996, and she highlighted how the conversation, and others like it, taxed her emotionally. When people act as the devil’s advocate in this way, Rupert concluded in her piece, it’s to run from accountability and hide behind the guise of unbiased logic or hypotheticals.

Jamieson’s research supports this conclusion: Having a personal conversation with someone who protests without purpose only makes for a counterproductive interaction.

In most scenarios, the devil doesn’t need an advocate.

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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TO ALEXEI LEONOV, the colors in space were much more beautiful than those on Earth. No photograph could match what the late Russian cosmonaut experienced while floating hundreds of miles above his home planet in 1965: the distant curve of blue suspended in the deep black of space; the sunset as lines of reds, greens, and yellows skimming the horizon. Other explorers have shared this otherworldly perspective, but back then no one saw it as Leonov did—from beyond the safety of a spacecraft during history’s earliest spacewalk.

With only a 16-foot tether as his lifeline, the pilot of the Voskhod 2 mission drifted alone through low Earth orbit. But after 12 minutes, awe turned to panic when his suit ballooned to the point where he couldn’t fit back through the shuttle’s airlock door. He feared that as the first to explore the vastness of space in a suit, he might also be the first to get lost in it.

These days, spacewalks, also known as extravehicular activities or EVAs, are commonplace. Astronauts aboard the International Space Station (ISS) have conducted 250 of them since 1998, spending hours in the extraterrestrial elements to install or fix scientific equipment. But even as astronauts have become more adept at roaming outside controlled environments and the technology behind their suits has improved, the risks of accidents or death remain.

In Leonov’s case, the drop in atmospheric pressure caused the air in his suit to swell to dangerous proportions. If he tried to release the gas and reduce pressure, he risked bleeding off too much oxygen and asphyxiating himself. He decided to take the chance and quickly opened a valve in his suit to slim it down some, then slipped back indoors. Meanwhile, the Soviet space agency cut off a national broadcast of the mission to avoid public alarm. Leonov returned to a hero’s welcome on Earth, and it wasn’t until he shared his story that everyone realized the danger he’d faced.

Since Leonov’s pioneering foray, countries have stepped up safety and training standards for spacewalks. NASA astronauts practice EVA procedures in water tanks and zero-gravity airplanes, spending nearly seven hours submerged for each hour in orbit. More recently, they’ve practiced in virtual reality.

As a result, astronauts today are well prepared for EVAs, retired NASA payload commander Jeff Hoffman says. He performed four spacewalks throughout his career. His debut, in 1985, happened to be the first unplanned one in the agency’s history, when he ventured outside his shuttle to try to fix a broken satellite. “It showed how good the training [for spacewalking] was,” Hoffman said of the three-hour EVA. “I felt very comfortable, even though it was unplanned.”

Equipment has improved since Leonov’s era too, enabling astronauts to trek around for longer. Almost like individual spaceships, spacesuits supply oxygen, regulate temperature, and vent exhaled carbon dioxide. Other small additions make EVAs more secure and comfortable, including devices crewmembers use to propel themselves around in short bursts, guardrails on the facades of structures that improve maneuverability, anti-fog coating inside helmets, and warm gloves made of many layers of insulation and tough, flexible fabric.

Still, the dangers are real. In 2013, Italian astronaut Luca Parmitano almost drowned during a spacewalk when his helmet flooded with water that had leaked earlier from the suit’s cooling system. Astronauts might also face exhaustion or blood-bubbling “bends,” caused by the same rapid pressure changes that also endanger scuba divers.

Space junk, traveling at 18,000 miles per hour, poses another risk—one that Hoffman says is getting worse as stuff accumulates in Earth’s orbit. In late 2021, NASA canceled an ISS EVA because of floating debris. Though no astronaut has been hit yet, a punctured suit could turn fatal fast.

Even as spacewalks become more regular, the potential for disaster will never be fully eliminated. After all, Hoffman says, it’s part of a job that involves sitting on a loaded rocket. “I was fully confident that if anything happened that we could do something about, we’d do the right thing. And if something happened that we couldn’t do anything about—why worry?” he explains. “I took the risk because we had useful work to do.”

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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WHEN ACTION PARK first opened its gates on a New Jersey ski mountain in 1978, people probably showed up expecting run-of-the-mill amusements: go-karts, a lazy river, maybe a casual wave pool or two. But the 2,700-foot Alpine Slide, a track made of concrete, fiberglass, and asbestos that zigzagged through the funfair, was something else entirely. Riders plopped down on a little sled at the top—no helmets, no straps, no guardrails—and went wherever gravity took them at alarming speeds.

Eventually a park-goer did die on the Alpine Slide, and, after five additional fatalities and countless head wounds, electric shocks, and broken teeth, the entire venue shut down in 1996. New owners repeatedly tried to reopen the cult favorite destination, but after continued safety issues, the park’s operators finally decided to rebrand it a decade later.

While no other attraction can match its brazenness, Action Park lives on in the many rides that push today’s thrill-seekers to the edge of their comfort zones. Remember to read the fine print before you board these rowdy machines.

Most dimensions on a roller coaster

When Japan’s Eejanaika went up in the early 2000s, the steel coaster’s “fourth-dimension” design had to undergo multiple safety upgrades before it could start stealing people’s breath away. While it maxes out at about 75 mph (slow in extreme ride terms), it sends passengers spinning both parallel and perpendicular to the track. The seats rotate 360 degrees forward, backward, and sideways as they plunge down a 213-foot drop and swoop through 14 zero-G rolls. Since Eejanaika opened, barely more than a dozen other new 4D rollercoasters have debuted around the world.

Most sprains after going to the “rodeo”

The mechanical bull at a local dive bar may seem like the adult version of a bouncy house, but it’s a force to be reckoned with. With their aggressive torque, angular jerks, and short bursts of acceleration, the bucking plastic cattle can mangle unsuspecting (and often inebriated) bodies with every snap and toss. A survey of US hospital admissions from 2000 to 2020 estimated that mechanical bulls caused upward of 27,000 sprains, contusions, fractures, and other assorted ouchies. The majority of patients hurt their hands and arms. In other words, an iron grip could be your downfall.

Most distance falling down on your butt

Many visitors who summit Mount Kilimanjaro—that is, the 15-story-high body slide in Brazil, not the ice-capped volcano in Tanzania—chicken out when they see the drop. If you make it up 234 stairs and decide to brave the plunge, you’ll have to do without the padding of an inner tube. As bodies zing down a 60-degree angle at roughly a mile per minute, a trickle of water helps prevent friction burns. Extravagant views of tropical hills and the amusement park below almost make the wedgies worth it.

Most unpredictable carnival attraction

A Tilt-A-Whirl is essentially a giant centrifuge for humans; the clockwise and counterclockwise spinning—mixed with gravity, friction, and shifts in incline—creates what physicists call a “highly unstable” experience. Mathematical models can’t even predict the motion of the cars after a few seconds. So it’s not exactly shocking that the carnival amusement is prone to accidents like displaced cars. A report from the Consumer Product Safety Commission ranks these gyroscopes between Ferris wheels and roller coasters in terms of danger; they were responsible for about 20 percent of ride-related deaths between 1987 and 1999.

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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THE MOST IMPORTANT moments of a day on Hōkūleʻa, a 62-foot-long deep-sea canoe, are sunrise and sunset. That’s when the navigator can know for sure where the sailboat is headed. In between, the swell—the direction of the waves—helps hold course, but “you have to have known what direction it’s coming from based on where the sun rose,” says Kaʻiulani Murphy. At night, the stars are an important guide: “The sky kind of gradually changes with your latitude,” Murphy says. But on cloudy days, it is impossible to find a true path without sunrise and moonrise.

Murphy is a watch captain for the Polynesian Voyaging Society, the oldest and best-known group dedicated to the wayfinding methods that first brought humans to Hawaii as early as 300 CE. Originally from Waimea, a small community on the Big Island, Murphy’s been navigating thousand-mile stretches of open sea without so much as a compass for decades.

In 1997, as an 18-year-old undergrad at the University of Hawaiʻi at Mānoa on Oahu, she attended a lecture by Nainoa Thompson, the Voyaging Society’s chief navigator. “I was just so enthralled with the stories he was sharing,” she says. By the following spring, she was doing her first trials on the open water. “I was one of the few people who didn’t get seasick,” she recalls. She cut her teeth as an apprentice navigator in 2000, when she served on part of the return leg of a trip to the remote Rapa Nui (Easter Island). She’s spent many of the days since then following the solar rhythm that led her ancestors across the ocean.

The founding members of the Polynesian Voyaging Society—which include historian Herb Kawainui Kāne, anthropologist Ben Finney, and expert canoer Tommy Holmes—crafted Hōkūleʻa in the mid-1970s. Knowledge of Hawaiian culture was at a nadir after decades of violent colonial influence that, among other things, denied or obscured the fact that ancient Polynesians sailed thousands of miles of open waters. “Hōkūleʻa was built at a time when I think we in Hawaii needed her most,” Murphy says. The boat’s design mimics that of the double-hulled vessels that once traveled more than 2,500 nautical miles from the Marquesas Islands and Tahiti. “When you step on board you almost feel like you’re stepping back in time,” Murphy says. “I think, This is what our kupuna, our ancestors, would have been sailing.”

While no one on Hawaii knew exactly how those first epic trips had unfolded, other Oceanic communities had maintained an unbroken chain of wayfinding knowledge. Traditional Micronesian navigator Mau Piailug offered to share the techniques his ancestors had preserved as oral history. In 1976, he joined Kāne, Holmes, and Finney on their newly built vessel and guided them along the historical route, which takes 20 days or more to travel.

Piailug passed on his skills to the Polynesian Voyaging Society’s navigators, who would eventually teach Murphy how to read the stars and swells. Hōkūleʻa—named for the North Star—has now sailed more than 140,000 nautical miles and has a larger sister named Hikianalia, constructed in 2012. The two canoes have traversed the Pacific on 10 major voyages, strengthening ties between Hawaiians and other Indigenous groups such as the Maori.

Growing up in a small community and watching her family farm taro, a traditional root vegetable, made Murphy eager to connect with pre-colonial Hawaiian culture. That fascination led her to Thompson’s lecture, and then into the swells. The group is “kind of what kept me on Oahu,” she says. But it also took her around the world—quite literally, as she served on several legs of a circumnavigation of the Earth in the 2010s. She eventually started teaching, first at Honolulu Community College and then at UH Mānoa, where she oversees the same class on ancient sailing she took at 19.

At sea, Murphy’s primary kuleana, or duty, varies. As watch captain, she coordinates the movement of the canoe and its crew, which ranges in number from eight to 14. Folks work in four-hour shifts; the rest of the time, they write in journals, practice music, craft gifts, and watch the ocean.

When Murphy serves as navigator, the job starts on land. The first step is plotting a detailed reference course—complete with an estimated schedule—using nautical charts and specs like currents and average wind. It’s something her ancestors wouldn’t have had on those first trips to Hawaii, but then again, today’s voyagers lack the multigenerational experience those explorers surely leaned on.

Once at sea, Murphy relies solely on ancient methods to keep to the plan. “As a navigator, you have to be really in tune to what’s going on in nature,” she says. For example, she often takes cues from seabirds: A pale, pigeon-like Manu o Kū means the boat is probably less than 120 miles from a coastline. The small, sooty noio has a much shorter range, so it’s a reliable harbinger of land. Seeing either helps the crew confirm its location relative to the islands and continents it cruises by.

Murphy says it’s “beautiful” to watch the renaissance of traditional Polynesian navigation. “In the beginning, there was a lot of trying to prove things, especially this ability to navigate,” she says. Today, multiple groups explore the seas in canoes modeled after their kupuna’s vessels. “Now we [have relearned] this knowledge, we want to make sure it is never lost again,” Murphy says. That means maintaining boats and building new ones, continuing the practice of voyaging, and teaching it to future generations.

But it’s not just about cultural preservation, she says—it’s about a way of connecting with the planet. For Murphy it all comes down to time with Hōkūleʻa, watching the sun rise and set, keeping an eye out for birds, and relying on the natural world for guidance. “There’s so much magic in that,” she says.

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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GENERALLY SPEAKING, humans will try to eat anything at least once. Some anthropologists theorize that prehistoric people sussed out what was edible by trial and error, but we haven’t stopped pushing our palates in new, sometimes dangerous directions. The risk of illness and even death is often baked into our favorite flavors and fares. Here are some beloved bites that can kill—if things go awry.

Fugu

A dash of danger is part of the appeal of this lean and mild whitefish, which is served as slivers of sashimi in select Japanese restaurants. Tetrodotoxin, a paralysis-inducing chemical that disrupts the connections between neurons and muscle cells, collects in the liver and sex organs of this family of pufferfish. Japan’s health ministry requires fugu chefs to be certified in properly cleaning and removing the potentially deadly body parts. Yet some diners insist that a hint of risk gives the dish its allure. A possibly apocryphal tradition holds that culinary masters know just how much toxin should linger on the meat to provide a pleasing tongue tingle.

Hot dogs

Franks have long been a leading cause of choking in young US children due to the all-American food’s shape, size, and texture. Health experts advise parents against cutting dime-size medallions for tykes to chew on; instead, the sausages should be sliced into thin strips, then chopped into smaller pieces. But that’s not the only way a wiener can get you: The American Institute for Cancer Research and the World Health Organization suggest limiting consumption of all processed meats, because emerging evidence links them to an increased chance of colorectal cancer. Hot dogs may also be associated with higher risks of cardiovascular disease, according to a 2021 study in the American Journal of Clinical Nutrition.

Almonds

Wild almonds are slightly different from the domesticated seeds found in grocery stores. These bitter varieties produce amygdalin, a compound that our bodies convert to cyanide. The sweet almonds we usually eat have a genetic mutation that means they produce less of this respiratory toxin than the fatal doses found in the wild. Some foodies claim that a sprinkle of the bitter varieties is the key to deepening the taste of nutty confections. Heating or boiling them beforehand is the best way to dissipate the poison.

Potatoes

This humble root vegetable’s sprouts, leaves, stems, and flowers contain a harmful compound called solanine. Even the flesh of the spud can have high quantities of the noxious stuff—at least once you see it go green. Potatoes, like almost all plants in the nightshade family, produce solanine to ward off insects. As they make the chemical, they amp up their chlorophyll too, creating an unappetizing shade of chartreuse. But don’t fear the oft-maligned green chip: Eating the occasional off-color potato is probably fine, though it may have a slightly acrid taste. Just don’t make a habit of chowing down on taters past their prime: an excess of solanine can cause vomiting, paralysis, and even death.

Wild mushrooms

A frequently cited proverb states that “all mushrooms are edible, but some only once.” Even safe fungi can be tricky, with many poisonous look-alikes that can lead amateur foragers astray. Amanita phalloides, for example, can resemble a benign white mushroom like the paddy straw to the untrained eye. But this unassuming species is called the death cap for good reason. It contains lethal amatoxin, which holds up even after thorough boiling. And don’t trust your nose or tongue to sound the alarm in time to save you: Writer Cat Adams reports in Slate that “many people who are poisoned claim the mushroom was the most delicious they’ve ever eaten.”

Maggot cheese

Casu marzu is a Sardinian sheep’s milk cheese with an added kick: living larvae of the Piophila casei fly. As maggots eat their way through the fermented dairy, their digestion transforms it, making it softer and creamier. Many diners praise its intense and unique flavor, which is said to be tangy, nutty, and a bit bitter. It also holds the Guinness World Record for the “most dangerous cheese” because the live grubs can contaminate the product with unsavory bacteria—and, if swallowed whole, can potentially nibble on the diner’s intestinal tissue. Unsurprisingly, this product is globally banned from sale, but adventurous eaters in the know continue to indulge.

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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DAN BLOCK has an easy charm and a twinkle in his eye—a natural charisma that would surely serve him in all manner of glamorous professions. That makes it all the more jarring to see him stick a power drill up his nose in front of a cringing crowd of onlookers.

After taking a moment to angle the machine just so, he turns it on, the bit rotating at dizzying speeds inside his head. The terrible whirring sound is enough to make even me—a stalwart masochist and the author of a book about the pleasure of pain—nearly black out from the rushing sensation of dread. But instead of straightforward revulsion or concern, my wooziness transmutes into a celebratory high. If the shocked silence that gives way to applause and relieved laughter is any indication, I am not alone in feeling a surge of something wonderful. The terrible act thrills performer and audience alike. But why?

First, there’s the question of what would compel someone—in this case my friend Dan—to put their body in peril. When he, a sideshow performer based in Austin, Texas, gets ready to use his face drill (or set a mousetrap off with his tongue, or inflate a balloon that’s been snaked through his nostrils, or hang weights from his eyelids, or…) his body senses the impending danger, and his gray matter gets to work. According to Arash Javanbakht, a psychiatrist and director of the Stress, Trauma, and Anxiety Research Clinic (STARC) in Detroit, Michigan, the two almond-shaped areas of the brain that form the amygdala oversee “salience detection and the creation of emotions.” In the most basic terms, he says, “Every time I see something, the amygdala decides if I should run away from it, attack it, eat it, or have sex with it.”

Faced with fear, excitement, and danger, this region calls other areas of the brain into action, gearing the whole noggin to fight-or-flight mode. This means doling out a blast of neurotransmitters like dopamine, increasing focus on the task at hand, and ramping up the sympathetic nervous system. The heart pounds, and blood pressure inside the muscles juices up the limbs in preparation for a chase or a rumble. “Breathing gets faster, mouth dries, we get a little bit sweaty,” Javanbakht explains. “I’m not suggesting that the daredevil doing some stunt is terrified, but there is that excitement.”

And, lucky for us, even bystanders can enjoy a secondhand rush. “We know that if you’re watching someone doing something related to fear or anger or aggression, you will have those same areas of your brain activate,” says Javanbakht. “That’s how empathy happens.”

This mirroring applies to movement as well. Using fMRI imaging, neuroscientists and physiologists have shown that when we watch someone do something, our brains seem to simulate the witnessed action. If we see a person jump into the air, for example, neurons light up in a similar pattern to the ones firing up when we jump ourselves—even if we are perfectly still. In that way, you can think of watching a stunt as a way to microdose the experience. Remember, for example, a time you saw a rock climber dangling off a cliff or a tightrope walker teetering in the sky. As an observer, you were in no real danger, but your body gave you some of the same signals it would set off if you were.

Internalized mimicry is helpful in that humans are very social animals, and we are constantly learning by observing each other. “There are great evolutionary advantages to being able to feel empathy. We don’t all need to have a near-death experience to appreciate that something is dangerous and we shouldn’t be doing it,” explains Brendan Walker, a former aeronautics designer and self-styled “thrill engineer” who tailors rides, installations, and other experiences to make them as evocative as possible.

Seeing another person cheat the reaper can also be instructive. “In nature, nothing happens for no purpose,” adds Javanbakht. When we watch someone defy death, be it by rock climbing or sword swallowing, we are present in the moment with them, participating from afar. “I’m actively in my own head, putting myself in that situation,” he says. “I’m practicing.”

Practicality aside, what’s the fun in activating your fight-or-flight response, or, stranger still, standing in awestruck wonder as someone else tongues the membrane between existence and the abyssal cleft of death? It turns out, there are major overlaps in how fear and excitement look and feel inside the body. What distinguishes the two is the context in which we experience those sensations. After all, Javanbakht notes, even something as pleasurable as falling in love comes with a pounding heart, shortness of breath, and clammy skin.

“What makes a difference in terms of being able to enjoy [the thrill] is the sense of control that we have,” he says. “Let’s say someone with a knife is chasing me on the streets. My feeling is very different than when someone with a fake knife is chasing me in a haunted house.” The important factor here is that one of the situations comes with the logical understanding of safety. Parts of our brain—the amygdala and other areas of the limbic system, or what Javanbakht calls “the animal inside of me”—sense the danger of the chase and get very worked up. But the prefrontal cortex, where we manage our emotions and think logically about how situations are likely to play out, understands theater and Halloween props and knows we are safe. That region helps us create a pleasurable context in which to enjoy the physiological cacophony of what feels like a brush with death.

Understanding why we aren’t necessarily afraid, however, doesn’t quite explain why we enjoy the sensation. Walker posits that the euphoric rush that comes with cheating death is also about “rewarding our persistence of life.” It’s a biochemical celebration of sorts—a way to feel joy and relief at continuing to exist. Evading danger, he says, creates a surge of happy-making transmitters, like adrenaline and dopamine. “I think it’s not even an emotion, it’s actually the movement of emotions,” he clarifies. “It is that movement, that rush of changing emotional space, that is what we term a thrill.”

Those fluctuations come in plenty of flavors, but we do have some sense of how they tend to unfurl over time. For example, when it comes to roller coasters, the high begins the moment you consider getting on, and it builds every time you make the choice to pursue that desire. Driving to the park, buying tickets, craning your neck to see the peaks and loops, waiting in line for your turn, all help psych you up for thrills. In 2007, Walker and a team of researchers from the University of Nottingham’s School of Psychology used wearable monitors and video cameras to measure physiological titillation on a ride consisting of one shocking, 180-foot vertical drop. They found something extraordinary: According to heart rate and sweat data, the most nerve-wracking, exhilarating part wasn’t clearing the precipice; it was the moment when the seat belt bar clicked into place. The actual experience of the drop registered at around 80 percent of the excitement of that moment of inevitability.

Even just anticipating someone enduring chills and spills can trigger a similar rush, thanks to our brains’ tendency to echo the feelings we observe in others. Even seeing an actor in a scary movie is enough to get our bodies worked up—a discovery that has given rise to the field of neurocinematics, or the study of how films affect our brains. “It’s a vicarious thrill,” says Walker. “You can live those emotions.”

We may not be able to do what the performer does, but through observing them, we have a chance to rejoice in death defied before our very eyes. It’s a way to feel fear, yes, but followed by a heady dose of mastery and control and jubilation. “Watching a performer playing at those dangerous edges is a form of entertainment,” said Walker. “[It] allows us to quite safely experience being alive.” Through witnessing the act, we feel the same fears, trials, victories, and, yes, thrills.

The secondhand jolt of another’s improbable persistence certainly has a compulsive draw for many of us. I asked Dan the drill sniffer, known to many as “The Amazing Face,” why he thought people were drawn to his shows of pain and derring-do. “I don’t think there is a singular reason,” he mused. “I think it’s like eating candy. Everyone has a sweet tooth, but we’re all looking for different things.” In his line of work, he sees people who wish they could emulate his acts, people who get a hit of fiendish glee at the thought of how bloody a high-stakes failure could be, and people who watch on with horror at feats that they themselves would never attempt. “Whatever we get out of it individually, everyone is looking to be entertained and to see the unbelievable.” Even knowing how Dan keeps his cranium intact doesn’t curb the terror. If you’re curious: He’s worked over the years to get to know—and subtly widen—the shape of his nasal cavity, and so has learned how to angle the bit to give it enough room to whirr without making contact. The real trick is not sneezing while it’s happening, which would-be blockheads on the Internet say takes lots of practice with less-lethal insertables.

Is it any wonder that we are drawn to witness the impossible made real? We as a species are facing a climate apocalypse, wars, pestilence, and famine. As pain clown poet laureate Steve-O of the Jackass franchise reminds us, escaping death is the ultimate unattainable fantasy: “Human existence is a prank on us because we only have one instinct, which is to survive,” he opined in the midst of a hot-wing-eating gag on YouTube in 2021. “And we only have one guarantee, which is we won’t.” Perhaps we are drawn to gawking at thrills because it allows us to snatch the joy of persistence from the jaws of certain death—even if just for a moment.

This story originally ran in the Fall 2022 Daredevil Issue of PopSci. Read more PopSci+ stories.

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The typical pimple is caused by clogged oil glands or bacteria in our skin, and while most pimples aren’t harmful, they can become infected (and painful), especially when they’re opened up to the outside environment. Still, so many of us cannot resist pinching them away. 

To get to the root of the pimple popping divide, we can look to one of our most basic emotions: disgust. 

Disgust evolved to protect humans from infectious diseases and poisons, Daniel Kelly, professor of philosophy at Purdue University and author of a book called Yuck! The Nature and Moral Significance of Disgust, told PopSci in an interview. For instance, we’ve learned to avoid common repulsive items, like rotten meat or poop, because they can contain microbes that are known to make us sick if ingested. Developing this internal ick-detector was important in keeping our ancestors alive, Kelly says, because we can’t actually see the tiny pathogens like viruses and bacteria that make us sick. 

However, some bodily fluids like blood, spit, or pus—including the oily ooze from a pimple—are often only seen as disgusting when they come out of our bodies. In this case, Kelly explains that our disgust is acting  like a bouncer enforcing a no re-entry policy: Once our bodily fluids are out in the big bad world, they can potentially be contaminated by bacteria or other pathogens, so we don’t want to put them back inside of us. This aversion towards disease is also why people recognize the tell-tale signs of sickness in others around them, like sweating or coughing.

But unlike snotty noses, you might be surprised to find that squeezing those angry whiteheads doesn’t always evoke the same yuck reaction—in fact, there’s a whole community of people that finds that final burst oddly satisfying.  

Popping on the brain

We obviously don’t all react in the same way when we see pus coming out of a pimple. And on a basic, primal level, even popping fanatics get at least a little disgusted. It’s all about whether your enjoyment outweighs your instinctive revulsion.

There might also be levels to one’s love (or disgust) of poking those blemishes. Some people are into watching YouTube or TikTok videos of pimple popping, but wouldn’t be tempted to squeeze their own zits. Watching it happen to someone else through a screen controls exposure—the viewer is not in any real danger of coming into contact with potential pathogens. A similar phenomena can be seen when horror fans watch scary movies. No matter how frightening or gross a film is, we know a zombie isn’t actually going to pop up and eat our brains. 

Even for people doing actual in-person popping, either on themselves or on someone else, there’s still an element of control involved. It’s not the same as suddenly coming upon an infected wound; while your conscious mind might immediately respond with an initial feeling of ick, your lizard brain and past experiences not getting sick from zit pus help you recognize that a simple pimple likely won’t put you in danger. 

[Related: The mites that breed on our faces are getting clingier by the day]

Differences in our brains also help explain why some people like pimple popping more than others. How each person reacts to pimple popping depends upon their brains, according to a 2021 paper in the journal Behavioural Brain Research. Scientists from the University of Graz in Austria had 38 popping enjoyers and 42 non-enjoyers watch 96 video clips that showed either pimple popping, water fountains, or steam cleaning. The fountain videos were used as controls because water coming from a fountain mimics pus coming from a zit, according to the researchers, while the steam cleaning videos served as oddly satisfying controls. 

The researchers had study participants complete a survey before the experiment to determine their pimple popping enjoyment, their disgust sensitivity, and their reward and punishment sensitivity. Then, participants watched the clips while their brain activity was measured in a functional magnetic resonance imaging, or fMRI, machine. 

The team found that people who liked zit squeezing videos reported a greater sensitivity to being rewarded, as well as better disgust regulation skills, than those who didn’t. In other words, pimple popping fans were more likely to feel arousal when rewarded with the satisfaction of pus spurting from a pimple and could better modulate the amount of disgust they felt while watching. Those self-reported qualities matched up with what the researchers found in the brain imaging part of the study.

[Related: What is a hangover? And can you cure it?]

The fMRI scans also revealed parts of the brain most responsible for making us a fan or hater of pimple popping: the nucleus accumbens and the insula. The nucleus accumbens is part of the brain’s pleasure system, and has been shown to modulate people’s responses to the things they dislike. When people who didn’t enjoy pimple popping watched the videos, their nucleus accumbens was deactivated and showed little to no activity. And while the nucleus accumbens was also deactivated in people who liked pimple popping videos, it was more active than in their pop-hating counterparts. The insula is another part of the brain that’s activated when we’re disgusted. The level of connectivity between the nucleus accumbens and insula also varied between the two groups, with the pimple popping fans having greater connectivity. The researchers hypothesized that the increased connectivity of the insula with the accumbens might be tied to better disgust regulation. 

Don’t worry pimple popping fans—just because you have a higher tolerance of disgust for zit squishing doesn’t mean you’re less likely to pick up on actual harmful things that will make you sick. Plus, even the most hardcore pimple popping fans still have that innate ick-response: the 2021 paper found that ultimately all participants were at least a little grossed out by pimple popping.

To pop or not to pop

Unfortunately for popping fans, dermatologists say you really shouldn’t DIY this particular task, regardless of how tempting it is to get rid of unsightly zits. Pimple popping breaks the skin and can cause infections and scarring. Blackheads and whiteheads should be left alone, although home treatments like benzoyl peroxide can help them clear up more quickly. If you’ve got a Vesuvius-level whitehead you really want to get out, go to a dermatologist because they’re trained to handle extractions properly. If you still have a squeeze craving, there are plenty of videos around the internet to satisfy you safely.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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How does an airplane stay in the air? Whether you’ve pondered the question while flying or not, it remains a fascinating, complex topic. Here’s a quick look at the physics involved with an airplane’s flight, as well as a glimpse at a misconception surrounding the subject, too. 

First, picture an aircraft—a commercial airliner, such as a Boeing or Airbus transport jet—cruising in steady flight through the sky. That flight involves a delicate balance of opposing forces. “Wings produce lift, and lift counters the weight of the aircraft,” says Holger Babinsky, a professor of aerodynamics at the University of Cambridge. 

“That lift [or upward] force has to be equal to, or greater than, the weight of the airplane—that’s what keeps it in the air,” says William Crossley, the head of the School of Aeronautics and Astronautics at Purdue University. 

Meanwhile, the aircraft’s engines are giving it the thrust it needs to counter the drag it experiences from the friction of the air around it. “As you’re flying forward, you have to have enough thrust to at least equal the drag—it can be higher than the drag if you’re accelerating; it can be lower than the drag if you’re slowing down—but in steady, level flight, the thrust equals drag,” Crossley notes.

Understanding just how the airplane’s wings produce the lift in the first place is a bit more complicated. “The media, in general, are always after a quick and simple explanation,” Babinsky reflects. “I think that’s gotten us into hot water.” One popular explanation, which is wrong, goes like this: Air moving over the curved top of a wing has to travel a longer distance than air moving below it, and because of that, it speeds up to try to keep abreast of the air on the bottom—as if two air particles, one going over the top of the wing and one going under, need to stay magically connected. NASA even has a webpage dedicated to this idea, labeling it as an “Incorrect Theory.” 

So what’s the correct way to think about it? 

Lend a hand

One very simple way to start thinking about the topic is to imagine that you’re riding in the passenger seat of a car. Stick your arm out sideways, into the incoming wind, with your palm down, thumb forward, and hand basically parallel to the ground. (If you do this in real life, please be careful.) Now, angle your hand upwards a little at the front, so that the wind catches the underside of your hand; that process of tilting your hand upwards approximates an important concept with wings called their angle of attack.

“You can clearly feel the lift force,” Babinsky says. In this straightforward scenario, the air is hitting the bottom of your hand, being deflected downwards, and in a Newtonian sense (see law three), your hand is being pushed upwards. 

Follow the curve 

But a wing, of course, is not shaped like your hand, and there are additional factors to consider. Two key points to keep in mind with wings are that the front of the wings, also known as the leading edge, is curved, and overall, they also take on a shape called an airfoil when you look at them in cross-section. 

[Related: How pilots land their planes in powerful crosswinds]

The curved leading edge of a wing is important because airflow tends to “follow a curved surface,” Babinsky says. He says he likes to demonstrate this concept by pointing a hair dryer at the rounded edge of a bucket. The airflow will attach to the bucket’s curved surface, and make a turn, and could even snuff out a candle on the other side that’s blocked by the bucket. Here’s a charming old video that appears to demonstrate the same idea. “Once the flow attaches itself to the curved surface, it likes to stay attached—[although] it will not stay attached forever,” he notes.

With a wing—and picture it angled up somewhat, like your hand out the window of the car—what happens is that the air encounters the rounded leading edge. “On the upper surface, the air will attach itself, and bend round, and actually follow that incidence, that angle of attack, very nicely,” he says. 

Keep things low pressure

Ultimately, what happens is that the air moving over the top of the wing attaches to the curved surface, and turns, or flows downwards somewhat: a low-pressure area forms, and the air also travels faster. Meanwhile, the air is hitting the underside of the wing, like the wind hits your hand out as it sticks out the car window, creating a high-pressure area. Voila: the wing has a low-pressure area above it, and higher pressure below. “The difference between those two pressures gives us lift,” Babinsky says. 

This video depicts the general process well:

Babinsky notes that more work is being done by that lower pressure area above the wing than the higher pressure one below the wing. You can think of the wing as deflecting the air flow downwards on both the top and bottom. On the lower surface of the wing, the deflection of the flow “is actually smaller than the flow deflection on the upper surface,” he notes. “Most airfoils, a very, very crude rule of thumb would be that two-thirds of the lift is generated there [on the top surface], sometimes even more,” Babinksy says.

Can you bring it all together for me one last time?

Sure! Gloria Yamauchi, an aerospace engineer at NASA’s Ames Research Center, puts it this way. “So we have an airplane, flying through the air; the air approaches the wing; it is turned by the wing at the leading edge,” she says. (By “turned,” she means that it changes direction, like the way a car plowing down the road forces the air to change its direction to go around it.) “The velocity of the air changes as it goes over the wing’s surface, above and below.” 

“The velocity over the top of the wing is, in general, greater than the velocity below the wing,” she continues, “and that means the pressure above the wing is lower than the pressure below the wing, and that difference in pressure generates an upward lifting force.”

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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The pace of our lives are closely intertwined with so many things: hormonal changes, literal growing pains, and (of course) dental development. Most of us don’t remember teething, but plenty recall having our wisdom teeth erupt and, if you live in a place that regularly removes them, getting them yanked out of your jaw. It’s just one dental milestone and one of three molar milestones, but until recently we had no idea why wisdom teeth emerged so late in life.

A new study in Science Advances suggests a reason: our jaws are simply late bloomers.

“It turns out that our jaws grow very slowly, likely due to our overall slow life histories and, in combination with our short faces, delays when a mechanically safe space—or a ‘sweet spot,’ if you will—is available, resulting in our very late ages at molar emergence,” said Gary Schwartz, a paleoanthropologist at the Institute of Human Origins at Arizona State University, who co-authored the paper, in a press release. It’s easy to forget that our teeth undergo quite a bit of mechanical pressure as they chomp down on food, as does your entire jaw structure. And that means your jaw needs to be developmentally ready to have teeth all the way at the back of our mouths nearest the joint. If wisdom teeth emerged earlier, the molars could actually damage the jaw they’re growing out of.

[Related: Ancient dental plaque shows humans have always loved carbs.]

All of this is the result of two fundamental things about humans: we have prolonged lives and short faces. Life, short as it may seem, is pretty stretched out for humans in comparison with other creatures, even other primates. We develop slowly—we take our time—and we spend an inordinately long period just becoming adults. And, unlike our primate cousins, our faces are quite flat and squashed. Just take a look at chimpanzees or gorillas; you’ll notice that their jaws protrude outwards such that their mouths are mostly in front of their brain (though you probably never thought of it that way). Our faces are pulled in, sitting beneath our braincase.

The combination of these factors means that our jaws can’t accommodate that final set of molars until fairly late in life.

Lots of people in the US get their wisdom teeth taken out, which might make you think that they’re some kind of evolutionary leftover—some artifact of a prehistoric life that’s no longer relevant. But the truth is that you don’t necessarily need to get them removed. In the UK, for instance, wisdom teeth are only removed if they become problematic, as the National Health Service notes that there is otherwise no proven benefit (but there is the added complication of having a minor surgery).

Either way, the teeth are not so much a leftover as they are a sign of our evolutionary progress. Our squashy faces and slow development are part of what makes us human, weird dental development and all.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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Around 15 years ago, a slogan began to appear on bumper stickers, license plate holders, and tote bags: Save the bees. The sense that these pollinators—and the food system they support—were in critical condition was all-pervasive. In 2014, an online poll in the UK found that respondents ranked the decline of bees as a more serious environmental threat than climate change.

But do we still need to save the bees?

The answer is complicated: The public began worrying about bees at a time when western honeybees were dying in alarming numbers from a mysterious syndrome, colony collapse disorder. Now, their populations are much more stable. However, wild bees, which play an entirely different role in our food system and environment, are still in trouble. 

Colony collapse

The recent intense focus on honeybee health began after the fall of 2006, when beekeepers from Pennsylvania began to notice that their hives were dying off over winter. “Those were colonies that had, a couple weeks earlier, looked healthy, full of strong bees,” says Nathalie Steinhauer, science coordinator of the Bee Informed Partnership, a national nonprofit that monitors honeybee populations. “And they came back and the apiary was basically just full of empty hives.” What made the event especially mysterious was that there was no discernible cause. There were no dead bees around to suggest starvation, nor traces of parasitic mites. The bees had simply vanished.

Over the winter, other beekeepers experienced the same die-offs, losing anywhere from a third to more than half of their hives. “It really acted like an epidemic,” says Steinhauer. Affected hives showed no obvious signs of stress, and scavengers strangely avoided the abandoned honey. The cluster of symptoms came to be known as colony collapse disorder, or CCD. The disorder was alarming enough that it led to a wave of research on honeybee health, including the monitoring now led by the Bee Informed Partnership.

But the last verified case of CCD occurred in 2008. Entomologists still don’t know exactly what caused this bee epidemic, but the most likely explanation is that exposure to pesticides, fungicides, and parasites made hives more vulnerable to some kind of pathogen—like a virus. “[The disorder] appears to have existed,” says Geoff Williams, president of the Bee Informed Partnership, and a bee pathologist at Auburn University. “But it just for whatever reason didn’t persist.”

Die-offs, but stability

So why is there a lingering sense that bees are still in trouble? Well, says Williams, honeybee mortality is still high—but not because of colony collapse. The term has been misapplied in the years since. CCD was a galvanizing force for bee conservation within the industry, and quickly captured public attention. Both beekeepers and the media have used the term to describe unrelated die-offs.

Bee hives can naturally collapse during the stress of winter. Entomologists don’t know what the baseline rate of collapse looked like before the 2006 CCD outbreak, because national counts only began in 2007. But over the last 15 years of data, there are no obvious trends. “On average, winter loss hovers around 30 percent,” Steinhauer says.

“Some years are worse, some are slightly better,” she says. “Overall, it’s higher than what beekeepers tell us is acceptable.”

Williams says it’s likely that honeybee losses each winter did increase over the last 20 or 30 years, before baseline data was gathered.

In the late 1980s, a parasitic mite called Varroa destructor arrived in the US. As it spread, Varroa put extra strain on hives—Williams says it’s hard to get exact numbers, but that old-time beekeepers say that they remember times when losses were about three times lower, around 10 or 15 percent. The damage from mites are compounded by the continuing spread of monocrop agriculture. Soybean farmers have taken over regions of the northern prairie, where honeybees often summer—which has reduced the variety of the bee’s diet, likely making them more vulnerable to illness. And the proliferation of neonicotinoid pesticides, which are particularly toxic to bees, adds even more stress.

[Related: Want to help the bees? Keep these out of your garden.]

Despite of winter losses, overall honeybee populations in the US have remained stable over the last 15 years, and have even grown globally. 

The key to understanding how populations can be stable through losses is to recognize that honeybees are a domestic species. They’re more like cattle than butterflies. Every year, American farmers spend hundreds of millions of dollars to rent honeybee hives to pollinate almonds, blueberries, cherries, and more. To get there, the hives travel across the country on the back of semi-trucks, usually following the growing season from Florida to California.

Losing hives can devastate a beekeeper (“picture 30 or 40 percent of cows or chicken dying every winter,” Williams says) but they can be regenerated.

Honeybee hives reproduce by fission, a lot like the way a cell divides. In the spring, a healthy queen can fly away with half of the workers to form a new hive, leaving queen-eggs behind to pick up the baton in the original colony. A beekeeper can start this process manually, but it takes time, cutting into the bottom line.

So the pressures on honeybees have real stakes for the livelihoods of beekeepers, and possibly the food system more broadly. In theory, a bad year could knock out enough honeybees to screw up fruit harvests across the country. But honeybees aren’t at risk of dying off and leaving entire ecosystems without pollination.

Wild bees

Western honeybees are just one of hundreds of bee species in North America. Threats to domestic honeybees also hit wild bees, which don’t have farmers nursing them back to health.

And this is where the slogan “save the bees” becomes confusing. While honeybee populations are currently stable, wild bees and other pollinators, including flies and moths, are in immediate trouble. The loss of these pollinators have ramifications for both agriculture and ecosystems.

Of the 46 species of bumblebees in North America, more than a quarter are in decline or threatened, says Jess Tyler, who works on pollinator conservation and science with the Center for Biological Diversity. “If bumblebees are representative of bees at large, that could be hundreds that are in decline, potentially,” he says. The data on wild bees is fairly sparse in comparison to honeybees, but plenty of once-common species, like the rusty-patched bumblebee, have been reduced to tiny remnant populations.

Both wild bees and domestic honeybees are critical in our food supply—one study estimated that wild pollinators provide roughly the same crop value as domestic honeybees. Honeybees aren’t especially efficient pollinators, especially for North American crops like tomato and sunflower. They’re used because they’re portable, easy to breed, and convenient for farmers who need pollination on a schedule. (Over the last 50 years, apiarists have tried to get the best of both worlds by domesticating new species, like the eastern bumblebee and the solitary blue orchard mason bee.) The benefits of wild bees go beyond agriculture: They also pollinate native plants, creating the backbone for diverse, non-agricultural landscapes. 

Wild and domestic bees require different kinds of support. And wild bees might need to be protected from domestic honeybees. Honeybee hives, for instance, can drive other bee species off of flowers after they’re done pollinating a crop. Even when they don’t compete, they can pass along diseases. “Honeybees are very messy,” says Tyler. “They’ll poop on flowers, and if another bee visits the same flower it can pick up a virus.” 

As a 2018 commentary in Science pointed out, some efforts to shore up honeybee populations that put hives in wildland far from crops might have actually hurt other types of bees.

[Related: City gardens are abuzz with imperiled native bees.]

According to another provocative commentary in the Journal of Insect Science earlier this year, honeybees are both a victim and driver of intensified agriculture. The author concludes that focusing on mites, malnutrition, or CCD as individual causes of honeybee decline misses the bigger picture. They’re actually suffering from industrialization, the model of farming that relies on large monocultures and off-farm inputs, like pesticides, fertilizers, seeds—and domestic pollinators.

“Honeybees are livestock,” says Tyler. “They’re cared for by humans. Their health is the result of what humans do to them.” And when industrial farms bring in high densities of honeybees, it might be inevitable that they will get sick.

Steinhauer thinks that while this framing is useful for understanding the problem, it shouldn’t be used to dismiss the struggles of working beekeepers. “In a lot of entomology departments, we are trying to improve industrial agriculture,” she says. Her work with Bee Informed Partnership pushes to reduce pesticides or improve farm diversity to improve the health of bees even within industrial farm contexts. “That’s going to be helping beekeepers next year.” She also points out that non-agricultural forces, like suburban construction and lawn chemicals, put pressure on both wild and domestic species.

If the critique from the Journal of Insect Science is right, more diverse, less chemical-drenched farms would make for healthier honeybees. Farms just might not need as many of them, because they’d also have wild pollinators.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

The post Do we still need to save the bees? appeared first on Popular Science.

Articles may contain affiliate links which enable us to share in the revenue of any purchases made.

LEFT TO THEIR OWN DEVICES, most children won’t hesitate to, say, lick a doorknob or wipe snot with their sleeve. But is there any truth to the idea that their affinity for getting dirty can be beneficial to their health?

That theory dates to the 1800s, when European doctors realized that farmers suffered fewer allergies than city slickers. However, it didn’t gain widespread attention until 1989, when British epidemiologist David Strachan discovered that youngsters with older siblings were less susceptible than other kids to hay fever and eczema. Strachan suggested that early childhood infections “transmitted by unhygienic contact” helped foster a robust immune system.

His theory, called the hygiene hypothesis, provides a convenient explanation for why allergies and asthma, as well as autoimmune disorders like multiple sclerosis and Crohn’s disease, have increased 300 percent or more in the US since the 1950s. Maybe Western societies have become too clean for their own good, and parents too fearful of a little dirt. “Whatever it is that’s happening in the modern world, it’s causing the immune system to be active when it doesn’t need to be,” says microbiologist Graham Rook of University College London.

As Rook notes, however, the hygiene hypothesis has its flaws. For example, some viral infections appear to trigger asthma, not prevent it. Most research now blames changes in the human microbiome, not a dearth of childhood infection, for at least some of the sharp rise in chronic diseases, from digestive disorders to kidney failure.

[Related: This pseudoscience movement wants to wipe germs from existence]

Getting a bit messy can help cultivate the thousands of microbial species that call the body home and keep it healthy. Providing that boost can be as easy as having pets, tending chickens, or playing in a green space. In fact, a 2020 study published in Science Advances found that when daycare centers in Finland replaced gravel yards with soil and vegetation, tykes saw almost immediate benefits to their immune systems, including an increase in disease-fighting T-cells. Eating a varied diet high in fiber helps too. And vaginal childbirth and breastfeeding promote healthy guts in newborns and nursing babies.

It’s also wise to go easy on the antibiotics. Although they can be lifesavers for patients with severe bacterial infections, there’s “a real risk of harm” from overuse, says John Lynch, a doctor at the University of Washington School of Medicine. “Regaining your native microbiota can be extremely hard to do,” he explains.

All this is not to say tots should be slobs. You definitely want them washing their hands regularly, and scrubbing high-touch surfaces is imperative to avoid unpleasant infections like norovirus, Rook and a colleague advised in a recent paper. Just don’t go overboard and sterilize everything. As it turns out, kids probably do need a few germs to stay healthy.

This story originally ran in the Spring 2022 Messy issue of PopSci. Read more PopSci+ stories.

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OUR ENTIRE SOCIETY runs on garbage, at least in a manner of speaking. Eons-old junk—coal and oil that began as ancient plants and dinosaur remains, among other dreck—has powered our electric grid since the beginning of the industrial age. Of the 3.8 trillion kilowatt hours of electricity the United States used in 2020, most came from fossil fuels. The problem is that this trash isn’t meant to keep lights on or charge up EVs; it’s supposed to stay deep beneath the surface, locking away the gases that now flood our atmosphere and cause disastrous warming.

The good news—and bad news—is that we’re making new batches of carbon-rich refuse all the time. In 2018, the average American generated an unsavory 4.9 pounds of waste every day. Could these fresh trash heaps help replace our dependence on dead dinos?

We already know, of course, that we can burn carbon-based products for energy. But simply setting trash aflame has its own nasty side effects. Incineration plants, which have been running in the US since 1885, emit nitrogen oxides, sulfur dioxides, particulate matter, lead, mercury, and dioxins, among other toxins. They also belch greenhouse gases out the wazoo: more than half of what coal spews. The process isn’t even very efficient, extracting just a fraction of the refuse’s potential power. “A lot of energy escapes in the process,” says Johan Enslin, executive director of the Energy Systems Program at Clemson University.

Luckily, firing up trash, be it new or millions of years old, isn’t the only way to turn it into fuel. Take natural gas: Deep beneath the earth, organic matter breaks down and compresses to form methane (chemically, CH₄). We call that byproduct natural gas, which has run a chunk of the grid since the 1960s, and which today contributes more power than coal and oil combined.

Our heaps of castoffs mean we’ve got that same gas topside too. Deprived of oxygen in landfills and manure ponds, modern waste breaks down into methane more or less the same way as the ancient subterranean stuff. There’s plenty of incentive to trap that gas: Methane is more than 25 times as potent as carbon dioxide in terms of trapping heat in the atmosphere, and municipal solid waste landfills are the third-largest source of human-related CH₄ emissions in the US.

Enter biogas, a combination of the carbon dioxide and methane that naturally creep up out of moldering garbage. Humanity has tapped these landfill burps in various forms since the late 1800s, and today more than half of the EU’s biogas production goes toward generating electricity.

There are a couple of different methods for turning that junk into voltage. The oldest involves a vessel called an anaerobic digester: Organic matter goes into an oxygen-deprived tank, where it breaks down over the course of days or months. The resulting gas is often used to power internal combustion engines or turbines that produce electricity and heat. Biogas can also generate voltage through fuel cells, which tap a chemical reaction to separate hydrogen atoms into electrons and protons. The negatively charged particles then run through a circuit, creating energy with fewer emissions than combustion.

Right now, biogas producers fall into three categories—biodigesters, landfill gas recovery systems, and wastewater treatment plants. Trash-heap-based projects currently make up the primary source of biogas production nationwide, bringing in some 17 billion kilowatt hours—less than half a percent of our annual usage.

Farms and wastewater treatment facilities could hold the key to boosting American usage. At present, just 20 dairies and livestock operations around the country turn their dung into power, which nets only around 173 million kilowatt hours—scarcely enough to keep the country alight for 30 minutes. But the EPA estimates there are more than 8,000 farms across the US that could plausibly recover biogas. That would rake in another 16 billion kilowatt hours of energy each year. And as of 2017, just 860 wastewater treatment plants in the States used their gold mine of garbage for biogas energy, leaving more than 15,000 other facilities to send similar sludge off to dumps and incinerators instead.

Sure, closing that gap still wouldn’t give us close to all the juice we need. But toasted trash could fill in a missing piece of the renewable energy puzzle. On days when the sun barely shines and the wind doesn’t blow, animals—and humans—will continue to poop.

Unlocking that potential will largely come down to making policy changes. The rest of the world has already shown us how it’s done. In 2009, the EU mandated that 20 percent of the bloc’s energy come from renewables, and as early as the 1990s, countries like Germany were using incentives to get greener power on the grid. So it’s no surprise that in 2015, the EU produced around half of the globe’s total biogas. With the Biden administration’s new goals of making the stateside power sector “carbon pollution-free” by 2035, the US may have a chance of catching up.

Even before White House mandates, the number of renewable-natural-gas-to-pipeline projects shot up from 219 to 312 between early 2019 and late 2020. According to the Environmental and Energy Study Institute, renewable methane and biogas sources could one day replace 10 percent of the natural gas used in the United States.

So could we ever run the entire electrical grid using nothing but garbage? Probably not. And wind, solar, and hydro arguably have the potential to power the whole thing on their own. But tapping the planet’s junk could help us make the most of methane that would otherwise keep filling our atmosphere. We just need to make sure we learn from the mistakes we made powering all our cars and factories on dinosaurs.

This story originally ran in the Spring 2022 Messy issue of PopSci. Read more PopSci+ stories.

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This post have been updated. It was originally published on January 2, 2020.

The holidays are officially over, and many of us are recovering from reconnecting with loved ones and take in some well-earned R&R. And while the vacation time could mean different things to people—catching up on competitive sports, consuming inordinate amounts of food, or finally confronting your racist uncle—one thing is almost ubiquitous: the looming sentiment of “oh no, I have to go to work again.”

It’s easy to understand why we get a little bummed at the prospect of reverting back to everyday life—dealing with the debilitating effects of jet lag is enough to take a person out of a good mood. But for a lot of folks, ever the most seasoned jet setters, the post-vacation blues can have actual health effects. “I absolutely feel sad after returning home from a trip,” says freelance journalist and travel writer Nneka Okona. “For me, the deflation starts around the last 24 hours of a trip. I feel really down and sometimes even teary; the more of a sensational experience, the harder and deeper the deflation tends to be.”

[Related: What is a toxin?]

But if vacations are supposed to be a significant boon to our happiness and wellbeing, why do we crash mentally afterwards?

Know the reason for the post-vacation blues

Jeroen Nawijn, a psychologist at the Breda University of Applied Sciences who’s studied vacations as they relate to quality of life, says that though people generally see a blissful boost on their days off, those benefits taper off quickly after returning home. “They most likely feel best during vacation because they have more freedom to do what they want,” he explains.

Suzanne Degges-White, a therapist and chair of the Department of Counseling and Higher Education at Northern Illinois University, echoes this sentiment. “Once we get back into the work world, the majority of us have to answer to someone about what we’re doing, how we’re doing it, and when we’ll be done,” she says. She also attributes the difficulty of reacclimating to the fact that quandaries and responsibilities don’t disappear when we go on vacation. “Many people dread the return as they know that problems may have stacked up in their absence. There may be a pile of new requests of their time on top of the unfinished tasks they left behind,” Degges-White adds.

[Related: For better sleep, borrow the bedtime routine of a toddler]

She also cites the influence of transitioning from a looser sleep-wake pattern on vacation to a more strict and regimented bedtime schedule. That, combined with sluggishness from overeating (and drinking, if that’s your style) can put a real drag on a person’s wellbeing, she says. Thankfully, there are ways to keep the vacation high going after you’ve put the good times past you.

Get ready for work before you return

Prepare yourself in advance for the sharp adjustment by adding some extra padding between your travel and work dates, Nawijn says, even if it’s just a day or half a day. Thinking ahead could also include making a to-do list for your first week back, keeping your work and living spaces clean and organized for you return, and prioritizing relaxation as you get back into the swing of things, Degges-White says.

Take another break soon

One more tip: start planning your next vacation right away. “The only thing that has continually worked for me is booking another trip as quickly as possible,” Okona says. “My blues are diminished greatly if I know I have something else to look forward to.” She also recommends nabbing a useful souvenir so that you have something to tie your new experiences with your life back home. (Instead of kitschy magnets and shot glasses, she opts for spice blends, unique snacks, and jams or jellies.)

[Related: The coolest science-themed destinations in all 50 states]

Checking off these little tasks should overall, prepare you better for the reality that awaits post-vacation. And hey, if all else fails, you can always try manipulating your memories to trick yourself into happily ever after.

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With millions of podcasts streaming online these days, it’s easy to get overwhelmed by the amount of variety in the audio-storytelling space. That’s why it’s sometimes better to stick with what you know, like PopSci’s two hit shows, “The Weirdest Thing I Learned This Week” and “Ask Us Anything.” Not convinced? We put our best episodes from this year into a fun, listenable list—and included other science podcasts we adore to help get you hooked. Bottoms up.

The Weirdest Thing I Learned This Week

Moose crash test dummies, famous ferrets, and deadly planets

This wonderful episode features science author Mary Roach, who joined the show to talk about her new book FUZZ: When Nature Breaks the Law. Her fact, which comes straight from the book, is all about why (and how) researchers created moose crash test dummies.

Ancient brain surgeons, the crows have eyes, and why radiators are so annoying

Actor and famous Schitt’s Creek impersonator Michael Judson Berry joined this episode, and it was a downright blast. Listen to Berry impersonate many members of the Rose family and learn all about why we’ve always drilled holes in heads, how radiators saved people during outbreaks, and why crows are, terrifyingly, even smarter than we thought.

Haunted vaginas, fairy floss, and books made of human skin

Halloween episodes of Weirdest Thing are always bangers, and this one is no exception. We learned that ectoplasm is real, but it’s not really the pink or green gooey slime we imagine. More dramatically, the material has been linked to a lot of scams and scandals through history.

Art crime doesn’t pay, canines cooking meat, and eggs done wrong

The comedian (and downright wonderful human) Josh Gondelman made this episode a giggly delight. From unsolved art heists to dogs cooking their humans dinner, this one’s a must-listen.

Science meets magic, high-tech murders, and bees

Jonathan Sims from the riveting horror fiction podcast the Magnus Archives joined the Weirdest Thing for this special recording. The group spun a (true!) story about the first murder reported via telegraph, discussed whether bees can tell time, and blurred the lines between science and magic.

Q&A: Punkin chunkin, mysterious shipwrecks, and midwestern scorpions

In the break between Season 4 and Season 5, host Rachel Feltman and producer Jess Boddy hopped on Zoom to listen to some listener voicemails. What ensued was, as always, wonderful and weird—but to Boddy’s delight, somehow Midwestern-themed. (Did you know scorpions live in Illinois?) The episode is a refreshing change of pace from the typical show format.

See the full list of Weirdest Thing episodes here.

Ask Us Anything

How can you safely send nude photos?

Guest-hosted by Associate DIY Editor Sandra Gutierrez G., the first episode of “Ask Us Anything” Season 2 was juicy and informative. From metadata to camera angles, Gutierrez explains everything you need to know about sending a steamy pic in the safest way possible.

What did dinosaurs taste like?

This is one of those questions that you might never consider—but once you hear it being asked, you’ll be ravenous for the answer. DIY Editor John Kennedy gets into the grisly details of how dinos might have tasted if you tossed them on the grill.

Why can’t we see more colors?

Most humans see the world in a generally consistent way. But other animals see even more colors than we can—so what’s the deal? Is it possible for us to perceive these “invisible” colors too? Science Editor Claire Maldarelli explains what is (and isn’t) possible.

See the full list of Ask Us Anything episodes here.

Other best science podcast episodes

The Outdoor Life Podcast: The mysterious chronic Lyme disease nightmare

Our sister magazine Outdoor Life launched their new podcast this year and took several deep dives on hot topics in the hunting and fishing worlds. This episode focusing on the latest research on chronic Lyme disease, however, felt relatable to a lot of people.

Flash Forward: What is the future of gender?

Former PopSci contributor Rose Eveleth’s podcast is a perennial go-to for our staff. This year’s gender episode really stood out to us, largely because of how it built off a thought experiment Eveleth ran six years ago. A lot has changed in gender science and policies since then, but at the same time, a lot of misunderstandings and questions remain.

Donut Podcasts: How these electric vehicles sparked the Tesla

Another sister publication of ours, Donut Media recently turned its popular YouTube channel into a freewheeling podcasting space. Their episode on the classic tech that fuels modern EVs was fascinating, especially with all the battery-powered trucks and sports cars that were unveiled this year.

For the Wild: Moral landscapes amidst changing ecologies

Indigenous science keeps growing in stature as a way to seek solutions against climate change, extinction, and other environmental problems. This episode, featuring Cal State University East Bay professor and biodiversity expert Enrique Salmón, combines philosophy, chemistry, and deep analysis to help humans rejigger their role in the natural world. It has the power to change minds and practices.

Apple News Today: Does blood hold the key to the fountain of youth?

PopSci writer Kat McGowan chatted about her magazine feature on reverse aging on one of Apple’s premiere podcasts. Listen to her dissect the sensational research that neurobiologists from Harvard and Stanford have been tinkering with for decades. What is fact and what is still fantasy at this point?

Radiolab: Elements

Here’s a nerd fest that you won’t want to miss. WNYC’s “Radiolab” stole our hearts with an entire episode dedicated to illuminating the more obscure parts of the periodic table through poetry, musical theater, and old-fashioned yarn spinning. Turns out, livermorium rhymes pretty well with zirconium.

The post Our favorite science podcast episodes of 2021 appeared first on Popular Science.

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This post has been updated. It was originally published on 5/28/2018.

Food is an excellent way to celebrate life’s adventures. From weddings to birthdays, and backyard summer barbecues (when safe from a public health standing, of course), good cooking is at the center of so many celebrations. Still, in the presence of such abundant deliciousness, we humans tend to—on occasion—overdo it. That’s where good old Tums antacids come in.

Too much fatty, rich, or fried food can lead to that dreaded indigestion and heartburn that sidelines you from the merriment and keeps you up at night. Many people, in these situations, turn to Tums and other similar antacids to relieve their symptoms. The Tums label advises taking only a few in one sitting, not exceeding 7,500 milligrams, which depending on the dosage (it comes in 500, 750, and 1,000 mg doses) can range anywhere from 7 to 15 tablets.

But what if you have like really, really bad heartburn, and you want to just nip it in the bud? Can you just take the whole bottle? In other words, can you overdose on Tums?

While death by Tums overdose is exceedingly rare, downing a bottles’ worth of Tums is ill-advised.

The reason we have so much acid in our stomachs in the first place is because it’s a key component to digestion. Without it, we wouldn’t be able to break down food and therefore wouldn’t be able to absorb nutrients from it.

But it’s also true that acid plays a key role in heartburn, caused by acid reflux. This condition occurs when the valve that covers the bottom of the esophagus (the tube of muscle that connects your mouth to your stomach) relaxes when it shouldn’t, allowing acid to flow back up the esophagus and cause that burning feeling in your chest.

Over time, this can lead to inflammation of the stomach lining, known as gastritis, as well as erosive sections, known as ulcers (though it’s far more common to get these two conditions via infection with a bacteria known as H. pylori).

All that—heartburn, acid reflux, gastritis, and ulcers—is painful. What do Tums do? The reason Tums work so well is because their main ingredient, calcium carbonate is basic and when exposed to the hydrochloric acid in your stomach, the carbonate group binds to the hydrogen. This gets rid of the free floating acid, but in the process frees up calcium ions, allowing them to be absorbed by the body.

That leads to the main potential downside to the question of how many Tums can I take: a decent amount of readily absorbable calcium. The mineral is vital to bone and overall good health, but too much can be toxic to the body, particularly the heart and kidneys.

We know about this link between calcium and health problems partially because it used to be quite a common syndrome. Back in the day, the only method we had to treat peptic ulcer disease (in which an ulcer forms in the stomach lining) was with a combination of milk and sodium bicarbonate, and then later calcium bicarbonate. It was not uncommon for this to lead to something doctors dubbed “milk-alkali syndrome,” which causes high blood calcium levels (hypercalcemia), which can cause irregular heartbeat, metabolic alkalosis (too basic of a pH in the blood), and acute kidney injury. Researchers think the kidney problems result from too much calcium and neutralizing agents building up in the kidneys, which prevents them from being able to filter these compounds out.

[Related: Is it safe to take expired medication?]

Once we invented newer drugs, like Pepcid, Nexium, and Prilosec, that block acid from being excreted into the stomach rather than neutralize it when it’s already there, the cases of milk-alkali syndrome plummeted.

However incidental case reports show that milk-alkali syndrome still pops up from time-to-time, and often it stems from taking far too much calcium carbonate, or Tums.

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So how many Tums can you take and how often can you take Tums? According to one report on recent cases of milk-alkali syndrome, the question is almost impossible to answer for the general population. When calcium carbonate was used to treat peptic ulcers, doctors often gave patients 20 to 60 grams of the neutralizing agent per day, and they noted, on average, that up to 35 percent of patients developed toxic symptoms. Other case reports show that people who took just 4 to 12 grams a day (that’s even less than the recommended maximum for Tums) went on to develop the syndrome. That same case report of milk-alkali syndrome found instances of the syndrome in people taking calcium carbonate daily to supplement their calcium intake.

In the reports, doctors note that certain individuals are far more susceptible to this syndrome than others. Those with impaired kidney function are at a higher risk, but sometimes, they note, it’s not easy to tell who is most susceptible.

Because of the variability in the number of grams of calcium carbonate it takes to lead to certain conditions like milk-alkali syndrome, it’s impossible to say how many Tums are too many Tums. As such, erring on the side of caution is best, taking only the recommended amount, and only supplementing for extra calcium if recommended by a doctor, is best. And if you find yourself taking that recommended maximum on a frequent basis, it could be a good idea to see a doctor to discuss how to improve your digestive ailment.

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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This story has been updated. It was originally published on September 12, 2017.

The bottle of NyQuil always seems to be grimy, faded, and buried beneath layers of toiletries when you come down with a sudden cold. Tired and sniffling, you peer at the label. The medication expired six months ago. At that moment, it’s easy to question the number printed on the bottle: How solid is that expiration date, exactly?

Gina Bellottie, a professor of pharmacology at Thomas Jefferson University in Philadelphia, says that, as a general rule, people shouldn’t take drugs past their expiration dates. But whether or not those dates set in stone, she says, is a loaded question.

The Food and Drug Administration (FDA) requires that drug companies put an expiration date on all prescription and over-the-counter medications. The date that gets stamped in is the result of numerous tests run before the medications even hit the market: Researchers store the drugs under the recommended conditions (room temperature or refrigerated), and check them over time to see if their potency remains intact or if their chemical compounds break down. But companies don’t keep an eye on the drug forever, so if the medications still work until the end of the test period—which is usually between six months and two years—drug makers call it a day. That makes the resulting expiration date simply the last point where the company has data.

“Beyond that date, the drug company doesn’t guarantee it,” Bellottie says. And without further testing, she says, it’s impossible to know if a drug will continue to work just as intended.

But some recent evidence suggests at least some drugs might still be okay. In 2017, ProPublica published an in depth investigation into the research and policy on drug expiration dates, noting that when expired medications are tested, even years later, many of them still retain their potency. The inquiry found that piles of expired drugs, with price tags of thousands of dollars, are thrown out every year, even though testing shows that they work just fine.

But until drugs actually go through longer testing regimens (and there’s nothing to suggest they will anytime soon), day-to-day medication management practice stays the same. “In terms of what I would recommend for one of my patients, it doesn’t change,” Bellottie says: Don’t take an expired drug without checking with a pharmacist first.

A multitude of factors, like storage conditions or the time since the container was opened, could impact the safety and potency of a drug, says Bellottie. It’s possible some drugs may be okay years later, but it’s difficult to say which of those would be without further testing.

If you absolutely must take an expired drug, Bellottie advises against taking one for a life-threatening problem. “For some drugs, the only risk would be well, maybe it won’t work as well,” she says. “If you have a headache, maybe that’s not a big deal. But if it’s for an emergency problem, there’s a risk when a drug doesn’t work the way it’s supposed to.” Further, she says, old medications, especially if they’re open, and especially if they’re liquid, could also become contaminated after a long period of time.

When in doubt, she says, just throw the entire contents of the medicine cabinet into a bag and take them to the nearest pharmacy. The pharmacist can tell you what’s okay to keep taking and what’s not—and let you know about any possible drug interactions or side effects to boot.

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WHEN FEIGE WANG was growing up in Shandong province, China, he liked gazing up at the night sky to look at the stars. Now, as a NASA Hubble fellow at the University of Arizona’s Steward Observatory, he looks much deeper into the darkness to contemplate the most distant objects ever studied.

His targets, quasars, are black holes surrounded by disks of gas and stars—the nuclei of primitive galaxies. Their dark hearts suck in nearby matter and crush the absorbed material into a superhot disk, which burns bright as it shoots out immense amounts of energy. That’s the feature that allows us to spot them from so far away. But because it takes billions of years for their light to reach Earth, we see these beacons in the blackness as they existed eons ago.

[Related: How old is the universe? Our answer keeps getting better.]

As one of today’s foremost quasar watchers, Wang uses them to gaze into the universe’s ancient history. “In the past couple years, I have been pushing to find the most distant ones,” he says, since every additional light-year of distance equals another year of cosmic time travel.

In 2021, using a trio of telescopes in Chile and Hawai’i, Wang and his colleagues discovered the farthest quasar yet. Dubbed J0313-1806, it’s more than 13 billion light-years away, which means Wang saw it as it was just 670 million years after the Big Bang—when it was practically a newborn.

Wang finds the quasar’s black hole particularly fascinating, because according to our current understanding of astrophysics, it shouldn’t exist.

J0313-1806 confounds scientists’ current theories. Black holes of its size are thought to grow from relatively small “seeds” that then suck up mass over time. One model states that the very first stars might have left such seeds in their wake after living fast and burning out young. Otherwise, clusters of stars collapsing in on themselves could come together to make good fodder.

But neither scenario can explain J0313-1806. Its center is around 1.6 billion times the mass of the sun, and about 500 times more massive than the black hole at the core of our own galaxy. At that point in the universe’s history, the cosmos simply hadn’t churned out enough stars to explain the sheer size of J0313-1806’s immense center.

Instead, Wang and his colleagues think that raw hydrogen may have seeded the massive object. It’s possible that a cloud of gas collapsed, eventually becoming dense enough to birth a black hole, which then ate up stars and other gas. But without other quasars of comparable age to observe, the black hole’s provenance remains a mystery.

“We have very little information about the large-scale environment of the earliest quasars,” Wang says, since observers are limited by the reach of current instruments.

[Related: Flickering light could help astronomers weigh supermassive black holes]

But he is optimistic that the next generation of sky-watching machines will help us uncover these secrets. The long-awaited James Webb Space Telescope, set to launch in late 2021 and take the throne of the 30-year-old Hubble, will allow astronomers to peer farther back into time than ever before—and take a closer look at J0313-1806. Other incoming scopes will help as well. Chile’s Vera C. Rubin Observatory, expected to open in 2023, will scour Earth’s southern skies for new quasars, among other things. The Nancy Grace Roman Space Telescope should enter orbit in 2025, where it will peer at infrared wavelengths to spot far-out matter.

Wang hopes such tools will reveal much more about how the earliest black holes grew. “The next decade will be a great time for studying the most distant objects in our universe.”

This story originally ran in the Fall 2021 Youth issue of PopSci. Read more PopSci+ stories.

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This story has been updated. It was originally published on October 20, 2017.

Before the mile run each year in middle school, on the dreaded walk down from the classroom to the course, my classmates would argue over the best way to prevent a side stitch. More so than turning an ankle or coming in last, that repetitive stabbing pain is what the majority of us dreaded most. Our cures ranged across the map from taught techniques, like breathing in through the nose and out through the mouth and not eating for three hours prior, to my favorite: Punching yourself in the stomach at the slightest hint of pain (don’t try it, it doesn’t work).

There’s a medical term for that stabbing side cramp: exercise-related transient abdominal pain, or ETAP. And it’s far from rare. Around two-thirds of runners experience them every year. But unfortunately for middle schoolers, elite athletes, and weekend joggers everywhere, this medical term does not come with a medical solution. There’s no standard advice for how to prevent a side stitch, says sports chiropractor Brad Muir, because we don’t know the mechanism that produces the pain in the first place. “It’s still up in the air.”

That’s partly because, even though side stitches are common, researchers haven’t really studied them. In 2015, a review article noted that after a few studies in the 1940s and 50s, there was a nearly 50 year gap in research on side stitches. Despite that, there are some basic things that we do know about ETAP: It’s more common in younger people; the number of reported cases tends to drop off as people get older. The pain is more common in activities where the upper body twists, like swimming, running, and horseback riding. Athletes of all levels get side stitches—elite athletes get them less often, but their stitches are no less painful than the ones in amateur exercisers.

About half of athletes said that they thought their stitches were triggered by eating or drinking, and some studies back this observation up. In the lab, drinking liquids with high concentrations of sugar were more likely to trigger a painful cramp than beverages with little or no sugar. Things like body mass index, body type, and gender haven’t been connected to the frequency or severity of ETAP.

What we do know about side stitches, the symptoms and risk factors, don’t provide much information about the underlying cause of the pain. One common theory posits that, during exercise, not enough blood (and therefore oxygen) gets to the diaphragm and causes the pain—but side stitches still occur in activities like horseback riding, which don’t tax the respiratory system. “The explanation of it being just the diaphragm never really held up to more scrutiny,” Muir says.

[Related: Why do my muscles ache the day after a big workout]

Another explanation is that jolting movements during exercise put stress on the ligaments in the abdomen that hold the organs in place. That explanation accounts for the role of food and drink in ETAP—putting something in the stomach would make it heavier, forcing those ligaments to work even harder. But it doesn’t account for the high rate in an activity like swimming, where muscle movements are smooth.

Bad posture or problems with a runner’s gait could also be a factor in ETAP, Muir says. There’s some evidence that playing around with certain vertebrae in the spine could reproduce the particular pain from a side stitch, indicating that biomechanical fixes could help with the problem. Friction and irritation in the tissue of the abdominal wall is yet another explanation.

One of the reasons it’s difficult to pin down an explanation for ETAP, Muir says, is that there are so many different components of the problem, and not all of them apply to each case. Four people might come in with their pain on the right side, for example, and then the next three all have the problem on the left. Muir says that it’s rare to have no clear explanation for an abdominal pain. “It seems to be in a class almost of its own.”

Because we don’t know exactly what causes a side stitch, Muir says there’s no standard advice for how to prevent it. The best thing to start with, he says, is a quick rundown of your history: Did you drink a lot of water before that run where you had a particularly bad cramp? Is there something you usually eat on days you’ve had an issue? If you play a sport, he says, the next step might be to have someone check out your form, and make any biomechanical adjustments.

Typically, ETAP will stop when you stop the activity. If it doesn’t, or the pain gets worse, Muir says it’s best to check in with a doctor to rule out any other gastrointestinal or abdominal problems unrelated to exercise.

But usually, side stitches, while incredibly annoying, are innocuous. And there’s no gold standard to make them go away, Muir says. “It’s all sort of trial and error.”

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This article was originally published on November 2, 2017.

In 2014, a woman visited a California doctor’s office complaining of a year and a half of watery diarrhea. She seemed healthy—she hadn’t lost weight and was in excellent shape. In fact, she had started running marathons two years prior, and typically ran about 20 miles every weekend. She also mentioned that she had noticed a correlation between her long runs and the uncomfortable bowel movements, which seemed to become less formed and more frequent as her intense training months dragged on. Her doctors advised the woman to stop running such long distances, and her gastrointestinal issues stopped within a month.

Kim van Wijck, a Netherlands-based physician and triathlete herself, remembers a similar experience with one a patient who was a professional middle-distance runner. The athlete tried everything—giving up caffeine and dairy as well as performing pre-race relaxation techniques—to make her gut less sensitive. But nothing eased the discomfort.

These women are not alone in either their grueling athletic pursuits, or their resulting intestinal distress. On November 5, more than 50,000 runners will gather for the TCS New York City Marathon, and the portapotties will absolutely be vital to a successful—and bearable—race.

Running causes a span of digestive issues that range from heartburn and acid reflux to frequent bowel movements. The most common, however, are those in the lower digestive system, which includes the small and large intestines. These issues can be as mild as bloating and flatulence to as severe as bloody stools. Doctors and researchers don’t know exactly how many runners experience these belly aches, but they estimate it’s around a third to a half at any given time. One study out of the British Medical Journal found that almost half the participants in the 1985 Drammen marathon in Norway reported some degree of runner’s diarrhea during and immediately following the race. Many physicians estimate that most people suffer some form of intestinal trouble eventually.

The good news is that these gut issues, while uncomfortable, are (usually) transient. Understanding why they occur might help some runners deal with the problems, or at least give them comfort in knowing why it’s happening and that they aren’t alone.

One reason for the distress could be that our delicate digestive organs aren’t getting enough blood during exercise; a condition known as ischemia. At any given moment, the heart pumps oxygen and nutrients to whatever organs need it most, which changes depending on the activity at hand. During an intense run, the skin and large muscles are the most urgent recipients, whereas the intestines don’t get as much attention.

That makes sense. While running, our glutes have more of a need for oxygenated blood than our stomachs. In fact, during peak physical exercise, blood flow to the internal organs can decrease by up to 80 percent. While that resource reallocation may be necessary during a track race or to flee from danger during a zombie apocalypse, the lack of blood compromises the mucus that lines the intestines, making it more permeable and prone to disturbance. In one review, Brazilian scientists found that lack of blood flow to the digestive system was the most significant factor in runner’s nausea, vomiting, abdominal pain, and bloody diarrhea.

The tummy troubles don’t end at the finish line, either. The morning- and day-after effects that runners often experience probably have to do with some slight intestinal tissue damage from the lack of blood flow, says van Wijck, though she makes it clear this injury is minor. “It’s kind of like a scraping of the skin,” she says. “Afterward there are new cells and no lasting problem.”

Why is it so common for runners to have runny poop?

There must be more to runner’s diarrhea than ischemia, or else the athletes would experience it at the same rates as those in other sports. The Brazilian researchers showed that the fleet-footed racers dealt with these problems almost twice as often as athletes from other endurance sports, like cycling or swimming. (Other athletes can get digestive issues, but they are usually much different than runner’s trots and are not as common. Swimmers, for example, sometimes deal with excessive burps.) Professional runners were also three times more likely to undergo a bout of diarrhea than recreational runners. Researchers think that the mechanics of sloshing your organs around for hours at a time is likely what amplifies the effect of exercise alone. Some studies have found that the constant gastric jostling for more than 52,000 steps can lead to an urgent needs to use the facilities, as well as flatulence and diarrhea.

Sadly, there aren’t many strategies a runner can use to direct blood flow towards their intestines, or to keep them steady during the race (marathon corsets are not advised). However, athletes can control their diets and how much water they drink—and this could make a difference in how a person’s digestive system performs during long runs. One study found that Ironman participants that ate foods that were high in fiber, fat, protein, and dense carbohydrates during and shortly before the race were more likely to experience problems. Those foods are all more difficult to digest than simple carbohydrates like straight table sugar. The intestines have to work harder to break them down, which is not ideal for an already weakened digestive system. Indeed, all the men who ate thirty minutes before the race threw up during the mile-long swim. (The study did not include women, which is frustrating to the writer, who is an Ironman 70.3 finisher.)

It’s probably best to stay away from hard-to-digest foods prior to racing, but researchers still aren’t completely sure what’s better. The carbohydrate-rich energy gels that are frequently distributed throughout races and that runners consumer before and intermittently during the race might not be any better.

While these are essentially simple carbohydrates in the form of sugar and are supposedly an easy-to-digest, quick energy source, studies looking into the effects they have on runners’ guts are mixed. One small study found that runners who frequently consumed these packets while racing did not experience significant gastrointestinal problems during a ten mile run. But another larger study found the opposite: For both men and women running triathlons and both half and full marathons, there was a correlation between these high-carb gels and reports of nausea and flatulence. Though, when researchers compared the finish times of competitors who consumed the gels to those who didn’t, they found that the ones who used the gels did, on average, achieve faster times. Some scientists recommend drinking beverages with more than two types of carbohydrates—like glucose and fructose—as opposed to a juice with a large amount of one kind of carbohydrate, which seems to make gastrointestinal symptoms worse.

Usually, runner’s problems have to do with the jostling effects of the sport and the decreased blood flow. However, a common habit of long-distance runners can also be exacerbating or triggering the symptoms: The frequent use of non-steroidal anti-inflammatory drugs (NSAIDS), such as ibuprofen. While useful for muscle pain, these can cause problems anywhere along the GI tract, from the esophagus to the colon. In a healthy gut, epithelial cells in the gastrointestinal tract, similar to those in our skin, hold tightly together to protect large molecules from passing through the intestines and into the bloodstream. A small study at the 1996 Chicago marathon hinted that ibuprofen made the mucus lining of the intestines more permeable, which could lead to gut trouble over time, and later studies back up these findings.

These drugs partly work through reducing blood flow to the digestive system, which is a problem that’s exacerbated through exercise, according to van Wijck, who led a study that found that damage markers in the digestive system were twice as high in runners who took these anti-inflammatory meds. And this isn’t just for runners. Its well known that NSAIDs, when taken in high quantities for an extended period of time, can cause gastrointestinal effects, like an inflamed gut, known as gastritis, and even small sores in the stomach lining, called ulcers. Heat and alcohol can also cause gaps between these epithelial cells as well.

While there is no foolproof method to prevent the runner’s runs, staying hydrated and eating foods that won’t aggravate the condition is probably best. And, just as runners practice the race course and the distance, they should also rehearse when to eat and remember when they will need to use the bathroom so that there are minimal to no surprises on race day. “You have to really listen to your body, which people already do when they have muscle pain,” says van Wijck. Paying attention to your gastrointestinal system with the same attentiveness, she says, could help to minimize the amount of discomfort you feel.

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This post has been updated. It was originally published on October 9, 2018.

When he was a child, Donald Unger’s mother and aunts warned that he shouldn’t crack his knuckles, because he would develop arthritis. To prove them wrong, he set out on a half-century long experiment, cracking the knuckles on his left hand at least twice a day, while leaving the right knuckles (mostly) uncracked.

After 50 years, Unger (then a doctor in Thousand Oaks, California) examined his hands—and found no evidence of arthritis in either one, and no other differences between them, either. He wrote to the journal Arthritis & Rheumatology with his findings in 1998. “This preliminary investigation suggests a lack of correlation between knuckle cracking and the development of arthritis of the fingers,” he wrote.

This particular “study” wasn’t exactly scientific—a sample of one isn’t nearly enough to reach a a research-backed conclusion for the entire human population, and Unger wasn’t a neutral observer. But since then, there’s been more rigorous research conducted into the same question, and it’s to largely the same conclusion: Cracking your knuckles probably won’t give you arthritis.

Kevin DeWeber, a sports and family medicine physician at PeaceHealth Southwest Medical Center in Vancouver, Washington, ran one such study—largely because he, too, is a knuckle-cracker. “I’ve been cracking my knuckles for my whole life. Once I developed a scientific mind, and once I got a job that put me in a position where I could do some research, I looked into it,” he says.

The study, published in the Journal of the American Board of Family Medicine in 2010, looked at x-rays of the right hands of over 200 people. About 20 percent of those people reported that they cracked their knuckles routinely, but they were not any more likely to have arthritis in their hands than the people who did not crack their knuckles.

Despite the results of that study and a handful of others, all reaching the same conclusion, the myth that knuckle-cracking will lead to arthritis persists. Why? DeWeber thinks the fracturing sound might have something to do with it. “Knuckle cracking is really annoying to the people who are not doing it,” DeWeber says. “The people who are annoyed want it to stop, so they come up with a story that will dissuade the knuckle-cracker.”

That fictitious story isn’t entirely unreasonable, DeWeber says, even though it’s probably wrong. Joints crack because tiny bubbles of air form in the fluid that surround them, and then rapidly collapse, producing the distinctive sound. Bubbles form and pop in a similar way in ship’s propellers, and in that environment they do cause damage, so it’s possible to make the argument that they’d harm joints, as well. “But the mechanics of a ship’s propellor and the mechanics of a knuckle are different,” DeWeber says.

[Related: You can injure yourself stretching—but it’s not easy]

Trauma to a joint can be a risk factor for arthritis, and the loud sound of a knuckle cracking might sound to some people like it’s a traumatic event. “You’re doing something forceful, so it seems like it’s hurting the joint,” DeWeber says. “It’s a natural conclusion people might come to, but it doesn’t have any supporting evidence.”

DeWeber is careful to note, though, that there isn’t a 100 percent conclusive answer to the knuckle-cracking arthritis query. It’s pretty likely that it doesn’t, and there isn’t a scientific reason that could explain a connection between the two. But to find out for sure, scientists would have to assign people to be knuckle-crackers or non-knuckle crackers, make sure they stuck to their instructions, and follow them for most of their lives, to see if arthritis develops. That’d be incredibly difficult, DeWeber says, so the research we have now is likely the best we’re going to get.

Unger won a 2009 Ig Nobel prize, which honors silly (but still significant) science, for his query into his own knuckle-cracking habits. During his own de-bunking of a well-meaning parental warning, he also questioned some other decrees he was given as a child—like that eating spinach was important. Unfortunately for Unger, though, that one isn’t a myth.

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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This post has been updated. It was originally published on August 23, 2017.

Urinary tract infections are insanely common. Alone, they make up almost 25 percent of all infections, and more than half of women will get at least one in their lifetimes. In parallel, they’re also becoming increasingly harder to treat as the bacteria become resistant to antibiotics. Some urinary tract infections (UTIs) now manage to survive multiple rounds of antibiotic treatment, require bacterial cultures, and last much longer than the usual few days. How can you tell if your or a loved one has an antibiotic-resistant UTI, and what can you do about it?

A classic UTI goes something like this: You feel a burning sensation when you pee, so you see a doctor who diagnoses it and prescribes an antibiotic, which kills the bacteria and clears up the infection in a number of days. Throw in a little cranberry juice for good measure, some extra water, and annoying trips to the bathroom about every 20 minutes, and that pretty much sums up your run-in with the unpleasant infection.

But what happens when your symptoms come back—or refuse to ever really go away in the first place? About 25 percent of women with acute UTIs experience another within six months of the first infection. If you’re an otherwise healthy person, this means the bacteria weren’t totally wiped out, and have regrown to once again wreak havoc on your urinary system (and life). Assuming you’ve taken the entire course of antibiotics, that means the strain of bacteria you were originally infected with is resistant to the particular antibiotic you took. If you’re lucky, a doctor can fix this by having your urine tested, so they can select a second round of antibiotics that’s known to work against the offending bacteria. If you’re really unlucky, it may take two or more rounds of this to knock the UTI from your system.

If you have two UTIs in a three month period, or more than three UTIs in a single year, you officially have a recurrent UTI (RUTI). But the reasons for developing a lingering one isn’t the same for everyone. And not all of them are the result of impervious bacteria. For example, people who are chronically dehydrated (as is often the case with seniors, especially the mentally impaired) are at an increased risk because they aren’t flushing out bacteria at a normal rate. Those who have catheters for other medical reasons are also at an increased risk, because the catheter itself can introduce new bacteria to sensitive areas. Postmenopausal women often have lower estrogen levels, which can harm the good bacteria that should remain in the vaginal flora. Finally, those with physical irregularities that lead to voiding dysfunction (or an incomplete release of urine) are also at risk, since this can keep bacteria from getting flushed out during trips to the bathroom.

[Related: Is urine actually sterile?]

With this in mind, most preventative measures are fairly intuitive. Things that are more likely to introduce bacteria into the urinary tract are risk factors. This includes sex more than three times a week, having multiple partners, using spermicides and diaphragms, or skin allergens like bubble bath, oils, deodorants, or sprays. Good hygiene is important to prevention (though less proven in medical data). This includes wearing cotton underwear, avoiding tight pants, and always peeing after sex. Evidence is mixed about the value of drinking cranberry juice, but doctors agree there is little risk, so go at it. There’s a ton of sugar in most cranberry juice products, however, so popping cranberry pills or pure cranberry juice is better than drinking juice cocktail.

Do RUTIs have anything to do with superbugs? Each time the bacteria in your system survive a round of antibiotics, it means that bacteria is resistant to that drug. Doctors start out prescribing relatively mild antibiotics on a three or five day regimen, at the first tier of “strength,” for your first UTI visit. But they escalate to the second and third tiers (and for longer regimens) as the infection persists. Last year, a woman in the U.S. was treated for a UTI, and the bacteria in her infection were found to be resistant to colistin—one of the strongest “last resort” antibiotics we have. Luckily the infection was susceptible to other drugs lower on the antibiotic ladder, but it’s certainly forced us to confront a reality where antibiotics may actually run out.

The fact that a colistin-resistant bacteria was found in a UTI case shouldn’t be looked over, many experts say. UTIs are such a common problem that they often aren’t taken seriously. They also disproportionately affect women—whose pain we tend to not take as seriously. But if left untreated, they can escalate until a patient urinates blood and experiences extreme discomfort and fever. If the infection reaches the kidneys, it becomes life-threatening. At least one scientist estimates that 8 million UTI cases occur in the US every year, probably 10 percent of which are antibiotic resistant.

[Related: Please stop freaking out about flesh-eating STIs]

Dr. Jeffery Henderson, Associate Professor at Washington University in St. Louis and part of the school’s Center for Women’s Infectious Disease Research, says that he’s noticed UTIs are becoming harder to treat. And he’s surprised by how quickly the antibiotics used to treat common infections are becoming unreliable. One class of them, he says, called fluoroquinolones, went from being almost completely reliable at the beginning of his medical education, to now working only 30 to 50 percent of the time. “We lost an entire class of antibiotics,” says Henderson.

Cases like UTI antibacterial resistance highlight the necessity of new antibiotic development, Henderson says. He and other researchers around the country are currently trying to understand the underlying mechanisms that sustain bacteria. This knowledge could lead to drug therapies that would target that process and stop bacterial growth.

UTIs and even RUTIs are almost never a life-threatening condition, and are not contagious (unless caused by an otherwise infectious sexually transmitted disease). And you can rest assured that, for now, even the most stubborn RUTIs eventually go away with continued communication and treatment—although like many medical conditions, you may always be at elevated risk. However, this increase in RUTIs serves as a reminder that bacteria are powerful and constantly evolving.

The post Why your UTI keeps coming back appeared first on Popular Science.

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This post has been updated. It was originally published on July 31, 2017.

Ever woken up the day after a workout and wondered what you did to deserve such pain?

I’m talking about muscle soreness. That pain can stem from several sources, and understanding what’s behind yours will help you best remedy it—and find ways to potentially prevent it in the future.

Why is my body in so much pain after a day at the gym?

“There’s muscle soreness that could be due to, say weight training, which can cause what we call delayed onset muscle soreness, which is kind of a diffuse soreness in the muscle,” says Thomas Brickner, head team physician for a number of sports at the University of North Carolina. “It usually starts a day or two after a new workout, or a workout that you’re not typically accustomed to.”

Delayed Onset Muscle Soreness (DOMS) is the kind that happens the day after you dive into your first barre class, first run in a few months, or first time trying out weights. And though it can feel like you can barely move, when worst comes to worst you can straighten your arms if need be.

We experience DOMS because of diffuse microscopic injuries to the muscles themselves and the inflammation that results from it. (It’s a common myth that it results from the build up of lactic acid. Lactic acid does cause that intense burning feeling during your last rep or right when your muscles are about to give in. But your body is able to eliminate it from your blood in a few minutes.)

[Related: How to work out for your mental health]

“Usually the delayed onset muscle soreness is just kind of a discomfort in the muscles themselves that is somewhat diffuse, but the pain is usually just kind of mild and [the muscles] won’t typically lose much in the way of motion,” says Brickner. You don’t typically have much in the way of swelling in the area either, he says. For example, if you did some bicep curls a day earlier, your biceps might feel sore, but you’d still be able to straighten your elbows.

How can I make the pain stop?

For DOMS, certain types of exercise may make you more sore than others, especially workouts that include what are called eccentric contractions—ones that cause the muscles to tighten and lengthen at the same time. A good way to visualize this would be to picture doing a squat: the quadricep muscles in your thighs are starting to lengthen as you lower your body, but they are also tightening so you don’t go down too fast. Running downhill can cause this too, Brickner says.

Usually, this type of muscle soreness goes away on its own in a couple of days. But when you are feeling the brunt of it, there are steps you can take to make yourself feel better while it runs its course, and potentially allow the muscles to heal faster, too. Brickner says staying hydrated is extremely important. Your muscle cells need water to properly repair damaged tissue through protein synthesis. If you are bold, he says, and have access to multiple bath-sized bodies of water, a contrast bath—going from a warm bath to a cold one—could be helpful as well. Contrast baths work by opening and closing blood vessels, which creates a “pumping action” that decreases pain and inflammation in the area. You also can’t go wrong with gentle massage of the muscles in pain, which research has shown to switch on genes that decrease inflammation as well as activate mitochondria-producing genes.

When do muscle cramps become more serious?

DOMS is painful, and can really wreck havoc on your daily activities. But you should still be able to do things, albeit a little more slowly. However, if you literally can’t straighten your arm a few days after a round of bicep curls, it’s probably time to call the doctor. Brickner says that this is a sign of rhabdomyolysis, a severe injury to the muscles from an excessive workout. Extreme exercise can actually cause cell death of the muscles themselves. When the cells die, they release toxins into the bloodstream, which can cause immobility of the muscles in question, stiffness, swelling, and a release of myoglobin into the kidneys, which can make your pee look bloody. Not so good.

“A lot of people go and they work out hard and they think, ‘Oh, the muscle soreness is normal, it’s normal soreness from working out,’ but it might not be,” says Bricker. “It might be rhabdomyolysis, which is an abnormal type of muscle soreness. If you have that awareness of what rhabdo is, that is very important thing.” Rhabdo is rare, but if you have intense muscle stiffness, pain and swelling paired with red or brown urine, it’s best to see your doc or head to the emergency room.

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Can I prevent my muscles from getting sore in the first place?

Anyone can fall victim to muscle soreness, whether you are a national championship-earning basketball player or someone who gets wiped out just walking up the stairs (I fall into the latter category). It all comes down to not pushing yourself too hard, especially if you are just now getting back into the swing of things when it comes to working out.

“I see that in our athletes every so often,” says Brickner. Oftentimes they are in great shape, division one athletes, but maybe they just got back from winter or summer break and do a ton of pull ups, more than they had done in weeks or months. Even though they are in great shape, he says, they just overdo it. And the result is muscle soreness.

How do you know not to overdo it and spend the next few days feeling stiff as a board? For the first few times doing a new workout, you should feel like you could keep pushing a little bit harder if you wanted to. For lifting, Brickner recommends picking a weight that doesn’t fatigue you. The weight that you lift should make you think ‘hey, I could go further’ the first few times. As for beginning runners, Brickner says, if you’ve never jogged before, start on an every-other-day basis, and maybe trying something like jogging for a mile and then walking for a mile to gradually build up your distance.

[Related: Here’s what would happen if you worked out like a strongman.]

“Almost all of these things occur because somebody goes into a program too quickly without training the body for it,” he says.

Beyond not wearing yourself out on round one, hydrating and having good nutrition for the workout you’re taking on might help (carbs for aerobic exercise like running, or protein for weight lifting). Warming up and cooling down is also essential to protecting yourself from injury, Brickner says.

“Muscle soreness can happen in the best trained athlete, it can happen in the least trained athlete,” he says. “I think that it can happen to anyone, but the prevention, no matter who you are, is to start off small with any activity that you’re not used to.”

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This is probably a question that you might have heard once or twice in conversations: Did food taste better in the past? It’s one of those things that just kind of gets tossed around as common sense sometimes—the idea that food, and particularly produce, just isn’t like it used to be. 

Unfortunately, we can’t go back in time and pluck a strawberry from a 1960s grocery store and compare it to one found in a supermarket today. Even if we could do that, it’s unlikely that everyone would agree that today’s strawberries are less flavorful than a fresh berry from decades ago. 

In some ways, taste is pretty objective. There are currently five recognized kinds of taste—sweet, sour, salty, bitter, and umami. When we eat food, various receptors (otherwise known as taste buds) react to those tastes and send a signal to the brain telling us what’s going on. But, in other ways, taste can be perplexingly subjective. Certain types of health conditions can impair your sense of taste, as can your mood, along with plenty of other environmental and genetic factors. For example, some people are more sensitive to bitter tastes, making foods that are particularly bitter less palatable. And this is often because of their genetics: Some folks who are more sensitive to bitter flavors—often dubbed supertasters—have a gene named TAS2R38, which heightens their perception of bitterness.

Your taste buds also change as you get older. Most significantly, evidence shows that the number of taste buds we have decreases as we age, and the ones that stick around shrink in size—all of which can affect our ability to detect the five tastes, and can alter our perception of food. 

The way we perceive food can change even by the day. A 2015 study in the journal Appetite analyzed the effect of mood on various tastes by collecting data from 550 people who attended a men’s hockey team season, which encompassed 4 wins, 3 losses, and 1 tie. Analysis showed that positive emotions during the game were associated with heightened sweet perceptions and diminished sour intensities. On the other hand, negative emotions were associated with spiked sour perceptions and decreased sweet sensations. 

On top of all this subjectivity, taste is just one component of what’s known as flavor, which is an incredibly complex mixture of what the tongue literally tastes, what the nose smells, things like texture, and how all that comes together to determine our perception. 

One thing we do know is that the way we produce and consume foods has changed a lot over the past half-century, and that can definitely affect taste.   

Perhaps the best example is the tomato. They’re incredibly popular and are often considered the highest value vegetable crop worldwide. A tomato’s flavor is determined by sugars and acids, which activate our taste receptors, and a set of volatile compounds, which trigger our smell receptors. The combination of the two creates the unique flavor that makes a perfect fresh pasta sauce or BLT so delectable.

Over the years, food scientists have realized the importance of those volatile compounds in particular in making tomatoes taste great. Today, tomatoes are bred to travel long distances without getting bruised and sit in storage without going bad. According to a 2017 study published in the journal Science, this genetic shift has led to a significant drop in the volatile compounds that contribute to a tomato’s aroma, which means we’re getting a less tasty product.

While the tomato has gotten a lot of attention, there are a number of other crops that have been bred similarly to accommodate for the demands of modern agriculture, which means that they’ve likely also lost some of their flavor they once had.

Still, there are other factors that contribute to how much we love one food over another that are far more difficult to study but are nonetheless important. Because flavor and taste have such a strong subjective quality, the nostalgic element of food can’t be ignored. My sister, mom, and I have attempted countless times to make my grandmother’s lemon bread, which we would devour every year around the holidays during my childhood. We always get compliments on it, but to us it tastes nothing like the real thing. It could be nostalgia; I’m also convinced she doubled the amount of lemon syrup. 

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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If you put a steamy cup of coffee in the refrigerator, it wouldn’t immediately turn cold. Likewise, if the sun simply “turned off” (which is actually physically impossible), the Earth would stay warm—at least compared with the space surrounding it—for a few million years. But we surface dwellers would feel the chill much sooner than that.

Within a week, the average global surface temperature would drop below 0°F. In a year, it would dip to –100°. The top layers of the oceans would freeze over, but in an apocalyptic irony, that ice would insulate the deep water below and prevent the oceans from freezing solid for hundreds of thousands of years. Millions of years after that, our planet would reach a stable –400°, the temperature at which the heat radiating from the planet’s core would equal the heat that the Earth radiates into space, explains David Stevenson, a professor of planetary science at the California Institute of Technology.

Although some microorganisms living in the Earth’s crust would survive, the majority of life would enjoy only a brief post-sun existence. Photosynthesis would halt immediately, and most plants would die in a few weeks. Large trees, however, could survive for several decades, thanks to slow metabolism and substantial sugar stores. With the food chain’s bottom tier knocked out, most animals would die off quickly, but scavengers picking over the dead remains could last until the cold killed them.

Humans could live in submarines in the deepest and warmest parts of the ocean, but a more attractive option might be nuclear- or geothermal-powered habitats. One good place to camp out: Iceland. The island nation already heats 87 percent of its homes using geothermal energy, and, says astronomy professor Eric Blackman of the University of Rochester, people could continue harnessing volcanic heat for hundreds of years.

Of course, the sun doesn’t merely heat the Earth; it also keeps the planet in orbit. If its mass suddenly disappeared (this is equally impossible, by the way), the planet would fly off, like a ball swung on a string and suddenly let go.

This article originally appeared in the November 2008 issue of Popular Science magazine.

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THERE’S PERHAPS nothing more ancient and unchanging than the sun, a yellow dwarf star that has illuminated Earth for over 4 billion years.

But our star, too, shall pass. And scientists are actually pretty certain about what will happen when it does. 

The sun powers itself by fusing, or combining, extremely hot hydrogen atoms inside its core. That creates helium and a lot of energy. But just as a music box will wind itself out, the hydrogen in the sun’s core will run dry. When that happens, in around 5 billion years, the sun will have to find a new power source. 

At first, that’s not a problem. Today, fusing hydrogen also lets the sun’s core push back against the outer layers pressing down. When the core can no longer hold out, hydrogen from those outer layers will flood in and heat up—giving the sun more fuel to fuse. All will seem well.

But this will come at a cost. The side effects of these events will cause the sun to redden, cool, and inflate to more than a hundred times its current size, swallowing the orbits of Mercury, Venus, and even Earth. The sun will transform into a red giant, just like the stars Arcturus or Aldebaran that we can see in our sky.

[Related: We still don’t really know what’s inside the sun—but that could change very soon]

It’s all for a fix of hydrogen that will only buy the sun an extra billion years of life. When that, too, runs out, the sun will be forced to reach for the next best thing: that helium it’s produced all this time.

When the sun begins to fuse helium, it might seem a return to normal. The helium will partly rebuild the ruins of the core, and the bloated star will lose much of its size. Astronomers call this the helium flash. But there’s a catch: The flash will burn off nearly a tenth of the sun’s perfectly good helium in mere minutes.

Afterwards, the increasingly geriatric sun faces a fatal problem: As fuel, helium just doesn’t compare to hydrogen. Fusing helium isn’t nearly as energy-efficient as fusing hydrogen, and it produces carbon and oxygen. It’s possible to fuse those, but it’s far more difficult and far more inefficient.

The remaining helium will only buy the sun another 100 million years or so.

When the sun can no longer fuse helium, it will enter another troubled time. It’ll puff back up, desperately flailing for any pockets of hydrogen or helium it can fuse. Even as the core starts to collapse, the star might push its outer rim ever farther away, maybe all the way past the asteroid belt.

This can only go on for so long. In the end, the sun will throw off all of its outer layers. Observers in the next star system might see a spectacular display, like a bright halo. For the sun we recognize, these 10,000 years are its moment of death.

It will leave behind a sort of celestial tombstone called a planetary nebula, even though planets aren’t involved—unless the dark, dead husks of what were once Jupiter, Saturn, Uranus, and Neptune manage to stop themselves from being blown away.

But for the sun, death is not the end. While about half its mass will flood out, the rest will crush together at the very center of the planetary nebula. This will turn into a tiny, bright, ultra-dense ember of the sun’s core, no larger than the Earth. This kind of smoldering remnant is called a white dwarf star.

So begins the sun’s long, last, lonely form. Over trillions of years, over a time that’s hundreds of times longer than the current age of the universe, that white dwarf will—very, very slowly—lose its remaining heat and fade to black.

This story originally ran in the Summer 2021 Heat issue of PopSci. Read more PopSci+ stories.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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This story has been updated. It was originally published on July 24, 2013.

Of all the bodies in our solar system, the sun is probably the one we want to give the widest berth. It gushes radiation, and even though its surface is the coolest part of the star, it burns at about 9,940 degrees Fahrenheit, hot enough to incinerate just about any material. As such, there are no plans to send a manned mission in its direction anytime soon (Mars is much more interesting, anyway), but it can’t hurt to figure out at what distance a person would want to turn back. You can get surprisingly close. The sun is about 93 million miles away from Earth, and if we think of that distance as a football field, a person starting at one end zone could get about 95 yards before burning up.

That said, an astronaut so close to the sun is way, way out of position. “The technology in our current space suits really isn’t designed to withstand deep space,” says Ralph McNutt, an engineer working on the heat shielding for NASA’s Messenger, a new robotic Mercury probe. The standard space suit will keep an astronaut relatively comfortable at external temperatures reaching up to 248°. Heat coming off the sun dissipates over distance, but a person drifting in space would begin encountering that kind of heat (the five-yard line) some three million miles from the sun. “It would then be a matter of time before the astronaut died,” McNutt says. Above 248 degrees, the suit would transform into a close-fitting sauna—the temperature would climb above 125 degrees and the person would become dehydrated and pass out, eventually dying of heatstroke.

Riding in the space shuttle, though, someone could get much closer to our star. The ship’s reinforced carbon-carbon heat shield is designed to withstand temperatures of up to 4,700 degrees to ensure that the spacecraft and its passengers can survive the friction heat generated when it reenters the atmosphere from orbit. If the shield wrapped the entire shuttle, McNutt says, astronauts could fly to within 1.3 million miles of the sun (roughly the two-yard line). But the integrity of the shield degrades rapidly above 4,700 degrees, and the cockpit would begin to cook. “I would advise turning away from the sun well before that point,” McNutt says. Much hotter than that, the shields would fail altogether, and the vehicle would combust in less than a minute.

Of course, just getting that close to the sun would be quite an accomplishment, says NASA radiation-health officer Eddie Semones. The constant exposure to cosmic radiation during the voyage would most likely prove fatal before the astronauts crossed the 50-yard line.

This article originally appeared in the August 2010 issue of Popular Science magazine.

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As a middle schooler, one of my life goals was the Presidential Fitness Award—an accolade given to those who passed a series of gym-class tests that included doing a number of pull ups, running a mile, and, among other things, the sit and reach: A flexibility test in which one sits with their legs outstretched in a V position and reaches their fingertips as far past their ankles as they can manage. That’s where things went sour for me. I could never reach quite far enough to be a presidential fitness scholar.

The sit and reach is essentially a modified version of another popular stretching exercise: touching your toes. For many people, such a maneuver is an easy way to begin or end any sort of workout. It’s part of the warm up or cool down routine in countless youth sports programs and gym classes.

And for good reason. For most people, toe touching is among the easiest stretching exercises to do, and it incorporates a number of different muscle and joint groups. But for me (and many of my peers) it’s sheer agony. Why? It turns out that the ability to touch your toes is the summation of a number of different physiological factors, many of which we have no control over.

“The two biggest factors are the flexibility of your hamstrings and and the range of motion of your hip joints,” says Jeffrey Jenkins, a physiologist at the University of Virginia School of Medicine. “But the other big factor is the relative length of your arms and your torso to your legs.”

Hamstrings are the set of three muscles that rest behind the thighs, running from your pelvis and hip area down to your knees. When you bend down to touch your toes, hamstrings do the most work. The range of motion of your hips is equally important. When you bend down to actually reach the ground, you have to be able to bend your hip joints forward. In conjunction with that, Jenkins says, you also have to be able to flex your lumbar spine. If you have an arched or a stiff back or a lot of injuries to your spine that inhibit your ability to bend forward, that could also alter how far down you can reach.

To a certain degree, you can work your hamstring muscles to make them more flexible. However, the flex your hips is beyond your control and unfortunately can’t be altered with any stretching program.

The other major physiological attribute that can’t be changed is the span of your arms and length of your torso compared to the height of your legs. Someone like Michael Phelps, who is famous for his long torso, long arms, and relatively short legs, would likely have no problem touching their toes without doing a single hamstring stretch. “On the other hand,” says Jenkins, “someone can be really flexible, but if their arms and hands are short relative to their legs, then even at their maximum flexibility they might still not be able to touch their toes, because their arms and fingers aren’t long enough to reach.”

Life is so unfair.

Why does the stretch even exist then?

Jenkins says that although there are some unjust aspects, overall the toe touch is not the worst measure of flexibility. There are ways to directly measure range of motion of specific muscle groups by using something called a goniometer, which calculates the exact angle of specific joints. But the toe touching exercise can also measure the flexibility of the whole body—to a certain degree.

“It involves the hamstrings, the hips, and the spine,” he says. “And, though it has it’s faults, I can’t really think of anything that’s that much better than it, in terms of easily measuring someone’s flexibility health.” Perhaps, he says, the straight leg raise—starting in a supine position, a person raises one outstretched leg as far as possible while keeping the other leg straight and using a goniometer to measure the angle between the legs—is a better measure of just hamstring flexibility than touching the toes, since it takes the confounding variables of leg and arm length out of the equation.

But if you are flexibility inept like me, there are some thing you can do to improve the elasticity of the body you have. It might not get you that coveted Presidential Fitness Award (though apparently President Obama did away with that back in 2012 anyway), but it could at least help you reach your ankles without experiencing excruciating pain and humiliation in your yoga classes.

Your muscle groups contain cells called muscle spindles. Whenever you stretch a muscle, these sensory receptors tell neurons within the muscle to fire a signal back to the central nervous system through the spinal column. This causes your muscles to contract, tighten, and resist the force to be stretched, resulting in that annoyingly painful feeling that most of us get when we first reach down to touch our toes or attempt to stretch other muscles. However, Jenkins says, if you are patient, this too shall pass.

If you hold the stretch for a minimum of six seconds, you can actually conquer the reflex. Around that time, the muscle’s golgi tendon organs—spindles of neurons that sit on the muscle fibers—kick in and inhibit muscle contractions, allowing your muscles to relax and lengthening the stretching you can do.

“That’s why we tell people to hold a stretch for at least 15 seconds. Often, it’s even better to hold it for 30 or 60 seconds,” says Jenkins. “The extra time ensures the the golgi tendon organ mechanism to kick in.” In fact, Jenkins says, there’s some preliminary evidence that holding static stretches for 30 seconds results in greater improvement in flexibility than holding it for 15 seconds, and just as much improvement as 60 seconds. And that one stretching session a day gave the same results as three times a day.

But for some people, the pain that accompanies those six seconds is just too severe. Certain folk’s central nervous systems interpret stretching as a more noxious stimulus than others. If you can get past that pain, then you can probably improve your flexibility. However, Jenkins cautions against enduring too much pain: If you’re in agony, you could be tearing a muscle. That’s not a good thing. And it’s hard to tell someone how to differentiate muscle tearing from the discomfort of the muscle contraction, Jenkins says, because experiences of pain are so subjective.

If you are able to push through what feels like a reasonable amount of pain and keep up a good stretching program, several studies suggest that you can actually elongate your muscle and build more sarcomeres and other structural units of muscle tissues. But most of what you are doing in a stretching program, Jenkins says, is training your nervous system to lose those intense inhibitory factors so your muscle fibers can relax more easily.

Okay, but how important is flexibility? Does it improve your overall health?

Generally speaking, more flexibility is a good thing. It promotes blood flow and, according to Jenkins, flexibility training and muscle elasticity itself can prevent certain kinds of injuries in sports and other recreational activities. “But in terms of specifically touching your toes, I am dubious about its effect on fitness and health because there are so many factors beyond your control,” says Jenkins.

He told me that I shouldn’t feel too bad about my toe touching deficiency. As a lifelong runner, I was concerned that perhaps my inflexibility could be affecting my running performance. But the opposite could also be true: There’s some evidence that improving flexibility in the lower limbs can actually decrease muscle strength and running efficiency.

So the next time I’m reminded of my inability to touch the floor, I’ll just remember that: My inflexibility might be making me a stronger, faster runner.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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The final frontier smells a lot like a Nascar race—a bouquet of hot metal, diesel fumes and barbecue. The source? Dying stars, mostly.

The by-products of all this rampant combustion are smelly compounds called polycyclic aromatic hydrocarbons. These molecules “seem to be all over the universe,” says Louis Allamandola, the founder and director of the Astrophysics and Astrochemistry Lab at NASA Ames Research Center. “And they float around forever,” appearing in comets, meteors and space dust. These hydrocarbons have even been shortlisted for the basis of the earliest forms of life on Earth. Not surprisingly, polycyclic aromatic hydrocarbons can be found in coal, oil and even food.

Though a pure, unadulterated whiff of outer space is impossible for humans (it’s a vacuum after all; we would die if we tried), when astronauts are outside the ISS, space-borne compounds adhere to their suits and hitch a ride back into the station. Astronauts have reported smelling “burned” or “fried” steak after a space walk, and they aren’t just dreaming of a home-cooked meal.

The smell of space is so distinct that, three years ago, NASA reached out to Steven Pearce of the fragrance maker Omega Ingredients to re-create the odor for its training simulations. “Recently we did the smell of the moon,” Pearce says. “Astronauts compared it to spent gunpowder.”

Allamandola explains that our solar system is particularly pungent because it is rich in carbon and low in oxygen, and “just like a car, if you starve it of oxygen you start to see black soot and get a foul smell.” Oxygen-rich stars, however, have aromas reminiscent of a charcoal grill. Once you leave our galaxy, the smells can get really interesting. In dark pockets of the universe, molecular clouds full of tiny dust particles host a veritable smorgasbord of odors, from wafts of sweet sugar to the rotten-egg stench of sulfur.

This article originally appeared in the February 2011 issue of Popular Science magazine.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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When you’re a kid, your stance on homework is generally pretty simple: It’s the worst. When it comes to educators, parents, and school administrators, however, the topic gets a lot more complicated. 

Collective educational enthusiasm toward homework has ebbed and flowed throughout the 20th century in the US. School districts began abolishing homework in the ‘30s and ‘40s, only for it to come roaring back as the space race kicked off in the late ‘50s and drove a desire for sharper math and science skills. It fell out of fashion again during the Vietnam War era before it came back strong in the ‘80s.

As the country mostly transitions back to full-time, in-person schooling, the available research on homework and its efficacy is still messy at best. 

How much homework are kids doing?

There’s a fundamental issue at the very start of this discussion: we’re not entirely sure how much homework kids are actually doing. A 2019 Pew survey found that teens were spending considerably more time doing schoolwork at home than they had in the past—an hour a day, on average, compared to 44 minutes a decade ago and just 30 in the mid-1990s. 

But other data disagrees, instead suggesting that homework expansion primarily affects children in lower grades. But it’s worth noting that such arguments typically refer to data from more than a decade ago. 

How much homework are kids supposed to be doing?

Many schools subscribe to a “rule of thumb” that suggests students should get 10 minutes of homework for each grade level. So, first graders should get just 10 minutes of work to do at home while high schoolers should be cracking the books for up to two hours each night. 

This once served as the official guidance for educators from the National Education Association, as well as the National PTA. It also serves as the official homework policy for many school districts, even though the NEA’s outline of  the policy now leads to an error page. The National PTA also now relies on a less-specific resolution on homework which encourages districts and educators to focus on “quality over quantity.”

The PTA’s resolution effectively sums up the current dominant perspective on homework. “The National PTA and its constituent associations advocate that teachers, schools, and districts follow evidence-based guidelines regarding the use of homework assignments and its impact on children’s lives and family interactions.”

Even with these well-known standards, a study from researchers at Brown University, Brandeis University, Rhode Island College, Dean College, the Children’s National Medical Center, and the New England Center for Pediatric Psychology, found that younger children were still getting more than the recommended amount of homework by two or three times. First and second graders were doing roughly 30 minutes of homework every night. 

Does homework make kids smarter?

In the mid-2000s, a Duke researcher named Harris Cooper led up one of the most comprehensive looks at homework efficacy to-date. The research set out to explore the perceived correlation between homework and achievement. The results showed a general correlation between homework and achievement. Cooper reported, “No strong evidence was found for an association between the homework–achievement link and the outcome measure (grades as opposed to standardized tests) or the subject matter (reading as opposed to math).” 

The paper does suggest that the correlation strengthens after 7th grade—but it’s likely not a causal relationship. In an interview with the NEA, Cooper explains, “It’s also worth noting that these correlations with older students are likely caused, not only by homework helping achievement but also by kids who have higher achievement levels doing more homework.”

A 2012 study looked at more than 18,000 10th-grade students and concluded that increasing homework loads could be the result of too much material with insufficient instructional time in the classroom. “The overflow typically results in more homework assignments,” the lead researcher said in a statement from the University. “However, students spending more time on something that is not easy to understand or needs to be explained by a teacher does not help these students learn and, in fact, may confuse them.”

Even in that case, however, the research provided somewhat conflicting results that are hard to reconcile. While the study found a positive association between time spent on homework and scores on standardized tests, students who did homework didn’t generally get better grades than kids who didn’t. 

Can homework hurt kids?

It seems antithetical, but some research suggests that homework can actually hinder achievement and, in some cases, students’ overall health. 

A 2013 study looked at a sample of 4,317 students from 10 high-performing high schools in upper middle class communities. The results showed that “students who did more hours of homework experienced greater behavioral engagement in school but also more academic stress, physical health problems, and lack of balance in their lives.” And that’s in affluent districts. 

When you add economic inequity into the equation, homework’s prognosis looks even worse. Research suggests that increased homework can help widen the achievement gap between low-income and economically advantaged students; the latter group is more likely to have a safe and appropriate place to do schoolwork at night, as well as to have caregivers with the time and academic experience to encourage them to get it done. 

That doesn’t mean financially privileged kids are guaranteed to benefit from hours of worksheets and essays. Literature supporting homework often suggests that it gives parents an opportunity to participate in the educational process as well as monitor a child’s progress and learning. Opponents, however, contest that parental involvement can actually hurt achievement. A 2014 research survey showed that help from parents who have forgotten the material (or who never really understood it) can actually harm a student’s ability to learn. 

The digital homework divide

Access to reliable high-speed internet also presents an unfortunate opportunity for inequity when it comes to at-home learning. Even with COVID-era initiatives expanding programs to provide broadband to underserved areas, millions of households still lack access to fast, reliable internet. 

As more homework assignments migrate to online environments instead of paper, those students without reliable home internet have to make other arrangements to complete their assignments in school or somewhere else outside the home. 

How do we make homework work?

Some experts suggest decoupling homework from students’ overall grades. A 2009 paper suggests that, while homework can be an effective tool for monitoring progress, assigning a grade can actually undercut the main purpose of the work by encouraging students to focus on their scores instead of mastering the material. The study recommends nuanced feedback instead of numbered grades to keep the emphasis on learning—which has the added benefit of minimizing consequences for kids with tougher at-home circumstances. 

Making homework more useful for kids may also come down to picking the right types of assignments. There’s a well-worn concept in psychology known as the spacing effect, which suggests it’s easier to learn material revisited several times in short bursts rather than during long study sessions. This supports the idea that shorter assignments can be more beneficial than heavy workloads. 
Many homework opponents add that at-home assignments should appeal to a child’s innate curiosity. It’s easy to find anecdotal evidence from educators who have stopped assigning homework only to find that their students end up participating in more self-guided learning. As kids head back into physical school buildings, the homework debate will no doubt continue on. Hopefully, the research will go with it.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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There are many luxuries in life, but water is decidedly not one of them. Most of us are aware that we all need the liquid to survive, but exactly how much of it is necessary is surprisingly complex. 

There’s a popular notion that we all need to be chugging eight cups of water everyday for optimal health. While it is true that staying hydrated will certainly help contribute to your body working at its best, there’s no evidence to suggest that consistently drinking eight glasses of water a day is needed. 

In reality, each person’s water intake needs vary, and they depend on a number of factors, including how much exercise you get, the weather conditions of where you are, what you eat, and other health conditions you might have. Taking all these factors into account, the purported eight glasses a day just doesn’t work for most people. And our bodies already have an easy way to tell us if we need water: thirst. You can quickly replenish your lost fluids with a good helping of water. The human body has a carefully calibrated system for deciding when it needs more hydration and by listening to its cues, you can ensure you stay on top of your hydration needs. 

The amount of water you need depends on your body size. According to a 2018 review, infants need less water (in the form of breastmilk or formula, of course) than young children, who need less water than teens and adults who generally need the same amount of the liquid, on average. There are other factors to consider in this equation, too. For instance, people who are lactating need the most baseline water than most other groups. 

Your activity level also plays a large role. If you are exercising a lot, then you are more likely to sweat more, which forces you to need more water to replenish that lost amount. This is especially true if you are exercising in a particularly hot or humid environment, or your workout is long or intense. 

Additionally, water is not the only source of hydration. In fact, according to a highly-cited 2005 report from the ​​Institute of Medicine, we get about 20 percent of our hydration from the food we eat. Some foods, like watermelon, are almost exclusively water. It also might surprise you that consuming caffeinated beverages, such as tea or coffee, which are often considered diuretics, don’t actually dehydrate you. While caffeinated beverages will likely make you have to pee, that effect is temporary, and won’t have a considerable effect on your overall hydration balance. In other words, all those cups of coffee you down every day are indeed contributing to your daily hydration needs.

Given that you don’t need to be chugging all those glasses throughout the day, how can you tell if you are staying on top of your hydration needs? The answer is surprisingly simple. Follow your thirst.  

While it is true that you can drink water to excess, it is incredibly hard to do. Hyponatremia occurs when your body does get too much water and the amount of water in your blood becomes so high that it throws your electrolytes, particularly sodium, off balance. The condition, whose symptoms include headaches, confusion, nausea, and muscle weakness, is incredibly dangerous, but thankfully rare. Listening to your body’s thirst—and noting when weather, exercise intensity, or other factors, might make you more likely to need extra hydration—will ensure you are getting all the water you need, no counting required. 

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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Unless someone finds well-preserved dinosaur DNA and decides to breed, say, free-range Velociraptors in an agricultural twist on the standard Jurassic Park scenario, we’re probably not ever going to taste the flesh of the roughly 700 species of extinct dinos. But we can hypothesize, and the answer is a lot more complicated than “dinosaurs probably tasted like chicken.”

Let’s get one thing out of the way first: If you’ve eaten any type of bird, you’ve eaten dinosaur. Modern birds are the last living therapods—the same group of animals that includes Tyrannosaurus rex and Velociraptor—so they’re not simply “descended from” dinosaurs, they are dinosaurs.

So yes, chicken (a dinosaur) tastes like chicken. Crocodilians (like alligators), which share a common ancestor with dinosaurs, also kind of taste like chicken. And that’s a good starting point when you’re thinking about what Stegosaurus or Compsagnathus might’ve tasted like.

“In evolutionary biology terms, there is an extant phylogenetic bracket of chicken-tasting animals—crocs and birds—surrounding the dinosaurs on the family tree, making it reasonable that the dinosaurs had a chicken taste too,” says Steve Brusatte, a paleontologist and professor at the University of Edinburgh.

But it’s not that simple. Every bird has a unique taste. If you’ve eaten duck in the US, it was probably the American Pekin, a domesticated mallard with a mild, somewhat gamey taste. Merganser, another type of duck, is quite fishy and some people find it unpalatable. Extinct dinosaurs likely had similarly varied flavor profiles.

There are also countless factors that go into making something taste the way it does, but two of the most important are muscle usage and diet.

Triceratops and Allosaurus likely had fast- and slow-twitch muscles like people and other animals do. Slow-twitch fibers are associated with dark meat—thanks to reddish hues linked to the oxygen-carrying protein myoglobin—while fast-twitch fibers are associated with white meat.

Smaller predatory dinosaurs probably had to move quickly to ambush prey and dart away from threats, so they might’ve had a fair amount of white meat. Velociraptor may have truly tasted like chicken. Larger dinos, on the other hand, likely had large muscles that were constantly moving and needed a lot of oxygen, so they might’ve more closely resembled beef or venison.

Animals can also take on the flavor of things they eat. Grass-fed beef can be a bit more earthy than corn-fed cattle, for example. Dinosaurs, however, probably didn’t eat much grass, as it didn’t evolve until the very end of their 165 million-year reign. Therapods had a varied diet, while herbivores chowed down on ferns, cycads, and conifers, to name some ancient plants that are still around today.

Today, deer eat a similar diet, so some dinosaurs could’ve tasted like venison. They also may have been gag-inducing—the spruce grouse, a chicken-like bird, spends its winters munching almost exclusively on conifer needles. If you eat one at that time, it can taste heavily of spruce, almost like turpentine, says Hank Shaw, a chef and outdoorsman who specializes in wild foods.

Ultimately, there’s no definitive answer for what extinct dinosaurs might’ve tasted like, but we can let our imaginations run wild. And if someone ever does acquire the ability to bring dinosaurs back from extinction, we’d do well to remember that the Jurassic Park movies don’t end with people eating their creations—more often, it’s the other way around.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

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The Guinness book of world records states that Michel Lotito died at age 57, of natural causes. But not before this competitive eater had consumed 18 bicycles, 15 supermarket carts, seven TV sets, six chandeliers, two beds, a pair of skis, a low-calorie Cessna light aircraft, and a computer.

It’s unclear what compelled Lotito to do this, and whether he was aware of the many ways he was jeopardizing his health.

First things first: No nutritionist, doctor, or even the trendiest of dieters would recommend or applaud eating a computer. But it begs a ridiculous yet perhaps equally intriguing question: Is consuming one really that dangerous? Many of the same metals that are found inside electronic devices—magnesium, iron, and sodium—are also found inside the human body. In the event of a dare, would consumption be possible?

Unfortunately, the benefits of eating a computer do not come close to outweighing the risks, many of which include death. The first potential peril is the choking hazard. Even competitive eaters have been unable to swallow much softer foods. In fact, last year, two Nathan’s contestants died after choking on a doughnut and a pancake, respectively, according to Metro News. Silicon and fiberglass are much harder to gulp down. Even Lotito cut his metallic meals into pieces that were one to two centimeters long. On top of that, anything that is long or sharp has the potential to scratch or tear the eater’s esophagus, the long tube that connects the mouth to the stomach.

If you did somehow manage (like Lotito did) to pulverize the computer and then swallow it without issue, heavy metal poisoning would be your next obstacle. Circuit boards sometimes contain tiny amounts of arsenic — not enough to kill you immediately, but if you ate several computers, the dose would add up. Aluminum, a common component found in the casings of both the computer and its hard drive, has no biological function in the human body and seems to gum up normal body processes. Some case reports have described that people in the end stages of liver disease who are no longer able to flush aluminum out of of their bodies suffer nerve damage, presumably from the metal. Older computer monitors also contain up to eight pounds of lead, as well as mercury, arsenic, cadmium, and beryllium, according to the Long Island manufacturing center, a recycling and e-waste drop-off site.

Most people are aware that lead isn’t great for you—immediate side effects can include nausea, vomiting, and abdominal pain. If the lead poisoning continues, the victim can eventually die, typically from kidney failure. In 2006, a child died after swallowing a small lead charm—eating an entire computer’s worth of the metal is a viable way of ingesting enough to kill. So how did Lotito survive? In the child’s case, the lead charm got stuck in the kid’s stomach, where acids slowly broke it down. If it hadn’t, the piece of metal would have passed through the digestive system quickly and would have caused less damage, according to Helen Binns, a professor of pediatrics and preventative medicine at Northwestern University’s Feinberg School of Medicine. “If you had a fishhook that got stuck in your intestines, that would cause problems,” she says. “If you swallow a bead or something like that, it just passes through your bowel.”

But metals aren’t the only form of toxic indigestion you might endure. The optical drive, the part that allows you to read CDs (unless you have a new Mac), is covered with a light-sensitive substance called a photoresist application. Studies have shown that this doesn’t seem to be very good for lab animals, though it was not fatal. When scientists gave it to mice and rabbits, it caused inflammation around their eyes and skin, as well as weight gain.

The flame retardants that keep your electronics from easily combusting are not delicious or nutritious, either. These substances surround the computer’s copper wires and drift into the atmosphere if burned or crushed as waste. In addition to disrupting fertility, some evidence suggests these flame retardant chemicals might also disrupt human hormone systems, according to the National Institute of Health, and some studies have shown a correlation between certain types of flame retardant and cancer.

Eating computers, though still not safe, has become less deadly over time. The European Union banned cadmium and lead from computers in 2006 and newer circuit boards are less likely to contain arsenic. In 2009, the Institute of Electrical and Electronics Engineers created environmental guidelines that companies and institutions can adhere to, and the even more recent Green Electronics Council grades companies according to how recyclable they are. However, old computers still turn up at recycling centers. “Sometimes people will hold onto things for a long time — we get 40 or 50 year old TVs,” says Jason Linnell, executive director at the National Center of Electronics Recycling. “They might have the lead, the mercury, cadmium. These are the types of materials that you want to prevent from going into the landfill.”

In the future, humans may eat computers on purpose. Right now scientists are developing nanocomputers that patients will be able to swallow like a pill. These tiny robots will be able to monitor your vital signs from the inside, and may also, in the future, be able to fill in one of your hundred hard-to-remember passwords. Prototypes already exist for people like astronauts, firefighters, and football players, whose caretakers want to make sure they do not overheat. Scientists are working on developing computers that are more biodegradable — like this computer chip made of wood-based nanocellulose.

Since most of us lack Lotito’s steel-crushing stomach, recycling is the much more appealing (and safer) option. “Things have definitely gotten better,” says Linnell. “We have a lot more well-qualified recyclers.” In some cities, you can even be fined for putting old computers in the pile with normal trash. Instead, many manufacturers take back old products and many cities offer e-waste deposit locations. There is no need to eat your computer.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

The post What would happen if I ate my computer? Asking for a friend. appeared first on Popular Science.

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When so much of our communication happens online, sexting and sending nude photos are as healthy and natural as having sex. 

A 2018 survey revealed 40 percent of Americans have sent at least one naked picture of themselves, while data from 2015 shows nine out of 10 adults have sexted. Contrary to popular belief, these activities are not restricted to single people on dating apps, but are very much a part of committed bliss. The same 2015 survey found that three out of four sexters were in long-term relationships, and they were more likely to say they were sexually satisfied than single people.

Being able to instantaneously swap photos with someone no matter the distance can be really fun, but ease can make you ignore potential complications. Just like having sex, sending nudes can have unintended lifelong consequences you might not be willing to deal with. But you can easily minimize risks and protect yourself by being safe.  

Sending nudes 101

Let’s go over the basics. Even if you sent your first nude decades ago with an original Motorola Razr, there might still be something you can learn to make the experience better and safer for you and the recipient of your sexy pics. 

There’s no such a thing as completely safe nude

We’re just going to go ahead and say it: Once you hit that send button, you’ve lost total control of your photo.

“Technology can’t fix untrustworthy humans, but it can help you express your boundaries and make it a little harder to violate them,” says Jacob Hoffman-Andrews, a senior staff technologist at the Electronic Frontier Foundation.

Sure, some apps will notify you when someone takes a screenshot of your picture, but they won’t actually prevent them from doing so. A recipient may also simply use another device to take a photo of the screen without alerting you. 

Are you or your partner underage? Do not take, send, receive, share, or store nudes.

There’s no nuances about this one—naked pictures of minors are child pornography, and their production, storage, and distribution is against federal law. 

Even if an image exchange was enthusiastically consensual, and you were the one who took a naked selfie, some states might still consider it a serious crime just because you’re a minor. Sorry. 

Abide by basic sext etiquette

This may go without saying, but there are basic rules of decency when it comes to sending nudes. First, if you receive one, don’t share it with anybody else—it is for you and you alone. When you share a private photo, you’re not only violating the trust of the person who sent it, but also making it more likely to end up in the wrong hands, or worse—on the internet. In some states, sharing naked pictures of people without their consent may also be a felony. Just don’t do it. 

[Related: An expert guide to love and sex during a pandemic]

Second, don’t post someone else’s nudes online. Same principle: Don’t be a jerk. 

Third—as with all sexy things—consent is key. Respect it. Don’t send unsolicited nudes, especially to people you don’t know. If you’re in a relationship with someone, no matter how casual, have a conversation about how they feel about unsolicited nudes. Some might welcome a sexy photo in the middle of their workday, while others might not. Talk to your partner about their likes and limits, and honor them.   

When in doubt, abstain

Send nude photos only to those you know and trust. This excludes people you’ve matched with on dating apps but never actually met, online contacts you’re not even sure are real, or people who give you the slightest hint they’re untrustworthy. 

“The biggest risk in sending a nude is that the person on the other end is less trustworthy than you think. Or that they are trustworthy today but become less so in the future—after a breakup, for instance,” says Hoffman-Andrews. 

Knowing who to trust is far from a perfect science, but just asking yourself the question before you send them a naked picture of yourself might save you some trouble. 

Yes, this sounds scary, but it doesn’t mean you should embrace full-on nihilism or stop sending nudes altogether. Instead, focus on managing the things you can control.

How to safely take a nude photo

The best way to keep a nude pic safe is to keep it anonymous. That way, even if your photos end up online, it will be hard to identify you. 

Crop out or cover your face 

Going faceless is the foundation of anonymity. If this doesn’t work with your artistic vision, be creative and opt for other ways to make you unidentifiable. Use sharp angles to keep your visage out of frame or shrouded in shadow, or shoot with a bright flash in a mirror, for example. 

If you wear a mask, make sure it covers enough of your face.

[Related: Take better selfies with these lighting and angle tips]

If you need tips, check out boudoir photography content on YouTube and TikTok. This will not only help you perfect the poses and angles that will show off your beautiful body, but you’ll also learn how to make your surroundings work in your favor. 

Consider your environment

If someone took a peek inside your room, they’d probably figure out a lot about you. Don’t let your unique style give you up. Find anything that may reveal personal information about you and make sure it’s not in the frame. This includes photos, diplomas, and sticky notes. 

Keep in mind that something doesn’t have to have your social security number on it to be revealing. People who’ve been to your home could easily identify it by a band poster or a painting on your wall. 

When choosing a setting for your nude, keep it as stripped-down as possible (pun very much intended). Blank walls and nondescript bathroom tiles are perfect backgrounds for sexy pics. 

Finally, stay away from large, open windows. Well-known landmarks could peek through and be enough to trace the photo back to your home and to you. Plus, you might want to keep the neighbors out of your photo session—unless you’re into that.  

The healing tool (an icon that looks like a bandage) will help you blur out information in the background, along with small tattoos, birthmarks, beauty marks, blemishes, and anything else you’d like to airbrush out.

[Related: Edit gorgeous photos right on your phone]

Downloading apps such as Snapseed (free for Android and iOS) or Photoshop Express (free for Android and iOS) to your phone or computer will help you tweak all the things you might have forgotten about while taking the picture. They will also provide you with a wide library of filters to get you looking even more like a snack. 

If you’re using a mobile device, turn off location services before taking the photo. On Android, swipe down from the top of the screen to open up the quick settings menu, and tap on the location icon to turn off your GPS signal. Additionally, open your camera app and tap the cog icon to go into its settings. Once you’re there, tap on the toggle switch next to Save location to stop the app from adding your whereabouts to your metadata.

On iOS, go to Settings, then Privacy, and select Location services. There, find the camera app and under Allow location access choose Never.

If you forgot to do this, you can remove location metadata from your picture later using macOS. Open the photo using Preview and hit command + I, or go to Tools and click on Show Inspector, which will show you all the information attached to your file. Under the More info tab (second to the right), choose the GPS tab (third to the right). Then, at the bottom of the dialog box, click on Remove Location Info. The GPS tab should disappear. 

You can do the same on Windows. Right-click on one or more files, select Properties, and go to Details. At the bottom of the dialog box, click on Remove Properties and Personal Information, and then check the box next to Remove the following properties from this file. At the bottom, click Select All, and then hit OK. This will erase all metadata from the selected files.

Turn of automatic syncing with your cloud services

Sending photos straight from your camera roll to your personal space in the cloud is handy, but it’s a liability when nudes are involved. 

Before you take your naked portrait, make sure to turn off syncing between your device and all connected cloud services. On Android, open the Google Photos app, tap on your avatar (top right) and then on Back up. Once there, turn off the toggle switch next to Back up & sync. On iOS, turn off iCloud photos by going to Settings, tapping on your name, choosing iCloud, then Photos, and turning off the toggle switch beside iCloud Photos.

Make sure to delete your photos from your camera roll and your trashcan, or move them to a secure folder before turning syncing back on. 

How to safely send a nude

You got the money shot. Now it’s time to deliver your sexy pic and rock your partner’s world.

Choose a secure platform

Anything that doesn’t have end-to-end (E2E) encryption—which protects your content from interception on its way to the recipient, and prevents the company that owns the platform from accessing it—is out of the question. This means no Facebook Messenger or Instagram. Snapchat uses E2E encryption on photos and videos, but not on messages, and although it lets you know when someone took a screenshot of your photo, it doesn’t prevent them from doing so. 

Your safest bet is Signal. It’s E2E encrypted, you can have messages disappear a minimum of five seconds after viewing, and secure chats prevent users from taking screenshots. It’s worth noting that this doesn’t prevent someone from taking a picture of the screen, but as far as traditional messaging apps go, Signal may be your best option. 

[Related: 6 secure alternatives to WhatsApp]

If you’re willing to spend money on your privacy, Disckreet is a messaging app designed to share racy texts and images. Available for iOS and Android, this platform is E2E encrypted, protected by a passcode, and gives users unilateral control over their content. This means you decide when your partner can see a photo you sent, and you can remotely delete the image from their phone. Diskreet’s free version limits the size and number of files you can share in one day, but you can subscribe for $1 a month for unrestricted sharing.

Even if they don’t do it, this will make it clear that when you shared those pictures, they were meant for your partner’s eyes only. If they share them or post them online, it legally constitutes a violation of your privacy. 

Exercise some good ol’ cybersecurity essentials

Make sure you’re being safe online overall. Start by securing all of your accounts and devices with unique and secure passwords, patterns, PINs, passcodes, or biometrics. If keeping track of all that information is too hard for you, download a password manager, and don’t forget to enable two-factor authentication on all of your accounts. 

[Related: How to do two-factor authentication like a pro]

You should already be doing all of this, but it is especially important if you’re swapping nudes. You want to make it as hard as possible for anyone to gain access to your sexy content by breaking into your accounts or devices.  

How to safely store a nude

What you do after you send a nude will depend on whether you want to delete it or add it to your personal archive. 

If you can, delete the picture on the platform you used to send it so neither you nor the recipient have access to it. If you want to leave absolutely no trace, you should also delete the file on your device. 

But maybe you took a very good nude and you don’t want it to be lost in oblivion. This is when you need to secure your file. Cloud storage services are susceptible to hacks and data leaks, so you may want to store your nudes locally. 

The easiest way is to move your photos to a password-protected folder on your device. On Android, go to the Files app, and then Images and Pictures. Select your nude by long-pressing on it, tap on the three dots in the top right corner of the screen, and choose Move to Safe folder. To access that folder, you’ll need to provide a security pattern, passcode or biometric feature, which can be the same one you use to unlock your phone or something completely different. You can also hide the folder, so if someone were to break into your device, they wouldn’t be able to see it or search for it. 

Windows 10 has a similar feature that allows you to use File Explorer to protect any file or folder with a password. Just right-click on the item, go to Properties, and then Advanced. Click on Encrypt content to secure data at the bottom of the dialog box, and click on OK, then Apply. From the next dialog box, pick whether you want to encrypt only the file or the entire folder where it’s located, then click OK. 

Apple’s computer operating system also allows you to create password-protected folders. Save your nudes inside a folder, open Disc Utility, and go to File, New image, and Image from Folder… Then, use the emerging Finder window to find the folder with your nudes, and click Choose. Under Encryption, pick your protocol, then enter and verify your password. Finally, under Image Format, choose read/write and hit Save. You can also protect single files on Preview as long as they’re saved as PDFs, and use the Notes app to create protected files with embedded photos.

There’s no built-in solution for iOS, but you can download a free file locker app that will do the same job as Android’s “safe folder” on your iPhone.  

[Related: Rip out your computer’s guts and craft an external hard drive]

Another alternative is moving your nudes to an external hard drive, which you can encrypt and store in a safe location. 

Safe nudes are a team effort

Nothing you do to ensure safe sexting will be truly secure if the recipient of your naked pictures cannot be bothered to set up a passcode to lock their phone.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

The post A complete guide on how to safely take, send, and store nudes appeared first on Popular Science.

Articles may contain affiliate links which enable us to share in the revenue of any purchases made.

Even though some end-of-summer festivities might be limited this year, that doesn’t mean celebrations (and drinks) are, too. Within our households or over video calls, lots of us are planning to raise our glasses and forget about how terrible 2021 has been to the world.

It’d be nice if we could do all that without a horrible, head-wracking hangover, though.

Before you start scheduling some recovery time on your calendar, know you can try to avoid them, and but if things get rough, you might be able to make that bottle-ache a bit milder. But that’s the best-case scenario, because we’re sorry to tell you one cold, hard fact: there is no cure for hangovers. Like, none. Zero.

What do you mean there’s no cure for hangovers?

Exactly that, actually. For starters, science still doesn’t quite know what causes a hangover. Literature on the subject has identified three possible culprits: the direct effect of alcohol on the brain and other organs, the effects of alcohol withdrawal from these organs; and other non-alcoholic factors, such as the physiological effects of compounds created when the body processes alcohol, like methanol.

It’s also challenging to define what a hangover is. The definition researchers generally agree upon is that it’s a condition characterized by a feeling of misery that can last up to 24 hours after the amount of alcohol in your blood drops to zero. As anyone who’s ever experienced a hangover will tell you, symptoms can vary both in nature and intensity, going from headache, nausea, and fatigue, to muscle aches, vomiting, lack of concentration, and anxiety.

The symptoms you experience after a night of drinking will depend on multiple factors, like how much you drank, for how long, what it was, if you ate, what kind of food you devoured, if you danced, or smoked, and more. And that’s not even taking into account genetic predisposition to hangovers or family history regarding alcohol addiction.

Considering these effects vary widely from person to person—and even from one event to another—it is very hard to study them, which makes hangovers a tough nut to crack. And then there’s the morality of curing them.

“A possible explanation for the lack of scientific interest is that many physicians and researchers regard the alcohol hangover as an adequate punishment for unwanted behavior,” Utrecht University researchers Joris C. Verster and Renske Penning wrote in their 2010 paper Treatment and Prevention of Alcohol Hangover.

According to them, it is possible that part of the scientific community may not want to find a cure for hangovers because doing so would make binge drinking that much easier.

Ok, so how do I deal with a hangover?

Since we don’t know what causes hangovers, there’s no drug or homemade remedy that will get rid of one entirely. In fact, the only scientifically proven method to avoid a hangover is moderate alcohol consumption or good old abstinence.

But since it is likely you will eventually have to deal with at least one hangover in your life, it’s a good idea to know there are things you can do to make the day after a party a little less miserable.

Rehydrate

Dehydration is one of the main symptoms of hangovers. Alcohol inhibits the production of antidiuretic hormone, preventing the kidneys from reabsorbing water and resulting in the overproduction of urine. Add that to sweating, vomiting, and diarrhea (all possible hangover symptoms), and you end up with a sure case of dehydration.

Drinking one glass of water for every alcoholic beverage you consume is a great way to prevent a bad hangover. If that ship has already sailed and you’re experiencing hangover-induced dehydration, you can always opt for a sports drink or make your own oral rehydration salts. All you need to do is mix two tablespoons of sugar and a 3/4 teaspoon of salt in four cups of water. Doing so will not only help you get that precious water back into your body, but will also restore your electrolytes.

Beware of congeners

If you’ve ever experienced a red wine-induced hangover, you know they’re some of the worst you can get, and congeners are to blame. These are the biologically active compounds that give alcoholic beverages their distinct taste, smell, and color. Research shows a higher concentration of congeners may have something to do with more severe hangovers, whereas drinking distilled spirits containing purer ethanol, such as vodka or gin, will result in milder or fewer hangover effects.

When it comes to avoiding hangovers, the lighter the color, the better—stay away from rum, whiskey, tequila, and red wine, which are among the alcoholic drinks with higher amounts of congeners.

Sleep well

Fatigue and muscle aches are two of the most common hangover symptoms, and you don’t have to be a doctor to know the best way to treat them: rest. But alcohol consumption disrupts sleep patterns, resulting in both less and worse sleep. Drinking also alters your circadian rhythm, which raises cortisol levels and causes a feeling similar to jet lag.

It might be difficult, but a good way to combat a hangover is just to sleep. Give yourself the time to get some rest and bounce back. And if you made the horrible decision of making plans for early the next day, God help you.

Be careful when taking Aspirin or paracetamol

When you’re suffering from a hangover that features an intense headache, your first instinct may be to take Aspirin or paracetamol. Studies have shown alcohol can cause an inflammatory response in the body, so anti-inflammatory drugs such as these could have a positive effect.

The problem is there’s no peer-reviewed evidence supporting Aspirin’s ability to fight a hangover, and research has found the use of the drug in combination with alcohol can result in stomach bleeding and liver damage. Before you think about taking any pills to fight off the consequences of a long night of partying, consult with your doctor—they may be able to recommend a better course of action considering your particular situation.

Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

The post What is a hangover? And can you cure it? appeared first on Popular Science.

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The healthiest way to eat a dessert (or any type of added sugar) is to not eat it. That being said, what is life if you don’t live it? For me, a life without the occasional glazed doughnut for breakfast or Sour Patch Kids at the movies is a life not fully lived. Most Americans, including doctors and nutritionists, would likely agree. Nevertheless, studies show that sugar, in excess, can contribute to the development of diabetes, obesity, and heart disease. So when you inevitably consume foods loaded with sugar, is there a way to do so that minimizes the impact on your health?

Recent studies suggest there could be.

First of all, there’s no reason to cut sugar completely out of your diet. That’s a pretty hard thing to do, says Leslie Bonci, a registered dietician and sports nutritionist. She says it’s unlikely that most people will stick to a sugar-free diet. Everyone, to a certain extent, has a desire for sweet-tasting foods—and for good reason. Sugar provides us with needed energy. So, if we eat a diet completely devoid of sugar, “psychologically, that can be devastating.” It’s much more productive to think about how to keep your sugar intake as healthy as possible.

Sugar often gets a bad rap because we eat it alone, in the form of soda and candy, or with other carbohydrates in various baked goods. Since these foods are loaded with simple carbohydrates, they spike our bodies’ blood glucose levels. When this happens, we immediately try to bring those spikes back down to normal levels by increasing the production of glucose-lowering hormones such as insulin and incretin. If we increase them too much too often, this mechanism stops working as it should, which can lead to type 2 diabetes.

But there are ways to try to prevent this. People can start, Bonci says, by simply eating less sugar, or eating it with other foods to avoid letting it become the focal point of a meal (goodbye, Sour Patch Kids lunch). Bonci says perhaps the best type of food to eat sugar with is protein. The consumption of protein triggers the release of glucagon, another hormone, which stabilizes insulin levels. So when eaten together, protein and sugar can sort of regulate each other. “Our bodies are pretty darn smart in that way,” she says.

An ideal way to implement this is with your morning coffee (that is, unless you drink it without any sugar). Coffee can be pretty bitter on its own, so rather than add a bunch of sugar to offset that, try mixing it with milk in the form of a latte, cappuccino, or cafe au lait. That way, Bonci says, you get that ideal mix of sugar and protein (from the milk), resulting in more balanced hormone and glucose levels.

Some recent research suggests that we should take it one step further: Eating all carbohydrates, including sugar, last. Studies on post-meal glucose and insulin levels in people with type 2 diabetes show that the order in which you eat various types of food matters. The most recent one, out in September of this year, had participants—all with type 2 diabetes—eat the same exact meal on three different days, but in various order. One day, they ate carbohydrates first, followed 10 minutes later by protein and vegetables, then protein and vegetables first, followed by carbs 10 minutes after, and finally everything eaten together at the same time.

Researchers measured their blood glucose, insulin, and glucagon levels just after the meals and every 30 minutes for the next three hours. They found that peaks in glucose levels when carbs were consumed last were all around 50 percent lower than when they were consumed first. Even eating everything at once produced a spike 40 percent higher than that seen when carbs came last.

That’s a pretty significant difference. In fact, according to the study, the effect of food order on postmeal glucose and hormone levels is comparable to the effect of drugs meant to regulate glucose. Many people with diabetes are told to limit the carbs and added sugar they consume. But this research suggests that just switching the order could be as good as limiting their intake altogether.

While the study was done on diabetics and it’s intended goal was to find a best practice for that group, study author Louis Aronne, a professor of metabolic research at Weill Cornell Medical Center, says everyone could use the information gained. Generally speaking, he says, “ I think it would be best to have salad, vegetables, and a protein, followed by dessert.”

Bonci adds that this method could also work, logically speaking, to help you eat less of the dessert or carb in general. If you’ve already loaded up on other foods, especially fiberful vegetables, then you will probably be less hungry when dessert comes around.

It’s probably fruitless to promise yourself you won’t eat any sugary treats this holiday season. Instead, try to eat the bird and Brussels sprouts first, followed by the stuffing and mashed potatoes, and then use whatever room you have left to dig into that delicious homemade apple pie.

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

This week, we investigated whether you can survive by eating a single type of food. While we wouldn’t recommend this as part of a healthy diet—and why would you when there are so many delicious foods out there—we made sure to answer the question accurately and scientifically. While you’ll have to listen to the entire episode for proper context, I will say that it’s not easy and it would take a lot of that single food item. We’re talking dozens and dozens of potatoes. 

The main reason this would be so hard is that there are many micronutrients, including various vitamins and minerals, that we need to survive. All foods have more of some and less of others, so relying on just one form of sustenance for all our nutritional needs is really challenging. There’s a reason that the U.S. dietary guidelines recommend eating a variety of fruits, vegetables, grains, meats, and cheeses.

Perhaps taking a deep dive into one food item is the easiest way to show that a varied diet is really the best thing you can do for your body. So if you want to know how many potatoes you’d need to eat to survive, be sure to tune in to this week’s episode of Ask Us Anything. Tune in here, and read the article that inspired this episode here.

The post Ask Us Anything: Can you survive on a single food forever? appeared first on Popular Science.

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This post has been updated. It was originally published on October 30, 2017.

From a basket of warm focaccia on the table at a restaurant, to flat loaves of naan accompanying a curry, bread is incorporated into many, if not most, meals around the world. Everyone loves carbs, especially bread. So, wouldn’t it be awesome if we could literally live off of this beloved food group? The short answer is yes, yes, it would, but the larger question is; is it even possible?

You could probably survive on quality whole grain bread that’s been fermented for a while. But eventually you would run into nutritional deficiencies, and in all likelihood, you’d eventually get sick of the carb-laden substance.

Many people have wondered whether humans can survive on just one food item. The question is valid: Eating just one thing would probably save a lot of time and effort and potentially a good deal of money. Plus, many food items do pack a considerable nutritional punch. But none can contribute everything, which is the main reason humans have evolved eating a varied diet. For example, technically potatoes contain all the essential amino acids you need to survive. But many of those amino acids are present in such small amounts that even if you consumed far more than a day’s worth of calories in potatoes, you would eventually run into many nutritional deficiencies.

The same goes for bread, though not all kinds are nutritionally sliced equal. Unlike potatoes or rice which are stand-alone plants, this carb is created from the combination of grains and water and some type of microbe. These microbes, yeast and certain types of bacteria, break the grains down, exposing the nutrients within them that humans normally wouldn’t be able to access. As the environmental news outlet Grist points out, the end product, bread, is far more nutritious than its main ingredient, whole grain.

If you compared the nutritional benefits of porridge, which is essentially whole grains soaked in water, to traditionally-made bread, the latter would come out on top because the porridge didn’t go through that fermentation process which releases key nutrients from the grains. But that’s if you made the bread the traditional way. Many breads made today are created with a combination of white flour and commercial yeast—leaving out the whole grains and the nutrients they provide.

[Related: Can you survive on a single food forever?]

So, if you wanted to attempt to survive just on bread alone, it would need to be made with whole grains and probably a yeast/bacteria combination that’s been proven to ensure the proper combination and diversity of bacteria are there to break those whole grains down. Perhaps one of the best breads that achieve this is traditionally-made sourdough, which is created with a combination of yeast and lactobacilli, a type of bacteria. The fermentation process is slow, ensuring the nutrients inside the whole grains are exposed.

But even sourdough might not be enough to survive. Eventually, just like the potato scenario, you would probably run into nutritional deficiencies. Even sourdough bread made with wild yeast, bacteria, and whole grains likely will not provide enough nutrients like vitamin C, B12, and D, as well as calcium. Without these key players, humans would run into some serious problems. With no vitamin C source, a person could develop scurvy, which results in weakness of the muscles and fatigue. Calcium is necessary to prevent osteoporosis, which results in weakened bone mass. Plus, humans need fat to survive as well, which sourdough bread doesn’t have.

If you did attempt to eat one food for an extended period of time, you would probably get sick of eating the item far before you gave yourself any severe nutritional deficiencies. That’s due to a psychological phenomenon called sensory specific satiety. Scientists have found that the more you eat something, there’s a corresponding decline in pleasantness. But some foods are more prone to this than others (like high protein foods), and some researchers have found that bread might be in fact fairly resistant to this phenomenon.

[Related: Learn your sourdough starter’s funky secrets]

While sourdough and other whole grain breads are extremely nutritious, they cannot provide everything. And sure, it might sound easy to eat the same thing for the rest of your life, but, for most people, it’s also probably incredibly boring. But if you want to simplify your diet, don’t fret. There’s plenty of simple food combinations, like rice and beans, yogurt and nuts, and pasta and vegetables that provide a more complete nutritional profile. But even with those, it’s always best to change those up as well. Eating the rainbow is still a pretty foolproof method.

The post Can you live on bread and water alone? appeared first on Popular Science.

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Sleep is a time suck. If you multiplied the average recommended number of hours we should sleep in a day—eight for a typical adult—by the number of days in an average lifespan (78.8 years in the United States), that would amount to about 9,587.3 days. That’s one third of your life spent unconscious. From an evolutionary standpoint, sleep is quite literally a waste of your time, yet it’s fought its way through countless years of adaptation in nearly every living animal on Earth. So it must be important, right?

In fact, researchers have found that sleep plays a vital role in the functioning of nearly every organ system in the body. At the same time, medical conditions, a busy schedule, and even the simple unavoidable act of aging constantly challenge the number of hours we allow ourselves. But that begs the question: how much sleep do we actually need? And can we train ourselves to need less?

First, let’s talk about that eight hour figure that gets tossed around. It’s far from some arbitrary number. It’s truly the number of hours we naturally crave, and there are two pretty strong pieces of evidence for it. In a series of experiments, researchers took study participants into a laboratory with no sunlight or other visual cues and, at night, gave them a non-negotiable, nine-hour-long opportunity to sleep. They did this each night for a number of weeks, and the results were always the same: even when provided with more time, humans will typically spend an average of eight hours catching up on their Zzz.

And that wasn’t the only study to support the eight-hour sleep schedule. Back in 1938, a sleep researcher named Nathaniel Kleitman and one of his students spent 32 days living in Mammoth Cave in Kentucky, one of the longest and deepest caves in the world—an environment completely void of sunlight. When they analyzed their sleep patterns, they found that they, too, slept about eight to eight and a half hours per night.

But what happens when we deprive ourselves, as many Americans do, of all or some of these recommended hours? It turns out, a lot. In 2003, David Dinges and Gregory Belenky, both sleep researchers at the University of Pennsylvania and the Walter Reed Army Research Institute, performed some of the most pivotal studies on the consequences of sleep deprivation thus far. Their goal was to figure out how little sleep a person could get away with, without having it affect their cognitive performance.

The two studies involved two-week-long experiments where researchers deprived participants of varying hours of sleep. Before they did so, they first allowed subjects to receive eight hours of sleep, followed by a series of cognitive tests the next day—which measured things like someone’s speed of response, how well they could interpret a written passage, and the number of times they dozed off for a second or two (what science calls a microsleep). All of this gave them a baseline for each subject’s normal cognitive performance.

The researchers on Dinges’ team then assigned the participants to one of four groups: one group was allowed eight hours of sleep for the following two weeks, the next six, then four, and the last group received zero hours of sleep for up to three days straight.

That last group, says Matthew Walker, the director of the sleep and neuroimaging lab at the University of California, Berkeley, showed just how much your cognitive performance suffers after just one night of total sleep deprivation. What Dinges and colleagues found (and what subsequent studies have confirmed) is that to your brain, one sleepless night is the cognitive equivalent of being legally drunk, says Walker.

The rest of the groups weren’t so far behind. While the group that received eight hours of sleep saw virtually no change to their cognitive performance throughout the two-week study, after just 10 days the participants that slept six hours each night were as cognitively impaired as those suffering from a night of total sleep deprivation. And the group that got four hours? It only took them three days before they reached that same level of impairment. By 10 days in, they were as cognitively impaired as if they had gone two days with no sleep. As the days went by, these detriments didn’t slow down. “If you looked at the data graphs, there’s no end in sight. That was the frightening thing,” says Walker.

When Dinges compared his results to his colleague’s at Walter Reed—who had done the same exact study but with odd hours (meaning seven, five, and zero hours of sleep), their findings were basically identical. Even the group that slept seven hours a night—which some people think of as a luxury, says Walker—were dozing off at a rate three times greater than the group sleeping eight hours a night just five days into the experiment. So, how much sleep can you take away before someone becomes cognitively impaired? Sorry, but the answer is less than one hour.

Okay, so that’s sadly settled: we should all be getting no less than eight hours of sleep per night. No exceptions. But we all lead extremely busy lives, especially during the workweek. Can we make up any of those hours lost during the week on the weekends (similar to those weekend warrior who still receive health benefits from only exercising on twice a week) so that you average eight hours a night? The researchers asked the same question.

After the sleep deprivation part of the study was done, the researchers then gave the participants three nights of “recovery sleep” where they were allowed as much as they wanted (unsurprisingly, most slept way more than eight hours). After those three days, they took the same cognitive screening tests. But the participants hadn’t returned to the baseline levels they had at the beginning of the study. In other words, if you are sleep deprived—meaning you are sleeping seven hours or less each night—then it takes you longer than a weekend to get back to baseline. And no one’s figured out how long it actually takes.

“People think that sleep is like the bank. That you can accumulate a debt and then hope to pay it off at a later point in time,” says Walker. “And we now know that sleep is not like that.”

The brain has no capacity to get back all that it has lost, Walker explains. Why is this? Why haven’t we evolved a way to make up for lost sleep the same way we can make up for days of starvation by storing calories as fat? The answer, Walker says, is simple: “Human beings are the only animal species that deliberately deprive themselves of sleep.” There is no storage system for sleep in the brain because life never needed to create one.

Undoubtedly, many of you are reading this and scoffing. If you regularly get six hours of sleep and feel just fine, why should you waste your time trying to squeeze in more?

Consider this: after the first night of reduced sleep, researchers in Dinges’ study asked the participants in the six-hour-a-night group how well they thought they did on the day’s cognitive tests. They replied that they did well—great, even. However, when the study researchers actually compared the two performances, the tests completed after six hours of sleep were significantly worse than the ones done after eight hours of sleep.

“You don’t know you are sleep deprived when you are sleep deprived,” says Walker, “That’s why so many people fool themselves into thinking they are one of those people who can get away with six hours of sleep or less.” Walker argues that there’s no way you can effectively train yourself to need less sleep. You may get used to feeling tired all the time, he says, but that does not mean you can suppress that tiredness and perform as well on cognitive tests as you would if you received eight hours.

But perhaps there is a positive twist—in the form of a mid-afternoon nap backed by science. Researchers who have looked at cultures that remain completely untouched by electricity, such as the Hadza of Tanzania, found that, especially in the summer, these groups tend to sleep biphasically: packing in six hours a night, and then a few hours again in the afternoon. This begs the question, Walker says, of whether human beings should stay awake for sixteen hours straight. In fact, everyone goes through an afternoon lull. Biologists have actually been able to measure this physiological dip in our alertness—what science calls a postprandial dip—through changes in our metabolic system, as well as adjustments in our brain waves, and in our cognitive reaction times. The universal cognitive pause means we might benefit from a nap around this time. “Perhaps human beings need to sleep biphasically for truly optimal performance, though that’s still unclear,” Walker says.

One thing science knows for sure, however, is that the less sleep you get each night, the less cognitively aware you are the next day, the day after, and every day after that. Simple.

In fact, Walker says, if you ever want proof of how much of an effect just one hour less sleep can have on human beings, just remember how you feel the days after daylight savings begins every March, when nearly the entire country has intentionally deprived themselves of an hour of sleep.

But perhaps the most relevant thing to remember, Walker says, is this: When someone tells you the reason they can only get five hours of sleep is that they simply have too much to do, “I tell them, I’m sorry, but there’s an irony in your statement. The reason you are left with so much to do could likely be because you are only getting five hours of sleep and your cognitive functioning is deficient, so it’s taking you forever to do everything.”

The post How many hours of sleep do you actually need? appeared first on Popular Science.

Articles may contain affiliate links which enable us to share in the revenue of any purchases made.

This post has been updated. It was originally published on June 1, 2019.

Stretching is good for your muscles—no newsflash there. Research shows that an active warmup before a workout prepares them for the intense activity, and a static cool down (you remember those circle-up and stretch exercises from elementary school?) helps the body relax and recover.

But is it possible to overstretch? We’ve all had that moment: You stand up or lean back to stretch, and, all of a sudden, extreme pain hits. Can a benign extending and lengthening session turn detrimental?

It’s entirely possible that you could stretch so much that you strain, or even tear, a muscle, but more likely than not, that pinch is probably just a startled nerve. Muscles contain special sensory receptor cells called muscle spindles. When you stretch, these cells send a signal to the neurons within the muscle to tell the central nervous system that you’ve gone too far. As a result, those muscles contract, tighten, and resist the pull. That reaction is what causes the initial painful feeling that people get when they attempt to stretch. It’s also the reason that some people feel such agony when they try to touch their toes: The quick pain caused by that neural cascade is just too great.

There is hope, though. You can prime your muscles to avoid the painful twinge of startled neurons, according to Jeffrey Jenkins, a physiologist at the University of Virginia School of Medicine. It’s simply a matter of patience. If you hold a stretch for 6 seconds or more, the reflex lessons. That’s because, at that point, the muscle’s golgi tendon organs (spindles of neurons that rest on muscle fibers) react and inhibit those ouchy muscular contractions. Finally, your muscles can relax, stretch, and lengthen.

Jenkins notes that if you have the mental fortitude to get past that those 6 seconds, you no longer feel the pain and can indeed improve your flexibility. However, if you are enduring a ton of agony, stop, as you could be tearing a muscle. In fact, it’s quite difficult to differentiate between a tear and the pain that comes along with the first moments of a good stretch.

The best thing to do is to know yourself—and your pain threshold. If you feel like you are in a level of discomfort that is far beyond what you normally experience, you should probably stop. At that point, the likelihood of you benefiting from the stretch versus the likelihood of you pulling or tearing a muscle tips. Indeed, in a small study published in 2017, researchers tested and compared the benefits and risks of static stretching to the point of pain in 22 physically active women. One group stretched to the point of true pain, whereas another group went only to the point of discomfort. Pushing yourself to the point of pain, the study found, had no advantages.

So, of course stretch however it benefits you, but remember that if you are experiencing agonizing pain, it’s far more likely to be doing harm than it is to be doing good. And don’t worry, the ability to touch your toes—or not—has little to do with your overall well being.

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Australian Boomerangs

The boomerang is one of humanity’s oldest heavier-than-air flying inventions. King Tutankhamen, who lived during the 14th century BC, owned an extensive collection, and aboriginal Australians used boomerangs in hunting and warfare at least as far back as 10,000 years ago. The world’s oldest boomerang, discovered in Poland’s Carpathian Mountains, is estimated to be more than 20,000 years old.

‘When the boomerang spins, one wing moves through the air faster than the other’

Anthropologists theorize that the first boomerangs were heavy projectile objects thrown by hunters to bludgeon a target with speed and accuracy. They were most likely made out of flattened sticks or animal tusks, and weren’t intended to return to their thrower—that is, until someone unknowingly carved the weapon into just the right shape needed for it to spin. A happy accident, huh?

Darren Tan is a PhD student in physics at Oxford University. He donned a ninja suit as the “Science Samurai” in a video for high school science students about boomerangs. In his video, he demonstrates how to fashion a boomerang from three strips of cardboard, by crossing and stapling them together so that they jut radially outward from the center.

Proper wing design produces the lift needed for boomerang’s flight, says John “Ernie” Esser, a boomerang hobbyist who works as a postdoctoral researcher at University of California and Irvine’s Math Department. “The wings of a boomerang are designed to generate lift as they spin through the air,” Esser said. “This is due to the wings’ airfoil shape, their angle of attack and the possible addition of beveling on the underside of the wings.”

But a phenomenon known as gyroscopic precession is the key to making a returning boomerang come back to its thrower. “When the boomerang spins, one wing is actually moving through the air faster than the other [relative to the air] as the boomerang is moving forward as a whole,” explains Tan. “As the top wing is spinning forward, the lift force on that wing is greater and results in unbalanced forces that gradually turns the boomerang.” The difference in lift force between the two sides of the boomerang produces a consistent torque that makes the boomerang turn. It soars through the air and gradually loops back around in a circle.

Protip: To really make a boomerang soar, hold it vertically and give it a good spin—and be careful where you aim!

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Lava Splatter

Great question. Glad you asked. While volcanoes might seem like the ideal natural incinerator for our massive amounts of garbage, there are a few obstacles between us and a magical geological trash chute to the center of the earth.

Americans generate about 4 and a half pounds of trash per person, per day, or 254.1 million tons total per year. In order to dispose of all that trash in a volcano, you’d need to first locate an active volcano, and lug the trash there. That’s the first problem. Not many people live near active volcanoes, so transporting trash to a volcano would cost time, money, and a whole lot of fuel. Then there’s the fact that an even smaller number live near the right kind of active volcano.

That sounds like a volcanically snobby thing to say (oh, we don’t associate with those sorts of geological formations) but it’s the truth. When you picture throwing garbage into a volcano, you’re probably thinking of a nice, friendly cone shaped volcano with a hole at the top. Something like this:

And in the middle of the crater, you’re probably picturing a lovely lava lake that looks like this:

Perfect for throwing trash into, right? But not all volcanoes are cooperative like that. The ideal trash incinerator would be a slow-erupting volcano that gradually spews lava out onto the surface of the earth, like the volcanoes in Hawaii, called shield volcanoes. But the majority of volcanoes on Earth are stratovolcanoes which occasionally have lava flows like Kilauea, but also have the unfortunate tendency to explode when the pressure of hot gas and magma inside the volcano gets to be too much. Long story short, you don’t want to throw trash into an explosive volcano (think Mount St. Helens) when it’s erupting. If you’re close enough to throw trash into the exploding mass of molten rock, ash, and gases, you’re already dead.

But say you happen to live in Hawaii, close enough to haul your trash up to the summit of your friendly neighborhood active volcano every day. In addition to worrying about your house getting destroyed by lava, there’s also some danger to you (or a garbage truck) that’s dumping trash into a placid lake of lava. See, in addition to the poisonous gases and lava splatter which are already normal hazards at the summit of a volcano, when cold trash hits a large mass of lava, it can cause some spectacular explosions, as a group of researchers discovered in Ethiopia in 2002.

Awesome, right? But that was a 66-pound bag of trash, about three and a half days’ worth for a U.S. family of four. Imagine if that was a larger amount. Rockfalls into lava lakes in Hawaii have sent lava 280 feet into the air, splattering fences and scientific webcams with molten rock. That’s a little too much danger associated with taking out the trash.

Not to mention the fact that you’ll be burning a bunch of trash, and any smoke generated will go straight into the atmosphere, creating a lot of air pollution. Today, trash incinerators are governed by a web of regulations that make sure the smoke from burning trash doesn’t get into our air (they try to filter out major pollutants like ozone, carbon monoxide, sulfur dioxide, etc).

So throwing the mass detritus created by human civilization into a volcano isn’t an option. But what about more specialized waste, like medical or nuclear? Things that tend to be really dangerous? Unfortunately, volcanoes aren’t hot enough to melt nuclear fuel or sterilize medical waste. Temperatures of lava range from 1292 to 2282 degrees Fahrenheit, which is hot, but not hot enough.

It is, however, hot enough to devour a can of Chef Boyardee in a spectacular manner. Enjoy:

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This post has been updated. It was originally published on April 6, 2020.

Before the invention of antibiotics, most of our dealings with bacteria—at least, the dangerous ones—ended in death. At least partly because of that, we have viewed hand sanitizer, the powerful bacterial annihilator that it is, as something we should use liberally without fear of health consequences. Now, after more than a year of living with the threat of the novel coronavirus (SARS-CoV-2), the stuff has become a steady fixture of daily life. Its role as destroyer-of-all-microbes has become a vital component to public health. But where do our delicate microbiomes fit into this microscopic battlefield?

Over the past decade, microbes have taken on a new, positive role in our lives. We’ve figured out that in addition to the bad microbes that can infect us, our bodies are teeming with good bacteria that help us digest food, potentially prevent autoimmune diseases, and even stave off infections from happening in the first place. Unfortunately, antibacterials don’t discriminate bad from good. And that puts users at a crossroads: Should we continue using things like hand sanitizer to avoid disease, or should we embrace germy hands for the sake of our health?

Under normal circumstances, the question of whether and when to use hand sanitizer comes down to a judgement call, as outlined in detail below. But in light of recent events—namely the presence of SARS-CoV-2, which causes the respiratory disease COVID-19—the guidelines for using hand sanitizer are far clearer: As long as the virus continues to spread throughout communities in the United States and around the world, apply hand sanitizer liberally and often. While washing your hands is best, using hand sanitizers that are at least 60 percent alcohol are a close second to killing any viruses that might be lurking on your hands. The benefits of using hand sanitizer to prevent COVID-19 far outweigh the potential risks to our skin’s microbiome, the delicate balance of bacteria, viruses, and fungus that live on our skin everyday.

[Related: The future of probiotics and gut microbiomes is bright]

But in a world in which SARS-CoV-2 stops being an immediate threat—and hopefully the currently available safe and effective vaccines will continue to help get us there—there are positives and negatives to the liberal use of hand sanitizer.

“One aspect of hand sanitizers that is usually overlooked is that they can affect bodies’ microbiomes in a few ways, and some of these ways could be bad,” says Jonathan Eisen, a microbiologist at the University of California at Davis. While they are killing potentially dangerous microbes, they are also altering the communities of beneficial bacteria on the skin.

While we can’t see any of them, millions of bacteria reside on our hands, skin, and inside our guts. Recently, scientists have begun to understand that every person has a proper balance of bacterial colonies that, among other things, keeps the body in check. When we use hand sanitizers, we are attempting to kill off almost every microbe that resides on our hand—the good and the bad.

In addition to killing off potentially beneficial bacteria, Eisen says, hand sanitizers could also contribute to antibiotic resistance. “Even though they generally do not contain standard antibiotics, when microbes become resistant to some of the sanitizers this can make it easier for them to be resistant to more important antibiotics,” Eisen says. You might just want to make sure you aren’t eating any harmful bacteria with your burrito, but doing this repeatedly—and as a general population—could come back to haunt us later. Antibiotic resistance is already a serious threat, and it’s getting worse.

So should we disinfect or not?

“I recommend that people use hand sanitizers with caution, and only if really needed,” says Eisen.

Consider what your hands have recently touched. If you just spent time in a hospital, a doctor’s office, or on the subway next to someone coughing and sneezing, grabbing the Purell is not a terrible idea. But if you’re just going about your normal day without touching too many other humans, it’s probably not necessary to sanitize yourself. That’s especially true if you have the opportunity to use regular ol’ soap. One 2009 study found that typical soap, when scrubbed on properly, is just as good at killing potentially infectious bacteria and viruses.

There’s still a lot of work that needs to be done to better understand the skin microbiome, especially the microbes that reside on human hands. While we know a lot about what types of bacteria typically live on us, we know less about what each one’s specific function is. If we can figure out how some microbes keep us healthy, then we might have a better answer as to how often, and in what situations, using a hand sanitizer is best. For now, follow Eisen’s advice and use it as sparingly as possible. Think of it as a last line of defense against the world’s grime.

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Monkey Business

Ah, the age-old question. When animals are going at it like, uh, animals, how does it end? Is there an animal version of the Big O?

It’s a bit hard to say, actually. “The short answer is that we don’t know much about orgasms in other species — in fact, scientists are still studying the significance/evolution of female orgasms in humans,” Marlene Zuk, a professor of ecology, evolution and behavior at the University of Minnesota, wrote me in an email.

Unlike humans, animals can’t tell us they’re having orgasms, so we can’t truly know what their experience is like. For the most part, we assume that male animals orgasm because there’s an ejaculation–though one can happen without the other, they usually go hand-in-hand. (Or something in hand.) The question of female orgasm is, as usual, more hotly contested, though all female mammals have clitorises.

Scientists can infer that animals–mostly primates–orgasm through recording physiological or behavioral aspects, like muscle contractions or changes in vocalization. Studies of primate orgasm have often focused on macaques, a subset of monkeys which are used often in research because they’re genetically similar to humans and have similar reproductive systems. According to Alfonso Troisi, a clinical psychiatrist in Rome who has studied female orgasm in Japanese macaques, they’re easier to study in the lab than gorillas or chimps. Macaques species tend to have longer copulations than other primate species like gorillas, which is a bonus if you’re trying to observe their mating behavior.

“In the lab, by artificial stimulation, it is possible to trigger female orgasm in virtually any primate species.”In a 1998 study, he and his co-author wrote that “Under specific circumstances, nonhuman primate females may experience orgasm.” But, the rate at which the females orgasmed was variable, and they weren’t exactly sure what caused them. Their study found that the level of dominance of the male macaque might play a role, for instance. But, as Troisi wrote me via email, “In the lab, by artificial stimulation, it is possible to trigger female orgasm in virtually any primate species.”

At the Institute for Primate Studies in Norman, Okla., psychologist William Lemmon and his grad student, Mel Allen, argued that “the female chimpanzee manifests most, if not all, of the indices of sexual arousal and orgasm that occur in women.”

They get more specific in the 1981 study:

sexual responses detected included transudate secretion, clitoral tumescence, vaginal thickening and expansion, hyperventilation, involuntary muscle tension, arm and leg spasms, clutching, facial expressions (eg, low open grin, low closed grin, eversion of the lips, protrusion of the tongue), and a panting vocalization.

Allen manually stimulated the clitorises and vaginas of female chimps in the course of writing his master’s thesis at the University of Oklahoma, “Sexual response and orgasm in the female chimpanzee (Pan troglodytes).” (Surely he had fun describing his work at parties.) As he and Lemmon wrote in their later paper, “Most of these females permitted stimulation to continue to sexual arousal. One of them allowed stimulation to continue to orgasm on ten separate occasions.” As they so dutifully recorded, the average number of “digital thrusts” required (performed “at an approximate rate of one to two per second”) before the onset of vaginal muscle contractions: 20.3. Poor Allen.

Stanford University anthropologist Suzanne Chevalier-Skolnikoff, in 1974, writing on homosexual encounters between female stumptail macaques:

On three recorded occasions, the female mounter displayed all the behavioral manifestations of orgasm generally displayed by males: a pause followed by muscular body spasms accompanied by the characteristic frowning round-mouthed stare expression and the rhythmic expiration vocalization.

And yes, drawings were involved.

Stumptail Monkey Orgasms

So, when it comes to primates, orgasms definitely seem to occur. What about the rest of the animal kingdom?

“Who knows whether it feels like a human [orgasm], but the external behaviour looks like it.”The male red-billed buffalo weaver is the only species of bird we know of that exhibits orgasm-like behavior, according to Tim Birkhead, a professor in Sheffield University’s Department of Animal and Plant Sciences. Birkhead spent years trying to observe the birds getting down, culminating in a study published in 2001. The buffalo weaver, a native of sub-Saharan Africa, has a fake penis–it has no sperm duct and doesn’t become erect, but when Birkhead and his colleagues manually stimulated a buffalo weaver’s mock member, the bird had what seemed to be an orgasm. As Birkhead described to me via email, “the bird shudders its wings and clenches its feet as it ejaculates– who knows whether it feels like a human [orgasm], but the external behaviour looks like it.” He says the organ is purely stimulatory, but they’re currently investigating its anatomy further.

And what of dolphins, widely touted as the only other species to have sex for pleasure?

First of all, orgasms aside, animals don’t get it on because they really want to make babies. They do it because it feels good (which ends up being good for the propagation of the species, too). As Daniel Bergner puts it in his book What Women Want:

The rat does not think, I want to have a baby. Such planning is beyond her. The drive is for immediate reward, for pleasure. And the gratification has to be powerful enough to outweigh the expenditure of energy and the fear of injury from competitors or predators that might come with claiming it. It has to outweigh the terror of getting killed while you are lost in getting laid. The gratification of sex has to be extremely high.

“Nowadays, there is little money around (even in the US), field researchers get no funds, and scientists working in the lab face the opposition of animal rights activists.”Tadamichi Morisaka, an assistant professor at Kyoto University’s Wildlife Research Center, says that dolphins do engage in masturbation without ejaculation “a lot,” as well as other non-breeding-related genital touching, called socio-sexual behavior, especially between males. However, “We have no idea that dolphins feel orgasm or not because there is no study to measure brain response during sexual activity in dolphins,” he told me via email.

Morisaka did catch the first spontaneous ejaculation ever recorded in a dolphin, which he published (with a mildly NSFW video) in a hyper-readable study in PLOS ONE. Spontaneous ejaculation has thus far been recorded in drowsy rats, guinea pigs, domestic cats, warthogs, horses and chimpanzees, according to the study.

As fun as this kind of research is to read about, watching animals get down in the hopes of detailing their climaxes in a scholarly manner appears to have gone out of style.

“The 1970s and 1980s were the golden years for primate research and animal ethology,” according to Troisi, who left primate research a decade ago. “Nowadays, there is little money around (even in the US), field researchers get no funds, and scientists working in the lab face the opposition of animal rights activists. In addition, this the era of neuroscience and molecular genetics. Few people pay attention to behavioral observation,” he wrote.

Hooking monkeys up in a dog-harness contraption and stimulating them with essentially a silicon monkey dildo, for instance, might be tough to get approved these days.

Other researchers echoed the sentiment. Kim Wallen, a professor of psychology at Emory University, says “animal studies have essentially disappeared.”

According to Wallen, there have been a variety of factors involved in the demise of animal orgasm research. For one thing, it’s easier to study human orgasms now that we can stick people in an fMRI scanner. Studying animal sex is hard–as evidenced by Birkhead’s account to Nature of what it was like to chase around mating birds: “I’d run after them, sweating profusely with my binoculars steaming up.”

Plus, the type of animal studies approved in the ’70s and ’80s might not make it past research review boards today. University of Toronto researcher Frances Burton’s 1970 work, which involved hooking monkeys up in a dog-harness contraption and stimulating them with essentially a silicon monkey dildo, for instance, might be tough to get approved these days.

And though it’s likely that most non-human primates have the ability to orgasm, we can’t really know for sure if it’s analogous to the human variety. As Zuk wrote me, “what all this points to is our own inability to know what other animals experience.”

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Warm Santa

At the yearly Rottnest Channel Swim in Western Australia, participants often smear their bodies with animal fat for insulation against the 70-degree water. But their own body fat also helps to keep them warm, like an extra layer of clothing beneath the skin. When scientists studied aspects of the event in 2006, they found that swimmers with a greater body mass index (BMI) appear to be at much lower risk of getting hypothermia.

The same effect has been demonstrated in hospitals where patients who’ve suffered cardiac arrest are treated with “therapeutic hypothermia” to stave off brain injury and inflammation. Studies have shown that it takes longer to induce hypothermia in obese patients than in their leaner counterparts. The extra fat seems to insulate the body’s core.

Under certain conditions, though, overweight people might feel colder than people of average weight. That’s because the brain combines two signals—the temperature inside the body and the temperature on the surface of the skin—to determine when it’s time to constrict blood vessels (which limits heat loss through the skin) and trigger shivering (which generates heat). And since subcutaneous fat traps heat, an obese person’s core will tend to remain warm while his or her skin cools down. According to Catherine O’Brien, a research physiologist with the U.S. Army Research Institute of Environmental Medicine, it’s possible that the lower skin temperature would give fatter people the sense of being colder overall.

But O’Brien points out that many other factors beyond subcutaneous fat help determine the rate at which we chill. Smaller people, who have more surface area compared to the total volume of their bodies, lose heat more quickly. (It’s often said that women feel colder than men; average body size may play a part.) A more muscular physique may also offer some protection against hypothermia, partly because muscle tissue generates lots of heat. “We have a joke around here that the person who’s best-suited for cold is fit and fat,” says O’Brien.

This article originally appeared in the January 2014 issue of Popular Science.

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For all of 2016, Andrew Taylor ate only potatoes. There were a few caveats to his potato diet: He ate both white potatoes and sweet ones, and sometimes mixed in soymilk, tomato sauce, salt and herbs. He also took B12 supplements. But, overall, he ate potatoes for breakfast, lunch, and dinner. He took four blood tests over the year which he claims all came back normal. He even lost weight and felt more energized.

“If you have to choose one food, if you’re one of the people that’s getting sent to Mars, choose potatoes,” says Taylor. “I’m not trying to be evangelical about potatoes, but it was a really good experience for me.”

First and foremost, it’s not a good idea to only eat one kind of food. To survive, we need 20 amino acids—of which nine are essential, meaning we can’t make them ourselves and must get them from food—as well as a plethora of minerals and vitamins. (And, obviously, we need water in addition to food to keep our cells hydrated so they don’t wither and stop functioning.) Throughout history we’ve often combined foods, like rice and beans, yogurt and nuts, and even macaroni and cheese to a certain extent, in an attempt, or by accident, to intake the proper balance of nutrients that you usually can’t attain from eating a single food item. But in times of famine, fasting, or strange double-dog-dares, there are a couple of foods a human could survive on…at least for awhile.

The potato diet

The potato is one good example. Andrew Taylor isn’t the only person in history who has relied almost exclusively on potatoes for sustenance. In the beginning of the 1800s, about a third of the Irish population got most of their calories from spuds. The average American ate about 113 pounds of these starchy tubers in 2015. “For the money and your blood pressure, you can’t beat a traditional baked spud,” says Joan Salge Blake, a clinical nutrition professor at Boston University.

Technically, the traditional white potato contains all the essential amino acids you need to build proteins, repair cells, and fight diseases. And eating just five of them a day would get you there. However, if you sustained on white potatoes alone, you would eventually run into vitamin and mineral deficiencies. That’s where sweet potatoes come in. Including these orangey ones in the mix—technically, they belong to a different taxonomic family than white potatoes—increases the likelihood that the potato consumer will get their recommended daily dose of Vitamin A, the organic compound in carrots that your mom told you could make you see in the dark, and Vitamin E. No one on a diet of sweet potatoes and white potatoes would get scurvy, a famously horrible disease that happens due to a lack of Vitamin C and causes the victim’s teeth to fall out.

Even with this combo, you’ll still need to eat a lot of spuds before you intake the right levels of everything. Consuming five potatoes would give you all the essential amino acids you need to build proteins, repair cells, and fight diseases. But unless you ate 34 sweet potatoes a day, or 84 white potatoes, you would eventually run into a calcium deficiency. You would also need 25 white potatoes a day to get the recommended amount of protein. Soybeans have more protein and calcium—but they don’t have any Vitamin E or beta-carotene.

Of course, there are a lot of health disadvantages to potatoes, especially when you eat them en masse. White potatoes are high in a kind of carbohydrate that causes your blood sugar to spike and then dip, which puts a strain on the insulin system. People who ate a lot of these tubers were more likely to get diabetes and become obese, according to multiple studies.

Andrew Taylor actually lost weight—probably from eating less overall and giving up sugar—which wasn’t his ultimate goal. He quit eating most food to train himself to get comfort and joy from other areas of his life. But now even though his spud experiment is over, he still gets pretty excited about potatoes. “It was just an experiment and turned out to be exactly like I wanted,” he says.

Foods you can survive on

No nutritionist would get on board with an all-potato diet. Nor would they recommend an all coconut, kale, seaweed, or yogurt one either. There’s a reason that the U.S. dietary guidelines recommends eating a variety of vegetables, grains, proteins, fruits, and oils. Eat any of these just by themselves and you would soon run into the same nutritional deficiencies that you would with a potato. Variety is important, and in this case, it’s vital. So don’t just eat a baked potato, load it with other healthy stuff, too.

**This article originally stated that we need 20 essential amino acids to survive, when, in fact, we need 20 amino acids in total, of which nine are essential. The article has been updated to reflect that. We regret the error.

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Everyone pees in the pool. That’s the safe and well-informed assumption that many chemists studying the safety of public, chlorinated swimming pools make. But let’s face it: once you jump in the pool and smell and feel the chlorine surrounding you, you quickly forget about any potential pool-peers and trust the power of the chemicals in the water. That’s probably not the best idea, though. The chemical byproducts that result from your urine and the chlorine aren’t as benign as you may think. And in the end, everyone would be doing a great public service if they would just stop peeing.

“If this was just one person peeing in the pool, then clearly that would not be a problem,” says Ernest Blatchley, an environmental engineer at Purdue University. “But we have evidence to suggest that there are circumstances where the concentration of these compounds could, in some cases, or in fact have, reached the concentrations that are detrimental to human health.”

First, let’s start with a little chemistry. Urine is made up of tons of different substances, all of which can interact with chlorine. But uric acid and a handful of amino acids pose the biggest threat. When each of these react with chlorine, they create are trichloraminen (sometimes called nitrogen trichloride) and cyanogen chloride. Both of these can be harmful in high enough concentrations.

The problem, says Blatchley, is that it’s incredibly difficult to determine just how concentrated these chemicals are in pool water at any given time. It depends on a whole bunch of other factors: How many people are using the pool, how well mixed it is, how warm the water is, and how long it’s been since someone changed the water.

The amount of trichloramine can be measured, but the tools used to do so aren’t generally available at pools. And cyanogen chloride is even harder to measure. “[It’s] a very dynamic chemical. It forms very rapidly but it also decays very rapidly, and it’s quite volatile,” says Blatchley. What that means, he says, is that once it forms in a pool, it doesn’t stick around very long. Of the two substances, Blatchley says cyanogen chloride is the most concerning. It’s a toxic substance, and once it reaches a high enough level, it can be detrimental to human health. But the problem is that because it forms and decays so quickly, it’s very hard to figure out how high those levels in a pool can get.

Trichloramine can caused respiratory problems when inhaled, especially in folks who already suffer from problems like asthma. It also causes irritation—it’s what creates that sometimes-overwhelming pool smell, and makes your eyes burn. Cyanogen chloride is an irritant too, and can actually affect the body’s ability to use oxygen. You’re not going to get a fatal whiff of the stuff in a pool—no matter how full of pee it is—but breathing it in definitely isn’t good for you.

Blatchley says that for the majority of swimming pools, and the majority of the time, the levels of cyanogen chloride won’t reach toxic levels. However, he says, that there are certain conditions in which that chemical could accumulate to unacceptably high concentrations—when you have a really crowded pool, for example.

“I think pretty much any pool that you put people in, you can count on people peeing in [it],” Blatchley says. Based on data that he and his team have conducted, as well a multitude of other studies done, he estimates that the average swimmer leaves behind somewhere between 50 and 80 milliliters of urine—”essentially a shot glass full of urine per swimmer.”

Young couple in swimming pool on sunny day. Water slide.

If everyone is peeing, why don’t we just chlorinate our pools more? Blatchley says that’s not the solution. The more chlorine you add, the more likely the chemical reactions that create those volatile compounds are to occur. Instead, he says, we should actually be working to disband this culture that it’s okay to pee in the pool.

Blatchley thinks that if people just understood the chemistry, they would think twice before urinating in a pool they’re sharing with others. He says he often relates it to secondhand smoking. It wasn’t that long ago that it was culturally acceptable to smoke in public in this country. That changed largely as a result of public pressure that grew out of a scientific understanding of the negative effects of secondhand smoke. “I think we as a culture have evolved to make it unacceptable. If people understood [the same] for pool chemistry, no one would subject their neighbors to cyanogen chloride.”

Even Michael Phelps—a swimming icon and symbol for both competitive and recreational swimming—has admitted to peeing the pool, commenting that chlorine kills it, so it’s not bad. But in reality, science says the opposite.

What Blatchley suggests is that people stop treating swimming pools like a cleaning machine—take a shower before getting in the pool, and step out to the restroom if you need to urinate. If we can stop this culture of routinely peeing in the pool, we can cut down on our chlorine usage— that would reduce the burden of organic compounds that react with chlorine, which would, in turn, result in less chlorine usage as well as improved water and air quality. In the future, Blatchley says “I’d like to see us take a proactive approach, rather than reactive.”

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

Human height can vary quite a bit, with the tallest folks reaching peaks of six, seven, and even eight feet tall, and the shortest people standing at two, three, and four feet in height. But most people will fall into an average range of between five and six feet. Why did we land at that particular height—and why aren’t we taller?

Natural selection and millions of years of time helped humans land at the heights we are at today. It’s clear that early humans with certain anatomies were more likely to survive and thrive, thus pushing the Homo sapiens population to the shape it is today.

Paleontologists know that body size and height shifted upward about 2 million years ago when early Homo species evolved from their ancestors, Australopithecus. In fact, as one 2012 study published in the journal Current Anthropology points out, “body size is one of the major features that distinguish australopiths from early Homo and early Homo from Homo erectus”.

But how we reached our modern heights and why our species isn’t still growing is still fairly a mystery. We explain all this and more on this week’s episode of Ask Us Anything. Tune in here, and read the article that inspired this episode here.

The post Ask Us Anything: Why do humans stop growing? appeared first on Popular Science.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

A glowing sunset. A field of wildflowers. A rainbow peeking out of the clouds. The world is teeming with colors we see everyday. But humans don’t see every color on the light spectrum. There is a whole world of color that we can’t recognize. 

Why can’t we spot these hues? We see colors thanks to our eyes and brains. Our eyes contain two types of cells called cone cells and rod cells. Rod cells enable us to see in grayscale, which comes in handy at night when hues are more subdued. Cone cells, on the other hand, enable us to see in color. Our two eyeballs contain a total of about six or seven million cone cells. Actually processing and seeing color also requires the use of our brains. When a certain wavelength of light passes through the cornea it hits one of those cone cells. The cells then send a signal through neurons up to the optic nerve which relays a message to the brain and processes that data.

These cone cells only pick up on a select range of colors. It’s likely we can only see this selection and nothing more because honestly, we’ve been able to survive and thrive just fine with just these hues. But it is true that detecting light with shorter wavelengths than we currently can now, for example, would allow us to see more purplish hues. On the other hand, seeing longer wavelengths, like in the infrared spectrum, would enable us to have the ultimate night vision. 

Hear more about the colors we can and can’t see and why on this week’s episode of Ask Us Anything.  

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

Warmer weather is upon us here in the Northern Hemisphere. While it’s a welcome reward for surviving the winter to peel a few layers of clothing off, springtime is also when those unwelcome spring allergies start to blossom. If you do suffer from recurrent seasonal allergies, you aren’t alone. According to the American College of Allergy, Asthma, and Immunology, more than 50 million Americans experience various types of allergies each year. In fact, according to that same report, allergies are the 6th leading cause of chronic illness in the U.S. But that begs the question, what exactly is an allergy?

An allergy is a condition in which the immune system generates an abnormal reaction to an otherwise harmless substance. That substance is called an allergen, and it can take countless forms—dust mites, mold, grass, pollen, and different types of food can all illicit reactions in some people while having zero effect on others.

When you have an allergy to something, your immune system sees this substance as potentially harmful, and it reacts in a similar way to how it would respond to a dangerous virus or bacterium—however this time there’s nothing dangerous out there. Find out why the immune system performs this unnecessary act of rebellion in this week’s episode of Ask Us Anything. 

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

At some point, almost every human has experienced daydreaming. It often happens in the late afternoon slump when thoughts of relaxing on the beach or curling up on your living room couch with a good movie are far more pleasing than looking at spreadsheets or meeting your deadlines. And while daydreaming almost certainly gets a bad rap for snatching up our productivity, the act itself might actually be good for our brains. 

So what is actually going on in our brains when we mentally doze off? While neuroscientists haven’t fully pinned down all the mechanisms through which our brains work when we daydream, what we do know is that we likely form these alternate-reality thoughts with the assistance of a cluster of brain regions called the default mode network. Researchers have found that this network is most active when we aren’t focused on any concrete thing in the world around us. 

While nothing is for certain, neuroscientists and psychologists surmise that this type of creative thinking may be helping our brains reflect on the past and plan for the future. Other researchers suggest that it might reduce anxiety, boost creativity, and improve memory. And while perpetually working and improving oneself is popular these days, there’s research to suggest that daydreaming and doing nothing is also really important for our brains.

For more of the nitty gritty details on daydreaming, listen to this week’s episode of Ask Us Anything. 

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

Viruses have been the talk of the town this past year, and for good reason. A fairly deadly one—SARS-CoV-2, which causes COVID-19—has found its way to every corner of the globe. This pandemic has shown just how dangerous viruses can be, and it’s definitely not the first to do so. But the world isn’t necessarily black and white, and viruses are no different. So in this episode of Ask Us Anything, I’m excited to give a spotlight to the do-gooders of the virus world. 

Yes, good viruses do exist. In fact, all sorts of microorganisms, from viruses to bacteria and fungi, exist in and on our bodies without harming us. Researchers have dubbed our resident viruses the “virome.” But viruses are a bit different from the bacteria and fungi that call our bodies home. Namely, they can’t replicate without a living host. They enter cells and hijack their controls to make copies of themselves. Pretty gnarly and sneaky, but even so, they can still confer benefits to the living beings they depend on—human or otherwise. 

For example, the development of the placenta was helped in part by a group of special viruses called ancient retroviruses. To hear about the numerous other ways that viruses have helped shape who we are today and what researchers are still discovering about how they help us thrive, listen to this week’s episode. 

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ON JULY 21, 1969, when the Apollo 11 crew was due to depart the lunar surface after a 22-hour visit, two speeches were placed on President Richard Nixon’s desk. “Fate has ordained that the men who went to the moon to explore in peace will stay on the moon to rest in peace,” read the contingency speech. Would Buzz Aldrin and Neil Armstrong live out the rest of their days staring at the blue glow of Earth from 250,000 miles away?

We’ve lost only 18 people in space—including 14 NASA astronauts—since humankind first took to strapping ourselves to rockets. That’s relatively low, considering our history of blasting folks into space without quite knowing what would happen. When there have been fatalities, the entire crew has died, leaving no one left to rescue. But as we move closer to a human mission to Mars, there’s a higher likelihood that individuals will die—whether that’s on the way, while living in harsh environments, or some other reason. And any problems that arise on Mars—technical issues or lack of food, for example—could leave an entire crew or colony stranded and fending for themselves.

No settlement plans are being discussed at NASA (leave those to pie-in-the-sky private groups like Mars One for now), but a crewed mission has been on the docket for some time, and could touch down as early as the 2040s. NASA’s “Journey to Mars” quotes an estimated three-year round-trip, leaving plenty of time for any number of things to go wrong.

“The real interesting question is, what happens on a mission to Mars or on the lunar space station if there were [a death],” says Emory University bioethicist Paul Wolpe. “What happens when it may be months or years before a body can get back to Earth—or where it’s impractical to bring the body back at all?”

Today’s astronauts travel to space by way of the Russian Soyuz, then spend a few months on the International Space Station. Because astronauts are in impeccable health at the time of launch, a death in the ISS crew would likely result from an accident during a spacewalk.

“In the worst case scenario, something happens during a spacewalk,” says Chris Hadfield, Canadian astronaut and former commander of the ISS. “You could suddenly be struck by a micro-meteorite, and there’s nothing you can do about that. It could puncture a hole in your suit, and within a few seconds you’re incapacitated.”

This hypothetical astronaut would only have about 15 seconds before they lost consciousness. Before they froze, they would most likely die from asphyxiation or decompression. 10 seconds of exposure to the vacuum of space would force the water in their skin and blood to vaporize, while their body expanded outward like a balloon being filled with air. Their lungs would collapse, and after 30 seconds they would be paralyzed—if they weren’t already dead by this point.

The likelihood of death on the ISS is low, and it’s never happened before. But what would surviving astronauts do if it did?

Prepare for the Worst

ISS and shuttle astronaut Terry Virts served two expeditions on the space station and one mission on the space shuttle. In total he’s clocked 213 days in space. But the astronaut says he’s never been trained to handle a dead body in space. “I did quite a bit of medical training to save people, but not for this.”

NASA’s official statement to Popular Science on the subject left a lot to be desired:

“NASA does not prepare contingency plans for all remote risks. NASA’s response to any unplanned on-orbit situation will be determined in a real time collaborative process between the Flight Operations Directorate, Human Health and Performance Directorate, NASA leadership, and our International Partners.”

“In my 16 years as an astronaut I don’t remember talking with another astronaut about the possibility of dying,” Virts says. “We all understand it’s a possibility, but the elephant in the room was just not discussed.”

But NASA’s out-of-sight-out-of-mind policy on death may not be the norm. Commander Hadfield tells Popular Science that all international partners who train for missions to the ISS (including JAXA and ESA) do in fact prepare for the death of a crewmember.

“We have these things called ‘contingency simulations’ where we discuss what to do with the body,” he says.

Hadfield discusses these ‘death simulations’ in his book An Astronauts Guide to Life. He sets the scene—”Mission control: ‘we’ve just received word from the Station: Chris is dead.’ Immediately, people start working the problem. Okay, what are we going to do with his corpse? There are no body bags on Station, so should we shove it in a spacesuit and stick it in a locker? But what about the smell? Should we send it back to Earth on a resupply ship and let it burn up with the rest of the garbage on re-entry? Jettison it during a spacewalk and let it float away into space?”

As Hadfield points out, a corpse in space presents some major logistical problems. The fact that a dead body is a biohazard is definitely the biggest concern, and finding the space to store it in is a close second.

Since NASA lacks a protocol for sudden death on the ISS, the station’s commander would probably decide on how to handle the body. “If someone died while on an EVA I would bring them inside the airlock first,” Hadfield says. “I would probably keep them inside their pressurized suit; bodies actually decompose faster in a spacesuit, and we don’t want the smell of rotting meat or off gassing, it’s not sanitary. So we would keep them in their suit and store it somewhere cold on the station.”

If submarines lose a crew member and can’t make it to land right away, they store bodies near the torpedoes—where it’s cold, and separate from the living quarters. The crew of the ISS already stores trash in the coldest spot on the station; it keeps the bacteria away from them and makes smell less of an issue. “I would probably store them in there until a ship was going home, where they would take the third seat on the Soyuz,” Hadfield says. They could also store a body in one of the airlocks.

Freeze-Dried Funerals

NASA may not have specific contingency plans for a sudden death, but the agency is working on it; in 2005 they commissioned a study from Swedish eco-burial company Promessa. The study resulted in a yet-to-be-tested design called “The Body Back.” The creepy-sounding system uses a technique called promession, which essentially freeze-dries a body. Instead of producing the ash of a traditional cremation, it would turn a frozen corpse into a million little pieces of icy flesh.

During the study, Promessa creators Susanne Wiigh-Masak and Peter Masak collaborated with design students to think about what this process might look like while en route to Mars. On Earth, the promession process would use liquid nitrogen to freeze the body, but in space a robotic arm would suspend the body outside of the spaceship enclosed in a bag. The body would stay outside in the freezing void for an hour until it became brittle, then the arm would vibrate, fracturing the body into ash-like remains. This process could theoretically turn a 200-pound astronaut into a suitcase-sized 50-pound lump, which you could store on a spacecraft for years.

If freeze-dried cremation isn’t an option, you can always “jettison” the body out on a forever path into the void. While the UN has regulations about littering in space, the rules may not apply to human corpses. “Currently, there are no specific guidelines in planetary protection policy, at either NASA or the international level, that would address ‘burial’ of a deceased astronaut by release into space,” says Catherine Conley at NASA’s Office of Planetary Protection.

But the laws of physics might trump the laws of humankind on this one. Unless we strapped a mini rocket to the deceased, they would end up following the trajectory of the spacecraft from which they were ejected. As the years went on and the bodies accumulated, that would make for a morbid trip to and from Mars.

Martian Burial Rituals

But the risks of dying along the way are nothing compared to the inevitability of dying once you get there. In promoting his own future space settlement plans, SpaceX’s Elon Musk has openly cautioned that, “If you want to go to Mars, prepare to die.” Which begs the question: if someone dies on the Red Planet, where do you put them?

If someone were to perish on the spaceship en route to Mars (or beyond), cold storage or a round of promession could be a fine solution. But there isn’t a morgue on the surface of Mars, and spaceships are usually low on extra space.

So what would Martian explorers do with a body? “I would expect that if a crew member died while on Mars, we would bury them there rather than bring the body all the way home,” Hadfield says.

That makes sense because of the long journey back, but it poses some potential contamination problems. Even the rovers exploring Mars are required by law not to bring Earth microbes to their dusty new planet. Spacecraft are repeatedly cleaned and sanitized before launch to help protect potentially habitable locales from being overtaken by intrepid Earthly microbes. But the bugs on a rover are nothing compared to the bacteria that would hitch a ride on a dead body.

This makes the issue of planetary protection even more nuanced, but a Martian graveyard might not be so far-fetched. “Regarding the disposal of organic material (including bodies) on Mars,” NASA’s Conley says, “we impose no restrictions so long as all Earth microbes have been killed—so cremation would be necessary. Though planetary protection does require documentation of disposal, to ensure that future missions are not surprised.”

But not everyone who dies in space will be treated like inconvenient cargo. Some of those corpses will actually save lives.

Worst Case Scenario

Space may be the final frontier, but it wasn’t always that way. Humans have spent millennia traversing difficult landscapes and putting themselves in bizarre and dangerous situations in the name of discovery. Thousands of lives have been lost in this pursuit, and on occasion the deceased have actually saved the lives of their comrades. Not through acts of deadly heroism, mind you, but through acts of cannibalism.

Don’t think for a second that this couldn’t happen in space. In the book The Martian, author Andy Weir wrote in a scene (spoiler) in which the Ares crew decides to go back to Mars to save a stranded Mark Watney. Johansen, the Ares systems operator and smallest crew-member (requiring the least amount of calories) on the mission tells her father that the crew has a last-ditch plan to make it to Mars if NASA won’t send them supplies for the trip. “Everyone would die but me, they would all take pills and die. They’ll do it right away so they don’t have to use up any food,” she explains. “So how would you survive?” her father asks. “The supplies wouldn’t be the only source of food,” she says.

While extreme, the crew’s plan to commit suicide so one member could save Watney is not totally unheard of. “That’s a time-honored tradition,” says bioethicist Paul Wolpe. “People have committed suicide to save others, and in fact religiously that’s totally acceptable. We can’t draw straws to see who we’re going to kill to eat, but there are many times when we’ve considered people heroes who jump on the grenade to save their buddies.”

Wolpe says the school of thought on cannibalism for survival is split. “There are two kinds of approaches to it. One says even though we owe the body an enormous amount of respect, life is primary, and if the only way one could possibly survive would be to eat a body, it’s acceptable but not desirable.”

Mars boasts a landscape so barren and dead, it would put the frozen mountains that drove the famous Donner party to cannibalism to shame. If anything interrupted the mission’s food supply, they’d quickly run out of alternatives.

But no space agency has an official policy on Martian cannibalism—yet.

A Journey Into the Void

Humans have only been traveling to space for a short time relative to our existence, but we’ve been pushing the boundaries of exploration for thousands of years—and we will no doubt continue to do so despite the risks. Every astronaut or space tourist wishing to embark on a journey to Mars will ultimately be forced to grapple with the reality of deaths both sudden and slow.

NASA may never have officially published a contingency plan for the Apollo moonwalkers, but they were prepared to lose the crew. In his biography, Nixon speechwriter William Safire recalled the tenuous Apollo 11 liftoff. “We knew disaster would not come in the form of a sudden explosion,” he wrote. “It would mean the men would be stranded on the moon in communication with Mission Control as they slowly starved to death, or deliberately ‘closed down communication,’—the euphemism for suicide.”

In fact, NASA had planned to shut down communication with the stranded astronauts and issue them a formal “burial at sea.” But even given that morbid hypothetical turn of events, everyone knew they would keep going to the moon. “Others will follow, and surely find their way home,” Nixon’s back-up speech read. “Man’s search will not be denied. But these men were the first, and they will remain the foremost in our hearts.”

As we enter an age of space exploration sure to be filled with rocket launches and crewed missions, the thought of death looms over every crew-member and decision maker.

Astronaut Terry Virts may never have casually chatted about dying over coffee with his friends, but he knew what was at stake when he launched into space. “I believe that it is worth it, and that any great endeavor will involve risk,” he says. “We consciously accept the unavoidable hazards that we face.”

Like most explorers, shuttle astronaut Mike Massimino is quick to say that the risk is worthwhile. “It’s about increasing our understanding,” he tells PopSci. “I think it’s worth the risk we take. Exploration has always taken lives and I’m sure it always will.”

The realistic options for a deceased crewmember—cannibalism, cold storage in the trash room, being freeze-dried and shaken into a million frozen flakes—lack the dignity we associate with the majestic endeavor of spaceflight. But Wolpe doesn’t think humankind will have a hard time adjusting to the harsh realities of posthumous treatment in space. We already accept that Earthbound explorers may suffer indignities if they die in the field. Wolpe sees Mount Everest as a perfect Earthly analogue for the future Mars missions: when people die, their bodies just stay there. Forever.

Every year around 800 people attempt to reach the summit of the mountain. Every year, some of those people die. And then another 800 people try the next year. These people want to be first, to be the best, to explore something marvelous and rare. And with this determination comes the risk of paying the ultimate price.

“If you climb Everest, you know that if you die you’re being left there,” says Wolpe. There’s no fancy method of cremation on Everest, no respectfully somber place to stow a body, no way to reasonably pick up a corpse for burial back home. Over 200 bodies lay across the mountain, some of them still visible on days when snow cover is light. Everyone who climbs past them is reminded that they’re risking their lives—and their chance at a proper burial—for a chance at reaching the summit. “You just accept that,” Wolpe says. “That’s part of climbing Everest.”

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

At first glance, a volcano’s hot lava seems ideal for incinerating our trash. But, like so many things in science, it’s so much more complicated than that. And the short answer is, the effort might not be worth the reward. 

If you did try to turn a volcano into a dump, you would likely run into a number of obstacles. First, humans produce a lot of trash. Americans alone generate, on average, about 4.9 pounds of junk per person per day. That’s 292.4 million tons of waste in total for the US annually, according to the Environmental Protection Agency’s most recent report in 2018. 

In addition to the giant load of trash we create, volcanoes ideal for rubbish dumping aren’t exactly easy to come by. The ideal trash incinerator would be one that erupts slowly and ever so gently spews hot lava onto the surrounding area. Those are called shield volcanoes, and they are common in Hawaii. An ideal example is Kilauea, which is located on the Big Island and is one of five volcanoes that together form the Big Island. Unfortunately, the majority of volcanoes on Earth are stratovolcanoes.

The last obstacle is a big one: Getting too close to hot lava is downright dangerous.  

For more details on this exhilarating albeit dangerous hypothetical journey from dumpster to volcano and back listen to this week’s episode of Ask Us Anything. 

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

Over the past several years, marijuana legalization has been sweeping across the US. In fact, as of April 2021, cannabis is legal for adults to use recreationally in 15 states as well as Washington, D.C. and medical marijuana is legal in 36 states. Given that cannabis is becoming more established as safe and accepted legally, this begs the question: Is it possible to overdose on it? 

Fortunately, there’s some good news: The Centers for Disease Control and Prevention has yet to report any deaths directly tied to excessive cannabis use. Further, marijuana is the most commonly used illicit drug in the United States. In fact, about half of US adults have tried it at least once, and about one in five adults under age 25 say they have used it in the past month, according to a 2020 report from the National Institute on Drug Abuse. So, statistically, if there were even a tiny chance of fatality from using too much, we would know it by now. 

However, that doesn’t mean it’s not possible to overdo it. As we describe in this episode,  smoking or ingesting too much marijuana isn’t exactly pleasant and can, indeed, cause harm. Listen to the episode and check out the story it was based on to find out the details.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

The sharp pain while exercising is dreaded and all too common. Despite our best efforts to stay well-hydrated, warm-up, and take it easy when needed, side-stitches still plague as many as two in three runners each year. And the stabbing ache doesn’t just plague joggers, but nearly every exerciser from swimmers to horseback riders. And though many may experience it, the science behind it isn’t well understood. 

Researchers have a handful of theories they’ve been bouncing around for the past few decades, at least, to attempt to explain the physiological underpinnings of the humble side stitch. Still the stitch endures, and remains somewhat of a mystery. Listen to this week’s episode to hear how close scientists are to solving the mystery of the side stitch and what you might be able to do to prevent yourself from getting one.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

This week on Ask Us Anything, we investigated an age-old question: How much sleep do we need? Or, perhaps how many of us might think about it these days, how little sleep can we get away with while still functioning normally? To answer that first question, we traced the history of sleep studies back to a pair of researchers who spent 32 days living in a Kentucky cave completely devoid of sunlight. Understanding how the researchers slept under those conditions helped inform us about the optimal amount of sleep humans need and how our circadian rhythms factor in. 

And in the past decade or two, sleep researchers have performed similar studies (in air-conditioned labs, not Kentucky caves) with more participants which have added to our understanding of how sleep affects the human mind and body. And while the number of hours of sleep adults need might not surprise you, what happens to your body and brain when you get just slightly less than that optimal amount will certainly be an eye-opener. 

Tune in to this week’s episode of Ask Us Anything (and read the story that inspired it) to find out more!

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

This time on Ask Us Anything, we took a deep dive into a black hole. Well, not literally. In fact, if you listen to this week’s episode, you’ll learn that if a person somehow did find their way to the entrance of a black hole and tried to enter, scientists have a pretty good idea of what would happen—and it’s not great. 

If you somehow could survive entering a black hole, then scientists don’t really know what happens to you next. They do know that you’ll reach something called the singularity, but that’s where things get wonky. The singularity is an infinitely dense point where space and time warp and cease to exist as we know them. Physicists and mathematicians have numerous ideas for what could happen in that place, but at some point, they all seem to break the laws of math and physics. Tune in to this week’s episode of Ask Us Anything (and read the story that inspired it) to hear all these possibilities. And rest assured: The nearest black hole is roughly 1,000 light-years away. 

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If you put a steamy cup of coffee in the refrigerator, it wouldn’t immediately turn cold. Likewise, if the sun simply “turned off” (which is actually physically impossible), the Earth would stay warm—at least compared with the space surrounding it—for a few million years. But we surface dwellers would feel the chill much sooner than that.

Within a week, the average global surface temperature would drop below 0°F. In a year, it would dip to –100°. The top layers of the oceans would freeze over, but in an apocalyptic irony, that ice would insulate the deep water below and prevent the oceans from freezing solid for hundreds of thousands of years. Millions of years after that, our planet would reach a stable –400°, the temperature at which the heat radiating from the planet’s core would equal the heat that the Earth radiates into space, explains David Stevenson, a professor of planetary science at the California Institute of Technology.

Although some microorganisms living in the Earth’s crust would survive, the majority of life would enjoy only a brief post-sun existence. Photosynthesis would halt immediately, and most plants would die in a few weeks. Large trees, however, could survive for several decades, thanks to slow metabolism and substantial sugar stores. With the food chain’s bottom tier knocked out, most animals would die off quickly, but scavengers picking over the dead remains could last until the cold killed them.

Humans could live in submarines in the deepest and warmest parts of the ocean, but a more attractive option might be nuclear- or geothermal-powered habitats. One good place to camp out: Iceland. The island nation already heats 87 percent of its homes using geothermal energy, and, says astronomy professor Eric Blackman of the University of Rochester, people could continue harnessing volcanic heat for hundreds of years.

Of course, the sun doesn’t merely heat the Earth; it also keeps the planet in orbit. If its mass suddenly disappeared (this is equally impossible, by the way), the planet would fly off, like a ball swung on a string and suddenly let go.

Send your questions to fyi@popsci.com. Can’t wait a month? Look for answers on our Web forum, popsci.com/fyilive.

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The colorblind don’t just suffer limited career choices (pilot is out). They also miss some of life’s biggest pleasures— vibrant sunsets, autumn foliage, the ability to determine if a tomato is ripe. “Nobody chooses a black-and-white TV over color,” says University of Washington ophthalmology professor Jay Neitz, who has ­devoted his career to studying color deficiency. “­Color makes us happy.”

Cone cells in the retina normally help the brain translate lightwaves into what we perceive as colors. When those cells lack red or green photopigments, it causes the most common colorblind disorder, one that afflicts 1-in-12 men in the U.S. and 1-in-230 women. It’s the most common ­single-gene defect in the population. So far, there’s no cure. Soon that may change.

Neitz and his wife, Maureen, with other scientists, have successfully tested a gene therapy on male squirrel monkeys, all of which are colorblind. First, they packed a normal human photopigment gene into a harmless virus, then surgically inserted it—via needle—under the monkeys’ retinas. Five months later, the moneys passed a color test in which they were awarded treats for picking colors on a computer.

Sticking a needle deep in a human eye, however, is risky. Among other things, it could cause blindness. So the Neitzes are working on a safer gene-delivery method, a shot that is delivered into the vitreous—the clear substance between the eye’s lens and retina. Such vitreous shots are already in wide use to deliver medication for conditions like macular degeneration. One problem, though: There’s no certainty that genes introduced into the vitreous will get where they need to go. “The virus itself will have to penetrate the retina,” to get to the cone cells, says Neitz. “We don’t have that working perfectly yet.” Human clinical trials are years away. Until then, a new company, EnChroma, makes glasses that enhance color perception for some types of deficiencies.

This article was originally published in the September/October 2016 issue of Popular Science.

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As we learned in school, water on our planet moves through a cycle: It evaporates from oceans, lakes, and other ground-based sources, forms clouds in the air, and then falls down again as rain, snow, or ice. But most water on Earth is sitting in our salt-filled oceans—so why isn’t snow as salty as the sea?

Simply put, water evaporates and leaves the sodium chloride, aka salt, behind. As the sun beams down on the ocean, it provides energy to water molecules and to the substances—such as salt—that are mixed in with it. Given enough of this energy, a water molecule can break away from its fellows and float up into the air as water vapor. But salt requires much more of a boost to break free. That’s because, in water, it breaks down into positively-charged sodium ions and negatively-charged chlorine ions. The electrical charge makes these ions attract water molecules, which cling to the charged ions more tightly than they hold on to other H₂Os. So as the evaporated water rises, it exists in a very pure distillation, free of salt and other compounds. Unfortunately, it doesn’t stay that way.

Higher up in the atmosphere, water molecules meet up with airborne particles like dust and soot, and often form droplets around them. These drops fall back to Earth as precipitation. Because of this formation technique, the droplets can carry airborne pollutants back down to Earth. (Think of that next time you stick out your tongue to catch a raindrop!)

Droplets can even form around salt particles, but the salt would be at a much lower concentration than in seawater. So could you ever get salt into the air? Certainly—you’d just have to heat it up to 2,575 degrees Fahrenheit, the boiling point of sodium chloride. Or move to a coastal area: Wind blowing over the ocean can carry saltwater spray, and fog can sometimes pick up compounds over the ocean, and then transport these molecules to dry land.

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While disturbing, stolen passwords may not be the best source of information on personal security habits. “When you’re collecting hacked passwords, you’re getting passwords that are hackable,” says Mark Burnett, an independent security expert. “Often times the data come from places that don’t have strong policies, or sites that no one really cares about protecting.” That may be why data-dumps like this one include so many obvious duds. Burnett’s own collection of 30 to 40 million leaked accounts contains password at least 150,000 times.

Other leaks suggest that more stringent security policies may not yield more sophistication. A 2009 hack revealed a long list of passwords with at least one number and one capital letter. Password1 topped the list, with P@ssw0rd and Passw0rd not far behind.

To improve account security, Burnett says to use at least 10 characters and avoid common phrases. But even that may not offer much protection. “The capability of cracking passwords has gotten so great. We have things to make them stronger, like two-factor authentication, but on their own, passwords are kind of at the end of their effectiveness.” That means while the worst passwords are obvious, there’s really not a best one either.

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Sour Patch Kids

It’s hard to imagine any kid made it out of the 90s without at least one formative tongue-burning experience due to the overconsumption of sour candies. Whether it occurred at a movie theater or during a childish competition over who could hold the sourest candy in ones mouth for the longest time, it happened. For some of us (myself included) the sour candy addiction continued into adulthood. While Generation Y’s pain felt over a burnt tongue has most likely subsided into distant memory, for those who continue to consume sour candies, one question persists: why do these delicious candies sometimes burn my tongue? And more importantly, is it possible to permanently damage my taste buds?

Three main ingredients make up the variety of candies we call sour: sugar, acid, and food coloring. We all know there is a despicable amount of sugar in the extremely sour candies we crave, but the citric and malic acid found in almost equal amounts goes undiscussed. In 2008, a few pediatric dentists decided to look into the erosion of tooth enamel and tested the pH levels of the most popular sour candies to see just how bad for your teeth these addictive snacks are. The study, published in the peer-reviewed Journal of the Minnesota Dental Association, Northwest Dentistry, was appropriately titled, “Pucker Up–The Effects of Sour Candy on Your Patient’s Oral Health.” Their findings will make your teeth hurt.

pH, a measure of acidity, has to do with the number of protons present. Water has a pH level of 7.0 while battery acid comes in at a low 1.0. Most sour candies have pH levels much closer to battery acid than water, and acidity can damage teeth. Bacterial tooth decay occurs when bacteria, which thrive on the sugar in candy, create acid that attacks the tooth. Sour candies contain both sugar and acid, and tend to stick to teeth, making them a triple threat. The aforementioned study found candy like X-treme Airheads (pH 3.0), Sour Punch Straws (pH 2.5), Sour Skittles (pH 2.2), Fun Dip Powder (pH 1.8), and Warheads Sour Spray (pH 1.6) were shockingly acidic.

To add another piece to the pH puzzle, vinegar has a pH of around 4.5 and Coca-Cola comes in at a 2.5-3.0. We all know Coca-Cola isn’t sour, so what gives?

“Sour is your taste perception of acid,” says Dr. Tom Finger at the Rocky Mountain Taste and Smell Center at the University of Colorado, adding that “perception is not just purely pH.” In other words, acidic content doesn’t equal sour taste. Why? One reason is sugar. The presence of sweet suppresses the sour, and your perception is altered. Still, a pH level of 2.5 is a lot of acid, and the amount of time the acid spends in your mouth does matter. The longer you hold the candies in your mouth, or the more you eat, the more your tongue will hurt. This is because the acid from the candy lowers the pH level of your mouth, and if it stays low for a prolonged amount of time it acidifies the epithelium, the layer of cells covering your mouth and tongue. Your epithelium doesn’t get as irritated when you drink Coca-Cola, because the beverage passes through your mouth quickly, whereas chewing so many delicious candies exposes the tongue to low pH levels for a long time.

When you consume a large amount of sour candy in one sitting, the epithelium becomes irritated to such an extent that the pH-sensitive nerve fibers activate. These nerve fibers are what signal pain to the brain. Two sorts of pH-sensitive detectors exist: ion channels, which react to strong acidity, and transient receptor potential channels, which react to chile heat. Both activate the same pain receptors, and so does food that’s too hot.

Time will heal the pain of sour candy. The saliva will eventually stabilize the pH level in the mouth, but if you want to speed up the process, drinking water or dairy (both higher-pH beverages) will help, too. Dr. Finger says it is highly unlikely a person would burn off actual taste buds, but in case you’re worried, they completely regenerate every 10 days to two weeks, meaning permanently damaging your precious taste buds is not possible.

So why do we continue to eat too many sour candies if we know the experience has potential to end in lingering pain? The pleasure of eating and tasting the candy, of course. Dr. Finger compared eating too many sour candies and burning the mouth to going out to a bar and drinking so much that the next morning brings a dreadful hangover. By overlooking the long-term ramifications, it seems we are able to continue to enjoy the short-term gratification of both sour candy and alcohol.

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Is your head constantly spinning with outlandish, mind-burning questions? If you’ve ever wondered what the universe is made of, what would happen if you fell into a black hole, or even why not everyone can touch their toes, then you should be sure to listen and subscribe to Ask Us Anything, a brand new podcast from the editors of Popular Science. Ask Us Anything hits Apple, Anchor, Spotify, and everywhere else you listen to podcasts every Tuesday and Thursday. Each episode takes a deep dive into a single query we know you’ll want to stick around for.

We’d all love to perform certain activities or eat certain foods such that we become illness-fighting ninjas. Unfortunately, it’s not entirely how the immune system works. The human body operates under tightly regulated conditions, and the immune system is no exception.

Plus, the concept of “boosting your immune system” until it can instantly fight off any infectious agent you might come into contact with doesn’t make much sense—your body would simply be exhausted from constantly being at the ready for so many diseases. There are countless cold viruses (known as rhinoviruses) and various forms of the flu (which is a big reason why the flu vaccine isn’t always as effective as doctors hope). There’s just no way to train the body to fight all of them.

But there is a way to make your immune system as beefed up as possible so that it’s ready to take on various infectious critters that come your way. So a little ninja-like, in a way? For all of the nitty-gritty details, tune in here, and read the article that inspired this episode here.

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This post has been updated. It was originally published on 1/12/2016.

America’s century-old system for counting calories in food comes from chemist Wilbur Atwater. In 1887, he began to research the energy we get from eating by measuring the nutritional value in different meals and subtracting the amount of energy left in people’s bodily excretions.

Atwater’s research has since been boiled down to the 4-9-4 rule: Each gram of protein, fat, and carbohydrate provides, respectively, 4, 9, and 4 calories of energy. The United States Department of Agriculture (USDA) has used these figures for decades, tweaking them only to account for different qualities—such as the digestibility—of specific foodstuffs.

[Related: How AI helped make the best calorie tracker]

But in the past decade, nutritionists have clamored for a reappraisal of calorie intake and nutrition information. For one thing, they say the present system ignores the difference between raw and cooked food. Harvard University researchers assert, based on mouse studies, that processed food is easier for the body to absorb, so it provides more calories. That goes for baked or blended food. Even a handful of chopped peanuts gives you more energy than whole ones.

In 2011, USDA researchers, with a grant from the nut industry, reported that the caloric value of pistachios had been overstated by 5 percent on the nutrition label. In 2012, they found almonds were overstated by 32 percent, or 40 calories per serving. So you might not want to take labels at face value.

This article was originally published in the November 2015 issue of Popular Science

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If you were a kid in the ’90s, or had a kid in the ’90s, you probably remember the Matilda scene—the scene—where the loathsome Miss Trunchbull made Bruce Bogtrotter eat an 18-inch chocolate cake in one sitting, in front of his classmates.

The punishment is torturous to watch, and the act is probably illegal. But if this were real life, would Bruce have died? No, he would not have suffered any sort of chocolate toxicity from it. A conservative estimate would have him eating probably only about a pound of pure chocolate. That’s not enough to kill somebody.

In the fact that it is almost impossible for the average human to die from eating too much chocolate.

“There certainly is a toxic dose of chocolate, and it can be fatal,” says Reed Caldwell, an emergency medicine physician at New York University Langone Medical Center. However, if attempted, he says, you are far more likely to wind up in the emergency room with a severely upset stomach (likely with vomiting) than with chocolate overdose.

Why are we having this conversation at all? Is there something that makes chocolate toxic? The cocoa bean, from which chocolate is made, contains a substance called theobromine, which is a plant alkaloid with a slightly bitter taste (other plant alkaloids include America’s favorite, caffeine, as well as cocaine, nicotine, and the effective chemotherapy drug Vincristine). In the human body, theobromine is, at most, a mild stimulant, acting similar to caffeine. Theobromine is also a vasodilator, meaning it can open up your blood vessels and cause your blood pressure to drop. It’s also a diuretic, so you could feel the urge to urinate more often.

Additionally, according the National Institutes of Health’s toxicology data network, theobromine also crosses the blood-brain barrier, that semi-permeable layer of blood capillaries that allow only certain substances into the brain. This suggests that it might share caffeine’s beneficial effects on mood, according to the report.

And, yes, at high enough levels theobromine can actually be toxic to humans (and at much lower levels in dogs). The combination of its vasodilation abilities, diuretic effects, and gastrointestinal upset means that, in very high amounts, theobromine can cause a rapid heart rate, loss of appetite, sweating, trembling, and a severe headache. And because of the effects on the cardiovascular system, which include a drop in blood pressure and increased heart rate, too much theobromine can be fatal.

But Caldwell says that’s extremely rare. For one, he says, you would need to consume a lot of the stuff (more on that below). For two, when you are a good chunk of the way through that consumption, an upset stomach would likely impede any more progress.

“Certainly, it can be fatal, but one thing that is helpful, and I don’t know if helpful is the right word, but some of the initial symptoms are nausea and vomiting,” says Caldwell. “So the initial toxicity symptoms may help prevent people from consuming a lethal amount.”

Okay, but say you are trying to channel your inner Bruce Bogtrotter, scientifically speaking, how much is too much?

For humans, theobromine is considered toxic at a dose of 1,000 milligrams of theobromine per kilogram of body weight. At this point, you would reach the level that toxicologists call the LD50 level, meaning the point in which 50 percent of the test population showed signs of illness.

If we say that an average human weighs 165 pounds, or 75 kilograms, to reach the level of toxicity for theobromine, or theobromine poisoning, you would need to eat 75,000 milligrams of theobromine.

Of course, different types of chocolate contain varying amounts of theobromine. On average, milk chocolate contains far less than dark. Milk and other highly processed chocolates contain about 2.4 milligrams of the toxin per gram of chocolate. Dark chocolate contains about 5.5 milligrams per gram. And baker’s chocolate? 16 milligrams per gram. So a typical adult human who needs to eat about 75,000 milligrams to be at a toxic level. That’s roughly:

711 regular-sized Hershey’s milk chocolate bars

OR

7,084 Hershey chocolate kisses

OR

332 standard- sized Hershey’s dark chocolate bars.

It’s not impossible, and dying from chocolate overdose would not be the most surprising thing a human was capable of, but Caldwell has never seen a case of theobromine poisoning in his career as an emergency medicine physician. Nor has he heard of any tales from his colleagues.

So unless you are seeking to get theobromine poisoning, you very likely won’t eat enough to cause a theobromine overdose.

How much is an okay amount of chocolate to eat? “For the otherwise healthy adult, without chronic medical problems like diabetes, most candy bars or boxes of chocolate that people receive for Valentine’s Day can be safely consumed today,” Caldwell says.

“As long as your significant other doesn’t give you a 20-pound chocolate bunny, you’ll be okay.”

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Reader Bob Fately asks:

Post your answer in the comments.

Submit your science and technology questions to fyi@popsci.com.

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Some fluffy white stuff is hitting the Midwest and East Coast this week, creating the perfect opportunity to catch snowflakes on your tongue.

“Everyone should eat snow because it’s really fun,” says Anne Nolin, a professor at the College of Earth, Ocean, and Atmospheric Sciences at Oregon State University. Her one condition: “You have to do it with a goofy look on your face.”

Nolin, who studies snow and ice in the climate system, says most snow is just as clean as any drinking water. To make their way from a cloud to the ground, cold water molecules have to cling to particles of dust or pollen to form the ice crystals that then grow into snowflakes in a process called deposition. These, Nolin points out, are the same tiny particles we normally breathe. Plus, as snowflakes fall, they have a harder time picking up soot and other air pollutants than raindrops, which are better at picking up these particulates.

Once the snow is on the ground, it stays clean until other things land on top of it. Everyone knows you shouldn’t eat yellow snow. Brown snow is off limits, too. That’s because as snow sits around, it goes through a process called dry deposition, in which dust and dirt particles stick to the snow. And Nolin says to steer clear of watermelon snow: It might look pretty and very pink, but it’s filled with algae that don’t do great things for digestion.

So as the storm hits over the next few days, feel free to collect some fresh powder on your gloves and take a bite. Nolin recommends pairing a clump of fresh snow with hot maple syrup, a treat she used to have in Vermont.

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Unfortunately, there’s pretty much no way to protect jet engines from geese or other large birds. In fact, fastening some sort of shield over a jet engine could actually make things worse.

From 1997 to 2007, reported animal strikes per civil flight more than doubled, reaching 7,600 in 2007—mainly glancing shots—in 54 million flights, according to Richard Dolbeer, former chairman of the volunteer organization Bird Strike Committee USA. Because most bird strikes occur less than 500 feet off the ground, experts blame the growing populations of Canada geese and other birds near airports.

Foie Gras Alert

When a goose or another bird is sucked into a plane’s engine, the resulting carnage can jam up the turbine enough to stop the engine. Most famously, a flock of geese shut down both engines of a 150-passenger Airbus A320 shortly after takeoff this January, forcing the pilot to make an emergency landing in New York’s Hudson River.

Although one might assume that airlines could shield jet engines with a screen or a set of bars, it’s simply not practical, says Russell DeFusco, vice president of bird-strike consultants BASH, Inc. A 12-pound goose hits a plane traveling 150 mph on takeoff with roughly the same force as dropping a grand piano from the second story of a building, says Matthew Perra, a spokesman for engine manufacturer Pratt & Whitney. Beyond the fact that any screen would create turbulence and inhibit free-flowing air from entering the engine, thus weakening its thrust, if the screen broke on impact, it too could be sucked into the engine and cause even more damage, DeFusco says.

Per FAA regulations, before a new engine model can be strapped to planes it must first prove that it can safely shut down after ingesting a four-pound bird carcass. This test might not be rigorous enough, however, considering that the largest Canada geese tip the scales at 14 pounds.

Bird-repelling techniques now in use at airports include draining fowl-friendly ponds and scaring off birds with firecrackers. The FAA is also working on a bird-detecting radar like the one Kennedy Space Center has had since a space shuttle’s 2005 run-in with a vulture.

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In October of 2019, three strong earthquakes hit the Philippine municipality of Tulunan, Cotabato. With multiple active fault lines snaking around the southern island, residents three hours away in Davao City felt the ground shaking. The first round of tremors kept me up at night. The second came two weeks later, and then the third just two days after. That’s when I lost count.

As people in Tulunan shared photos and videos of the destruction, I felt helpless. The anxiety of not knowing what to do or what would come next flooded my mind. Little did I know, my worries were just beginning.

“The vast majority of earthquakes are caused by the sudden release of stresses built up by movements of tectonic plates,” says Morgan Page, a research geophysicist with the U.S. Geological Survey. The “instrumentally detectable aftershocks,” she adds, typically go on for months to years. That’s exactly what happened in Tulunan and Davao City—we experienced hundreds of aftershocks throughout November. Page also notes that “the rule of thumb following a large earthquake is that there’s about a five percent chance that it will trigger an even larger earthquake.” “So in most cases,” she says “the aftershocks remain smaller than the mainshock. But everyone should be aware that sometimes an even larger earthquake can occur.”

The earthquakes in the Philippines may not have been all natural. The region around Tulunan is rife with mining activity, which could lead to “induced earthquakes,” says James Gaherty, a professor at the School of Earth and Sustainability at Northern Arizona University. Induced earthquakes are “are almost always very small and very rarely damaging,” he explains, but they can build up to larger events. On November 18, a magnitude 5.9 earthquake hit the municipality of Kibawe, Bukidnon, about 70 miles away from Davao City. This time sleeping was next to impossible.

Just as continued aftershocks take a toll on infrastructure, they can also eat away at people’s mental health. Earthquakes and post-traumatic stress disorder (PTSD), a condition that affects upwards of 7 percent of the world’s population, both manifest over time. I, for example, have have been grappling with anxiety for a decade; the recent earthquakes just brought out the worst of it. Now, I feel like I need to get ahead of everything, be prepared for everything, have back-up plans for everything. It’s a fight-or-flight response, cranked up to the nth degree.

Indeed, that description might not be too far off, according to medical experts. Anxiety is “a completely normal response to an abnormal situation, and more specifically, a frightening situation,” says Molly Ansari, an assistant professor of counseling at Bradley University in Peoria, Illinois. “The anxiety that develops following something such as an earthquake serves as a warning signal to our bodies to protect us from future danger. For example, ‘helpful anxiety’ may urge individuals to make earthquake safety kits, install mechanisms to make their homes more stable, purchase insurance, etc.”

The thing is, it’s not easy to predict how earthquake-induced anxiety may affect an individual—or how someone who’s still learning to cope with anxiety might fare with aftershocks. For me, after four strong tremors, it didn’t feel like “helpful anxiety” anymore. The difficulty in sleeping topped a long list of symptoms that Ansari highlights: excessive worrying, irritability, flashbacks, and constant fear of the next disaster. I checked at least three of those adverse effects.

Ansari, who’s a licensed clinical counselor specializing in trauma, says that earthquakes can indeed cause worry and fear, even in those who’ve already survived and thrived after one. But she also notes that it can be tough to tell if those reactions are a result of anxiety or PTSD, which is a more specific expression of anxiety. “The symptoms often overlap and can be mistaken for the other,” she explains. “It’s common for someone who is diagnosed with PTSD to [broadly] experience anxiety.”

So how does one parse the two? Ansari says a clinician would look at the etiology, or set of causes of the symptoms. “Typically, when a diagnosis of PTSD is given, an individual has experienced an intense feeling of anxiety in response to an event, such as a natural disaster.” With general anxiety, on the other hand, Ansari says the symptoms likely have “presented themselves in a variety of circumstances” and have a more longstanding history.

In short, if the anxiety was a direct result of a traumatic experience and triggers severe behavioral and psychological symptoms—agitation, hyper-vigilance, social isolation, flashbacks—it may be diagnosed as PTSD. Ansari also stresses that someone with pre-existing anxiety who hasn’t received treatment or support “may be more susceptible to developing PTSD following a traumatic event.”

While earthquakes do fall in the category of traumatic events, there’s little research on how widely they can cause PTSD and general anxiety. Last year, the Asian Journal of Psychiatry published a study connecting the 2016 Aceh Earthquake in Indonesia with a statistically significant rise in comorbidity from PTSD, depression, and anxiety. A public health scientist at the University of Miami conducted similar research on Puerto Ricans displaced by Hurricane Maria. He’s currently examining how island residents fared when hundreds of aftershocks hit their homes earlier this year.

As Ansari puts it, “there’s still so much to research” with PTSD following natural and human-made disasters. “I think the most interesting factor is when I get asked ‘who will get PTSD’ or ‘will I get PTSD’? The answer to that is, ‘we don’t know.‘ But it’s always interesting to see what common factors exist with those who get PTSD and those who do not. The same can be asked about general anxiety disorder.”

For residents of the southern Philippines, a region whose fault geology is still poorly understood, according to Gaherty, there’s still the question of whether they’ll ever be able to sleep with ease. But as Ansari points out, there are ways to cope and get help for general anxiety and PTDS. In addition to counseling and prescribed medications like Buspirone, Ansari suggests joining support groups for survivors of natural disasters, practicing relaxation techniques like meditation, and establishing life routines that build predictability. She also says it’s wise to engage in activities that foster a sense of empowerment and control, including creating art and journaling. The latter has done wonders for me: Every time I can put how anxiety affects me into words, I feel empowered.

It’s been eight months now since the first strong tremor in Davao City and a few weeks since the aftershocks eased up. The anxiety still creeps in every now and then, but I’m learning to calm my mind and continue on with life. That might not hold true for my neighbor, however, or the person who lost their home in the hills of Tulunan. Everybody experiences mental health disorders differently, and because of that, we each have to find our own way of coping with disaster. The important part is that we acknowledge the struggles, no matter what the aftershocks might look like.

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Follow all of PopSci’s COVID-19 coverage here, including the most recent numbers, tips on how to make your own masks, and advice on what to donate for health care workers.

Everyone wants to be that person that never gets sick. The one at the office who somehow skips out on the bug that’s traveling from cubicle to cubicle, or the one that doesn’t come down with a cold even when their entire family falls victim. Today, in the wake of the COVID-19 pandemic, this goal seems even more imperative.

The idea of being able to do certain activities or eat something specific to boost your immune system such that you can become an illness-fighting ninja sounds incredibly enticing. But unfortunately, it’s not exactly how the immune system works. There’s no way to bolster your disease-fighting white blood cells to make you impenetrable to the coronavirus. However, there are things you can do—namely getting enough sleep, eating well, and taking in proper doses of certain vitamins, like Vitamin D— that will help ensure your immune system is working at its best in the event you do become infected with SARS-CoV-2, which causes COVID-19.

Our bodies’ immune systems are broken down into two different categories, innate and adaptive. The former is made up of non-specific proteins and cells that come to action in any type of injury or illness, even a scrape to the leg. But the latter—the adaptive immune system—is far more specific. When you get a cold, the flu, or the novel coronavirus, cells within your adaptive immune system rush out to identify exactly what that sickness is. Once they do, they cleverly design immune cells to find and kill that infection. Those cells remain in the body such that when you come in contact with that virus or bacteria or other infectious agent again, your immune system knows exactly what to do. That’s why it’s incredibly difficult, if not impossible, to get the same (exact) infection twice.

This memory mechanism is very cool and convenient. It’s also why vaccines work. The vaccine is a tiny bit of virus or bacteria (usually a dead version). When injected, your immune system creates cells that kill the intruder. Your immune system then remembers the infection so that when you come in contact with it again, your body knows exactly how to kill it. But the key component here is the sequence of events: Come in contact with the virus, then develop immunity to it. Unfortunately, it can’t work the other way around. So the idea of boosting the immune system until it can fight off any infection you get just doesn’t make any sense. There are countless cold viruses (known as rhinoviruses) and various forms of the flu (which is a big reason why the flu vaccine isn’t always as effective as doctors hope) and there’s no way to train the body to fight all of them.

But there is hope. Your innate and adaptive immune system both need the right types of cells in the right quantities to work properly. If you want to give yourself a fighting chance, figuring out the best way to maintain the right number of immune cells is key. How do you do that?

“That’s the million dollar question,” says Megan Meyer, director of science communication at the International Food Information Council, a nonprofit organization focused on providing science-backed nutrition research to the public.

As a whole, “our immune system is tightly regulated,” says Meyer. We don’t have the tools to boost one part versus another. And even if we did have that ability, it wouldn’t necessarily benefit us. Having an increased number of a certain type of immune cell is not a good idea if there’s no immediate infection. It could potentially lead to overall inflammation in the body or even an autoimmune disease, and there’s just no need for it. You don’t want an immune system in a constant state of activity; you want one that can act quickly and effectively when an infection hits.

That being said, Meyer says, what we eat and our patterns of behavior can impact an immune system’s overall health. And in certain cases, this has been well documented with thorough studies.

There are the obvious factors, like getting the proper amount of sleep (eight hours for adults). Sleep affects the immune system in a number of ways. Some studies show that when you are sick, sleep might help to distribute certain immune cells to the lymph nodes, where they go to work fighting off infections. Sleep also plays a key role in actually creating the right immune cells to fight off disease. In one study, researchers gave participants the hepatitis A vaccine. That night, they sent half the study participants to bed for a full night’s sleep and had the other half pull an all-nighter. Then, they looked at how effective the vaccine was by analyzing the amount of antibodies—proteins produced by the adaptive immune cells that are specific to certain infections, in this case hepatitis A—the participants produced in response to the injection. Four weeks later, on average, the ones that slept regularly on that first night had twice the number of antibodies to the hepatitis infection than the ones that didn’t get their Zzzz.

In terms of nutrition, eating a well-balanced diet will keep your immune system balanced, too. On a macronutrient front, studies show that protein might be particularly important for a strong immune system. Protein is key to forming not only immune cells but every cell in the body. For immune cells though, protein contains an amino acid called L-arginine, which studies done on populations with both influenza as well as people with severe burn wounds, that L-arginine helped generate helper T cells, the ones that show the rest of the immune system what the virus looks like so that it can generate specific cells to fight it. “So consuming protein with L-arginine is a way to ensure the right amount of T cell proliferation is happening in individuals,” says Meyer. Consuming protein is a way to ensure the right amount of T cell proliferation is happening in the event you are confronted with an infectious virus.

On the micronutrient scale, there are also a few standouts. Perhaps the most well-studied is zinc. A few very good, double-blind, placebo-controlled trials using zinc lozenges at the start of a common cold (known as the rhinoviruses) significantly reduced the duration and severity of the infection. A comprehensive review of nearly 20 trials and more than 1,700 participants showed that zinc decreased symptom duration of the common cold as well. And researchers have an idea of the mechanism through which it works. Due to the unique shape of the rhinovirus as well as the nutrient, zinc is able to literally attach itself to the virus, and prevent it from further infecting the person. So eating foods with zinc on a regular basis—which include red meat, seafood, and whole grains as well as some fortified foods like breakfast cereals—and taking zinc supplements can prevent and decrease the severity of the infection, says Meyer.

While zinc, by far, has had the most promising studies done, other micronutrients have also shown to influence the immune system. For example, a study done in Japan with healthcare workers who are constantly exposed to infections like influenza showed that taking green tea catechins, a type of flavonoid antioxidant, corresponded with a lower-confirmed incidence of influenza, though that lower amount was not significant. Researchers have also studied the effects of Vitamin D supplementation on the immune system. One study, out of the British Medical Journal, found that Vitamin D supplementation provided a reduced risk of acute respiratory tract infection. And another, done on school-aged children in Japan, found that Vitamin D supplementation reduced the risk of influenza A. But more studies are of course needed before any more definitive conclusions or recommendations can be drawn.

This all means that eating a wide variety of fruits and vegetables will probably help your body maintain a healthy and stable immune system; one that can jump into action as soon as you need it. And of course, get your flu shot. No excuses.

Have a science question you want answered? Email us at ask@popsci.com, tweet at us with #AskPopSci, or tell us on Facebook. And we’ll look into it.

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Most of us learned what we know about eye color from a chart in grade-school biology. You know, the one that shows that two brown-eyed parents will likely have brown-eyed kids, and two blue-eyed parents are pretty much destined to have blue-eyed kids. It might have come with little color codes, clear-cut percentages, and neat lines of inheritance. But the story of how eye color is passed down is more complicated—and unpredictable—than we’re taught.

Why eyes look different colors

Humans get their eye color from melanin, the protective pigment that also determines skin and hair shades. Melanin is good at absorbing light, which is especially important for the iris, the function of which is to control how much brightness can enter the eyes. Once it passes through the lenses, the majority of the visible light spectrum goes to the retina, where it’s converted to electrical impulses and translated into images by the brain. The little that isn’t absorbed by the iris is reflected back, producing what we see as eye color.

Now, that color depends on the kind and density of melanin a person is born with. There are two types of the pigment: eumelanin, which produces a rich chocolate brown, and pheomelanin, which renders as amber, green, and hazel. Blue eyes, meanwhile, get their hue from having a relatively small amount of eumelanin. When the pigment is low in stock, it scatters light around the front layer of the iris, causing it to re-emerge are shorter blue wavelengths. This makes blue an example of what is called “structural color,” as opposed to brown and to some extent, green and hazel, which would be defined as a “pigment colors.” It’s in part the same reason the sky is blue—an atmospheric light trick known as the Rayleigh effect.

Green eyes are interesting because they combine light scattering and two kinds of pigment: They hold slightly higher amounts of eumelanin than blue eyes, as well as some pheomelanin. Hazel eyes come from the same combination, but they have more melanin concentrated in the outer top layer of the iris. Red and violet eyes, which are much rarer, come from a minute to complete lack of pigment. In fact, red eyes have no melanin whatsoever, so all we’re seeing is the reflection of the blood vessels. When there’s some pigment, but too little to cause wavelengths to scatter, the red and blue interact to produce a rare violet.

An imperfect circle of genes

Though we used to think eye color came from a relatively simple pattern of inheritance, in recent years scientists have found that it’s determined by many genes acting in tandem. What’s more, tiny tweaks on a gene can result in different shades in the iris. “When you have mutations in a gene, they’re not just acting in a vacuum,” says Heather Norton, a molecular anthropologist who studies the evolution of pigmentation at the University of Cincinnati. “The proteins that they produce don’t just do what they do independently.”

The two genes currently thought to be most strongly associated with human eye color are OCA2 and HERC2, which are both located on chromosome 15. OCA2, the gene we used to think to be the sole player in eye color, controls the production of the P protein and the organelles that make and transport melanin. Different mutations in the OCA2 gene ramp up or tamp down the amount of protein that’s produced in the body, changing how much melanin is sent to the irises. (If you’re wondering why some kids are born with blue eyes but end up with green or hazel ones later in life, it’s because these organelles take a while to mature and start shuttling melanin around).

The HERC2 gene, meanwhile, acts like a helicopter parent for OCA2. Different mutations in this gene act as a switch that turns OCA2 on and off and determines how much P protein it encodes.

Those are just the two genes we know about in detail so far. Newer studies have linked as many as 16 genes to eye color, all of which pair with OCA2 and HERC2 to generate a spectrum of different iris colors and patterns. With all these variations in the interaction and expression of genes, it’s hard to say for sure what a child’s eye color will be based on their parents’. “While what you might have in your HERC2 genotype matters, it also matters what you have at [other parts of chromosome 15],” Norton says. “Even though you might have two copies of the allele that’s more commonly associated with blue eye color, if you have a mutation somewhere else in your genome that does something to modulate how that P protein is produced or distributed, that’s going to influence phenotype.” What she means is, if a kid does shockingly end up with brown eyes, there’s no need to flip out and reach for the paternity test. It’s just the rich tapestry of genes.

Norton notes that most of what we know about the complicated genetics of eye color, we know through genome-wide association studies (GWAS), which track visible traits in subjects with varying DNA profiles. But she also points out that there are huge gaps in the range of populations we’ve documented to figure out how eye color is genetically influenced. “Given that most of what we know about how these genetics have been done in studies of Europeans, when you think about some of these genetic interactions, there may be mutations that influence eye color, skin color, or hair color that are more common in other parts of the world,” Norton says. “We don’t know about them because we don’t look.”

There are several research groups around the world trying to flip this bias by conducting GWAS studies in Latin American and South African populations; some have even found novel gene segments affecting skin pigmentation in different communities. One day, the same may be revealed about eye color.

Why choose one …

Now you might be wondering, what causes people—and sometimes really cute huskies—to have a different color iris in each eye? The condition is called heterochromia for short, and there are several kinds: partial heterochromia, where part of the iris is a different color; central heterochromia, where the inner portion of the iris is a different color than the outer ring; and complete heterochromia, where one iris is a completely different color than the other.

The vast majority of cases of congenital heterochromia (when people are born with the condition) are completely benign, but in rare cases it can occur as a symptom of disorders like Horner or Waardenburg syndromes. If heterochromia develops later in life, it’s most often the result of eye injury, head trauma, melanoma, or sporadically, glaucoma treatments. But in the majority of people it happens by random mutation, leading to one eye getting more or less melanin than it should. Try and put that in a chart.

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From a nutty, aged cheese to the floral finish of dark chocolate, delicious tastes perpetually bombard our tongues. Here’s how a tongue takes these flavors from the plate to the mind.

The tongue, which anchors the body’s system of taste, is a piece of muscular flesh covered in a mucous membrane. To the human eye, our tongues appear dotted with tiny bumps called papillae. Often mistaken for taste buds themselves, these bulb-like dots actually contain groups of taste buds.

Three types of taste-sensing papillae dot the tongue. Fungiform papillae, concentrated mostly at the tip and sides of the muscle, usually contain one taste bud on their mushroom-shaped tips. Foliate papillae, arranged into reddish folds on the sides of the tongue, contain many taste buds organized around these crevices. Larger, dome-shaped vallate papillae sit toward the back of the tongue and, like foliate papillae, can house as many as 250 taste buds each.

A fourth type—filiform papillae—is the smallest and most numerous on the tongue. This type contains fine hairs that connect to nerves associated with touch, allowing you to feel the texture of what you’re eating, but they don’t contain any taste buds.

While these different types of papillae vary in structure, they typically organize taste buds around crevices, which collect broken-down food chemicals released when you chew. These crevices also house glands that secrete saliva.

Taste buds are complex little growths, too. Each one contains a collection of between 50 and 150 taste receptors and supporting cells, all nested together like cloves in a bulb of garlic. While each person’s taste bud count varies, humans tend to have between 2,000 and 5,000.

Each taste receptor is specialized to detect one of five flavor types: sweet, sour, bitter, salty, or umami. Contrary to what you may have learned in school, different areas of the tongue don’t detect different flavors—instead, each taste bud has all five taste receptors built in. Each receptor has small hair-like proteins called microvilli, which bind to specific chemical compounds corresponding to the flavor type it specializes in—and scientists are still figuring out how chemicals fit into the receptors. Deeper into the tongue’s flesh, these cells attach to nerves specifically involved in taste, which connect them to the rest of the nervous system.

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When Edgar Allen Poe had to find a bird annoying enough to drive a man insane, the choice was easy: a raven. Corvids—the avian family that includes ravens and crows—are notorious for causing mischief to humans and animals alike. They steal food, knock over trash cans, harass dogs, tailgate raptors, raid nests for eggs, and engage in all kinds of behaviors that have people wondering, “Why are these birds such jerks?”

Kaeli Swift, a corvid researcher and lecturer at the University of Washington, knows all about birds’ devious reputation. Of the behaviors she’s asked about most, her explanation usually boils down to, “they’re smart.”

Corvids are famous for their intelligence. Ravens can use tools to get food (and even use other crafty birds as tools), and plan ahead like apes and small children. Crows have demonstrated the ability to recognize individual human faces and harass people who have harmed them. In the process, both birds might come of looking a little … dickish.

Swift talked us through some of the rude corvid behavior she hears about most often, and explains why it happens.

Mobbing

Mobbing is perhaps the most noticeable of the bullying corvid behaviors. A hawk or owl will be hanging out in a tree, not bothering anyone, when a group of crows will come along and harass it—dive-bombing and screeching—until it’s forced to fly away. Jerks!

Swift says we should cut corvids a break on mobbing, though, given that lots of birds do it. “It’s simply a prey species responding to a predator,” she says. “We just notice it more with crows because they’re big and loud.” Even tiny birds like chickadees, titmice, and wrens are known to hound potential threats on the wing. And while the behavior can be seen all year round, corvids tend to get more wary and protective during the spring-to-summer breeding season.

But what about when crows harass a bird that isn’t a predator, like a fish-eating osprey? In those instances, Swift says the birds may just be responding to a species that fits the general frame of a predator—a “better safe than sorry” approach, she calls it. Mobbing may also serve a social purpose: one corvid showing off to others that it can handle danger.

Pulling tails

Crows and ravens have a particular knack for stealing food away from other animals, often just by annoying them. Both groups are omnivorous, so they can adapt their wits to most any scenario involving dinner. For instance, a flock of ravens might swoop in when a pack of wolves is enjoying a fresh kill, even if the hunters aren’t into sharing. Instead of waiting around for the scraps, the birds have learned to sneak up behind feeding wolves and nip them on the tail. The mammal turns and gives chase, leaving the carcass open for other ravens to feast. This sort of parasitism can be a real problem for wolves: Swift says “the theft rate is so high that it actually determines pack size.” Jerks!

Crows and ravens also use their tail-pulling trick on a host of other animals, including domestic dogs. Pets that feed outside often serve as the best targets, like the poor sled dogs Swift first saw victimized in Alaska—but some corvids will pull the tails of dogs just minding their own business. In fact, Swift has observed so many other creatures, from cats to eagles to parakeets, getting goosed by a corvid, she’s started a #PullAllTheTails hashtag on Twitter to put the impish behavior on display in one place.

Raiding nests

About half of the diet of an urban crow comes from human trash, Swift says, both in landfills and from the revolting pile at the end of your driveway. Believe it or not, nearly 40 more percent comes from bugs. Eggs make up just a small part of a crow’s meals, but Swift says she hears from an inordinate amount of people concerned with protecting their backyard nests from hungry corvids.

It’s another unfair bit of a corvid’s rotten reputation. “Lots of animals eat eggs,” Swift says, ”everything from deer to bunnies. Because crows are obvious and large, we notice them at nests instead of smaller animals that eat eggs more often, like snakes or squirrels.”

Crows and ravens use their big brains in all sorts of ways to outsmart other creatures to survive. How much longer do they deserve to carry around a badge for being the jerks of the bird world? Quoth the Raven: “nevermore.”

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Every year, a handful of the wet weather events in the tropics swell into hurricanes. These monster storms crash into coastlines and can inflict billions of dollars of damage, earning their reputation as some of nature’s scariest disasters. They have the potential to kill thousands and wreak ongoing environmental and economic chaos. So why not try to hit them before they hit us?

Since the dawn of nuclear explosives, citizens and scientists alike have speculated that the government might be able to repurpose weapons of war as weapons of weather. Most recently, President Donald Trump asked why we couldn’t just nuke hurricanes out of the sky. Meteorologists are wincing at the reappearance of this all-too-familiar myth.

“It doesn’t make sense at all,” says Falko Judt, a meteorologist who specializes in hurricanes at the National Center for Atmospheric Research.

“It is a spectacularly bad idea,” says Gary Lackmann, a meteorologist and professor at North Carolina State University’s department of marine, earth and atmospheric sciences.

Okay, so the concept inspires the meteorological equivalent of a massive eye-roll. But why is the idea of nuking a hurricane such a dud—and what explains the myth’s longevity?

First, a refresher on hurricanes, AKA tropical cyclones. They’re among the most powerful storms on the planet, and with good reason: They harness the heat of Earth’s oceans and turn it into whirling tempests. Hurricanes are fueled by warm ocean water (at least 80°F throughout) and usually develop over tropical seas. They take place when a weather disturbance, like a thunderstorm, literally spirals out of control. The storm’s winds pull warm air toward it. As it interacts with warm sea water, the water evaporates and starts to rise. Clouds form above, and more air rushes into the low-pressure zone created below. Soon, the swirling mass gains momentum and begins to move, dragging water along with it and growing larger and larger until it hits land. It’s the weather equivalent of a steam engine that converts water into mechanical work.

The results can be terrifying. The low-pressure systems whip up winds and shove water toward the shore, where torrential rains and gales of wind crash into beaches, landscapes and people. Severe flooding, property damage, and loss of life follow.

We know hurricanes need warm ocean temperatures to get going. But how can you get them to slow down? That’s hard, Judt explains. To really stop a hurricane from forming, he says, you’d need to cool down the ocean, suck the humidity from the air, or blow strong winds against the grain of the storm. And the jury is still out on what really causes smaller storms to turn into hurricanes. Some smaller disturbances can peter out, but others get out of control quickly. The factors that tip the balance either way aren’t entirely clear. “We’re not really sure yet,” he says. “About 90 percent of precursor disturbances do not become hurricanes.”

Storm modeling has become more and more advanced over the years, and the dynamics occurring inside storms are being demystified by data-gathering daredevils who fly planes directly into their centers. But there’s still a way to go, says Judt, and many questions about storm dynamics and formation remain unanswered. Without knowing exactly what factors lead to runaway growth, it’s difficult to know exactly what methods might stunt a would-be hurricane’s development.

But Judt’s list of potential hurricane busters doesn’t include nukes, because nuclear weapons are puny compared to nature’s wrath. If you nuked a hurricane, he explains, the resulting shockwave would do nothing to disrupt the storm. “A nuclear weapon is very powerful, but it’s not nearly as powerful as the hurricane itself,” he says.

That’s an understatement. The massive energy inside a hurricane is the equivalent of a 10-megaton nuclear bomb exploding every 20 minutes, he says. During its brief lifespan, a single hurricane generates wind energy equivalent to half of the energy consumed by the entire population of Earth in one year. The energy it releases in the form of clouds and rain is the equivalent of 200 times world’s energy-generating capacity. It would simply take too many nuclear bombs to defang a storm, says Judt—and more than likely, the cyclone would just turn from a spiraling menace to a nuclear spiraling menace.

That hasn’t kept scientists from giving it serious consideration. During Project Plowshare, a program designed to test peaceful uses for nuclear explosives beginning in the 1950s, the U.S. detonated 35 warheads in the hope they could help with everything from mining to, yes, weather control.

Jack Reed, a scientist at Sandia National Laboratories, ran with the concept of halting a hurricane with a nuclear weapon in 1959. At the time, it was still unclear just how powerful a punch these storms could pack, and Reed was convinced that nuke-shooting submarines could reduce wind speed enough to kill the circulation that pushes storms ashore.

But though he called for a test of the concept, writes historian Vince Houghton, “Not a single person with any kind of authority was willing to even entertain the idea of nuking hurricanes. Later in life, Jack Reed bitterly chalked this up to his idea being ‘politically incorrect.'”

The incorrectness of the idea isn’t just a function of public mistrust of nuclear weapons. “Spreading around a bunch of radioactive contamination for no real reason doesn’t seem like a good idea to me,” says Edward Waller, a professor at the Ontario Tech Energy Systems and Nuclear Science Research Center who studies nuclear emergency preparedness and response.

Though it’s unclear just how much material a nuclear hurricane could spread, says Waller, it’s not something anyone should be prepared to risk. In the nuclear world, he explains, there’s a concept called “ALARA,” or “as low as reasonably achievable,” that calls for people to use as little radiation as possible in the name of protecting as many people as possible.

“There are justifications for using radiation all the time,” he says. “But if a task or if a process can be done without using radiation, you don’t [use radiation].” And if the laws of physics make it extremely unlikely that a nuclear warhead will circumvent a deadly storm, you don’t shoot one into the sky. Since the idea strikes storm experts as preposterous, there has been little ink spilled on how exactly a nuke-icane would play out as it hit land. But it’s easy to envision the potential outcomes. “Can you imagine radioactive rain from a nuclear hurricane?” asks Lackmann.

People who lived in Europe in 1986 don’t have to. That’s when the Chernobyl disaster belched a cloud of radioactive contamination that dispersed across virtually the entire continent. Areas that experienced rainfall during the disaster saw higher deposits of radioactive contamination, and people as far as Asia and North America were dosed with fallout, too. However, the health effects were mostly endured by those who were close to the reactor when it melted down.

Depending on where a hypothetical hurricane attack took place, some of the contamination might not hit land. But even if the rainfallout didn’t bring severe harm, says Waller, it could hurt people anyway. “It would be putting undue stress on the population,” he says. Large-scale evacuations could put lives at risk through accidents or leave vulnerable populations uncared for—and the sheer stress of worrying about the unknown effects of hurricane nukes could cause additional health problems.

People who live through hurricanes are already at risk for depression, anxiety, and PTSD, and those who are evacuated during natural disasters experience emotional and mental impacts, even when their homes don’t end up getting destroyed. After the hasty evacuation of people from the area near the Fukushima nuclear plant in 2011, for example, more than 1,000 people died, and displaced locals experienced a range of health problems due to the disruption.

Bottom line: The suggestion that scientists turn weather into war is past its expiration date. But thanks to the scary possibilities presented by the world’s ever-more-modern nuclear arsenal, it’s doubtful the cry to nuke clouds will die down any time soon.

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We all know the families populated by towering basketball players versus the petite households with builds best suited for, say, horse jockeying or wrestling. There’s probably a fair amount of height variation within friend groups, too: The tallest friend takes the selfies, while the shortest struggles to fit in the frame. But despite these drastic variations, humans pretty much fall within a normal height range: In the United States, healthy men are, on average, 5 feet and 9 inches tall while women are typically 5 feet and 4 inches. Thanks to middle school science class, we know that we inherit height from our parents. Why, though, do most people stay within these standard limits? Why don’t we all grow to be 10 feet tall?

Why we will likely never reach extreme heights

We can thank evolution for this, says Terence D. Capellini, a human evolutionary biologist at Harvard University. “Height is not just about height,” Capellini says. “It’s about the overall biological growth of an organism, at least in humans.” Researchers surmise that how tall we become isn’t an isolated piece of our extremely intricate genome. Rather, it’s intertwined with other growth processes, like organ development. Over millions of years, natural selection has forged the blueprint for the human genome and therefore influenced body and organ growth through linked genes and subsequent tissue growth. Our height, then, is simply a byproduct.

Besides genetics, environmental factors like proper nutrition and modern healthcare can impact height. Still, genes take on the lion’s share of the work, accounting for 70 to 80 percent of the result. Height generally evens out around puberty and that’s when those evolutionary mechanisms step in. When we reach our predetermined heights, a biological mechanism called programmed senescence eventually turns off the genes responsible for growth. Most people grow taller until puberty ends, their bones continuously lengthening. This process occurs at the growth plates, two layers of cartilage located in children’s vertebrae and long bones, such as the femur and tibia.

We grow quickest as fetuses, says Jeffrey Baron, a pediatrician and head of Growth and Development research at the National Institutes of Health. The added centimeters generally decrease afterwards. In fact, fetuses grow about 20 times faster than five-year-olds. Infants’ growth plates are also highly active, causing them to grow rapidly. As a child gets older, growth plate activity slows down. Eventually, in mid- to late-adolescence, the growth plate activity ceases and teenagers reach their adult height.

Compare the growth process to a wind-up toy train, Baron says. Winding up the train’s spring causes the coil to tighten with potential energy. Upon release, the train zooms forward but gradually slows and putters out as the spring winds down. When we use up our genetically programmed growth potential, like the unwinding spring in the toy train, our growth slackens and eventually stops.

What scientists know—and don’t know—about height inheritance

Hundreds of genes likely influence height. In fact, a study out in 2018 found over 500 height-related genes. These genes manipulate the behavior of growth plates and control bone length.

“For most of us, it’s not just one gene that makes us short or tall,” Baron says. “It’s many, many different genes.”

Though rare, mutations in height-related genes can trigger unusually tall stature. “The Princess Bride” actor André the Giant had pituitary gigantism, a condition in which the pituitary gland produces too much growth hormone, which controls height. There are other conditions that affect height, too, such as skeletal dysplasias, which result in shortened and often malformed bones.

The conditions that result from excess growth hormones also carry serious health risks, according to a February 2019 Endocrine Society study. These include heart failure, bone disease, and an overall “impaired quality of life.”

By recording thousands of people’s heights in genome-wide association studies, which look for genetic variations that occur more frequently in groups of people who all share the same physical traits, researchers aim to better understand the links between height inheritance and disease susceptibility.

Clarifying the mysterious relationships between genomes could transform how we treat diseases. For example, genetic variants causing short stature may also make it more likely for someone to develop coronary artery disease (CAD), according to a 2015 NEJM study. And, if we are able to pin down certain genetic variations more precisely, then in the future, genome editing techniques like CRISPR, which can correct faulty genes, may facilitate new growth disorder therapies.

If you’re still hoping that humans someday reach greater heights, keep a close eye on the Nordic region. Last year, researchers concluded that populations in Denmark, Finland, Norway, and Sweden have grown progressively taller each generation.

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Most of us have become used to sitting for extended periods of time suspended in 60-ton metal machines. Aside from hearing the compulsory airplane safety warnings at takeoff, most people don’t think much about how flying impacts our bodies and minds. But some pretty weird stuff happens when we’re seven miles above sea level: Air pressure drops, our taste buds go partially numb, our skin dries out, and some of us cry. Actually, many of us do. Virgin Atlantic conducted a Facebook survey in 2011 that found 55 percent of respondents said their emotions were heightened on flights. In response, the airline introduced “weepy warnings” before particularly sad movies in-flight. But why do we weep once in the air?

While peer-reviewed studies on the science behind the “Mile Cry Club” are few and far between, scientists across fields from film to psychology to medicine have taken interest in the topic. And while they haven’t identified a definitive cause, researchers think it’s likely a combination of oxygen deprivation, dehydration, and stress.

As planes ascend to their cruising altitudes, air pressure drops–that’s why our ears pop–to levels equivalent to the outside air pressure you’d experience while hiking through the mountains in the Swiss Alps (6,000-8,000 feet above sea level). This resulting low cabin air pressure causes a reduction in the amount of oxygen carried in our blood, a condition called hypoxia. Hypoxia has a slew of potential symptoms, including fatigue, confusion, impaired decision-making, and notably, it wreaks with our ability to handle emotion.

On top of this, the air conditioning systems on airplanes dries the air until there’s 25 to 30 percent less humidity, causing dehydration (which explains why we get drunk more quickly inflight).

While mild hypoxia won’t impair a healthy person very much (a good thing, considering pilots operate under these conditions routinely), Jochen Hinkelbein, a Berlin-based medical researcher and president of the Society for Aerospace Medicine, says that hypoxia makes us more vulnerable to psychological and physical changes. He added that though he’s perfectly healthy, he often falls asleep during takeoff because of these dramatic pressure and humidity changes, which both can make you feel dizzy and tired.

These physiological changes may then lay the groundwork for our brains to start considering our uncomfortable surroundings. Though passengers may not be conscious of their emotional vulnerability, our brains are working overtime on airplanes due to claustrophobia, travel stress, and fatigue, according to clinical psychologist Jodi De Luca of Erie Colorado Counseling.

“We have little control over our environment while we are traveling by plane,” says De Luca, who studies the impact living in a high-altitude mountainous region has on mental health. All of these stressors trigger some people’s fight-or-flight response, she says.

This causes the body to produce more stress hormones called cortisol which influence our emotions by increasing our blood pressure and heart rate, making us less able to cope with them. Couple that with some oxygen deprivation, dehydration, and a corny movie, and it’s no wonder Virgin Atlantic reported that “41 percent of men surveyed said they hid under blankets to hide their tears.” It might also explain why toddlers, who are prone to temper tantrums anyway, are even more likely to fall into a deconstructive crying fit while on board a flight. Though, no studies have explicitly studied this connection.

Stephen Groening, a professor of Comparative Literature, Cinema, and Media at the University of Washington, has been studying this phenomenon in the context of in-flight entertainment for years. He says the content of films people report crying during doesn’t matter. Most recently, his friend told him that he wept watching Thor on a flight to Australia. He thinks another contributing factor is the environment travelers find themselves in. When we watch movies on the plane, we’re much closer to screens—and people—than we’re used to.

“It’s not so much about the content, it’s about being in a situation where you’re isolated, but at the same time you’re surrounded by strangers,” Groening says. “You have this physical closeness for an extended period of time that you don’t have in any other situation.”

While there’s no definitive mechanism scientists can point to just yet, most researchers surmise that it might just be a combination of all these factors that give us the weeps. This subconscious discomfort, combined with the physical changes Hinkelbein describes, likely explains why we cry on planes, explains Groening.

De Luca concurs: “Emotions govern our lives more than we know, and our environment influences our emotions more than we realize.”

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An unexpected cold breeze, almost tripping over your own feet, a particularly high note hit by a singer. All are vastly different experiences, but they share one thing in common: They can cause goosebumps. But what exactly are goosebumps, and why do we get them? Scientists have a good understanding of the first question, but why they happen is still a bit of a mystery.

The most straightforward thing about goosebumps is their name. When geese are freshly plucked, their skin creates raised bumps where the feathers were. The mechanism that creates goosebumps on humans is also pretty simple. At the end of hair strands closest to the skin, known as the root, are tiny muscles called erector pili. When these muscles tense up, or contract, they cause the hair to stand straight up.

Surprisingly, scientists are not entirely sure why we get goosebumps. But they think they are likely a hand-me-down survival mechanism from our ancestors. Somewhere in the human lineage, we were once covered in much thicker, longer hair than we are now. When early humans would get cold, their hairs would lift and separate slightly. This would trap a small amount of air close so to the skin, effectively creating a layer of insulation.

That all makes perfect sense, but why do we get goosebumps when experiencing something pleasurable, like the sound of beautiful music?

Dr. Mitchell Colver, a researcher at Utah State University, studies goosebumps and why they form in scenarios when people aren’t cold. Specifically, he studies “frisson”, or the waves of pleasure running over the skin. It’s a sensation as many as two-thirds of humanity feels.

The latest theory, he says, is that it’s a part of our fight-or-flight response, an innate survival mechanism that causes us to react within milliseconds to stimuli like unexpected noises—think sticks snapping nearby while walking in the woods at night. Without having to think about it, those snaps immediately cause our body to deploy adrenaline, a chemical that stimulates increased breathing, sweating, and a racing pulse. All of these physical responses primes our bodies for action (flight or, as they say, fight).

Adrenaline also triggers goosebumps. Colver says our brains are so fine-tuned to keep us alive that our ancestral habit of anticipating snapping sticks carries over to our experience of music and art.

“The vocal cords of a skilled singer are trained to scream in tune. So some of the ways vocal cords vibrate when singing are similar to the vibrations of someone screaming bloody murder,” says Colver. So if you’re listening to music and something unexpected happens in a song (a high note, chord change), and our fight-or-flight response reacts. Something is wrong! Goosebumps deployed. Once we our cognitive abilities kick in to tell us to settle down and enjoy the art, the fight-or-flight response is halted. We even get a flush of dopamine, a happiness-inducing chemical, out of the experience.

No longer sensing the tune as a warning call, we recognize it as something beautiful and pleasing, says Colver. “It’s like evolution is rewarding us for figuring out something isn’t a threat.”

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The feeling you get as soon as you step off a merry-go-round is a hard one to forget. You crash to the ground only to look up and watch the sky continue to spin. You’ve stopped moving, but this dizzying feeling continues. Why?

No matter what method you use to spin—run around rapidly in circles, whirl in an office chair, or spend some time on the merry-go-round with your friends—your body reacts in the same way.

When you spin around quickly, your eyes see a lot of different information in a very short time, which can be disorienting. But your body is ready for sudden changes like that, and it tries its best to keep its visual field looking normal. If what you saw started spinning with every movement your body made, the world would be a very befuddling place. In fact, it would be pretty hard to do anything.

The process that keeps you oriented doesn’t have much to do with your eyes at all. Instead, it all begins inside your ears. Way past the outer area that you can see, rests three semicircular canals (think elbow pasta shape). They are each situated at 90 degree angles of each other. The canals are lined with extremely tiny strands of hair. Inside each canal (where you would normally find the cheese in your elbow-shaped mac n cheese meal), is two layers of thick gelatinous fluid.

Scientists call them endolymph and cupula. As you move around, these fluids slosh inside the ear canals. That sloshing hits those itty bitty strands of hair, making them move back and forth. Those hair movements are key. The ear picks up on what direction the hair cells are moving and uses nerve cells to send a signal to the brain with all of that information.

Once you stop moving, the fluids stop sloshing and the hairs no longer pick up movement and that alert signal to the brain halts. However, that process is far from perfect. When you move really fast, like if you spin around in circles a bunch of times or spend far too long on a merry-go-round with your friends, that fluid in your ears swishes around at an even more rapid speed. That makes sense because you are spinning really quickly.

The problem comes when you stop. Your muscles are able to start and stop really quickly without any issues. But that fluid doesn’t work as fast. Even though you stopped, that fluid is still moving. And it takes some time for it to finally stop. While it’s still moving, those hairs are still picking up on the motion and sending signals saying, “I’m moving” to the brain. The brain receives that signal but at the same time knows the body is perfectly still. The resulting feeling? An extreme case of dizziness. Luckily, it’s only temporary.

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Fall is upon us, and that means the kids are finally back in school and the hot, humid summer days are all but behind us (hopefully). But the cooler air also signals the start of the inevitable cold and flu seasons that run rampant through close-packed classrooms, and circulate back out to parents and coworkers. When the sneezes start, though, they can set off a moment of panic—is this just an average cold-weather cold, or the more serious flu?

One of the biggest differences between the two viral infections is how fast the sickness sets in, says Cynthia Benson, the assistant medical director of the emergency department at Overlook Medical Center in New Jersey. With a cold, someone might wake up with a bit of a sore throat and runny nose, and slowly start to feel worse over the course of a day or two. The flu, on the other hand, has a fast onset. “You’re fine when you go into work, and by lunch, you’re really sick,” Benson says. “You feel like you get hit with a ton of bricks.”

Some of the symptoms do overlap—the sore throat, the stuffy nose—but a cold tends to be concentrated in the upper respiratory system, with sneezing and watery eyes. The flu is less likely to come along with a runny nose, but instead will cause muscle aches and chills. Depending on the particular strain of the flu circulating, it can also cause an upset stomach or diarrhea. The real hallmark of the flu, though, is a high fever, Benson says. A cold might cause a low grade, borderline fever, she says, but with the flu, body temperature spikes.

Can you diagnose yourself?

Adults usually know when they have the flu, as opposed to a run-of-the mill cold, Benson says. “People know themselves. They can differentiate between feeling just crappy and run down, and having the flu,” she says. Benson says there tends to be more incorrect self-diagnoses of the flu when it’s a particularly bad season: People have colds, but are more likely to be worried that they have the flu.

For kids, though, it can be harder to tell what virus is causing their sniffles. Babies and toddlers can’t necessarily identify what they’re feeling. Kids tend to have more nausea when they’re sick, both from a cold or from the flu. “That’s why we tend to do more flu testing in those ages,” Benson says. The flu is particularly dangerous for young kids, who can become dehydrated quickly and suffer more complications, so it’s more important to know for sure if they have it. Keep an eye on their breathing patterns and activity levels if they start to seem ill, Benson says. “A two year old who is listless, and has decreased energy—that should be a big red flag the child is really sick.

For healthy adults, the flu and colds can generally be treated the same way—with hydration, over-the-counter medications, and rest. Taking Tylenol (brand name for acetaminophen) or another non-prescription analgesic like Advil or Motrin (both ibuprofen) to bring down a fever can also help cut down on the misery of a flu. Keep an eye on the active ingredients in your medications of choice, though: many contain acetaminophen, which can be toxic to the liver at high doses. Doctors and pharmacists can help with cold medicine selection, and field questions or concerns.

Benson also says that flu-sufferers should stay home, at least for the first few days. “[The flu is] not the kind of thing you should push through,” Benson says. “You expose other people, and it makes it harder to recover.”

Even if someone just has a cold, if they can, they should stay home from work for the first day or so, she says. “If you take off the first day of [a] cold, you will probably get better a little faster,” she says. The first few days of any illness are also when you’re most contagious, so staying in bed can help protect those around you.

The best treatment, though, is to prevent sickness from striking in the first place. “Hand washing is key,” Benson says. “As kids go back to school, I’ve seen more and more parents in with upper respiratory infections. Hand washing is super important if someone in your household comes down with a sickness. I tell them to wash hand towels, change out toothbrushes.” Stay away from people who are already sick, and don’t share cups and utensils.

And most importantly, Benson says, get a flu shot. “Vaccination, vaccinate, vaccinate—I can’t say it enough.”

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Tick season is in full swing, which means the tiny pinhead buggers are likely lurking in the tall grass along your hiking trail or clinging to the overgrown bushes in the woods by your home. For humans, regular tick checks are part of the summer routine. For furry hiking companions, though, there’s a far simpler strategy: products like Frontline and Advantix go on once, and protect against pests for an entire month.

Unfortunately, no similar products exist for humans—we don’t have one-time use methods that can keep the bugs at bay for an extended time. But they seem to work so well for our canine best friends, so why don’t we have them?

Thomas Mather, an entomologist and the director of the TickEncounter Resource Center at the University of Rhode Island, says its not because the active ingredients wouldn’t work for people, or that the materials are wildy toxic. It’s likely because we bathe much more regularly than dogs do.

Spot-on repellent treatments, like Frontline, are squeezed out of an applicator onto a dog’s back. The medication diffuses across the oils of their skin and into their hair follicles, and its released from there throughout the month. If you give your dog too many baths, the treatment can lose its potency, Mather says—so in people, who probably shower every day or every other day, it likely wouldn’t last very long.

“People would wash it off,” Mather says. “It would be something you had to reapply all the time.”

Flea and tick-prevention collars, like Seresto, work in a similar way—by releasing an active medication onto an animal’s skin. But humans wouldn’t be able to just put it on their ankle and see the same effect, Mather says. “People wouldn’t keep it on all the time, and you don’t get the protective benefit if you keep putting it on and taking it off.”

The products are essentially pesticides, which kill or impair ticks (and fleas, and other bugs) on contact. Frontline is made from Fipronil, which is also used in agriculture and for indoor pest control. It’s considered moderately hazardous by the World Health Organization, though there hasn’t been much research into its effects on human health. Right now, it isn’t a part of any products intended for human use.

The other major tick-preventing pesticide, permethrin (which is found in Advantix), is a component of medications already in use for people: like rinses to treat lice, or lotions for scabies, a condition where small mites bury into the skin.

In the early 1990s, Mather developed and patented a permethrin soap, with the idea that it would facilitate regular application of the tick-preventing chemical. “I did experiments with hamsters, and showed that if you wash hamsters infested with deer ticks you could prevent [them] from being infected with Lyme,” he says. Mather says he offered his formulations to some drug companies for further testing and potentially to create into a product intended for human use, but none took it up.

Permethrin products to prevent ticks and fleas are already on the market, in the form of permethrin-treated clothing. The chemical can bind to fabric, and repel or kill bugs even after its been washed multiple times. Research shows that wearing treated clothing can significantly cut down on ticks and tick bites, and the pesticide is better at warding off ticks than DEET, the ingredient in most bug sprays.

The United States military has used permethrin-treated clothing since the 1990s, and it hasn’t shown any significant safety concerns. “The military has used this technology for years,” Mather says. “It’s not clear why it’s not more widely used in general.”

Creating a long-term, long-lasting product might be theoretically possible for humans, Mather says, but it would take a company devoting resources towards creating one. While there haven’t been any major toxicity concerns with permethrin thus far, in order to create a product for widespread public use, companies would need to do far more testing to figure out what the safe level of the product is.

In the meantime, he says, it’s best to save the currently available products for the non-human animals in the house.

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The moon is more than just a pretty face to gaze upon at night. It helps direct our ocean currents and tides, the movement of Earth’s atmosphere and climate, and even the tilt of our planet’s axis.

So what would happen to Earth, and us, if it promptly disappeared without notice? Would we survive it? Sadly, probably not.

Right away, we would notice that “nighttime” would be significantly darker. The moon’s surface reflects the sun’s light, brightening our night sky. Without that indirect glow, any areas that don’t have access to artificial light, like country roads or wooded campsites, would become far riskier to travel through at night.

The moon’s sudden absence would also confuse animals. In a 2013 review in the Journal of Animal Ecology, researchers found animals that use vision as their primary mode of interacting with the world benefit (survival-wise) from the moon’s presence. That’s no big surprise, but it does have interesting implications for the question at hand. Many predators, like owls and lions, rely on the cover of darkness with just a bit of moonlight to hunt effectively. With no moon, they would have trouble finding food. Rodents, on the other hand, tend to hide more when the moonlight is strong. It’s easier for their predators to detect them. With no moon, they would thrive. “I think you’d see some shifts in which species are common and which species are rare in a system,” says the study’s lead author Laura Prugh, a wildlife ecologist at the University of Washington.

The next immediate difference would be the tides. Because the moon is so close to us, the pull of its gravity impacts our planet. That force is strong enough to pull our oceans back and forth, what we call “the tides.” Without the moon, tides would rise and fall at a much slower rate, about one third of their current fluctuation, says Matt Siegler, a research scientist at the NASA Jet Propulsion Laboratory, who works on the Lunar Reconnaissance Orbiter. The tides wouldn’t completely stop moving as the sun also has some gravitational pull on the oceans, too, but not nearly as much as the moon.

A two-thirds reduction in tides would drastically alter coastal ecosystems, potentially destroying many of them and disrupting the flow of energy, water, minerals, and other resources. Entire ecosystems exist in the ocean areas between high and low tides. In these spaces, many species of crabs, snails, barnacles, mussels, sea stars, kelp, and algae rely on the daily coming and going of the tide for survival. These ecosystems in turn feed migrating and local birds as well as land mammals like bears, raccoons, and deer.

Tidal movements also help drive ocean currents, which in turn direct global weather patterns, as the currents distribute warm water and precipitation across the globe. Without them, regional temperatures would be much more extreme; as would major weather events, says Jack Burns, who heads the Network for Exploration and Space Science at the University of Colorado, Boulder. And it’s not just ocean tides, he says. The moon’s gravitational pull similarly moves molecules in the atmosphere.

Because of this climate-stabilizing force, large moons are one of the main things researchers look for when identifying planets that could host life, Burns says. “A planet outside of our solar system needs to have a pretty good-sized moon in order for the weather systems to be calm enough to produce civilization like ours,” Burns says. Without this celestial body, he says, researchers have argued that life as we know if might not exist at all.

A missing moon could cause even more disruptive changes, although on a much longer time scale. Without the moon’s gravity holding the Earth in place, the tilt of our home planet’s axis would probably shift drastically over time. Earth could go from no tilt with virtually no seasons, to a drastic tilt with extreme seasonal weather changes and ice ages in just a few hundred thousand years, Siegler adds. He points to Mars as an example, with its extreme climate variations as the tilt of its axis changes dramatically. It has no large, stabilizing moon to stop it.

On a more human level, without the moon, we would lose a source of inspiration and scientific information. “We’re pretty lucky to have had the moon there as an easy destination to go for,” Siegler says. “It motivates us.” He pointed out how much the moon has taught us—things about the origins of our own planet, how other planets form, and how the dinosaurs went extinct. “There’d be a lot of information we’d just miss out on,” he says.

Thankfully, there’s no evidence that the moon is going to self destruct or collide with another orbitor anytime soon.

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An earlier version of this article stated that the Earth exerts a greater force of gravity on the moon than the moon does on Earth. When, in fact, the two forces are the same. We regret the error.

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Our sun is a fairly average star in the Milky Way—not the brightest, not the biggest, and only 4.5 billion years old. It’s only unique in that its light and heat sustains all the life on the only inhabited planet we know of in the universe. Luckily for us, it didn’t burn out before we showed up a few hundred thousand years ago. But how could it have that much fuel? Why hasn’t it been snuffed out like a candle or a campfire? And when will it finally burn out?

This was a pressing question in the 19th century, says Catherine Pilachowski, an astronomy professor at Indiana University. At the time, humans only understood two ways the sun could be generating energy: Either it was creating heat and light through gravitational contractions—pulling itself in at the center and emitting energy (in the form of heat that we feel on Earth), therefore getting smaller over time—or it was literally on fire, like the chemical reaction we see on Earth when we light a match or start a campfire. Thinking that either method could have been the sun’s modus operandi, scientists at the time calculated exactly how long the sun could have existed using both methods. But neither result squared up with what we knew the age of the solar system to be—4.5 billion years. If the sun were contracting or burning, it would have run out of fuel long before we came around. Clearly, something else was going on.

A few decades later and armed with Einstein’s famous E = mc2, which confirmed anything that has mass must have an equivalent amount of energy, 1920s British astronomers proposed that the sun was actually converting its mass into energy. However, instead of a furnace that converts wood and coal into ash and blackened carbon (emitting light and heat along the way), the center of the sun is more like a gigantic nuclear power plant.

The sun contains a massive number of hydrogen atoms. Typically, a neutral hydrogen atom contains a positively charged proton and a negatively charged electron that orbits it. When this atom meets one of its fellow hydrogen atoms, their respective outer electrons magnetically repel each other like bodyguards. This prevents any of the protons from meeting each other. But the sun’s core is so hot and so pressurized that atoms whiz around with so much kinetic energy that they overcome the force binding them together and electrons separate from their protons. This means the protons, usually stuck inside the hydrogen atom’s nucleus, can actually touch, and they join together in a process called thermonuclear fusion.

Just like inside a nuclear reactor, atoms inside the sun’s core slam into each other every second. Most often, four hydrogen protons fuse together to create one helium atom. Along the way, a tiny bit of the mass in those four miniscule protons is “lost;” but since the universe conserves matter, it can’t just disappear. Rather, that mass gets converted into a dramatic amount of energy—every second, the sun radiates 3.9 x 10²⁶ watts of power. (This is such a huge amount of energy that there is honestly no Earth-centered analogy. Perhaps that number can be contextualized like this: This amount of watts is far more than all of the electricity the entire world would use, at current rates, over several hundred thousand centuries.)

The efficiency of thermonuclear fusion is a major reason the sun has kept radiating heat for so long—the energy released by turning just one kilogram of hydrogen into helium is the same as burning 20,000 metric tons of coal. Because the sun is so massive, and relatively young, scientists estimate it has only used about half of its energy-producing hydrogen.

Eventually, the sun’s core will convert all of its hydrogen inside to helium and the star will die. But don’t sweat it. That won’t happen for about another 5 billion years.

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Unfortunately for us, the line of disease transmission does not end with germy children and coughing colleagues. Dogs, cows, mosquitos, ticks, mice, sushi, your neighborhood cat lady’s beloved roving Romeo—the list goes on—are all opportunity for disease. But why? How does one disease affect multiple species? Aren’t we all too different?

Not at all. Infectious diseases arise from contact with parasites, bacteria, and viruses. While many diseases are species specific, like a dog-specific cold virus, others, such as the influenza virus, are able to mutate and insert pieces of DNA from other organisms into themselves. If they gather enough DNA from one species, this enables them to invade and infect that animal. These illness-causing organisms move from one species to another so often that we’ve even created a name for them, zoonotic diseases. The diseases can spread directly from one infected species to another or they can live inside another species, an intermediate host, who isn’t susceptible to the infectious organism but interacts with other animals that are.

New zoonotic diseases (or at least ones that we had never heard of) pop up all the time. Consider this case: In February’s American Journal of Tropical Medicine and Hygiene, researchers reported on a 26-year-old woman whose irritated eye prompted her to, with the help of a mirror, identify and remove a small, translucent worm from inside it. She then went to a doctor who pulled out 14 more. The perplexed MD sent the tiny crawlers to infectious disease experts at the Centers for Disease Control who later identified the microorganisms as Thelazia gulosa, a type of nematode worm. The young woman’s case turned out to be the first reported one of this particular organism (which usually infects cows’ eyeballs) infecting a human.

If that makes your skin crawl, there’s more bad news: Unvaccinated dogs are risks for rabies, kids’ sandboxes can harbor parasites, and if you’re west of the Mississippi, the prairie dogs you meet could carry the bubonic plague, says Susan D. Jones, a veterinarian at the University of Minnesota.

And the worst news: We’ll probably never be able to eliminate them for good. In many cases, breathing contaminated air, drinking infected water, or otherwise touching an infected animal’s feces can transmit viruses, bacteria, and parasites to you. What makes all this worse is the increasingly interconnected world we live in, which heightens the chances of infectious diseases spreading from one place to another, says Jones. The speed at which we are able to transport goods and livestock today means we can far more easily expose animals to diseases novel to them. And because of the high level of human involvement in all of this animal and goods handling and transferring, “it is impossible [to] completely remove humans from these kinds of infection chains,” says Jones.

Luckily, in the United States, the risk of acquiring one of these interspecies diseases from a household animal is fairly minimal. The majority of pets, like dogs and cats, are up-to-date on their shots. Those vaccinations protect both us and them from infectious diseases such as rabies.

“Vaccinating ourselves and our pets creates a sort of ring of immunity around us and a barrier to viruses circulating in wild animals,” says Jones. Researchers call this kind of disease protection, herd immunity. It’s why getting the flu vaccine is so important; it doesn’t just protect you, it protects those with weaker or still-developing immune systems like your grandmother or baby cousin.

So if it’s not our drooling, furry best friends, what animals, aside from other humans coughing and sneezing on us, are getting us sick?

Live animals (other than the family dog) and their poop is one source, but not the only one, says Muhammad Morshed, a zoonotic disease expert at the University of British Columbia in Vancouver. Improperly cooked or contaminated food can exact its revenge and turn a romantic date for two into a far less romantic tango with the toilet.

For example, raw foods, like sushi, can harbor parasites. To kill them off, distributors must freeze the raw meat at minus 25 degrees celsius before sending it along to its destination. When that doesn’t happen, a consumer can unwittingly eat one and become ill.

While you might feel like the victim sitting sick in bed, humans can also spread diseases to other species. In fact, the 2009 pandemic H1N1 flu was misnomered “swine flu”; the first recorded positive herd of pigs didn’t get the virus from a fellow swine, but rather from a sick employee who entered the barn. We humans can even infect sea creatures, Morshed says, as human waste routinely causes disease in unsuspecting aquatic creatures like dolphins who swim into clouds of our feces. For the crime of species-to-species disease transmission, all of our hands, hooves, paws, and proboscises are dirty.

However, there is good news. Experts are understanding zoonotic diseases far better than they have in the past. In the age of Louis Pasteur, researchers zeroed in on the singular bacterium, virus, or parasite, says Jones. Now researchers focus on infectious diseases as a worldwide ecological phenomenon. They focus on how all the microorganisms work together and fill particular niches. For example, by looking at the threat of disease more holistically, experts can pinpoint vectors such as mosquitoes that spread the diseases and study the environmental impacts that make transmission more likely.

“When scientists started to see diseases as being more of an ecology, I think that really helped science to understand diseases like malaria or West Nile virus,” says Jones.

And, despite the ubiquity of zoonotic diseases, prevention is possible. Jones says everyone can do his or her own part by getting vaccinated, keeping a healthy weight to boost the immune system, abstaining from smoking (which can dampen our body’s natural defenses), and regularly washing their hands. So don’t skip the sink—even if no one is looking. Your entire species will thank you.

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People forego eating meat for a variety of reasons. Some do it in an attempt to eat healthier meals while others make the shift because they think cows and pigs are simply cuter than they are delicious. Some might even switch over because they think it will help the planet. But what would happen if every single human decided to become a vegetarian? Would we be harming or helping our planet? It turns out, reducing our animal product intake (especially red meat) might not be such a terrible place to start.

How exactly does meat consumption affect the environment?

Red meat production, which includes all of the steps that go into supplying the animals that turn into hamburgers, takes a toll on the environment in the form of greenhouse gases and the land we use.

“Red meat production has major impacts on almost every aspect of [the] environment,” says Walter Willett, a Professor of Epidemiology and Nutrition at Harvard. “The greenhouse gas production is probably one of the most serious and acute because it’s apparent that our planet is warming faster than anybody anticipated even just a few years ago.”

Willett says this comes from two steps in the cattle production process. The first is that we lose a lot of energy in the process between growing the grains that we feed the cattle and using the animals for food. That’s because many farm animals, especially cattle, are inefficient converters, meaning that they consume more food than they are able to provide. The second problem is the amount of methane that cows create. On average, cows produce around 100 to 500 liters of methane per day in the form of flatulence. That methane is about 30 times more potent as a heat-trapping, or greenhouse gas.

“The biggest piece of grain use is about 45 percent, which is fed to animals, largely cattle,” says Willett. “We produce a huge amount of carbon dioxide and methane in that process. Then we eat the red meat, and the red meat itself is very damaging to human health in the amount that we consume it. That is both damaging planetary and human health at the same time.”

So, to sum up, cow farts plus the massive amount of grain production needed to feed them is pretty disastrous for both land use and greenhouse gas production.

“Certainly the way that we produce meat currently and in the quantities that we produce meat, it’s much more impactful on the environment from a variety of indicators including carbon footprint, land use, and water use,” says Martin Heller of the Center for Sustainable Systems at the University of Michigan.

What if we all became vegetarians?

If meat, especially red meat, is so bad, what if we just stopped eating it all together? Would that solve all of these problems?

Switching from an omnivorous to vegetarian diet could reduce a person’s carbon footprint by about 30 percent, says Martin Heller, an engineer at the Center for Sustainable Systems at the University of Michigan. However, he says, some meat might not be a terrible thing if you’re struggling with the idea of giving it up.

“The caveats to why a vegetarian diet may not be the lowest. There are opportunities [for] using ruminant animals to eat grass on land that isn’t suitable for cultivation of other crops,” he says. “There’s kinds of small niche types of productions systems that are rather atypical in our current agricultural production that could offer situations where significant high quality calories could be produced at a lower impact than growing a field of beans.”

In other words, if there’s grazing land that couldn’t sustainably grow anything, that land could be used for cattle. That way, cattle could be raised in a way that doesn’t destroy our environment. And if we only raised cattle on this type of land, that would end up reducing our worldwide consumption of red meat dramatically, says Willett.

There’s also the concern for human health. Just because a plant based diet is in fact plant based, that does not mean it’s necessarily healthy.

“You do need to be careful there, because not all plant foods are health foods,” Willett says. “Coca Cola and Dunkin Donuts are plant-based foods and are obviously bad for human health. But, a plant-based diet should really focus more on fruits, vegetables and whole grains, and for protein sources, legumes and seeds would be much better for human health than the average American diet.”

So, if I’m a vegetarian, am I at least environmentally off the hook?

Giving up meat, especially red meat, isn’t a bad start to making your dietary carbon footprint shrink a bit. However, even if you’ve done that, there’s other ways to make sure that you are making the most sustainable choices.

“For example, a vegetarian may be eating a diet with major environmental impacts because they are eating berries flown in from South America or tomatoes grown in greenhouses in January,” Willett says. “Those have very big environmental impacts and greenhouse gas production.”

You’ve probably heard about eating locally and in season, but sometimes this isn’t a perfect system either. Willett recommends looking not just at the distance your food has traveled, but also at the transportation involved, especially when it comes to fruits and veggies.

“There’s no single factor that captures all of this. Local has value, but not all local is the best sometimes,” Willett says. “Driving a truck in from 100 miles away is relatively local but may have much more adverse environmental impact than bringing some fruits [in from] several hundred miles away by train in large amounts.”

Additionally, it may be worth it to think about your region and the stress that certain types of foods have on the local environment, both in the cases of animal-produced food and plant-based food.

“There’s big differences in water use for producing dairy, milk, in California versus Wisconsin, right?” says Heller. “Not only because there’s water shortages in California so they don’t get enough rain so it requires more irrigation, but also because the region is under water stress. Using that irrigation water in those regions is much more impactful both for environmental systems as well as other users of the water.”

Eating right for the environment is certainly enough to make your head spin, but the moral of the story is reducing the amount of meat (especially red meat) and thinking twice about where your favorite foods come from and how they got there is a pretty good start.

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The shivers, the shakes, the chills—we’ve all experienced a fever at one time or another. When we take our temperatures and the thermometer reads anything above 99 degrees, many of us immediately believe we are afflicted with some kind of infectious microbe. But, in fact, having a fever doesn’t always signal infection. Yes, contagions like strep throat or the flu, are the most common reason for an elevated temperature, but it’s surely not the only one. More uncommon ailments like brain injury, reactions to legal and illegal drugs, and even cancer can raise your body temperature above its natural level. But don’t freak out, yet. Knowing what the causes are and how they can occur can help you make the most informed decision about your elevated body temperature.

As most school children can tell you, the average human body temperature is around 37 degrees Celsius (or 98.6 degrees Fahrenheit). But experts says that that perfect temperature comes with a full degree of variation, both higher and lower, to account for a variety of factors including a person’s age, what time of day it is, and their physical activity level at the exact time their temperature was taken.

In general younger people tend to have higher body temperatures, while older people run cooler. That’s for a variety of reasons but for one, older people are often less active than younger, energetic folks. The energy used to run a mile or play a soccer match can increase our core body temperatures. That’s also why we sweat so much during intense exercise, so that we can cool our bodies down. Our internal systems also run hotter during the day than they do at night.

By medical standards, a person has a fever if their temperature rises above 38.2 degrees Celsius (100.4 degrees Fahrenheit), although some people may have medically significant fevers below that temperature (as is often the case with elderly people, or very young infants). However, fever or it’s more official-sounding medical name “hyperthermia” is not a universally defined term. Some doctors refer to fevers as only elevated temperatures caused by infections and inflammation, while others use it to describe all situations where a person’s temperature rises above 100.4 degrees Fahrenheit.

The majority of fevers are caused by an infection. This can include not only viruses and bacterial infections, but also parasites, urinary tract infections, and appendicitis. Less common causes of infection, but causes all the same, include things like malignant tumors, tissue ischaemia (a condition in which not enough blood gets to a particular tissue in need), and reactions to certain drugs. Drugs that can cause reactions include illegal substances like Ecstasy, prescription drugs like antidepressants such as SSRIs, and in rare cases, antipsychotic medications. Other causes of fever include inflammation after surgery or from a brain injury, endocrine disorders, and even cancer.

But what’s actually happening in your body when you feel the urge to wrap yourself in an excessive number of blankets? Dr. Edward Walter, of the Royal Surrey County Hospital in England, says that still, researchers don’t completely understand how the body establishes and maintains a fever. When an infection is present, viruses or bacteria either contain or trigger the production of a pyrogen (any substance known to cause a fever) by your immune system. These pyrogens carry messages to an area of the brain known as the organum vasculosum lamina terminalis. There, it produces a bunch of chemical messengers called prostaglandins. These compounds alter the normal signaling in the hypothalamus, causing it to reset the body’s resting temperature to a higher level.

If an infection is not the instigator, there are a number of different mechanisms that can trigger a fever. Inflammation can often cause fevers because some of the chemicals produced during the inflammatory process are pyrogens. Similarly, some of the drugs that can cause fevers have pyrogenic characteristics. A class of antidepressants known as SSRIs can affect the “thermostat” level by changing the chemical messengers in the brain. Brain damage can cause fever through direct trauma to the areas that regulate temperature.

Fevers, then, are what doctors call a physiological response, and not actually a part of a disease or infection itself. In fact, because many animals also have fever responses to infection, researchers say there is some reason to think fevers may be an evolutionary adaptation to help the body fight the disease-causing micro-organisms. Because of this, scientists are still debating whether it might in fact be beneficial to let a fever run its course without lowering it with medicine. It’s still common practice for doctors to lower fevers with a class of drugs called antipyretics (like ibuprofen and acetaminophen), but that’s mostly to make people more comfortable, not to help them recover.

Not lowering a fever goes against a very strong cultural tendency to worry over an elevated temperature. Social scientists and historians point out, before the invention of vaccines, fevers were frequently deadly, and our fear of them has deep roots in diseases like smallpox and scarlet fever. In contemporary society, doctor’s have named parental anxiety over their children’s temperature “fever phobia,” as they fear things like seizures and permanent brain damage as a result of the high heat. And while these things are possible (and especially dangerous for young infants), they only occur in extremely high fevers over 105 degrees, which are extremely rare in infectious conditions.

It’s worth noting, though, that seizures and brain damage are more common from another heat-related condition—heatstroke. In heatstroke, (which is also, somewhat confusingly, called hyperthermia), the body generates excess heat due to its inability to shed it through natural mechanisms like sweating. In this way, it’s not an internal change in heat-regulation in the hypothalamus, but an inability for the body to keep itself cool. This happens most often for people like athletes during periods of exertion, but is also a danger for older folks living alone during heat waves.

To return to the original question, as long you haven’t just performed some intense exercise in the middle of the summer heat, there is a good chance your hot forehead is caused by an infection. If it’s over 100.4 degrees Fahrenheit you definitely have a fever, and if it’s over 104 you should probably see a doctor. If you know you have ingested drugs of any kind (in particular party drugs or antipsychotics), or if you know have a thyroid condition or a history of cancer, there is a chance these things may have caused the fever and you should also see a doctor. But if you’ve got a low fever and none of the above conditions, you’re probably fine holing up with a cup of soup and some movies and riding out the chills at home.

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Once difficult and expensive even for the most technologically advanced labs, genetic testing is fast becoming a cheap and easy consumer product. With a little spit and 200 dollars, you can find out your risk for everything from cystic fibrosis to lactose intolerance.

But it’s important to remember that not all genetic tests are created equal. And even the best clinical genetic test, carried out in a medical lab under a doctor’s supervision, isn’t perfect—genes are important, but they don’t seal your fate.

Who should get a genetic test?

Genetic tests are diagnostic, so anyone who is curious about their health can get one done. But they’re more informative if you think you might be at risk for a genetic disorder.

Heavy-duty genetic tests have been used as a clinical tool for almost half a century—long before 23andMe and Ancestry.com began offering direct-to-consumer tests. Let’s say that many women in your family have had breast cancer. You can get a genetic test to see if you may have inherited an abnormal version of the BRCA gene, known to increase your risk for breast cancer.

Heidi Rehm, associate professor of pathology at Harvard Medical School, is the director of the Laboratory for Molecular Medicine, where patients get tested for diseases that can be traced to specific genetic roots. She says it is most common for people to get tested when they either suspect or know that they have a genetic disease; it may have affected multiple people in their family or they could show symptoms of something widely known to be genetic, like sickle cell anemia. For these people, genetic tests can provide a much-needed explanation for an illness and help doctors determine the best course of treatment. Babies are often tested for genetic diseases, either while they are still fetuses or shortly after birth.

Others get genetic tests if they and their partner both have family histories of an inherited disease—even if they don’t have the disease themselves. For example, cystic fibrosis is linked to one particular gene, but you have to inherit the abnormal version of the gene from both your parents to get the disease. If you only inherit one copy, you may never know—you won’t display any of the symptoms. But if you and your partner both carry one copy of the faulty gene, your child could still inherit two copies. Genetic tests can forewarn you of that possibility.

But Rehm says there has been a recent trend of healthy people getting tested to predict whether they’ll get certain diseases. “I do think there are settings where predictive genetic testing is incredibly important and useful,” Rehm says; for example, knowing that you’re at risk for breast cancer gives you the opportunity for early intervention (remember when Angelina Jolie got a double mastectomy upon finding out she had a mutated BRCA gene?)

But Rehm also points out that genetic tests may not be as straightforward as they seem. For example, some genes are thought to increase risk of getting a certain disease, but it might only happen if you have specific family history, or you might be able to reduce your risk with lifestyle changes. So remember that a genetic test isn’t the final verdict—there are other factors at play too.

Can a genetic test predict my medical future?

Not entirely—its scope is limited. For starters, not all diseases are caused by genes. Plenty of conditions stem from environmental and lifestyle factors; they may interact with your genes, but the external factors are the real trigger.

But even if a disease is caused solely by faulty instructions written in your genes, you won’t necessarily be able to test for it. That’s because genetic tests are mainly used for diseases that are “penetrant,” a term that scientists use to describe a strong connection between having a certain gene (or multiple genes) and getting a disease.

Genetic tests are surprisingly simple on the surface. All that’s required of you is a small sample of cells, like a blood sample or saliva (which doesn’t have DNA itself, but picks up cheek cells during its journey out of your mouth). It get sent to a lab where sequencing machines match up small pieces of synthetic DNA with your DNA to figure out the overall sequence.

Once they have your sequence, geneticists can compare it with “normal” or disease-causing sequences. In the end, they might give you a “yes” or “no” answer, or sometimes you’ll get a probability—a measure of how much your genes increase your risk of developing the disease. Then, it’s up to your doctor to figure out what these genes (in combination with your lifestyle, family history and other risk factors) mean for your health.

With penetrant diseases, there’s a “very, very high” ability to explain the disease, Rehm says. For example, the breast cancer-related gene BRCA1 can give you a 60 percent chance of getting breast cancer (in Jolie’s case, with her family history, the risk was 87 percent.)

This makes genetic tests better at detecting so-called “rare diseases,” says Steven Schrodi, associate research scientist at the Marshfield Clinic Research Institute’s Center for Human Genetics, but they’re less useful when it comes to more common diseases, like heart disease or diabetes. Genetics can increase your likelihood of getting these disease, but scientists still don’t know quite how much. Part of the problem is that there may be dozens or hundreds of genes responsible for these diseases, Schrodi says.

“We have an incomplete understanding of why people get diseases,” Schrodi says. “A large part of it hinges on how we define diseases. Perhaps physicians have inadvertently combined multiple diseases together into a single entity.”

Consumer genetic tests—the ones where you send in samples from home—sometimes claim to test for these more complex traits, but be careful: Their results might not be very medically relevant, Rehm says. If they tell you that your genes make you twice as likely to develop diabetes, for example, that’s a marginal increase that doesn’t significantly affect your risk, especially when you take into account lifestyle factors.

Can genetic tests predict how long I will live?

Genes do seem to play a role in determining lifespan. After all, some family reunions stretch from great-great-grandparents all the way down to infants. Scientists have studied centenarians—people who lived to be 100 years old—and found that people with certain versions of genes involved in repairing DNA tend to live longer.

This makes sense because aging leaves its mark on your DNA. Environmental factors can damage DNA, and even the routine chore of replicating cells can introduce errors as the three billion units of your DNA are copied over and over. Long-lived individuals have different sequences that seem to make their cells better at keeping DNA in mint condition.

But figuring out your expiration date is more complex than just testing for a few genes, says Jan Vijg, professor of genetics at Albert Einstein College of Medicine. In theory, you could design a test that looks at specific genes that might measure your risk for developing Alzheimer’s Disease or other age-related diseases, or your risk for aging quickly. “To some extent, yes: Biomarkers will tell you something about your chances of living a long life,” Vijg says. “Still, that will only work if you live a careful life.” And that means no accidents, infections, or cancers.

Aging also affects the exposed ends of your DNA, called “telomeres.” DNA is stored as chromosomes, those X-like structures that you may have seen in biology textbooks. The most vulnerable parts of the chromosome are the chromosome’s tips, which get shorter as you age because they aren’t properly replicated. But while telomere length might let you compare your DNA now with your DNA from a decade ago, you can’t compare your own telomeres with other people’s telomeres. There’s a lot of variation between individuals, Vijg says. Some of us are just old souls (on the genomic level, that is.)

The methylation test, which looks at how the presence of small chemical groups attached to your DNA changes as you age, might be a better bet. A study at UCLA showed that changes were slower in longer-lived people. But Vijg is hesitant: “I would not put my hopes on that as a marker to predict when exactly you’re going to die.”

For now, just enjoy your life, because you can’t predict death. And if you decide to unlock the secrets of your DNA with an at-home test, don’t take those results for more than their worth.

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Every summer, reporters from around the world call Ollie Jay to ask one question: Does consuming hot liquids in the summer really cool you off?

“I think the old wives’ tale of drinking a hot drink on a hot day really resonates,” Jay says. He now heads the Thermal Ergonomics Laboratory at the University of Sydney. But back in 2012, while at the University of Ottawa’s School of Human Kinetics, he published a paper which found that hot drinks can cool you down, at least to a certain degree.

Jay and his team had nine men cycle for 75 minutes with a fan blowing at them, evaporating any sweat. The volunteers drank water ranging in temperature from an icy cold 35°F to a hot 122°F. The researchers found that when the men cycled and drank hot water, they lost 56 kilojoules more of energy in the form of heat compared to when they drank room temperature water. But when the volunteers drank the chilly liquid, they actually gained 21 kilojoules compared to the same situation.

“It’s kind of this paradoxical idea,” says Jay. “A cold fluid feels cooler when it goes inside of you, but it doesn’t really make you cooler because you reduce your sweating.”

The key to this energy exchange is good ol’ sweat. For every gram of perspiration which evaporates from your skin, you lose approximately 2.43 kilojoules of energy. The men who drank hot water gained 52 extra kilojoules of heat from the water. But when the sweat started pouring off their bodies, the men also lost 108 kilojoules of heat from sweat evaporation. When it came to chilly drinks, the opposite happened. The men produced much less sweat, and therefore experienced less evaporation. While the cold water cooled them down by 138 kilojoules, that wasn’t enough to counteract the 159 kilojoules retained from decreased evaporation on their skin. When the cyclists drank room temperature water, the amount of heat they gained versus the amount they lost stayed the same.

Okay, so drinking hotter drinks makes you sweat more and lose more heat, whereas colder drinks cool you down, but not quite enough. So should everyone start downing hot tea in the middle of a scorching August afternoon? Probably not.

“I never really advocate people drinking hot fluids on a hot day,” Jay emphasizes. For one, he says, the heat lost from evaporation isn’t actually all that substantial. For another, the experiment also took place in front of a fan. That ensured that every drop of sweat the cyclist produced was evaporated and contributed to the overall heat lost. If the sweat drips off your face or you wipe it off with a towel, that means that bead of sweat didn’t evaporate from your skin and you didn’t experience the benefits of the heat loss through sweat evaporation.

But, what was the connection between the water’s temperature and the mens’ sweat levels? The experiment didn’t change the volunteers’ internal body temperatures. So how could the body have known whether to turn down or up the sweat production?

Jay hypothesized that it must have happened somewhere along the water’s path. There were nerve endings in either the mens’ stomachs or mouths called thermoreceptors which could sense temperatures and exerted much of the control over sweat rates. So in 2014, he ran a new experiment. Volunteers either rinsed their mouths out with water of varying temperatures, or directly injected the water into their stomachs through a nasogastric tube in order to completely bypass the mouth.

It turned out that gargling water didn’t change sweat levels. However, the water pumped directly into their stomachs did. Cold water made the volunteers sweat less while hot water made the volunteers sweat more.

But these receptors in the stomach are hardly the only temperature receptors in your body. As you may know, after an intense workout, many people put ice packs on the back of their necks to cool down. “That feels really good, right?” says Jay. “But that’s not cooling your brain down.”

Blood might be rushing by just underneath the skin, but there’s not a lot of heat being exchanged between the ice and your blood. Instead the nerve endings there act as temperature receptors, just like in the stomach, and make you feel cooler even if you aren’t.

You might have experienced something similar at night if you woke up feeling too warm. Your feet have nerves with a similar function. “In bed, one of the first things you’ll try to do to feel cool is to pop your feet out from under the bottom of the sheet,” says Jay. “The amount of extra cooling you get is obviously not going to be that much, but it has a disproportional influence on how cool or how hot you feel.”

So now you know that you can thank the temperature receptors in your stomach for the relief you feel after a giant slushie and for the sweat you create when you gingerly sip a steaming cup of coffee. But if you are looking for the best way to cool down on a hot summer day, you should probably just head indoors or at least out of direct sunlight.

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Have you ever sneezed so loudly in the middle of the night that you’ve woken yourself up? Think about it. The answer is likely no. In fact, many sleep researchers and neuroscientists think it’s essentially impossible to sneeze while you sleep.

First, a caveat. To date, there doesn’t seem to be any published studies that questioned whether we sneeze during our sleep. Instead, physiologists and sleep researchers have attempted to answer this question based on our current understanding of how our brains and bodies work while we sleep.

“As far as I know, I don’t think people sneeze during sleep,” says sleep researcher Steven Shea, director of the Oregon Institute of Occupational Health Sciences at Oregon Health and Science University. “I’ve studied hundreds of people sleeping, and I’ve never witnessed anyone sneezing during sleep…but, I’ve never provoked them, either.”

Shea recalls a story which suggests this hypothesis may be true. He once saw a boy with a chronic cough. “He was coughing probably every 10 to 15 seconds of his waking life,” Shea says. But, the boy’s parents told him that the child would stop once he fell asleep. “True enough. I was looking at his brain waves and as soon as he went into the lightest state of sleep, his coughing stopped. And then he would wake up in the middle of the night, cough again, but then he would fall back to sleep and not cough.”

Shea has some guesses as to why that boy stopped coughing—and why we don’t sneeze—in our sleep.

For one, while in bed, many of us are exposed to fewer things that’ll make us sneeze. There aren’t as many people or pets kicking up dust in the dead of night when we’re catching up on our needed zzz. And for those of us who experience the photic sneeze reflex—sneezing when you see the sun or other bright light—chances are, you’re sleeping in a darkened room.

But aside from external reasons, there are physiological ones, too. We experience two different types of sleep throughout the night: REM and non-REM. REM, or “rapid eye movement,” sleep takes up about 20 to 25 percent of our night. During this time, we vividly dream, our eyes flicker wildly under our lids, and our brainwaves look similar to those when we’re awake. Non-REM sleep, on the other hand, results in that deep, peaceful slumber. These two kinds of sleep may have different ways of keeping us from sneezing while we’re otherwise dead to the world.

With non-REM sleep, it simply takes more to penetrate into our subconscious. In non-REM sleep, explains Shea, there’s a lot more filtering and suppressing going on. For instance, getting tapped lightly on the hand doesn’t register as strongly in your brain when you are asleep as it does when you’re awake. You can actually see this effect on an EEG monitor. When sleeping human subjects are tapped on the hand, they will produce less electrical activity than if they were tapped with the same strength while awake. (It’s probably why you sometimes have to violently shake someone to successfully wake them.)

During slow wave sleep, a type of non-REM sleep, the thalamus and the cerebral cortex (the brain’s relay station and the outer, folded portion, respectively) activate each other to keep things quiet in our brains. “The thalamus and the cerebral cortex are in this dance,” Shea says, “where they’re controlling each other, and it’s sort of blocking the sensory input.” However, Shea points out that this relationship doesn’t block things completely, it just makes it tougher for stimuli to get through.

“But the beauty of sleep is that it’s almost immediately reversible when there’s a dangerous situation,” Shea says. If there’s a strong enough stimulus (like the smell of smoke or obstructive sleep apnea), it can pierce through that sleepy, muted stupor and wake us up. Shea reckons that if we were to sneeze in the middle of the night, it would be because some external stimulus that typically causes sneezing would wake us up first, and then we would sneeze.

Sleep consultant Don Watenpaugh, vice president of the Texas Society of Sleep Professionals and member of the Sleep Research Society, agrees. “The brain can’t sleep and actively listen, see, smell, [and feel] at the same time,” says Watenpaugh. “However, if a sensory stimulus is strong enough, it can wake us up. This includes things that make us sneeze.”

REM sleep, on the other hand, prevents sneezes in a potentially different way. During REM sleep, while we’re dreaming of flying on dragons or fighting bad guys, our brains put our bodies on lockdown to keep ourselves from actually acting out our dreams. “A sneeze is a big coordinated muscular activity,” says Shea, but because of that REM-induced lockdown, “some of those muscles are semi-paralyzed,” and the ability to sneeze nearly impossible.

Instead, Watenpaugh says, we might just incorporate the sneeze-inducer into our dreams: perhaps you walk through a jungle thick with cobwebs, or compete in a mad dash through a dusty Ancient Roman track. Sleep tight!

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News articles over the past few years have implicated everything from sunlight’s ultraviolet radiation to burnt toast as potential carcinogens, or cancer-causing substances. So, should you be rushing to cut these everyday exposures out of your life? Well, it depends on the material you are talking about, and how much and how often you are in contact with it.

There’s no doubt that certain substances do increase your risk of developing cancer. For example, public health organizations maintain that the chemicals in cigarettes are formidable carcinogens—and these claims are backed by years of research. Even ultraviolet (UV) radiation (found in sunlight) has been shown to change cells in ways that make them cancerous.

But the evidence isn’t always so convincing. Although scientists might disagree on whether a specific substance is a carcinogen, they do reach a consensus that carcinogens increase your risk of developing cancer, and in many cases that’s all—it doesn’t mean that you’ll definitely develop cancer or that it will happen right away.

How do carcinogens cause cancer?

The first steps in the transformation of a normal cell into a cancerous cell happen at the level of the DNA, a remarkably complex foundation for our normal functions; in three billion individual nucleotides (the alphabet of DNA’s code), it encodes all the instructions required for any cell to survive.

But as cells divide and pass down their DNA, these instructions have to be re-copied each time. It’s pretty hard to make perfect copies each time (just try typing out War and Peace without making any typos.) With billions of new cells produced in an individual each day, there are a lot of opportunities for error. And when those mistakes happen in the parts of the genome that code instructions for processes like cell replication, you can end up with a cell that grows abnormally quickly.

The body isn’t helpless against these errors. Just like us writers over here at PopSci, cells have proofreaders. These proteins can identify and fix individual mistakes and other types of DNA damage. However, some cells have more robust repair responses and others are more vulnerable, says John Groopman, a professor at Johns Hopkins University. This gives people different baseline levels of resilience against cancer development. A recent study suggested that two-thirds of the mutations that lead to cancer are just routine errors that arise in the DNA during replication.

But the other big mutation source comes from our environments, including which carcinogens, and in what amounts, we are exposed to. And to complicate things further, carcinogens work in different ways to lead to these mutations. For example, UV radiation damages parts of the DNA, while arsenic keeps your cells’ repair mechanisms from fixing mistakes. That’s why cancer is often thought of as a cumulative process: Many factors can lead to the transformation of a cell from normal to cancerous, including inherited and carcinogen-driven DNA damage and faulty repair mechanisms.

How do I know which carcinogens are worth worrying about?

Some words of wisdom about carcinogens: “It’s very important that we don’t drive ourselves crazy,” says Linda Birnbaum, director of the National Institute of Environmental Health Sciences and the National Toxicology Program. “Try to make reasonable decisions and avoid excessive exposure.”

However, when it comes down to it, many carcinogens do pose a real risk. Take smoking, for example. The most important thing you can do to decrease your risk of cancer is to quit smoking, says Susan Gapstur, vice president of the Epidemiology Research Program at the American Cancer Society. That advice is based on years of correlational studies that found increased rates of lung cancer in people who also smoked cigarettes as well as studies looking at the effects that the chemicals in cigarettes can have on cells’ DNA.

But not every study saying that they’ve found another household carcinogen holds the same level of merit. For example, there might be only one study showing that a substance can cause cancer—”Findings from one study shouldn’t prompt undue concern,” Gapstur says. Other times, studies might only study a substance’s cancer-causing abilities in a laboratory setting, in animals, or at doses that are unrealistic for human exposure. Substances are listed as “known carcinogens” if there is sufficient human data, Birnbaum says.

This disparity is a root cause of much of the confusion around carcinogens, some experts say. Despite what it might seem like, not everything causes cancer, says Jakob Jensen, associate dean and professor of communications at the University of Utah. From his work in cancer communications, Jensen has found that the widespread conception that carcinogens are everywhere makes people feel like it’s out of their control and that there’s nothing they can do to decrease their risk of developing cancer. But that’s not true.

If you want learn more about carcinogens, check out the lists of carcinogens published by the World Health Organization’s International Agency for Research on Cancer, the National Toxicology Program (under the umbrella of the National Institutes of Health), or the American Cancer Society. These organizations do the hard work for you: They comb through existing studies and evaluate what they actually mean for your cancer risk.

What can I (reasonably) do to protect myself from carcinogens?

A glance at the list of carcinogens might initially overwhelm you and as just one individual, you will never need to worry about all of them. Ever heard of 1,2-Dichloropropane? It’s a byproduct of making dry cleaning chemicals, so unless you work in the chemical manufacturing industry, you probably don’t have to worry about it. Many of the items listed are used in manufacturing, and some are more dangerous than the items they turn into (for example, vinyl chloride can cause liver cancer, but is safe once it is turned into solid PVC pipes, found in many homes). A number of them are actually drugs, some of which actually treat cancer itself.

That being said, you’re not off the hook: There’s a lot that you can do to actively minimize your risk of developing cancer from other major carcinogens, like UV radiation, tobacco, alcohol, and certain viruses, for starters. Carcinogens are surprisingly slow-acting, which gives you the opportunity to systematically make good decisions over time, Jensen says.

“The period of time that it takes from the beginning of a cancer in your body to the time that it’s diagnosed can cover decades,” Groopman says. “As a consequence of that, it gives us extremely long periods of time for early detection screening and prevention strategies.”

As Birnbaum advises, reduce your exposure as much as possible. For example, you can’t always avoid the UV radiation in the sun’s rays, but wearing sunscreen with UV protection on particularly sunny days and avoiding artificial tanning beds can help. Quitting smoking and drinking less alcohol can improve your health in more ways than just reducing cancer risk. And getting vaccinated against cancer-causing viruses like hepatitis B and C and human papilloma virus (HPV) will also provide some proven benefit; viruses have long played a role in causing cancer, and five more types were added to the National Toxicology Program’s Report on Carcinogens just last year.

A good place to start is your daily lifestyle. It might come as a surprise, but a nutritious diet and physical activity can reduce your risk of cancer. Obesity and diabetes contribute to certain types of cancer because they affect levels of hormones, immune system activity, and disrupt other processes in the body, Gapstur says. Regular cancer screenings are also invaluable because they can catch abnormal cells before they cause cancer symptoms.

“Being healthier at the time of diagnosis also means that you’re going to do better in terms of therapeutic course,” Groopman says. “The healthier you are, the healthier you’ll be.”

We just have to face it: there are carcinogens in the world around us, and we can’t avoid them all. But, being exposed to carcinogens isn’t synonymous with getting cancer. There’s a lot that we can do to reduce our risk. So, be smart and don’t stress out—we have more power against carcinogens than we might think.

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The supplement aisles of most grocery stores and pharmacies in the United States are bursting with probiotics. These billions of bacteria stuffed into once-a-day capsules claim to provide digestive relief, among other benefits. They’re extremely popular, with sales of $36.6 billion in 2015. And for good reason. For many people, various gastrointestinal issues come and go pretty much forever, causing chronic discomfort or worse. But according to gastroenterologists and other scientists, these tiny bugs might not be doing the jobs they claim to do.

“The truth is, there’s just not a lot of completed studies out right now that prove that certain probiotics can help people with specific conditions,” says Matthew Ciorba, a gastroenterologist and director of the Inflammatory Bowel Disease program at Washington University in Saint Louis.

Despite the supermarket shelves exploding with probiotic brands claiming to be good for your gut, most of the probiotics on the market today have not been through any sort of clinical trials to prove they do anything at all. And an even smaller number of them—virtually none—have gone through the Food and Drug Administration (FDA) before reaching consumers. Typically, all medications, either prescribed or over-the-counter, that claim to treat a specific condition must go through the FDA to ensure they are both safe and effective—meaning they’ve been proven to do what they say they do—for consumer use. But supplements that don’t treat specific conditions aren’t forced to go through this vigorous screening process. And somehow, probiotics have managed to nestle themselves into this rather nebulous category.

Probiotics are essentially strains of bacteria that are thought to benefit your gastrointestinal tract. Our bodies are teeming with bugs that help to digest food, protect us from toxins, and keep the lining of our intestines healthy. In the past two decades, scientists have come to understand how important these tiny organisms are to our health and survival.

And as they’ve started to figure that out, supplemental probiotics have started appearing in stores, claiming to help ease digestive discomfort. Most of these early probiotics were strains of lactobacillus and bifidobacteria, which are the same bacteria used to ferment foods and are found naturally in yogurt and kimchi. But none of them actually went through rigorous clinical trials or the FDA to prove their effectiveness—and the bacterial players haven’t really changed much over the years, says Ciorba. And so while they’ve been touted as a “cure all” for digestive distress, no one knows for sure what they do or what conditions they might treat.

Ciorba says that when probiotics first became popular, the FDA was not completely sure how to handle them. “Not only was it a natural product, but it was also a live product. And it was being used in all these different populations to presumably treat diseases,” he says. Now that the FDA is more actively involved, there’s better research being done on these supposedly miraculous microbes. But just as there is no such thing as a standard, universal antibiotic that cures all bacterial infections, there is no universal probiotic—no cure-all beneficial bug to fix your gut. It’s going to take a lot of time, effort, and research to figure out what bacterial strains help what conditions, says Ciorba. We may one day be able to design and purchase probiotic strains tailored to fix our problems, but we’re not there yet.

A combination of misleading marketing and media hype keep us clambering for probiotics in spite of their ineffectiveness. “I have patients with Crohn’s disease and ulcerative colitis who we have medicines that we know exactly what they do, and exactly how they work, and what the chances of them working are,” Ciorba says. “And patients will say, ‘well I don’t want to take that, I’d rather take a probiotic.’ Well we know that a probiotic does not help you in clinical trials that have been done. And they say, ‘well, I’d rather give it a try.’” Plus, probiotics have the added benefit of being sold over the counter. Buying a bottle of probiotics online is an easier pill to swallow than telling your doctor how unhappy you are with you bowel movements.

But Ciorba admits that patients aren’t the only ones to blame. “In the past, doctors haven’t been very good at figuring out what gastrointestinal symptoms are related to.” Doctors still haven’t completely pinned down what causes irritable bowel syndrome, for example, a condition that affects about 11 percent of the population worldwide. So it’s not shocking that patients would seek out some kind of natural remedy.

Where exactly do probiotics stand?

Ciorba says there is still a place for probiotics today, but it’s important for consumers to first figure out exactly what is at the root of their stomach ailments. He says many gastroenterologists do recommend probiotics, but it depends on the condition their patient has. And almost all of the probiotics they recommend have been through clinical trials to prove they are effective. For example, each capsule of the probiotic Align contains one strain of bifidobacteria that was specifically tested and proven somewhat effective in treating one particular subgroup: Women with irritable bowel syndrome (with a predominance for diarrhea, as opposed to the type that causes constipation). Ciorba says that in his own practice, he has indeed found Align to be helpful for some patients.

For people who have diarrhea resulting from recent antibiotic use, several strains of Lactobacillus and the probiotic yeast Saccharomyces boulardii can limit the duration or intensity of the symptoms. Ciorba frequently recommends the probiotic Culturelle, which contains a strain of Lactobacillus, for that as well as for bacterial and viral infections that cause gastrointestinal symptoms, as it may shorten their duration. But for other GI diseases—inflammatory bowel diseases like Crohn’s disease and Ulcerative Colitis, for example—it’s more complicated. Studies have not found probiotics to be effective against Crohn’s disease, and they appear to be only help some Colitis patients with mild cases of the disease.

The bottom line, Ciorba says, is that “there is tremendous excitement and enthusiasm about how we are going to use the microbiome in order to change health. But that is a process that is still going to take time.”

In the meantime, Ciorba advises against buying and using probiotics “just because they are good for your gut.” While they are generally safe and benign for most people, because they are living products, there is always a chance they could make you sick—which is one of the major reasons the FDA is now regulating them more strictly. In the future, Ciorba says, all probiotics that claim to treat certain conditions will almost certainly need to get clearance through the FDA.

What will the probiotics of the future look like?

Ciorba says researchers are trying to pinpoint exactly how these bugs benefit us humans. All bacteria, including the ones in probiotics, create metabolites, which are small molecules that perform specific purposes inside your gut. Some metabolites help break down certain food products and keep our intestines healthy, for example. If researchers can figure out how to isolate those metabolites, they might be able to create medications that include just the most helpful molecules. But that research is just getting started, and Ciorba suspects scientists might eventually realize that the bacteria themselves are necessary. “The bugs are a good delivery mechanism. They get whatever it is the metabolites do to the right location,” says Ciorba. “Right against the wall of the colon, or within the mucus, or somewhere that taking a metabolite may not be good enough.”

For now, Ciorba says, it’s not necessary—or even prudent—to take probiotics if your digestive health is pretty good. But if you are keen on trying them, do it in a rational way, he says. If a month of daily probiotic supplements don’t make you feel noticeably better, it’s probably not worth spending your hard earned cash on these misunderstood bugs.

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Body odor is a universal human experience. As such, we as a species put a lot of time, money, and effort into finding ways to eliminate unpleasant natural stenches. But most of us put less time, if any, into understanding what actually causes our malodorous condition. But understanding the processes that create b.o. is the first step to creating a less smelly future.

George Preti, an organic chemist at the Monell Chemical Senses Center in Philadelphia, says the amount of odor you produce—and the power of its stench—is actually based in-part by your genetics, which help determine what types of molecules your body produces, and in what quantity. And your body is truly a b.o. wonderland: different regions of the body produce their own strange molecular secretions and play host to different sorts of microbes. In order to generate odor, you need the proper combination of microbes and secretions. That blend only happens in certain prime locations.

The human body has two types of sweat glands: eccrine and apocrine. Eccrine glands are present all over, and typically secrete sweat that is mostly made of water. Their purpose is to keep your body cool when you’re exposed to heat or enduring intense exercise. Apocrine glands, however, are located in targeted areas of the body—the armpits, for example—and they don’t really do much to cool you down. Instead they release proteins and lipids, and those molecules are the real smell culprits. Bacteria that live on the outside of your armpits feed on the secreted lipids, allowing them to thrive. They also disrupt the outer shell of the proteins that are secreted, releasing odor.

All the teeny tiny organisms on your skin interact with your body in some form or another, and they are all capable of instigating some sort of odor. The reason certain odors are worse than others, says Preti, is because microbes become ecologically adapted to the environments that they are in. At some point, some kind of microbe-induced smell might have served a purpose. Studies in other animals have found that such odors can have physiological effects on the body that promote reproduction, which in turn helps you pass on your genes and create new humans for microbes to feast on.

These days, we tend to do everything we can to mask and eliminate these odors. But Preti says a lot of our most common efforts are misguided. Despite popular belief, Preti says, eating spicy food, onions, curry, or garlic is not going to make your body produce more potentially smelly proteins. But certain foods can still make you smell worse: if pungent foods contain fat-soluble compounds that dissolve in your body fat, they’ll often get released in your sweat. So you won’t make more odor proteins, but you may add a note of garlic to your signature perfume.

But one popular theory—that the sweat you produce when you are nervous is more smelly than the sweat you produce if you are trying to cool yourself down—is actually quite true. That’s because the sweat you produce as a result of an anxious moment contains more apocrine secretions, which are the ones that contain those smell-inducing proteins.

If you are trying to reduce the odor you produce, Preti says that deodorants and antiperspirants do a decent job (deodorants mask the smell with a fragrance while antiperspirants reduce the amount of sweat). As for probiotic deodorant, which is meant to promote certain bacterial colonies over others, Preti says until evidence-based research shows certain strains are significantly effective, consumers should be wary of the claims made by these products. His biggest piece of advice, rather, is just trying to relax throughout the day. Do your best not to provoke those apocrine glands.

But your big takeaway should be this: you’re almost certainly less smelly than you think you are. “I’ve smelled so many T-shirts of people who come into our lab saying that they have the worst body odor in the world,” Preti says. “We smell it using a rating scale, and it’s hardly ever bad.” Humans tune out the smells we smell all the time, but when you’re hit with a spike in smelly sweat, you’re likely to imagine it’s worse than it is—because your nose has a front row seat. “But they are not producing the odor at social distances,” Preti says. “That would be an extremely unusual case.”

So if you think you have the worst body odor in the world, you probably don’t. And the odor that you do produce isn’t really your fault—it’s just the interaction of your naturally-produced proteins with typically harmless bacteria on your skin. And if you are still concerned, just ask a considerate friend (who is standing an appropriate distance away) if they can smell anything funky. The answer will probably be no.

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This article has been updated to reflect the fact that body odor is based partly on genetics, but it’s not the most significant factor.

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Most people have been perpetually reminded since childhood that breakfast is a must. But in recent years, nutritionists and scientists have called this crucial eating time into question. And despite a plethora of research, the scientific community still hasn’t come to a solid conclusion as to when the best time to eat your first meal of the day really is.

The short answer, says sports nutritionist and registered dietician Leslie Bonci, is that it depends on how old you are and your daily habits. For kids, studies have shown that eating a meal first thing in the morning has a positive influence on cognitive performance in school, especially on task-oriented behaviors—and particularly in students younger than 18. But for us older folks, the exact time that we chow down on our first meal of the day is really about personal preference. But often, Bonci says, our personal preferences are reflective of our daily habits.

There are those people who are simply never hungry when they wake up—taking even a few bites of food might make them feel physically sick to their stomachs. “But those are often the people who are eating later at night,” Bonci says, “or aren’t doing anything physically strenuous in the morning.” Despite the three-meal-a-day regimen that has become ingrained into modern society, the human body doesn’t really work on such a rigid schedule. If you eat a big meal the night before, you aren’t necessarily going to be hungry just because it’s breakfast time, says Bonci. Those that wake up starving are typically the ones who ate a light meal the evening prior, or ate a large meal, but much earlier in the day.

But whether one eating habit is better than another is still up for debate. According to Bonci, there haven’t been any conclusive studies that found eating breakfast to have a positive effect on weight loss or weight maintenance. There haven’t been enough conclusive studies to prove that adults receive a cognitive benefit when they eat in the morning, either. Of course, Bonci says, if you are diabetic or have other chronic health conditions, you shouldn’t abstain from eating breakfast. Further, if you exercise first thing in the morning, it’s best to eat after your workout to rehydrate and replenish your lost calories. But her advice for otherwise healthy people? Just eat when you are hungry.

Eating when you are hungry ensures that you don’t overeat later on in the day, Bonci says. And as for the type of food? According to Bonci, breakfast doesn’t necessarily have to be the traditional American meal of cereal, eggs, or pancakes. In fact, she says, in many Asian cultures, there isn’t really a specified “breakfast food.” People simply eat a varied diet regardless of the mealtime or type. “If you want leftover pepperoni pizza, that’s perfectly acceptable,” she says—though she adds that it’s also important to change it up and eat a balanced diet.

But while the jury is out on the importance of a morning meal, Bonci emphasizes the importance of hydrating as soon as you’re up and about. If you’re hungry, eat! And if you’re not hungry, drink a nice big glass of water. And whether you eat breakfast at dawn or save your first meal until the day has moved well into lunch territory, breaking your fast with a balanced meal is always a good bet.

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Learning to crack an egg is a culinary rite of passage. Do it correctly, and the shell swiftly breaks, spilling the liquid contents out in one fell swoop. Do it wrong, and you end up with yolk on your hands and shell in your bowl. Luckily, science has hatched a formula that is nearly infallible. All it requires is knowledge of a few basic physics principles.

To complete the perfect crack, you need to know where and with what force. “You want to initiate a crack at the flattest part of the egg, which is the middle,” says Volker Blum, a materials scientist at Duke University.

Like all objects, eggshells have breaking points, or limits beyond which they cannot absorb more force. That limit is lowest where the egg is weakest—its center. That’s precisely because the center area is the flattest, says Sinan Keten, a mechanical engineer at Northwestern University. Contrastingly, the top and bottom of an egg are the strongest—and therefore hardest to crack—because they have the most curvature. Think of a structure that is rounded as opposed to flat, like an arched doorway or an arched bridge. The arch is able to hold a heavier load without breaking because it distributes that weight more evenly. This is true for an egg, too. In fact, if you hold an egg between two fingers at each pole and squeeze as hard as you can, it’s extremely unlikely you’ll be able to apply enough force to crack it. That’s because the shell’s curves evenly distribute the pressure you’re applying.

Now that you’ve found the cracking sweet spot, you need to make a swift initial crack that results in a fracture that’s just large enough for your thumbs to fit through. The rest is all about effort.

According to fracture mechanics, once you’ve created a crack in an object, that fissure will expand only slightly until you’ve applied the amount of force needed for the break to reach something called its critical crack length. Once achieved, the rift will grow rapidly as long as that force remains steady. If you’ve ever walked across a frozen pond of thin ice and watched a crack form beneath your feet, it’s the same basic idea. Soon after the critical crack length is reached, you fall through the ice. To successfully open an egg after cracking it, you have to apply the force necessary to the cracked edges for them to start and continue expanding. Be careful not to overdo it, though. Pulling the shell edges away from each other too harshly can result in shell destruction.

Ultimately, a clean, fast break across the egg-quator and some even-handed prying will save you a scrambled mess.

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