What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions

by Randall Munroe

I studied physics in college, so there’s a lot of stuff I feel like I’m supposed to know—like the mass of an electron or why your hair sticks up when you rub a balloon against it. If you ask me how much an electron weighs, I feel a little rush of anxiety, like it’s a pop quiz and I’m going to be in trouble if I don’t know the answer without looking it up. But if you ask me how much all the electrons in a bottlenose dolphin weigh, that’s a different situation. No one knows that number off the top of their head—unless they have an extremely cool job—which means it’s okay to feel confused and a little silly and take some time to look stuff up. (The answer, in case anyone ever asks you, is about half a pound.)

Engineers working with cold industrial equipment have to watch out for this oxygen buildup, since liquid oxygen is pretty dangerous stuff. It’s highly reactive and tends to cause flammable things to spontaneously ignite. A really cold object can set your house on fire.

“Stand on the other side from where the physics is happening” is actually a good general rule for scientific equipment.

Dr. Mahowald explained that when you release a plume of iron vapor, the iron rapidly reacts with oxygen in the air to condense into iron oxide particles. “Iron oxide particles aren’t particularly hazardous for air quality,” she said, although if there are enough of them, they could certainly be bad for your lungs. That’s not necessarily because of any properties specific to iron oxide—it’s just that your lungs are designed to breathe air.

Robin Dunbar famously suggested that the average human maintains about 150 social relationships. The total number of humans who have ever lived is somewhere north of 100 billion. A 1017-year road trip would be long enough to replay the lives of every one of those people in real time—in a sort of unedited documentary—and then rewatch every one of those documentaries 150 times, each time with a different commentary track by the 150 people who knew the subject best. By the time you finished watching this complete documentary of human perspective, you’d still be less than 1 percent of the way to the edge of the universe, so you’d have plenty of time to rewatch the whole project—each human life with all 150 commentary tracks—100 times before you finally arrived.

I was wondering whether there’s a way to use my welder as a defibrillator? (The specific model I own is an Impax IM-ARC140 arc welder.) —Łukasz Grabowski, Lancaster, UK You should definitely not use your arc welder as a defibrillator, and after reading your question, I honestly don’t think you should be allowed to use it as an arc welder, either.

an 80-kg human contains about 110,000 calories of energy, so a T. rex would need to consume a human every two days or so. [*] The city of New York had 115,000 births in 2018, which could support a population of about 350 tyrannosaurs. However, this ignores immigration—and, more important, emigration, which would probably increase substantially in this scenario.

A geyser is sort of like an upside-down rocket. If you calculate Old Faithful’s thrust the same way you would a rocket engine, by multiplying the rate of mass flow by its speed, you come up with a few thousand pounds of force. This is similar to the thrust of a fighter jet’s ejection seat, which tells us that it’s clearly powerful enough to launch a person high into the air.

if you’re ever faced with some kind of frightening illusory phantom, just remember this handy optics rule: If you can see it, you can shoot it with a laser.

There’s a surprisingly large amount of research into the physics of swing sets, partly because pendulums are really interesting physical systems and probably also because all physicists were once children. Children who play on swing sets quickly learn that they can get themselves going by pumping—kicking out their feet and leaning back, then tucking in their feet and leaning forward. Physicists call this “driven oscillation,” and a series of studies since the 1970s have analyzed exactly how pumping a swing works and what the most efficient way to do it is. What the physicists found, after half a century of research, was that children know exactly what they’re doing. Rhythmically kicking and leaning with their hands on the chains seems to be just about the optimal strategy for powering a swing using the rider’s body. For a while, some physicists theorized that a better strategy for pumping a swing might be to stand on the seat and raise and lower your body, by alternately crouching and standing upright, but further calculation showed that the kids have it figured out.

Q If you collected all the guns in the world and put them on one side of the Earth, then shot them all simultaneously, would it move the Earth? —Nathan No, although in my personal opinion, if you could get them to stay there, it would make the other side of the Earth a nicer place to live.

Q Where or how can one commit a murder and not be prosecuted for it? —Kunal Dhawan There’s a famous legal article by law professor Brian C. Kalt arguing that there is a 50-square-mile area of Yellowstone National Park in which people can commit felonies with impunity. The Constitution has clear rules about where juries must come from, but because of a mistake in drawing district lines, prosecuting a crime in this area requires that the jury come from an area with a population of 0. But don’t head out on a crime spree just yet. I asked a federal prosecutor about the “Yellowstone loophole.” He laughed, then said that you would absolutely be prosecuted if you tried to take advantage of it. I brought up the arguments that Professor Kalt made in his article. He replied, and I quote, “Law professors say a lot of stuff.”

Note to Keira: If your dad tells you not to build stuff with peanut butter, don’t listen to him. If he complains about the mess on the table, then just sneak jars into your room and build the tower on the carpet there. You have my permission.

We can make buildings pretty tall. The tallest buildings are almost 1 kilometer tall, and we could probably make buildings 2 or even 3 kilometers tall if we wanted, and they would still be able to stand up under their own weight. Higher than that might be tricky.

Elevators and the wind are big problems, but the biggest problem would be money. To make a building really tall, someone has to spend a lot of money, and no one wants a really tall building enough to pay for it.

By weight, the single most valuable thing that’s been bought and sold on the open market is probably the Treskilling Yellow postage stamp. There’s only one known copy of it, and in 2010 it sold for more than $2,300,000. That works out to at least $30 billion per kilogram of stamps.

Tire rubber particles are a major source of microplastics in our rivers and oceans, where they affect the chemistry of the water and are often eaten by marine animals. Research into the effects of these microplastics is ongoing—for example, in 2021, a study linked salmon die-offs in the Pacific Northwest to a chemical from tire rubber in stormwater runoff.

My college friend and I have had this debate for years now: If you put a million hungry ants in a glass cube with one human, who’s more likely to walk out alive? —Eric Bowman Everyone always assumes that if you put two animals together like this, they’ll battle to the death, which is a very Pokémon-esque view of biology. I think both the human and the ants would be in danger more from the glass cube than from each other. And if they do get out, I think it’s you and your friend who would be in danger.

Eyes first evolved about half a billion years ago, and in that time, the Permian extinction is probably the worst thing they’ve seen.

They say all roads lead to Rome, which would be helpful if it were true, but a glance at a map shows that a lot of roads are on totally different continents.

Of course, you can’t build Rome in a day. First of all, it’s already been built, so the people there would get mad if you tried to build it again.

High-quality diamonds are expensive, but it’s hard to get a handle on their exact price because the entire industry is a scam the gemstone market is complicated.

Many illegal drugs are, by weight, more valuable than gold. Cocaine’s price varies a lot, but in many areas it is in the neighborhood of $100/gram. [*] Gold is currently less than half that.

To defeat friction, we could levitate the capsule with magnetic fields and make it progressively smaller and lighter to accelerate and steer it more easily. Oops—we’ve accidentally built a particle accelerator.

I literally thought of a particle accelerator as answer to this question 🥹🥹🥹 I still got it 🥹🥹🥹

A modern smartphone is smaller than ENIAC or UNIVAC, but it has a lot more digital switches. UNIVAC had a little over 5,000 vacuum tubes packed into its 25 m3 case. An iPhone 12 has 11.8 billion transistors packed into the phone’s 80 mL case, which is about a trillion times more computer per liter. If you built an iPhone with vacuum tubes instead of transistors, packed together with the same density as they were in UNIVAC, the phone would be about the size of five city blocks when resting on one edge.

I like how it’s totally not clear what the rest of this claim is supposed to be. “THE MORE YOU KNOW . . .” . . . what? The happier you are? The more cultured you are? Are you better able to survive a life-or-death trivia contest? If I were doing the show I would replace it with “YOU JUST LEARNED THAT.”

Using 105 watts for Sisyphus’s metabolic rate, we can estimate that his maximum long-term output would be 260 watts, or a little more than an open refrigerator. So if you want to have a pointless object in your front yard wasting energy forever for no good reason, then instead of plugging in your refrigerator, just have Sisyphus push a rock up a hill. It would reduce your electric bill, and the climate-change impact would be negligible,

Diseases you could get from drinking an infected person’s blood include hepatitis B and C, HIV, and viral hemorrhagic fevers such as hantavirus and Ebola. I’m not a doctor, and I try not to give medical advice in my books. However, I will confidently say that you shouldn’t drink the blood of someone with a viral hemorrhagic fever.

That said, drinking or eating blood is not unheard of. It’s a taboo in many cultures, but “black pudding,” which is largely blood, is a traditional British dish, and there are similar dishes all around the world. Maasai pastoralists in east Africa once lived mainly on milk, but also sometimes drank blood, drawing it from their cattle and mixing it with the milk to form a sort of extreme protein shake.

No matter which way you look at it, the bottom line is that we live our lives surrounded by tiny spiders on a world completely dominated by a gigantic star. Hey, at least it’s not the other way around.

The claim that household dust is mostly dead skin is widespread; if you google it, you’ll find a lot of articles both supporting and debunking it. [*] Part of why this is hard to pin down is that household dust isn’t any one specific thing. It’s just a disgusting salad made from whatever happens to be lying around your house. It can include soil, pollen, cotton fibers, crumbs, powdered sugar, glitter, pet hair and dander, plastic, soot, human or animal hair, flour, glass, smoke, mites, and countless blobs of hard-to-identify gunk stuck together. There’s definitely some skin in there, but it’s not usually the main ingredient. Surveys of dust from the floors of offices and schools have found that a majority of it wasn’t organic matter at all, and a 1973 study in Nature of various environments found that skin cells made up between 0.4 percent and 10 percent of the airborne dust.

Q My 7-year-old son asked us over dinner recently at which point potatoes melt (I assume in a vacuum). Please advise. —Steffen Potatoes don’t really melt at any temperature. The starches break down and gelatinize, which is part of the normal cooking process; as the heat rises, the different components will sublimate at different temperatures. But what I want to know is, do you normally add “in a vacuum” to all his questions and assume that’s what he meant?

Even if you flew through edge-on, so you spent as much time as possible in the dense galactic disk, your odds of hitting a star would be only about 1 in 10 billion. (Your odds of hitting a planet would be a thousand times smaller.) For comparison, that’s about the same as the odds of deciding to call Barack Obama, picking up your phone and dialing 10 random digits, and getting his cell number on your first try.

California’s Food and Agricultural Code § 27637 bars anyone from making false or misleading statements about eggs. Luckily, I don’t live in California, so I’m free to share my egg theories.

The flow rate over Niagara Falls is at least 100,000 cubic feet per second, which is actually mandated by law. The Niagara River supplies an average of about 292,000 cubic feet per second to the falls, but much of it is diverted into tunnels to generate electric power. However, since people get mad if you turn off the world’s most famous waterfall, the generation facilities are required to leave at least 100,000 of those cubic feet per second flowing over the falls for everyone to look at (50,000 at night or during the off-season).

There’s some good news: Deep in the Sun, the photons carrying energy around have very short wavelengths—they’re mostly a mix of what we’d consider hard and soft X-rays. This means they penetrate your body to various depths, heating your internal organs and also ionizing your DNA, causing irreversible damage before they even start burning you. Looking back, I notice that I started this paragraph with “there’s some good news.” I don’t know why I did that.

Would landing a robotic probe count as touching the star? I don’t know; that’s sort of a philosophical question. But if you want to touch the star with your hand, then the answer is never. Even when a star cools to room temperature, there’s no way to touch it with your own hand and survive. And if you don’t care about the survival part . . . . . . then technically you could touch the Sun now.

And thank you to the federal prosecutor who told me that committing crimes is bad but asked to remain anonymous because “it’s funnier that way.”

A T. rex would likely be willing to eat several days’ to weeks’ worth of food in one meal, so if it has the option, it might eat a bunch of people at a time, then go for a while without eating.

In fact, according to Rifle magazine, a gun writer once claimed that at a thousand yards, he could catch ordinary rifle bullets with a baseball glove. Of course, he was being figurative—you wouldn’t see the bullet coming, so you’d be just as likely to catch it with your face as with your glove.

We associate mushroom clouds with nuclear weapons, but really, they’re just what happens when you dump a lot of heat energy into the air all at once. It doesn’t really matter what the source of the heat is—if there’s enough of it and it’s released fast enough, it will create a mushroom cloud.

The dinosaur extinction, famously caused by a meteor impact in what is now Mexico, was also accompanied by one of these blorps, the Deccan traps in what is now India. The outpourings were already happening by the time the space rock arrived, though they seem to have gotten a lot worse around that time. Scientists are still debating how the two events were connected and how much each one contributed to the extinction. The main extinction seems to have happened right at the moment of impact, so it was definitely the key, but all that lava couldn’t have helped the situation.

The oxygen masks on commercial airliners are often connected to lumps of potassium chlorate. When the mask drops, a pin is pulled out, and a chemical reaction heats the potassium chlorate to produce oxygen.

TIL!

If you drink all of someone’s blood, there’s a 100 percent chance that they’ll die.

This is correct whether I mean the fruit or an iPhone; the spider weighs about as much as each.

To those of you who are at the Department of Energy, hi! I’m a huge fan of your work, and of energy in general.

It’s common knowledge that Mount Everest is the tallest mountain on Earth, measured from sea level. A somewhat more obscure piece of trivia is that the point on the Earth’s surface farthest from its center is the summit of Mount Chimborazo in Ecuador, due to the fact that the planet bulges out at the equator. Even more obscure is the question of which point on the Earth’s surface moves the fastest as the Earth spins, which is the same as asking which point is farthest from the Earth’s axis. The answer isn’t Chimborazo or Everest. The fastest point turns out to be the peak of Mount Cayambe,‡ a volcano north of Chimborazo. You just learned that. ‡ Mt. Cayambe’s southern slope also happens to be the highest point on Earth’s surface directly on the equator. I have a lot of mountain facts.

In practice, sunscreen forms an irregular layer over the grooves and bumps of your skin, and most of the “sunburning” happens through the thinner “windows.” Between the irregular layer and the fact that most people don’t apply sunscreen thickly enough, SPF ratings are probably too high by a factor of 2 or more.

There are no room-temperature stars in the sky right now because the universe isn’t old enough. The first generation of white dwarf stars are still hot from their collapse. It will take many billions of years for them to cool down. The universe is still young.