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

by Randall Munroe

Why does your hair stand on end when you rub a balloon on it, anyway? The usual answer from science class is that electrons are transferred from your hair to the balloon, leaving your hair positively charged. The charged hairs repel each other and stick out. Except . . . why do electrons get transferred from the hair to the balloon? Why don’t they go the other way? That’s a great question, and the answer is that no one knows. Physicists don’t have a good general theory for why some materials shed electrons from their surfaces on contact while other materials pick them up. This phenomenon, called triboelectric charging, is an area of cutting-edge research.

You can feel this “cold radiation” by looking up at the stars on a summer night. Your face will feel cold since your body heat is pouring away into space. If you hold up an umbrella to block your view of the sky, you’ll feel warmer—almost as if the umbrella is “blocking the cold” from the sky. This “cold sky” effect can cool things down to below the ambient air temperature. If you leave out a tray of water under a clear sky, it can turn to ice overnight even if the air temperature stays well above freezing.

Cold objects can condense the air itself, causing liquid oxygen to collect on their surfaces like dew. If they’re cold enough, they can even freeze it solid. 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.

One of the biggest hazards of ultracold materials is that they often don’t want to stay ultracold. When liquid nitrogen or dry ice warm up and turn to gas, they expand a lot, often pushing all the regular air out of the room. A bucket of liquid nitrogen can turn into enough nitrogen gas to fill a room, which is bad news if you breathe oxygen.

In real life, when people want to vaporize iron, [*] they generally don’t just put it over a heat source. They either use induction heating to heat the iron with electromagnetic fields or electron beams to vaporize it a little at a time. One nice thing about electron beams is that you can use a magnetic field to curve the beam around, so the really exciting and dangerous stuff happens on the other side of the iron from your delicate equipment.

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

Based on US crash rates, the odds of a driver traveling 46 billion light-years without a crash would be about 1 in 101015. That’s roughly the same as the probability of a monkey with a typewriter typing out the entire Library of Congress, with no typos, fifty times in a row. You’ll want a self-driving car, or at least one with one of those alarms that warns you if you drift out of your lane.

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.

At that point, the pigeons wouldn’t be pulled down by the Earth’s gravity—the Earth would be pulled up by the pigeons’ gravity.

Tyrannosaurus rex weighed about as much as an elephant.

A mirage is a reflection of the sky; light from the sky comes down near the surface and then bends up toward your eye, so it looks like it’s coming from the ground.

When you look over the water, you sometimes see land and water floating above the surface, because of the funny paths the light takes. These shimmering clumps of land and buildings floating above the horizon are called a Fata Morgana, so named because people thought they looked like the floating castles of the sorceress Morgan le Fay.

If you want to shoot a laser at a Fata Morgana, just aim straight at it. It’s not really there, but the path the laser takes will be the same one the light reaching your eyes takes. The thing floating in the sky is an illusion, but illusions are made of light. So, 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.

Typing and writing speeds are so different because the bottleneck in writing books is how quickly our brains can organize, produce, and edit stories. This “storytelling speed” has probably changed much less over time than our physical writing speed has.

If the Earth were of uniform density, removing layers would make you lighter. But our planet gets denser the deeper you go, and the density cancels out the mass loss. The planet is getting a little lighter as you remove the surface, but you’re also getting closer to that dense core. The net effect is that removing the Earth’s outer layer makes its surface gravity stronger.

The little sand patch would contain 99 percent of the pile’s individual grains, but less than 1 percent of its total volume. Our Sun isn’t a grain of sand on a soft galactic beach; instead, the Milky Way is a field of boulders with some sand in between.

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,”

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.

can seem like pumping your feet to swing higher must violate conservation of energy somehow. How can you push against nothing? But you’re not pushing against nothing; you’re pushing, indirectly, against the crossbar of the swing set.

When you swing up to about 20 degrees, you lose more energy to drag than you gain by pumping. An 8-foot swing can actually carry you higher than a 30-foot one!

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.

Space may be hot, but it’s the hottest place you can freeze to death.

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.”

Sixty-six million years ago [*] a big rock from space hit the Earth near the present-day city of Mérida, Mexico. This impact led to the extinction of most of the dinosaurs.

If you were living on the other side of the world—say, in Jakarta or Perth—and you were away from the shore during the brief coastal flooding, you wouldn’t notice much else. Unlike 66 million years ago, there wouldn’t be global firestorms from ejected debris reentering the atmosphere. No volcanic eruptions would be triggered. There would be some dust thrown into the air, but there wouldn’t be global cooling from volcanic aerosols.

Maybe people just aren’t worth enough. The EPA currently uses $9.7 million as the “value of a statistical life,” although they go to great lengths to point out that this is absolutely not the value they place on any actual human life.

The standard answer to “What kind of dead stuff does the oil in the ground come from?” is “Marine plankton and algae.” In other words, there are no dinosaur fossils in those fossil fuels.

But fossil fuels bear fingerprints of their origins. The various characteristics of coal, oil, and natural gas depend on the organisms that went into them and what happened to their tissues over time. It depends on where they lived, how they died, where their remains ended up, and what kinds of temperature and pressure they experienced.

There are a few things required for oil to form, including the quick burial of large amounts of hydrogen-rich organic matter in a low-oxygen environment. These conditions are most often met in shallow seas near continental shelves, where periodic nutrient-rich upwellings from the deep sea cause blooms of plankton and algae. These temporary blooms soon burn themselves out, dying and falling to the oxygen-poor seabed as marine snow. If they’re quickly buried, they may eventually form oil or gas. Land life, on the other hand, is more likely to form peat and eventually coal.

In a broader sense, all water in the ocean has at some point been part of a dinosaur. When this water is used in photosynthesis, molecules from it become part of the fats and carbohydrates in the food chain—but a lot more of that water is in your body right now in the form of water. In other words, your plastic toys contain a lot less dinosaur than you do.

There are five big mass extinctions in the fossil record, and all five of them [*] were accompanied by large amounts of lava blorping onto the surface.

The water is held above the surface by suction—the lack of air pressure over it pushing it down. Physicists will point out that technically it’s the pressure of the air on the rest of the ocean pushing the water up, not suction inside the column pulling it, which is true. But, just between us, once you understand that, it’s still sometimes easier to think of it as suction. I think that’s fine. Just don’t let the physicists hear you.

When a tropical cyclone was approaching the coast of Florida in 2001, marine biologists observed blacktip sharks heading out into the open ocean ahead of the storm, probably to escape the rough currents and pounding waves in the shallow coastal waters. Research by marine scientist Michelle Heupel and colleagues suggests that the sharks weren’t responding to the wind or the waves—instead, they started their evacuation the moment they sensed the barometric pressure dropping below the normal level for the season.

The suction that lifts water is created by the weight of air pressing down on the ocean’s surface, and air pressure isn’t strong enough to lift a column of water more than about 10 meters high. By the time your column of water reached 10 meters or so, the surface wouldn’t lift any higher no matter how much you lifted the enclosure. Instead, a vacuum would open up at the top and the water at the surface would start to boil in the low pressure.

When you see pressure quoted in “inches of mercury” or “mmHg,” they’re measuring the height of the column in a mercury suction aquarium.

The night of March 18 to 19, 2008, was cloudy across much of North America, but the skies were clear in Mexico and the southwestern United States. If you had looked high in the sky at just the right time that night, you might have seen a faint dot appear for about 30 seconds in the constellation Boötes. This light was the flash from the collapse of a supermassive star about 10 billion light-years away, [*] thousands of times more distant than Andromeda. It set a new record for the most distant known object visible to the naked eye. These collapsing stars emit jets of energy from their north and south poles for reasons we don’t completely understand. The spin axis of GRB 080319b happened to line up directly with Earth, so we were caught right in the jet—which is why it was visible even billions of light-years away. The explosion shot a pencil-thin beam of light across the universe, like a cosmic laser pointer aimed directly at our eye.

In 1956, oceanographer Henry Stommel suggested that, because of differences in temperature and salinity between the surface and the deep ocean, if you connect the surface and the deep ocean with a tube and push water through it, it might continue flowing indefinitely. The tube wouldn’t create perpetual motion. The steady flow is possible because the surface and depths of the ocean aren’t quite in equilibrium, thanks to a subtle imbalance in how temperature and salinity equalize between them. Since the water inside the tube can equalize temperature with its surroundings through the wall of the tube but not exchange salinity, Stommel’s calculations showed the tube could upset the equilibrium and cause the ocean to mix. A 2003 experiment with a PVC tube over the Mariana Trench (not extending all the way to the bottom!) confirmed that this effect could cause a slow exchange of water.

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.

It might seem confusing that someone navigating toward Earth’s north pole would be attracted to the MRI’s south pole, but that’s because the Earth’s pole names are backward. The “north” end of a magnet is the one that points toward the Earth’s north pole, which means the Earth’s north magnetic pole is technically a south magnetic pole, and vice versa. This is deeply annoying to me, but there’s nothing we can do about it, so we might as well move on.

A 2004 simulation by Douglas L. T. Rohde and colleagues estimates that the identical ancestors point is likely somewhere between 5000 and 2000 BCE. At that date, everyone who left descendants at all is an ancestor of everyone. Each lineage from that date has either died out or expanded to include all living humans, and so all living humans share the same set of ancestors from that point backward.

Imagine a “vehicle” anchored with Kevlar straps to a pivot in the center of the track, balanced with a counterweight on the other side. In effect, this would be a giant centrifuge. This lets us apply one of my favorite weird equations, which says that the edge of a spinning disk can’t go faster than the square root of the specific strength [*] of the material it’s made of.

The particles in the Large Hadron Collider’s beam go very close to the speed of light. At that speed, they complete 500 miles (30 laps) in 2.7 milliseconds.

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.

The sluggish speed of light means that you’d have to arrange the components of your phone to work in parallel as much as possible. That way, a computation at one end wouldn’t be stuck waiting for a result of a computation at the other. This sounds ridiculous, but modern computers have exactly this problem. If a chip is running at 3 GHz, light—and electric signals—don’t have time to cross from one end of the computer to the other during a single clock cycle. Different parts of your computer are out of sync with one another. If two parts are going to go back and forth quickly, circuit board designers need to place them physically close to one another, so they’re not held back by the sluggish speed of light.

The Sun sets later for taller people, because the higher up you are, the farther you can see over the horizon. In addition to later sunsets, taller people also experience earlier sunrises, which means that days last longer for them in general. If you’re near the equator at sea level, every extra inch of height corresponds to nearly a minute of extra daylight per year, and it’s even more at higher latitudes.

Refrigerators don’t cool their surroundings, they heat them. Refrigerators work by pumping heat from their interior to their exterior. The inside gets colder, and the outside gets hotter. If you open the door, the fridge will struggle endlessly to draw up heat from the front and disperse it out into the air via the coils, only to have the air flow right back in. Then it has to start all over, like Sisyphus forever rolling a boulder up a hill.

It would reduce your electric bill, and the climate-change impact would be negligible, since the power would come from a renewable energy source (the infinite spite of Hades, God of the Underworld).

There’s a well-known factoid that claims you’re always within a few feet of a spider. This isn’t literally true—spiders don’t live in the water, [*] so you can get away from them by swimming, and there aren’t as many spiders in buildings as in fields and forests. But if you’re anywhere near the outdoors, even in the Arctic tundra, there are probably spiders within a few feet of you.

If house dust comprises up to 80 percent dead skin, how many people worth of skin does a person consume/inhale in a lifetime?