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

by Randall Munroe

Standing near a hot object can kill you very fast—for more on this, flip to basically any other random page of this book—but standing near a cold thing won’t freeze you instantly. Hot objects emit thermal radiation that heats up things around them, but cold objects don’t emit cold radiation. They just sit there.

Once you’ve built your apparatus to vaporize iron, you’ll want to stand back, since vaporizing a 1-meter cube of iron will take about 60 gigajoules of energy. If you vaporize the iron over the course of three hours, your apparatus will have roughly the same total heat output as a raging house fire.

Dr. Mahowald said the vaporized iron would contribute to climate change by absorbing small amounts of sunlight and radiating it as heat. But iron in the atmosphere could also help slow down climate change, by fertilizing the ocean and encouraging the growth of algae that pull CO2 out of the atmosphere.

If someone built a highway out of the Solar System, most drivers wouldn’t make it past the asteroid belt. Truck drivers, who are used to driving long distances on highways, have a lower per-mile crash rate than ordinary drivers, but they would still be unlikely to reach Jupiter.

As far as we know, the edge of the observable universe isn’t the edge of the actual universe. It’s just the farthest that we’re able to see, because there hasn’t been time for light to reach us from any farther parts of space. There’s no reason to think space itself ends at that particular point, but we don’t know how much farther it goes. It might just continue forever. The edge of the observable universe isn’t the edge of space, but it’s the edge of the map.

Light in the atmosphere doesn’t go in a perfectly straight line. Air slows light down, and denser air slows the light down more. When the air on one side of the beam is being slowed down more than the other side, it makes the light bend in that direction.

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.

Your weight comes from the Earth’s gravity pulling you down. The Earth’s gravity comes from its mass. Less mass should mean less gravity. Remove mass from the Earth, and you’ll lose weight.

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.

Jupiter is only a little denser than water, so a 50-foot-wide Jupiter would only weigh about 2,500 tons.

Based on the textbook definition of temperature, space is hot, at least here in the Solar System. The molecules in space are individually moving very fast, which means that each one has a lot of energy, and temperature is usually defined as the average kinetic energy of the molecules in a substance. But there are so few molecules in space that even though each one has a lot of energy, the total amount of heat energy is small, which means it doesn’t warm things up very much. It may be warm in theory, but it feels cold in practice.

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

“Soil liquefaction” is a boring-sounding phrase for a terrifying thing. Under certain conditions, such as earthquakes, soil can flow like a liquid, which is extremely alarming for anyone who lives on the ground. The material in the impactor would undergo this same transformation, flowing outward across the surface in an omnidirectional landslide of supersonic soil liquefaction.

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. The dead matter carries the chemical imprint of its history—altered and jumbled in various ways—for millions of years. After we dig it up, we spend a lot of effort stripping the evidence of this story away, refining the complex hydrocarbons into uniform fuels. When we burn the fuels, their story is finally erased, and the Jurassic sunlight that was bound up in them is released to power our cars. [*]

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.

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.

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.

First, here’s a general rule of thumb: You can’t use lenses and mirrors to make something hotter than the surface of the light source itself. In other words, you can’t use sunlight to make something hotter than the surface of the Sun.

Laws give people power. If a law is complicated, it empowers people who can afford lawyers to interpret it. “Laws that are complicated, arbitrary, and unintuitive empower the state,” says Jonathan Zittrain, professor of international law and the Harvard Law Library’s director, “since prosecutorial discretion means they can pick whom to enforce against and be selective in discriminatory ways.” But making laws simpler and vaguer doesn’t necessarily move that power from the state to the people. You could get rid of a lot of laws and replace them with “everyone just needs to behave properly.” But that leaves it up to law enforcement to decide the meaning of “properly.”

so I asked for his thoughts on what ammonia would do to the stomach. The good news, he told me, is that the reaction wouldn’t produce chlorine gas. Ammonia is a base, so it would react directly with the acid in your stomach and neutralize it, forming a salt. The salt, ammonium chloride, is mildly irritating to your digestive system but not particularly harmful in itself. However, the above reaction also produces a lot of heat, so you’d suffer stomach burns as the acid and the ammonia neutralized.

It’s actually much easier to guess what a star would taste like: sour. The sour receptors on our tongue are activated by free hydrogen ions, which we usually encounter in food in the form of acidic liquids. The bulk of a star’s atmosphere is made of hydrogen ions, so it would very directly activate those receptors, giving a star an overwhelmingly sour taste.