What If?

Author: Randall Munroe

• There’s one thing you would not see: earthworms. There were no earthworms in New England when the European colonists arrived.

• As the ice sheets withdrew, large chunks of ice broke off and were left behind. When these chunks melted, they left behind water-filled depressions in the ground called kettlehole ponds.

• Below the ice, rivers of meltwater flowed at high pressure, depositing sand and gravel as they went. These deposits, which remain as ridges called eskers,

• A hundred thousand years ago, Earth was near the end of a similar period of climate stability. It was called the Sangamon interglacial, and it probably supported a developed ecology that would look familiar to us.

• A billion years ago, the continental plates were pushed together into one great supercontinent. This was not the well-known supercontinent Pangea—it was Pangea’s predecessor, Rodinia.

• Bromine is liquid at room temperature, a property it shares with only one other element—mercury.

• The Gedser Wind Turbine in Denmark was installed in the late 1950s, and generated power for 11 years without maintenance.

• When radioactive particles travel through materials like water or glass, they can emit light through a sort of optical sonic boom. This light is called Cherenkov radiation, and it’s seen in the distinctive blue glow of nuclear reactor cores.

• Above 8000 meters—above the tops of all but the highest mountains—the oxygen content in the air is too low to support human life.

• But if you’re even more pedantic, it is true. The ocean is colder than space.

• Temperature is a measure of the average kinetic energy of a collection of particles. In space, individual molecules have a high average kinetic energy, but there are so few of them that they don’t affect you.

• REENTERING SPACECRAFT HEAT UP because they’re compressing the air in front of them (not, as is commonly believed, because of air friction).

• An ant’s brain might contain a quarter of a million neurons, and thousands of synapses per neuron, which suggests that the world’s ant brains have a combined complexity similar to that of the world’s human brains. So we shouldn’t worry too much about when computers will catch up with us in complexity. After all, we’ve caught up to ants, and they don’t seem too concerned.

• In fact, that’s where their name comes from—the word asteroid means “starlike.”

• We got our first confirmation of what asteroids looked like in 1971, when Mariner 9 visited Mars and snapped pictures of Phobos and Deimos.

• Things get really hot when they come back from space. As they enter the atmosphere, the air can’t move out of the way fast enough, and gets squished in front of the object—and compressing air heats it up.

• As a rule of thumb, you start to notice compressive heating above about Mach 2 (which is why the Concorde had heat-resistant material on the leading edge of its wings).

• Jeff Potter’s excellent book Cooking for Geeks provides a great introduction to the science of cooking meat, and explains what ranges of heat produce what effects in steak and why. Cook’s The Science of Good Cooking was also helpful.

• 100 kilometers—the formally defined edge of space—the picture’s not much better.

• As the probably apocryphal story goes, steelworkers in Pittsburgh would cook steaks by slapping them on the glowing metal surfaces coming out of the foundry, searing the outside while leaving the inside raw. This is, supposedly, the origin of the term “Pittsburgh Rare.”

• It’s not just a problem of hitting the puck hard enough. This book isn’t concerned with that kind of limitation.

• If you’re like me, when you first saw this question, you might’ve imagined the puck leaving a cartoon-style hockey-puck-shaped hole.

• If you’re like me, when you first saw this question, you might’ve imagined the puck leaving a cartoon-style hockey-puck-shaped hole. But that’s because our intuitions are shaky about how materials react at very high speeds.

• The common cold is caused by a variety of viruses,1 but rhinoviruses are the most common culprit.

• The world is big,[citation needed ] but there are a lot of people.[citation needed ]

• If the optimist says the glass is half full, and the pessimist says the glass is half empty, the physicist ducks.

• The Sun is really bright,[citation needed ] and its light illuminates the Earth.[citation needed ]

• If you’re like me, you were told never to eat mushrooms you found in the woods. Amanita is the reason why.

• The frightening thing about Amanita poisoning is the “walking ghost” phase—the period where you seem to be fine (or getting better), but your cells are accumulating irreversible and lethal damage. This pattern is typical of DNA damage, and we’d likely see something like it in someone who lost their DNA.

• Bone marrow is also central to the human immune system. Without it, we lose the ability to produce white blood cells, and our immune system collapses.

• There are other types of rapidly dividing cells in the body. Our hair follicles and stomach lining also divide constantly, which is why chemotherapy can cause hair loss and nausea.

• The initial side effects of doxorubicin, in the few days after treatment, are nausea, vomiting, and diarrhea—which makes sense, since the drug kills cells in the digestive tract.

• Losing your DNA would most likely result in abdominal pain, nausea, dizziness, rapid immune system collapse, and death within days or hours from either rapid systemic infection or systemwide organ failure.

• X-Plane is the most advanced flight simulator in the world. The product of 20 years of obsessive labor by a hardcore aeronautics enthusiast3 and community of supporters, it actually simulates the flow of air over every piece of an aircraft’s body as it flies.

• X-Plane tells us that flight on Mars is difficult, but not impossible. NASA knows this, and has considered surveying Mars by airplane.

• There’s no surface to hit; Jupiter transitions smoothly from gas to liquid as you sink deeper and deeper.

• But I’ve never seen the Icarus story as a lesson about the limitations of humans. I see it as a lesson about the limitations of wax as an adhesive.

• There are hopes that carbon nanotube-based materials could provide the required strength—adding this to the long list of engineering problems that can be waved away by tacking on the prefix “nano-.”

• having the same genetic code on both copies of a chromosome, is called homozygosity.

• IF YOU WANT TO transfer a few hundred gigabytes of data, it’s generally faster to FedEx a hard drive than to send the files over the Internet.

• IF YOU WANT TO transfer a few hundred gigabytes of data, it’s generally faster to FedEx a hard drive than to send the files over the Internet. This isn’t a new idea—it’s often dubbed “SneakerNet”—and it’s even how Google transfers large amounts of data internally.

• A human falling with arms and legs outstretched has a terminal velocity in the neighborhood of 55 meters per second.

• What can you do in 26 seconds? For starters, it’s enough time to get all the way through the original Super Mario World 1-1, assuming you have perfect timing and take the shortcut through the pipe.

• The formula for the fraction of ground coverage by a large number of arrows, some of which overlap each other, is this:

• There wouldn’t even be a cool whirlpool at the surface—the opening is too small and the ocean is too deep. (It’s the same reason you don’t get a whirlpool in the bathtub until the water is more than halfway drained.)

• If a piece of text contains n bits of information, in a sense it means that there are 2n different messages it can convey.

• GPS timing is incredibly precise; of all the problems in engineering, it’s one of the only ones in which engineers have been forced to include both special and general relativity in their calculations.

• Breathing in this situation would be difficult. It’s hard to suck in air against the weight of the water, which is why snorkels can only work when your lungs are near the surface.

• At somewhere around 6 atmospheres, even ordinary air becomes toxic.

• At some point, our growing Earth would reach the point where adding more mass causes it to contract, rather than expand. After this point, it would collapse into something like a sputtering white dwarf or neutron star, and then—if its mass kept increasing—eventually become a black hole.

• After several centuries, it would be close enough to the swollen Earth that the tidal forces between Earth and the Moon would be stronger than the gravitational forces holding the Moon together. When the Moon passed this boundary—called the Roche limit—it would gradually break apart,9 and Earth would, for a short time, have rings.

• Air resistance is proportional to speed squared, which means that when it’s going fast, the arrow would experience a lot of drag.

• THEY SAY LIGHTNING NEVER strikes in the same place twice. “They” are wrong.

• These storms can generate a flash of lightning every two seconds, making Lake Maracaibo the lightning capital of the world.

• Introverts understand; the loneliest human in history was just happy to have a few minutes of peace and quiet.

• A neutron star is what’s left over after a giant star collapses under its own gravity.

• If the star is heavy enough, it overcomes that quantum pressure and collapses further (with another, more massive explosion) to become a neutron star. If the remnant is even heavier, it becomes a black hole.2