What If?: Serious Scientific Answers to Absurd Hypothetical Questions

by Randall Munroe

For the kinds of radiation coming off spent nuclear fuel, every 7 centimeters of water cuts the amount of radiation in half.

To see what Times Square looked like before a city was there, we turn to a remarkable project called Welikia, which grew out of a smaller project called Mannahatta.

When these chunks melted, they left behind water-filled depressions in the ground called kettlehole ponds. Oakland Lake, near the north end of Springfield Boulevard in Queens, is one of these kettlehole ponds.

The ice sheets also dropped boulders they’d picked up on their journey; some of these rocks, called glacial erratics, can be found in Central Park today.

Hyenas were mainly found in Africa and Asia, but when the sea level fell, one species crossed the Bering Strait into North America. Because it was the only hyena to do so, it was given the name Chasmaporthetes, which means “the one who saw the canyon.”

Blue-green algae, or cyanobacteria, were the first photosynthesizers.

When cyanobacteria first appeared, the oxygen they breathed out was toxic to nearly all other forms of life. The resulting extinction is called the oxygen catastrophe.

After the cyanobacteria pumped Earth’s atmosphere and water full of toxic oxygen, creatures evolved that took advantage of the gas’s volatile nature to enable new biological processes. We are the descendants of those first oxygen-breathers.

Our most lasting relic will probably be the layer of plastic we’ve deposited across the planet. By digging up oil, processing it into durable and long-lasting polymers, and spreading it across the Earth’s surface, we’ve left a fingerprint that could outlast everything else we do.

Our plastic will become shredded and buried, and perhaps some microbes will learn to digest it, but in all likelihood, a million years from now, an out-of-place layer of processed hydrocarbons—transformed fragments of our shampoo bottles and shopping bags—will serve as a chemical monument to civilization.

In a billion years, these feedback loops will have given out. Our oceans, which nourished life and kept it cool, will have turned into its worst enemy. They will have boiled away in the hot Sun, surrounding the planet with a thick blanket of water vapor and causing a runaway greenhouse effect.

hundred billion or so humans have ever lived, but only seven billion are alive now (which gives the human condition a 93 percent mortality rate).

world of random soul mates would be a lonely one. Let’s hope that’s not what we live in.

A 1-watt laser is an extremely dangerous thing. It’s not just powerful enough to blind you—it’s capable of burning skin and setting things on fire.

At the top of the Luxor Hotel in Las Vegas is the most powerful spotlight on Earth.

Fluorine is the most reactive, corrosive element in the periodic table. Almost any substance exposed to pure fluorine will spontaneously catch fire.

The melting gallium under it would soak into the aluminum, disrupting its structure and causing it to become as soft and weak as wet paper.6

There’s no material safety data sheet for astatine. If there were, it would just be the word “NO” scrawled over and over in charred blood.

In the Clarendon Library at Oxford University sits a battery-powered bell that has been ringing since the year 1840. The bell “rings” so quietly it’s almost inaudible, using only a tiny amount of charge with every motion of the clapper. Nobody knows exactly what kind of batteries it uses because nobody wants to take it apart to figure it out.

And thus, we arrive at our answer: Centuries from now, deep in concrete vaults, the light from our most toxic waste will still be shining.

The scholarly authorities on freezing to death seem to be, unsurprisingly, Canadians. The most widely used model for human survival in cold air was developed by Peter Tikuisis and John Frim for the Defence and Civil Institute of Environmental Medicine in Ontario.

But in the Death Zone, there’s so little oxygen in the air that your veins lose oxygen to the air instead of gaining it.

Given humanity’s current knowledge and capabilities, is it possible to build a new star? —Jeff Gordon

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

The common cold is caused by a variety of viruses,1 but rhinoviruses are the most common culprit.2 These viruses take over the cells in your nose and throat and use them to produce more viruses.

While colds are no fun, their absence might be worse. In his book A Planet of Viruses, author Carl Zimmer says that children who aren’t exposed to rhinoviruses have more immune disorders as adults.

Amanita bisporigera is a species of mushroom found in eastern North America. Along with related species in America and Europe, it’s known by the common name destroying angel.

Some human cells do divide constantly. The most rapidly dividing cells are found in the bone marrow, the factory that produces blood.

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.

In cases of severe radiation poisoning, the immune system collapse is the primary cause of death. Without a supply of white blood cells, the body can’t fight off infections, and ordinary bacteria can get into the body and run wild.

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.

“It’s not the fall that kills you, it’s the sudden stop at the end.”

In general, if you have a child with yourself, 50 percent of your chromosomes will have the same stat on both sides. If that stat is a 1—or if it’s a multiplier—the child will be in trouble, even though you might not have been. This condition, having the same genetic code on both copies of a chromosome, is called homozygosity.

While most passenger cars have some kind of artificial speed limits imposed by the engine computer, the ultimate physical limit to a car’s top speed comes from air resistance. This type of drag increases with the square of speed; at some point, a car doesn’t have enough engine power to push through the air any faster.

The lift forces are relatively minor at normal highway speeds, but at higher speeds they become substantial. In a Formula One car equipped with airfoils, this force pushes downward, holding the car against the track. In a sedan, they lift it up.

The bottom line is that in the range of 150–300 mph, a typical sedan would lift off the ground, tumble, and crash …

Claude Shannon—who almost singlehandedly invented modern information theory—had a clever method for measuring the information content of a language.

He showed groups of people samples of typical written English that were cut off at a random point, then asked them to guess which letter came next. It’s threatening to flood our town with information! Based on the rates of correct guesses—and rigorous mathematical analysis—Shannon determined that the information content of typical written English was 1.0 to 1.2 bits per letter.

Imagine you tied a rope tightly around the Earth, so it was hugging the surface all the way around. Now imagine you wanted to raise the rope 1 meter off the ground. How much extra length will you need to add to the rope? Though it may seem like you’d need miles of rope, the answer is 6.28 meters. Circumference is proportional to radius, so if you increase radius by 1 unit, you increase circumference by 2π units.

A typical lightning strike delivers enough energy to power a residential house for about two days. That means that even the Empire State Building, which is struck by lightning about 100 times a year, wouldn’t be able to keep a house running on lightning power alone.

Even in regions of the world with a lot of lightning, such as Florida and the eastern Congo, the power delivered to the ground by sunlight outweighs the power delivered by lightning by a factor of a million.

Air holds water. If you walled off a column of air, from the ground up to the top of the atmosphere, and then cooled the column of air down, the moisture it contained would condense out as rain.

If you collected the rain in the bottom of the column, it would fill it to a depth of anywhere between zero and a few dozen centimeters. That depth is what we call the air’s total precipitable water (TPW).