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

by Randall Munroe

Good news: You can’t inhale a person, and also dust is not mostly dead skin.

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.

We don’t really understand triboluminescence. When materials scrape together or are split into pieces, electric charges are sometimes pulled apart in a way that lets them snap together to release energy. But there are a lot of ways atoms can bonk against one another, and scientists have trouble figuring out exactly what combination of effects is producing light in any particular experiment.

But despite their different appearances, Life Savers flashes and lightning have a lot in common. They both involve electric charges being pulled apart by materials mechanically rubbing against one another, and in both cases light is produced by the energy release when those charges equalize.

And when it comes down to it, we don’t understand lightning, either. We know updrafts in storms cause electric charges to build up between the top and bottom of the storm, and we think it involves the wind blowing past rain or ice, but the details of how the charges separate are still a mystery.

In fact, thanks to the laws of thermodynamics, just about every electric device that consumes power eventually turns that power into heat at the same rate. A 60-watt lightbulb produces light, but that light hits a surface and heats it up. In the end, it produces the same 60 watts of heat as a 60-watt space heater.

If you don’t want to run your toasters empty, you could try making lots of toast, but you’ll quickly have more than you can eat. If each toaster can hold two slices, and it takes about 2 minutes to toast each one, then your toaster will go through about 30 loaves of bread per hour. At peak, you’ll be consuming bread at the rate of a medium-size American town.

The change in the pull of gravity would cause the oceans to slosh around a little, with the sea settling on a new “sea level” that follows the contours of the new geoid. Without Japan’s gravity, the ocean would shift slightly toward the other side of the Earth; sea level would probably fall by a foot or two around east Asia, and rise by the same amount around South America.

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.

When a fluid flows through an opening fast enough, the pressure within the fluid drops due to Bernoulli’s principle. Water always “wants” to boil, but is held together by air pressure. When the pressure abruptly drops, bubbles of steam form in the water. This is called “cavitation.”

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 periodic discussion of turning off the falls again for maintenance, and probably to see what cool stuff they can find while they’re at it.

As you walk, pulses of fire would sweep the land, many of them set by people to encourage the maintenance of grasslands that supported herds of bison.

If you leave the snow there, it will slowly get less and less deep as it settles down and compacts. This means that even if 6 feet of snow fell everywhere, it would only be 6 feet at first. Before long, it might be 5 feet. (This happens to humans, too. You get shorter throughout the day as your body compresses a little!)

If astronauts didn’t have UV-blocking suits, they’d sunburn much more quickly than on Earth. (There are stories that Apollo astronaut Gene Cernan tore enough layers of insulation in his spacesuit to get a bad sunburn on his lower back.)

That means that if you put on a second layer of the same sunscreen, it should reduce that 1/20th by another 1/20th, for 1/400th total reduction. If that were true, 2 layers of SPF 20 sunscreen would be equivalent to SPF 400 sunscreen! Five layers of SPF 20 sunscreen would be equivalent to SPF 3.2 million, enough to block the UV at the Sun’s surface.

On a neutron star, which is much smaller and denser, any matter made of molecules is flattened out into a thin layer of atoms by the intense gravity, but on an Earth-size stellar remnant, some structures could support themselves.

If a planet with oceans gets too hot, the atmosphere can fill with water vapor. This water vapor can trap more heat, leading to a feedback loop of out-of-control warming that continues until the oceans boil away. Something like this may have happened to Venus in the distant past.

Birds have a nictitating membrane, a transparent “third eyelid” that they can blink to protect and moisturize their eye. Many other animals have them, although humans and our evolutionary relatives have lost them. That bit in the corner of your eyelid is the vestigial remnant of your nictitating membrane.

This effect also happens when big ice sheets on land melt. Their water causes the sea level to rise overall, but since their gravity no longer pulls the ocean toward them, the sea level can actually fall in the area around the sheet. On the other side of the world, it will rise by more than you’d expect. If or when Greenland melts, the flooding will be worst in Australia and New Zealand. For more on this, see How To, chapter 2, “How to Throw a Pool Party.”

some home telescopes, such as the wood-framed Sunspotter, use lenses to project a detailed image of the Sun onto a sheet of paper, like a high-resolution version of a pinhole camera. They’re a little expensive, but they’re a great tool for safely viewing sunspots or solar eclipses.

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.

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.