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

by Randall Munroe

But if you ask me how much all the electrons in a bottlenose dolphin weigh, that’s a different situation. No one knows that number off the top of their head—unless they have an extremely cool job—which means it’s okay to feel confused and a little silly and take some time to look stuff up. (The answer, in case anyone ever asks you, is about half a pound.)

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.

Cold things and hot things are different. [citation needed] 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.

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.

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

It turns out that any passive optical system follows a law called “conservation of étendue.” This law says that if you have light coming into a system from a bunch of different angles and over a large “input” area, then the input area times the input angle [*] equals the output area times the output angle. If your light is concentrated to a smaller output area, then it must be “spread out” over a larger output angle.