What If? 2

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

Author: Randall Munroe

Completed: Nov 2022 (Full list of books)

Overview: If you like XKCD you’re going to enjoy this book, but if you like XKCD, you probably already knew that. Randall answers some truly ridiculous questions with the scientific rigor usually reserved for graduate studies. Many of the questions were one he originally answered on the What If website, but it was wonderful to look back at those and fun to see the new questions readers sent in. I’ve used similar questions in class to get students thinking about problems in a different way. It is wonderful to see how they solve problems that aren’t abstractions in a book but also don’t have a specific “right” answer.


  • 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.
  • What the physicists found, after half a century of research, was that children know exactly what they’re doing. Rhythmically kicking and leaning with their hands on the chains seems to be just about the optimal strategy for powering a swing using the rider’s body.
  • Really big objects can get extremely hot from even a tiny amount of heat production per unit of volume. Even the core of the Sun, where nuclear fusion happens, would be pretty cold if you could somehow isolate a piece of it. A cup of solar core material produces about 60 milliwatts of thermal energy. By volume, that’s about the same heat production rate as the body of a lizard, and less than that of a human. In a sense, you’re hotter than the Sun—there’s just not as much of you.
  • It might seem confusing that someone navigating toward Earth’s north pole would be attracted to the MRI’s south pole, but that’s because the Earth’s pole names are backward. The “north” end of a magnet is the one that points toward the Earth’s north pole, which means the Earth’s north magnetic pole is technically a south magnetic pole, and vice versa. This is deeply annoying to me, but there’s nothing we can do about it, so we might as well move on.
  • When you crush sugar in the dark, it emits flashes of light. This phenomenon is called triboluminescence. The light can be pretty faint, but the old Wint-O-Green flavor of Life Savers candies are famous for producing an especially bright flash, which is thanks to an additive used for flavoring. Most of the light emitted by sugar through triboluminescence is ultraviolet, but certain Life Savers contain methyl salicylate, which is fluorescent. It absorbs the invisible ultraviolet and emits it as blue visible light.
  • If you’re not familiar with it, I recommend doing a quick image search for “glass beaches of Vladivostok” —you won’t regret it!
  • 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.
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