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What If?

Randall Munroe · 2014 · 9 ideas · 9 min

Taking absurd hypothetical questions completely seriously — and running the actual physics and math on them — reveals genuine scientific insight buried inside seemingly ridiculous scenarios.

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Why this book

Munroe's argument, made implicitly through dozens of case studies, is that rigorous scientific reasoning applies just as well to gloriously silly questions as to serious ones — and that working through an absurd hypothetical (What if everyone on Earth jumped at once? What if you tried to hit a baseball at near light speed?) with real physics, real math, and real research is both hilarious and genuinely educational. Each chapter answers a reader-submitted question with actual calculation, cited science, and deadpan humor about the collateral devastation involved.

It matters because it makes hard science approachable by starting from curiosity and absurdity rather than a textbook chapter, showing that the same tools scientists use to understand serious phenomena — orbital mechanics, thermodynamics, epidemiology — are perfectly capable of, and often clarified by, being pointed at questions nobody has any practical reason to ask.

Who should read it

Curious readers of any background who enjoy physics, absurdist humor, or both will find this an easy, delightful way into real scientific reasoning. It's especially good for people who think they "aren't science people" but love a good thought experiment.

About the author

Randall Munroe is an American cartoonist and former NASA roboticist best known for creating the webcomic xkcd; What If? grew out of his blog feature answering hypothetical science questions from readers.

The ideas

01Absurd questions are a legitimate gateway into real physics02A ball hit at relativistic speed would devastate the stadium before it reached the plate03Everyone on Earth jumping at once wouldn't do much to the planet04Draining the oceans would trigger climate chaos, not just reveal the seafloor05A worldwide power outage would unfold in a specific, predictable sequence06A mole of moles would be an ecological and thermal catastrophe07Machine-gun jetpacks and rocket-powered flight run into their own physics limits08Munroe treats uncertainty and estimation as part of the answer, not a failure of it09Even destructive thought experiments end with practical safety reasoning
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About this summary. Wisdomly re-expresses a book's ideas, arguments, and structure in our own words — nothing here is the author's text. Summaries are a map, not the territory: if the ideas land, the full book is worth your money and your evenings.