Book Review

‘What If?: Serious Scientific Answers to Absurd Hypothetical Questions’ by Randall Munroe

If you’ve ever contemplated questions such as “How close would you have to be to a supernova to get a lethal dose of neutrino radiation?” or “If you suddenly began rising steadily at 1 foot per second, how exactly would you die?” then Randall Munroe’s “What If?: Serious Scientific Answers to Absurd Hypothetical Questions” is the book for you.

Munroe calculates the thrust-to-weight ratio of an AK-47 because he wants to know whether these firearms could be used for a jetpack. His findings? “With enough machine guns, you could fly.” He computes the speed of a baseball pitched at 90 percent of the speed of light to imagine its destructive effects. Answer: Due to the “constant fusion at the front of the ball,” he writes, “[e]verything within roughly a mile of the park would be leveled.”

Munroe is the Cambridge-based former NASA roboticist turned celebrity cartoonist behind the uber-popular website xkcd. (Camera-shy, he’s also about as hard to spot in the real world as a quark particle.) Xkcd is home to his geeky Web comic and his “What If” feature, as well as some impressive genre-bending innovations like the monstrous “Click and Drag’’ comic (about 46 feet long if you printed it out) and a film called “Time” released in “episodes” of one frame per hour, which just won a 2014 Hugo Award for best graphic story.


Since 2012, average folk have been submitting oddball “What If?” queries, usually based on some scientific or science-fiction premise. Munroe selects the most promising or disturbing ones each week and posts his math-supported conclusions on his site, interspersed with his charmingly-amateur stick-figure cartoons and references to pop culture touchstones like “Lord of the Rings,’’ Dungeons & Dragons, and “Gremlins.”

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“What If?” the book is a compilation of these Q&As, around half of which are new, and half are “updated and expanded versions” of his most popular investigations.

To be fair, not all of Munroe’s musings concern terrifying, gruesome, or apocalyptic ends such as lighting strikes, drained oceans, firing a hockey puck at a goalie at Mach 8, or the opener, “What would happen if the Earth and all terrestrial objects suddenly stopped spinning, but the atmosphere retained its velocity?”

Other replies contemplate the plain silly, such as the likelihood of replicating the scene from the film “300” where thousands of arrows blot out the sun, or how to construct a Lego bridge from New York City to London. One problem: “Lego bricks don’t make a watertight seal when you connect them together.”

It’s fun to watch as Munroe tackles each question and examines every possible complication with nerdy and methodical aplomb, his distinctive scribblings providing clever running commentary of peanut-gallery jokes as his train of thought (sometimes) happily derails. The delightfully demented “What If?” is the most fun you can have with math and science, short of becoming your own evil genius.


The most disturbing queries, such as “Is it possible to cry so much you dehydrate yourself?,” he lists in a recurring feature called “Weird (and Worrying) Questions From the What If? Box.” These get no reply, aside from (as in the previous example) a small cartoon dude asking “. . . Karl, is everything OK?”

Munroe’s funniest material often arises after he’s riffed beyond the question at hand to imagine something even more absurd. When someone asks what would happen if the earth’s population jumped up and down at the same time,
Munroe tells us “The crowd takes up an area the size of Rhode Island,” adds up their combined poundage, and deduces that nothing much would happen.

The weirdness begins when he fantasizes the fates of all those fresh Rhode Islanders. Massive cellphone failure, language barriers, food shortages, violence. “The state becomes a chaotic patchwork of coalescing and collapsing social hierarchies.” Mwahaha. A little stick figure girl quips, “I should get back to Dublin.”

To balance every calculation of Yoda’s telekinetic “[f]orce power” (about 19.2 kilowatts, it turns out) or worst-case astrophysical cataclysm, Munroe explores more heady musings, such as the odds of finding your soul mate, or when Facebook will contain more profiles of the dead than living. When he predicts the effects of a magnitude minus-7 Richter-scale earthquake — “[a] single feather fluttering to the ground” — we feel the tug of Munroe’s playful yet existentially-tinged worldview, and all that geek logic and number-crunching becomes unexpectedly poignant.

Ethan Gilsdorf is the author of “Fantasy Freaks and Gaming Geeks.” Contact him at or on Twitter @ethanfreak.