What If? Serious Scientific Answers to Absurd Hypothetical Questions, written by Randall Munroe and published in 2014, is a collection of humorous yet sound answers to unusual queries about science. From how many laser pointers it would take to light up the Moon to how many LEGO bricks would be needed to bridge the Atlantic Ocean, What If? bravely answers dozens of weird inquiries with answers that, though true, are often stranger than the questions they resolve.

Author, cartoonist, and engineer Randall Munroe is the creator of the popular web comic xkcd, whose stick figures also illustrate the text of What If? After earning a degree in physics, Munroe worked for NASA as the Langley Research Center in Virginia. For his work on xkcd, he was nominated for the Hugo Award for Best Fan Artist in 2011 and 2012, then won the Hugo Award for Best Graphic Story in 2014. An asteroid is named in his honor.

The ebook version of the original 2014 edition forms the basis for this study guide. Readers are cautioned that some of the descriptions of unusual physical effects on humans are slightly gruesome.

Summary

Munroe warns readers not to try the activities described in the book, most of which are dangerous or lethal, illustrating the physics of extreme situations.

Each chapter begins with at least one question, although some address more than one. However, most chapters focus on a single question, with fairly elaborate discussions that lead to several minor conclusions and one major one. A questioner wonders what would happen if the Earth suddenly stopped spinning; the answer is that the atmosphere, continuing to spin, would become a giant wind storm that would destroy everything in its path and kill nearly all humans, except those living near the poles or in underground tunnels.

A baseball pitched at 90% of the speed of light would cause an explosion that would wipe out the stadium and much of the surrounding city. For protection from radiation, it’s safer to swim at the surface of a pool of water that contains spent nuclear fuel rods than to walk around outside. The New York City area, 500 million years ago, was a lifeless set of islands off the coast of Africa. The odds of finding one’s soul mate are one in 10,000. The amount of laser light required to illuminate the Moon would cause the Earth to catch fire, killing everyone.

A periodic table of the elements made of bricks of each element would quickly catch fire and then explode with the force of a nuclear bomb. If everyone on Earth stood in Rhode Island and jumped together, it would make a big noise but wouldn’t affect the planet. A mole is a number, 6x10^23; it’s also a creature, and a mole of moles would be as big as a planet the size of the Moon. A standard hair dryer, left running in a one-meter-square box, will heat the box to 140 degrees; an indestructible box containing a hair dryer putting out 187 terawatts would cause massive worldwide destruction.

If humans disappeared, the last artificial light left burning would shine for centuries from spent underground nuclear fuel that glows with Cherenkov radiation. A large Russian-made machine gun, the GSh-6-30, fired at the ground can launch the user upward with 40 Gs of acceleration. If a person floated up from the ground steadily at one foot per second, they would suffocate after eight hours and then freeze solid. A submarine orbiting the Earth would suffer heat loss and run out of oxygen in about three days.

A printer can counterfeit a million $100 bills a year, but these would be dwarfed by the 1 billion bills printed legally each year. A nuclear bomb detonated in a hurricane would have little effect on the storm. Small turbines attached to downspouts in a rainy area would save a user $1.14 in electricity each year. All 300 sextillion stars in the universe can be named using a system of 24 letters. To increase the air temperature in front of her by 20 degrees Celsius, a bicyclist would have to ride at 200 meters per second, five times faster than the fastest pros; the heat would be fatal. Measured in computer drives, the internet would barely fill up an oil tanker. C4 strapped to a boomerang is a bad idea if it misses the initial target.

A bullet traveling through a lightning bolt would be unaffected, but one struck by lightning while lying still would melt. Though humans are slow at calculations, their total brain capacity still exceeds that of all computers. An asteroid 1.75 meters across would have to weigh 500 million tons to possess Earthlike gravity, but you could go into orbit around it by running and jumping off.

A steak dropped straight down from space would get charred, but the interior would remain uncooked. A hockey puck would have to travel faster than Mach 2 to knock a goalie into the goal. To avoid a cold, everyone on Earth would have to spread out until they were evenly spaced 77 meters apart. A glass half full of water but with a vacuum in the bottom would break, launching the top half upward. Because TV and radio signals are moving to the internet, Earth no longer sends out loud broadcasts for aliens to observe. Without their DNA, people would die within hours. Airplanes can’t fly on planets with no atmosphere, but a small plane could fly on Saturn’s moon Titan until it froze in the minus 200-degree weather.

When Yoda lifted the X-wing out of a bog, he used about 25 horsepower. The state with the most airline flyovers is Virginia. It would take 10 tanks of helium to fill a balloon big enough to save someone who fell out of an airplane. Getting every person off the planet would use all available resources and possibly destroy the Earth. A human clone has a vastly increased chance of severe genetic damage.

The highest a person can throw roughly equals the height of 14 giraffes. Trillions of neutrinos travel through us each second; it would take a supernova, exploding at the distance of the sun, to give a person a lethal dose of neutrinos. Driving fast over a speed bump doesn’t cause injuries, but it destroys the car’s tires and suspension. Two people, walking randomly on an Earth-type planet, would get within a kilometer of each other once every 3,000 years.

It’s much cheaper for an orbiting spacecraft to use a heat shield to return to Earth than carry enough fuel to slow itself out of orbit. To transfer files, FedEx will probably always have more capacity than the internet. The tallest vertical drop, lasting 26 seconds, is Mount Thor in Canada; the longest wingsuit base jump is 3.3 minutes. Arrows can blot out the sun if a tight column of archers each fires 300 arrows per second. If most of the Earth’s seawater were transferred to Mars, it would flood that planet until only a few volcanoes peeked out.

The number of possible Twitter messages is so large that a billion people reading them for 10 billion years would hardly make a dent in them. A bridge from London to New York made of LEGO bricks would cost trillions of dollars; it would be cheaper to move the entire city of London to New York. The longest possible sunset, seen while driving a car, is 95 minutes. The odds that a person you call up has just sneezed is one in 40,000. If the Earth grew by one centimeter per second, after 100 years, its gravity would have increased sixfold, and people would no longer be able to survive. An arrow shot through calm air in zero gravity would travel five to ten kilometers, the trip lasting several hours.

If the sun suddenly went out, several things would get better, but the downside would be the death by freezing of all humans. Six printers can keep up with the editorial changes to Wikipedia, but the cost would be several million dollars per year. At the present rate of membership, there’ll be more dead people on Facebook than live ones by about 2130. Though the British Empire today contains mainly a few scattered islands, the sun still never sets on it. It’s not possible to stir tea fast enough to boil it.

If a day’s worth of lightning struck the same spot at once, it’d deliver enough power to run the United States for five minutes, but it also would cause two atom bombs’ worth of damage. The human who got farthest from everyone else probably was one of the astronauts in the lunar orbiter when it was on the side of the Moon opposite from the astronauts who landed there. If all the rain in a thunderstorm landed in one giant drop, it would destroy everything for miles around.

The odds of a student getting a perfect score on the SAT’s math section by guessing randomly are essentially zero. A bullet made of solid neutrons would be so heavy and its gravity so strong that, if you touched it, your finger would be torn open, and all your blood would leak out, forming a ball of blood around the bullet. The worst earthquakes generally have a Richter number of nine; a magnitude 15 quake would explode the Earth.

Two dozen other questions, scattered throughout the book, get quoted for their sheer absurdities but go unanswered. A chapter of further resources appears at the end.