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53 pages 1 hour read

Randall Munroe

What If?: Serious Scientific Answers to Absurd Hypothetical Questions

Nonfiction | Book | Adult | Published in 2014

A modern alternative to SparkNotes and CliffsNotes, SuperSummary offers high-quality Study Guides with detailed chapter summaries and analysis of major themes, characters, and more.

Chapters 31-50Chapter Summaries & Analyses

Chapter 31 Summary: “Weird (and Worrying) Questions from the What If? Inbox, #6”

Question: “What is the total nutritional value (calories, fat, vitamins, minerals, etc.) of the average human body?” (142). A cartoon suggests that the questioner needs the answer quickly.

Question: “What temperature would a chainsaw (or other cutting implement) need to be at to instantly cauterize any injuries inflicted with it?” (142). A cartoon suggests that the questioner needs the answer quickly.

Chapter 32 Summary: “Yoda”

Question: “How much Force power can Yoda output?” (143).

Yoda’s greatest feat of strength is raising the X-wing spacecraft from a swamp on planet Dagobah. Assuming, per Wookieepedia, that gravity on Dagobah is 90% of Earth’s, estimating the size of the X-wing at five metric tons, and judging, per the relevant Star Wars film, the craft’s rate of rise at 0.39 meters per second, the amount of power Yoda generates is roughly 19 kilowatts or 25 horsepower.

When the emperor zaps Luke, the power generated—comparable to that emitted in the lightning from a Tesla coil—is roughly 10 kilowatts, though sustained imperial zaps might reach megawatt levels.

Chapter 33 Summary: “Flyover States”

Question: “Which US state is actually flown over the most?” (146).

The most frequently flown-over state is Virginia. Next are “Maryland, North Carolina, and Pennsylvania” (147). Much of the cause is Atlanta International in Georgia, the world’s busiest airport, with constant flights up the busy eastern US corridor.

Many large, lightly populated states like Wyoming and Idaho have high ratios of flights-over to flights-to. The least flown over is California, partly due to fueling restrictions that force international travelers to land and refuel there.

Chapter 34 Summary: “Falling with Helium”

Question: “What if I jumped out of an airplane with a couple of tanks of helium and one huge, un-inflated balloon? Then, while falling, I release the helium and fill the balloon. How long of a fall would I need in order for the balloon to slow me enough that I could land safely?” (150).

It would take ten large rental tanks, containing 250 cubic feet of helium each, to fill a balloon large enough to slow the fall. Especially in the thin air of airliner altitude, the tanks will drop at high speed; rapid balloon inflation and tossing empty tanks become priorities.

Chapter 35 Summary: “Everybody Out”

Question: “Is there enough energy to move the entire current human population off-planet?” (153).

Lifting a person off the planet requires four gigajoules, or one megawatt-hour—a month’s household use of electricity. To lift everyone would take about 5% of annual worldwide electricity use. However, more energy is needed to lift the rocket itself and its fuel load: “A 1-ton craft needs 20 to 50 tons of fuel” (155). Lifting all of humanity thus would require multiple trillions of tons of fuel. Alternatives include space elevators and nuclear propulsion.

Chapter 36 Summary: “Weird (and Worrying) Questions from the What If? Inbox, #7”

Question: “In Thor the main character is at one point spinning his hammer so fast that he creates a strong tornado. Would this be possible in real life?” (157). No.

Question: “If you saved a whole life’s worth of kissing and used all that suction power on one single kiss, how much suction force would that single kiss have?” (157). No comment.

Question: “How many nuclear missiles would have to be launched at the United States to turn it into a complete wasteland?” (157). No comment.

Chapter 37 Summary: “Self-Fertilization”

Question: “If a woman were to have sperm cells made from her own stem cells and impregnate herself, what would be her relationship to her daughter?” (158).

It takes two parents to make a baby. Each parent contributes a copy of their DNA; any defective genes, which might cause diseases, usually get overridden by the other parent’s healthy genes. If a fetus gets both sets of DNA from the same parent, the odds of getting both copies of any defective genes rise sharply. This is why people don’t mate with their close relatives: the chance of inheriting two deficient copies—the “inbreeding coefficient”—goes up, and the chance for birth defects rises accordingly.

Chapter 38 Summary: “High Throw”

Question: “How high can a human throw something?” (168).

Humans are the only creature that can hit targets reliably by throwing. It’s hard to do: A baseball pitcher must time the ball’s release to within half a millisecond, yet it takes five milliseconds for that signal to travel down the arm. This is like dropping a drumstick from ten stories up and having the stick strike the drum right on the beat.

Throwing a ball skyward is harder still. The average person can hurl a ball up about 15 meters, the height of three giraffes; a professional pitcher could manage 10 giraffes or more.

Chapter 39 Summary: “Lethal Neutrinos”

Question: “How close would you have to be to a supernova to get a lethal dose of neutrino radiation?” (174).

Neutrinos almost never interact with other forms of matter. Trillions pass through your body every second; on average, a single neutrino will interact with your body once every few years. A lethal dose would require an enormously powerful neutrino event.

A supernova—a giant star exploding—might fit the bill. One as far away as the sun would be a billion times brighter than a hydrogen bomb going off against your eyeball. At the sun’s distance, even if the explosion didn’t obliterate you, the number of neutrinos released by a supernova would be significant enough to deliver a fatal dose of radiation, about four sieverts.

Chapter 40 Summary: “Weird (and Worrying) Questions from the What If? Inbox, #8”

Question: “A toxin blocks the ability of the nephron tubule reabsorption but does not affect filtration. What are the possible short-term effects of this toxin?” (178). A cartoon lampoons this question.

Question: “If a Venus fly trap could eat a person, about how long would it take for the human to be fully de-juiced and absorbed?” A cartoon character says, “Seven years, if the person is chewing gum” (178).

Chapter 41 Summary: “Speed Bump”

Question: “How fast can you hit a speed bump while driving and live?” (179)

Driving over a speed bump at high velocity usually won’t cause injury, but it will damage the car. At speeds much higher than 120 miles per hour—commonly the upper limit set by the engine’s computer—the air passing over and under a vehicle can cause it to rise off the ground and then crash.

Driving over the speed limit in Pennsylvania generates a ticket that adds $2 for every mile over the limit. A car traveling at 90% of the speed of light would be subject to a fine of more than $1 billion. Also, it would destroy much of the city.

Chapter 42 Summary: “Lost Immortals”

Question: “If two immortal people were placed on opposite sides of an uninhabited Earthlike planet, how long would it take them to find each other?” (183).

Assuming they walked randomly 12 hours a day, they’d meet in 3,000 years. This requires, though, that they always can see at least one kilometer in any direction—no deep forests or other such viewing obstacles.

Smarter search patterns include walking along coastlines—people are more likely to be there than deep in the interior—and leaving markers that point where they’re headed. Also, they should follow quickly any fresh trails: The other person may be walking there.

Chapter 43 Summary: “Orbital Speed”

Question: “Is it possible for a spacecraft to control its reentry in such a way that it […] would not require the expensive (and relatively fragile) heat shield on the outside?” (187). Two similar questions also are cited.

Getting to space is pretty easy; staying there is hard. Earth’s gravity is nearly the same in low orbit; you must hurtle at eight kilometers per second—10 times faster than a rifle bullet—so that you’ll fall around the planet's curve. Using rockets to slow back down would double fuel requirements. It’s much cheaper to use a heat shield and slam into the air.

Chapter 44 Summary: “FedEx Bandwidth”

Question: “When–if ever–will the bandwidth of the Internet surpass that of FedEx?” (192).

In 2014, FedEx planes were capable of shipping computer drives containing 100 times as much data as the entire internet. As internet speeds increase, so does the capacity of drives, so it’s unclear when, if ever, that ratio will change. For any given file transfer, the internet is much, much faster; despite that, large companies sometimes ship physical copies of giant-sized data transfers.

Chapter 45 Summary: “Free Fall”

Question: “What place on Earth would allow you to free-fall the longest by jumping off it? What about using a squirrel suit?” (195).

Canada’s Mount Thor, with the world’s tallest vertical face, permits a human to fall freely for 26 seconds. A jumper in a wingsuit can extend fall time to well over a minute. The world-record wingsuit flight from a mountain, jumped from the Eiger in Switzerland, is just under three and a half minutes.

Chapter 46 Summary: “Weird (and Worrying) Questions from the What If? Inbox, #9”

Question: “Could you survive a tidal wave by submerging yourself in an in-ground pool?” (199). The author believes this question satisfies the requirements for both sounding dumb and being actually dumb.

Question: “If you are in free fall and your parachute fails, but you have a Slinky with extremely convenient mass, tension, etc., would it be possible to save yourself by throwing the Slinky upward while holding on to one end of it?” (199). No comment.

Chapter 47 Summary: “Sparta”

Question: “In the movie 300 they shoot arrows up into the sky and they seemingly blot out the sun. Is this possible, and how many arrows would it take?” (200).

Assume a battalion of archers 40 rows deep and crammed together four to a square meter—“mosh pit” density—who somehow can each fire nearly one arrow per second. The arrows will block less than 2% of the sunlight. Gatling-type bows releasing 300 arrows per second, launched north at dawn, would shade 99% of the morning sunlight, but they would overfly the battlefield and miss everyone.

Chapter 48 Summary: “Drain the Oceans”

Question: “How quickly would the oceans drain if a circular portal 10 meters in radius leading into space were created at […] the deepest spot in the ocean?” (204).

The oceans are so big that, despite the enormous amount of water pouring into the portal, sea level would drop only one centimeter per day, and the process would take hundreds of thousands of years. When the water level falls by five kilometers, the continents will have blended together, an enormous ecological disaster will occur, and the oceans will be reduced to inland seas. The drain is no longer connected to most of the remaining seawater, and the process stops.

Chapter 49 Summary: “Drain the Oceans: Part II”

Question: “Supposing you did drain the oceans, and dumped the water on top of the Curiosity rover, how would Mars change as the water accumulated?” (210).

Most of Earth’s seawater, transferred to Mars, would slowly drown nearly all the land area; only a few volcanic islands would break the surface. The new seas would freeze over; the ice would migrate toward the poles through a long process.

Chapter 50 Summary: “Twitter”

Question: “How many unique English tweets are possible? How long would it take for the population of the world to read them all out loud?” (217).

There are about 2x10^46 possible “meaningfully different” tweets in English on Twitter. If a billion people start reciting these tweets continuously, “they won’t be able to make a meaningful dent in the list in the lifetime of the Earth” (200).

Chapters 31-50 Analysis

Sometimes the answer to a science question isn’t exact but a percentage based on the odds of something occurring. Many of the questions in What If? are answered in this form. Chapter 37, for example, explores the odds that a person who gives birth to her own clone will find that the baby has birth defects. Chapter 39 describes the startlingly small odds that any of the millions of trillions of neutrinos that course through a person’s body every year will touch it.

Chapter 42 discusses how to improve the odds of meeting up with another person. Such searches often end successfully at places called focal points or Schelling points, named for Thomas Schelling, the economist who developed the concept. He realized that “people can often concert their intentions or expectations with others if each knows that the other is trying to do the same.” (Schelling, Thomas. The Strategy of Conflict. Harvard University Press, 1980, page 57.)

The way they do this is to reason out where the other person will be. If, for example, someone tells you, “Meet me in Manhattan tomorrow at noon,” you can make an intelligent guess as to where they’d go if they had the same instructions. In Manhattan, the most famous meeting place is Grand Central Station, and, in one test, a majority of subjects did decide to meet there (Schelling, Page 55 footnote). Clearly, this isn’t a perfect system—only a majority, and not all, of test subjects, got it right—but it’s much better than making a random choice.

Chapter 45 mentions base jumps made by people wearing wingsuits. It’s hard to stay aloft for long in such suits—which have material stitched between arms and legs that, stretched out, serve as wings—so some divers have taken to airplanes to lengthen the trip. The longest wingsuit jump from an aircraft is more than nine minutes. (“Longest (Duration) Wingsuit Flight.” Guinness World Records.)

A number of the book’s questions—“How many Lego bricks would it take to build a bridge capable of carrying traffic from London to New York?” (222)—involve scales so absurdly large that they beggar the imagination. Questioners must compete to get their queries answered publicly, so they’re naturally tempted to posit extreme situations.

The author, well versed in mathematics, has the tools to provide the answers; his solutions have the élan and technical virtuosity of a concert musician. Thus, one reason that readers ask, and the author answers, unusual questions is so that he can amaze us, both with the enormity of the answers and the dexterity of his mental performance. His efforts should earn him a standing ovation; perhaps his Hugo Award for Best Graphic Story, earned during the same year What If? was published, will suffice.

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By Randall Munroe