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Summary: What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions by Randall Munroe

What If? 2 (2022) is Randall Munroe’s follow-up to the New York Times best-selling What If? Like its predecessor, it comprises Munroe’s serious scientific answers to the absurd, funny, and whimsical questions submitted to him by readers, ranging from “How big would a snowball be if rolled from the top of Mt. Everest to the bottom?” to “Could a person eat a cloud?”

Introduction: Serious silliness.

How was the universe made? What is the meaning of life? What happens to us after we die? And how many humans would a Tyrannosaurus Rex need to eat to reach its recommended daily caloric intake?

This summary can’t tell you the answers to the first three questions – but it might just give the answer to that last one!

Randall Munroe is the creator of the beloved webcomic xkcd as well as a physicist and a NASA alum. And he believes there’s no such thing as a silly question. Since 2012, Munroe has been inviting readers of his blog to send in the most absurd hypothetical questions they can think of – and answering them as seriously and scientifically as possible. This summary collects Munroe’s answers to some of the strangest questions he’s ever received. Yes, like that one about the Tyrannosaurus Rex.

The answer, by the way, is about half a human adult, or one ten-year-old child. Or, if you want to avoid a scenario where you’re eaten by a T. Rex and there’s a McDonald’s nearby, approximately 80 Big Macs.

Book Summary: What If? 2 - Additional Serious Scientific Answers to Absurd Hypothetical Questions

What would happen if Jupiter was shrunk to the size of a house and placed in a suburban street?

Do you want the bad news first, or the good news?

Well, let’s go with the good news: Jupiter is roughly the same density as water. If Jupiter was house-sized – so, let’s say about 50 feet wide – it would only weigh 2,500 tons. Meaning, your new neighbor isn’t about to mess around with your gravity by forming a black hole.

The bad news is that Jupiter isn’t actually made of water. Before Jupiter was, well, Jupiter, it was a big diffuse cloud of gas floating through space. Then, gravity caused this gas cloud to collapse in on itself. When gas is compressed it gets hot. Seriously hot. Jupiter, much like Earth, is formed of a thin, cool surface layer that keeps a lid on a scorching hot interior. As in, tens of thousands of degrees hot. Like all things that are blazing hot and super-compressed, Jupiter’s interior wants to expand. It doesn’t, but only because its own super-strong gravitational forces counteract that impulse.

Shrink Jupiter down to the size of a house and that massive gravitational force disappears.

So here’s what would happen.

Jupiter would expand rapidly outward in a boiling-hot fireball. That’s going to have quite a negative impact on property values in your street; because your street is going to be obliterated. In fact, your whole neighborhood is toast.

But, hey, let’s finish off with some more good news. This explosion will be fairly contained. When it’s not densely compressed, Jupiter’s molten hot core will cool rapidly. And Jupiter will return to its original form – as diffuse clouds of gas floating through the sky.

If the territories of Earth’s countries extended into the sky, which country would own most of the galaxy?

If every country’s territory extended infinitely upward, then Australia would be known not just as the land of kangaroos and the Hemsworth brothers but as the controller of the galaxy. How does this work?

Well, the Earth rotates, meaning that galactic airspace would actually change hands from country to country over the course of every 24 hours. But countries in the Southern Hemisphere, like Australia, have an unfair advantage here. The North Pole points away from the center of the Milky Way, leaving the southern hemisphere advantageously angled toward the galaxy’s core. The galaxy’s core – which by the way is a supermassive black hole – would rotate through the airspace of Australia, South Africa, Lesotho, Brazil, Argentina, and Chile. When the galaxy’s core was centered in Australian airspace, it would be able to lay claim to more galactic territory than any other country.

The Northern Hemisphere isn’t left with nothing, though. It’s angled toward the outer galactic disk where there’s plenty more cool stuff happening. For example, right as the galaxy’s core passes across the Pacific Ocean in the Southern Hemisphere, a black hole known as Cygnus X-1 would pass over the airspace of North Carolina. Cygnus X-1 is currently very busy devouring a supergiant star – and claiming a supergiant, star-devouring black hole as part of your airspace is pretty metal.

As well as Cygnus X-1, the galaxy’s outer disk contains millions of planetary systems. Like the star 47 Ursae Majoris which is known to have three planets orbiting it and would pass through US airspace every day. Let’s say there’s life on even one of those planets. For 12 minutes out of every 24 hours, any crimes committed on one of those three planets would technically fall under the legal jurisdiction of the state of New Jersey. Of course, by the time it came to prosecute, the statute of limitations would have likely elapsed: the commute from 47 Ursae Majoris to a New Jersey district court would take approximately 40 light years.

How many people would you need to actually build Rome in a day?

First things first – we all know how the expression goes. Rome was categorically not built in a day. But could it have been?

Well, the question assumes that simply putting more people on the job would speed up its completion. That’s almost definitely not the case as anyone who’s ever tried to plan a get-together of three-plus people can tell you; more people can mean more problems. And in the case of building Rome in one day, those problems include but aren’t limited to training and organizing a massive number of people to do specialized construction work all while avoiding bottlenecks as enormous crowds of laborers move around the relatively small city and coordinating supply chains to deliver huge loads of building materials when and where they’re needed.

But, hey, let’s go with the question anyway. A civil engineer called Daniel M. Chan has come up with a nifty formula for estimating how long a construction project will take to complete based on its cost and its actual size. Let’s say, using a very rough guesstimate, that Rome has a real estate value of US $150 billion. And let’s say that construction costs work out to about 60 percent of that value. So $90 billion. According to Chan, that means Rome would take between ten and 15 years to build. Not quite a day.

But let’s try and speed this up. According to the author’s estimate, it would take roughly 2 billion hours of labor to build Rome from start to finish. In other words, if eight billion people were on the job they could knock it over in little more than 15 minutes.

OK, this approach might work for more straightforward building projects like roads and standard buildings. But Rome is a city filled with artistic and architectural masterpieces, like the ceiling of the Sistine Chapel. How can we account for that when we’re working out how many people it would take to build Rome in a day?

It took the famous Renaissance artist Michelangelo four years to cover all 523 square meters of the Sistine chapel’s ceiling in his stunning frescos. That works out to about one square meter every 16 hours. Rome’s area is 1,285 square kilometers. So it would take 20 billion hours, working at Michelangelo’s meticulous pace to construct all of Rome. If eight billion workers all pitched in, they could do it in about 2 and a half hours.

So there you are – eight billion people could build Rome in somewhere between 15 minutes and two-and-a-half hours. Next question! How much spaghetti is needed to feed 8 billion people lunch after they’ve just built Rome in under a day?

Assuming you’re in a totally indestructible glass tube extending from the ocean’s surface to its bottom, what would it be like to stand at the deepest part of the ocean?

The answer to that question depends on whether or not you brought a nice thick sweater and a torch with long-life batteries down to the bottom of the ocean with you. If your totally indestructible glass tube stretched from above the surface of the sea right down to the deepest depths of the Mariana trench, you’d be three times deeper below sea level than the world’s deepest mines. In a mine, the deeper you go, the hotter you become. That’s because mines are drilled into rocks, which grow hotter the closer they get to Earth’s core. But the temperature at the bottom of the ocean is only slightly above freezing. So, you’re going to be cold. On the plus side, you’ll be able to see one of the least-visited sites on the planet, the floor of the Mariana Trench.

Just kidding. You won’t be able to see much at all, unless the sun passes directly over the mouth of your glass tube, which it will do exactly twice a year, around April 20 and August 23. After that, it’s another six months of total darkness. Unless that appeals, you should probably get in your elevator and come out.

You did put an elevator in your totally indestructible glass tube, right?

I’ll take that silence to mean no. Well, at this point, you could always knock a hole in the side of your glass tube to let in water, which, in turn, will carry you up above sea level. But make sure you’re standing well clear of the hole itself. When that hole opens, a supercharged jet of seawater is going to charge through it. In fact, even if you could somehow stand clear of the hole, just letting a whole bunch of water rush into the bottom of your tube isn’t the best idea. The column of water that would rush upward would have a Mach number of 1.3. If you tried to ride this column of water upward, you wouldn’t survive the impact. Your best bet would be to let water through in a slow controlled fashion – perhaps through a tap at the bottom of the tube. After your tube has filled up with a kilometer or two of seawater, only then would it be safe to fully open the bottom of the tube to let more seawater rush in. And provided you had a giant plunger on hand to keep all the water safely underneath you, you’d be back above sea level in less than a minute, traveling on a giant fountain of icy water at a speed of 500 miles per hour.

Okay, let’s revise that packing list, shall we? Sweater, torch, tap, giant plunger … you’re good to go!

Could a person eat a cloud?

Clouds are made of air and water. And water’s edible, right? Or potable, at least? So in theory, there should be nothing to stop a person from eating a cloud – apart from, you know, common sense, having better things to do with one’s time and the challenges of getting a cumulonimbus to sit still on your plate.

But here’s the problem. Unless you could come up with some way to squeeze the air out of the cloud before you started chewing it, it’s going to be impossible to ingest.

Let’s say you put a piece of cloud in your mouth. You can swallow the water it contains. But you’ll be left with an abnormally large quantity of air inside you. Your body will need to let the air escape – in this case, by burping. The thing is, once air has been inside your body, it absorbs moisture. When you burp out that nice warm moist air and it meets the cool outside air, it will condense. And form cloud. More cloud. You’ll end up burping cloud faster than you can eat it.

Let’s imagine you could extract a cloud’s water content by passing the cloud through a very fine sieve or by ionizing the water drops and extracting them with an electrical charge. In that case, you’d definitely be able to eat a smaller-sized cloud. A cloud the same size as a small house would contain between 2 and 3 liters of water, which just so happens to be the maximum amount of liquid the average human stomach can comfortably hold at one time.

There’s certainly no other foodstuff you’d be able to eat in house-sized quantities. Even an extremely low-density food like cotton candy is way denser than a cloud – at most, you’d be able to eat about 1 cubic foot of cotton candy in one sitting. On the plus side, it might be more delicious than your average cumulonimbus.

How big would a snowball grow if it was rolled from the top to the bottom of Mt. Everest?

Snowballs only grow in size when they’re rolled through wet, sticky snow which adheres to their surface. Mt. Everest is covered in dry, fluffy snow. So, even if you did manage to roll a snowball from the top to the bottom of Mt. Everest, your snowball would stay about the same size it was when you first rolled it.

Hypothetically, if Mt. Everest were covered in wet, sticky snow, how big would your snowball grow? Well, the bigger a snowball gets, the more snow it picks up. So it stands to reason that the more time a snowball spends rolling, picking up more and more snow, the faster it will grow. After all, we wouldn’t use the word snowballed to refer to exponential growth if it weren’t 100 percent accurate … would we?

Yeah … about that. The more snow a snowball picks up, the greater its surface area becomes. Each new patch of snow has to cover way more area, meaning a snowball’s growth will actually slow the longer it spends rolling. Unless you’re using snowballed to refer to something that starts growing at exponential speed and then slows right down, you’re not using it right.

Now, the journey from the summit of Mt. Everest to base camp isn’t all downhill slope – there are lots of flat glacial valleys where a snowball would roll to a stop. But the mountains’ three main slopes each have drops of about 5 kilometers. Theoretically, a snowball rolling down one of these slopes could ultimately grow to between 10 and 20 meters wide.

Theoretically – but not practically. In reality, a snowball would collapse under its own weight before it reached a width of more than a few meters. It would then break up into smaller snowballs, which would each start to grow until they, too, broke apart into even more smaller snowballs, which would each start to grow, and so on and so on.

In short, if you tried to roll a snowball from the top to the bottom of Mt. Everest, it wouldn’t grow very big. The avalanche you might cause, on the other hand, could be fairly substantial.


Science doesn’t have to be serious, and math needn’t be monotonous! Stretching your brain by trying to find the answers to silly questions is a great way to train your analytical mind, while still having some fun.


The book [What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions] by [Randall Munroe] is a sequel to the bestselling book [What If? Serious Scientific Answers to Absurd Hypothetical Questions] by the same author. The author is a former NASA roboticist and the creator of the popular webcomic xkcd. The book is a collection of humorous and informative answers to some of the most bizarre and improbable questions that the author has received from his readers or imagined himself.

The book covers a wide range of topics, such as:

  • What would happen if you rode a helicopter blade, built a billion-story building, made a lava lamp out of lava, or jumped on a geyser as it erupted?
  • How to create an emergency pantry stocked with enough food for the timeframe of your choice—from two weeks to three months to a full year
  • How to cook food and boil water when your kitchen appliances aren’t working
  • How to safely heat and light your home when the power is out
  • How to deal with medical emergencies and mental health issues when professional help is not available
  • How to communicate with the outside world and stay informed of the situation
  • How to deal with common problems and challenges that may arise during a disaster

The book is written in a witty and engaging style, with detailed explanations, calculations, diagrams, and illustrations that make it easy to understand and enjoy. The book also provides useful tips and tricks that can help you solve everyday problems or satisfy your curiosity. The book is suitable for anyone who loves science, humor, or both.

The book is available in hardcover, paperback, audiobook, and ebook formats. The hardcover edition has 368 pages and costs $17.71 on Amazon. The paperback edition has 368 pages and costs $17.88 on Amazon. The audiobook edition has a length of 6 hours and 30 minutes and costs $13.99 on Amazon. The ebook edition costs $14.99 on Amazon.

The book has received positive reviews from critics and readers who have praised its originality, creativity, and humor. The book has a rating of 4.5 out of 5 stars on Amazon based on 9,537 ratings. The book has also been nominated for the Goodreads Choice Award for Best Nonfiction in 2022. Some of the comments from the reviewers are:

  • “This book is hilarious, fascinating, and educational. It answers some of the most absurd questions you can think of with serious scientific rigor and logic. It also makes you wonder about things you never thought of before. It’s a great book for anyone who likes science or comedy or both.”
  • “I loved the first What If? book and this one is even better. It has more questions, more answers, more illustrations, and more fun. It’s amazing how much research and effort the author puts into each answer. He also adds some personal anecdotes and jokes that make it more entertaining. It’s a book that you can read over and over again.”
  • “This book is a perfect blend of science and humor. It answers some of the most ridiculous questions you can imagine with serious scientific facts and calculations. It also shows you how to apply science to everyday situations and problems. It’s a book that will make you laugh, learn, and think.”

In conclusion, [What If? 2: Additional Serious Scientific Answers to Absurd Hypothetical Questions] by [Randall Munroe] is an excellent book that can entertain and educate you with its scientific answers to absurd hypothetical questions. It covers a wide range of topics, from physics and astronomy to biology and psychology. It provides clear and detailed explanations, calculations, diagrams, and illustrations that make it easy to understand and enjoy. It’s a must-read for anyone who loves science, humor, or both.

Alex Lim is a certified book reviewer and editor with over 10 years of experience in the publishing industry. He has reviewed hundreds of books for reputable magazines and websites, such as The New York Times, The Guardian, and Goodreads. Alex has a master’s degree in comparative literature from Harvard University and a PhD in literary criticism from Oxford University. He is also the author of several acclaimed books on literary theory and analysis, such as The Art of Reading and How to Write a Book Review. Alex lives in London, England with his wife and two children. You can contact him at [email protected] or follow him on Website | Twitter | Facebook

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