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"I’ve always thought that one of the the great things about physics is that you can add more digits to any number and see what happens and nobody can stop you."
Randall Munroe in "Diamond"

What If? is a blog by Randall Munroe, the creator of the Stick-Figure Comic xkcd, started 10 July 2012. Updated erratically, he answers off-the-wall reader questions using math, science, and xkcd-style cartoons. Randall has a Twitter feed, @whatifnumbers, of numbers he comes up with while writing the blog. He's also published a book, What If?: Serious Scientific Answers to Absurd Hypothetical Questions, containing several of the more popular answers and some new ones. The book received a follow up, What If 2, in 2022.

Not to be confused with the trope What If? or What If?, a Marvel series speculating on changes to the Marvel universe.

Think of it as textual MythBusters with hypothetical scenarios.

This blog provides examples of the following tropes:

  • 20% More Awesome: The first image of "Great Tree, Great Axe", where all the seas in the world are gathered into one.
    Megan: I'd say the 30% increase in width makes it 20% more brooding and about 9% more majestic.
  • Absurdly High-Stakes Game: In "Cannibalism", discussing how it would be determined who eats whom, he suggests flipping coins and making it into "the tournament bracket to end all tournament brackets."
  • Acquainted with Emergency Services: One of the "Weird and Worrying Questions" from someone named Brittany is how many cats it would take to bring down an airliner by meowing at the right frequency. The illustration is Randall calling the FAA.
    Is there a "Brittany" on the no-fly list? ... Yes, with cats. That sounds like her. OK, just making sure you were aware.
  • Added Alliterative Appeal: The Alt Text of the first image in "Three Wise Men".
    "several star-struck sages spiral southward"
  • The Air Not There: Averted; the presence of air is accounted for when imagining how each scenario would turn out.
    • "Relativistic Baseball". The ball, moving at 90% the speed of light, would never even reach the batter, because the ball will undergo nuclear fusion with the air molecules in the atmosphere. The result would be similar to a thermonuclear bomb exploding.
    • "Glass Half Empty". There are three glasses, the original water and air one, and two with vacuum and water. If the top half is vacuum, not much would happen other than a loud sound caused by air rushing in into the vacuum. If it were the bottom half, the results would be much more dramatic.
    • Later installments that involve something magically disappearing (like in "Vanishing Water") assume that the space left is replaced with air, to avoid a "glass half empty" scenario.
  • All-Natural Snake Oil: "Europa Water Siphon" discusses the idea of siphoning water from Europa and selling it as bottled water. Randall mentions that although there's no point in this, since water from Europa is chemically the same as water in Earth, the plan could work with the right marketing.
  • Alt Text: The first few entries didn't have any alt text for the images. However, around the time that "Tie Vote" was published, the author started adding xkcd-style jokes and comments to the alt text. He's since gone back and added them to every single image, but these after-the-fact versions are only short descriptions of the image rather than jokes (although some of them are still funny).note 
  • Alien Geometries: In one of the notes in Pyramid Energy, "Assume a spherical pyramid in a vacuum". Obviously, it wouldn't then be a pyramid, but that's part of the joke.
  • Anti-Climax: The book ends this way. In the last chapter, "Richter 15", Randall quickly answers the question of what would happen if a magnitude 15 earthquake hit New York (Earth would be torn to shreds), then decides that after a book filled with horrific and disturbing scenarios, it seems fair to look at some more benign ones, and starts discussing incidents that would trigger the low end of the Richter scale, such as a penny falling off a dog (magnitude -4). The book ends with a scene of Cueball sitting peaceably against a tree, and the caption:
    "Sometimes it's nice not to destroy the world for a change."
  • Apocalypse How: That's how the articles often tend to end. Scope and severity vary. Lampshaded in "Vanishing Water":
    "Why can't the questions ever be, like, 'what if I saw a really good movie' or 'what if I adopted a puppy'?"
    • Subverted with "Richter 15" from the book, where he explores what events would generate a negative reading on the Richter scale, because "sometimes it's nice not to the destroy the world for a change."
    • From the book, the result of making the periodic table out of 1-liter blocks of each element would result in a Class 1/Class 2, as the transuranic elements would decay and produce a massive continuous nuclear blast, obliterating whatever city the table was in and spreading radioactive material all over the world.
    • When "Proton Earth, Electron Moon" is said to result in, by far, the most destructive What-If scenario to date, long-time readers know they're in for something special. The final result of said scenario is a black hole with mass equal to the entire known universe.
  • Artistic License – Cars: A rare one for Randall, but it still happened. A question on how much power can be produced by The Force compares Yoda's power output to that of a Smart Car, with Yoda popping out of the front hood of said car. However, the Smart Car is a rear-engine car, with the front flap covering various auxiliary components.
  • As the Good Book Says...: Parodied.
    • Randall butchers a line from Revelation Chapter 6 in the sixth image of "Great Tree, Great Axe":
      "And I looked and saw the angel open the second seal, a gigantic woodpecker emerged. The people wailed and cowered in terror as its wings blotted out the Sun."
    • Again in the third image of "All the Money", this time butchering 1 Timothy 6:10:
      Alt Text: Dinosaurs loving money is the root of all evil.
  • Attention Deficit... Ooh, Shiny!:
    • "Frozen Rivers" gives us a minor, if amusing, example.
      Main text: Melting ice takes a lot of energy, but the ice in this scenario would be spread out in thin strands across the country, so it would all melt pretty fast.[1]
      Footnote [1]: Strangely, solid ice usually melts faster than snow—not only in terms of weight, but in terms of inches melted per day.[2]
      Footnote [2]: Or[3] centimeters.
      Footnote [3]: Woah, I can nest footnotes!
    • invoked In "Drain the Oceans: Part II", Munroe admits to being a Quicksand Box victim in the alt-text of the eleventh map.
      This looks like the map for a game where I would ignore the objectives and just sail around.
    • Used in "Ink Molecules" to explain why Randall can't remember Avogadro's number.
      Offscreen: OK, did you really pay no attention in chemistry class?
      Randall: I tried! But there was this really cool bird outside the window.
      Alt Text: 'It was this huge hawk eating a pigeon!' 'For the whole semester?' 'There were a lot of pigeons around my school.'
    • In "Phone Keypad": "sasha has a gf; gf has adhd".
      "Ooh, a bird!"
  • Awesome, but Impractical:
    • According to "All the Lightning" from the book, which all but quotes the trope name verbatim:
      Generating power from lightning is like building a wind farm whose blades are turned by a tornado: <strike>awesome</strike> impractical.
    • Hilariously Double Subverted in "Snow Removal". Using a flamethrower to melt snow in front of your car is actually more efficient than using a giant microwave emitter. But it's still hilariously inefficient: you'd make about seventeen feet per gallon of fuel.
  • Baby Planet: Discussed in "Little Planet".
  • Bad News in a Good Way: From "Into the Sun":
    There's some good news: Deep in the Sun, the photons carrying energy around have very short wavelengths—they're mostly a mix of what we'd consider hard and soft X-rays. This means they penetrate your body to various depths, heat your internal organs, and ionize your DNA, causing irreversible damage before they even start burning you. Looking back, I notice that I started this paragraph with "there's some good news." I don't know why I did that.
  • Bad News, Irrelevant News:
  • Bait-and-Switch: In "Bouncy Balls", after noting that a bucket of 3,000 one-inch bouncy balls weighs about as much as a small child, we see a "thought experiment" of a kid being thrown at the hapless test subject, as if the intent is to see the result of the impact of the child and the test subject. Black Hat is, unsurprisingly, the thrower. The test subject catches the child and admonishes the guy throwing the kid. Black Hat then chucks yet another one-inch ball at the test subject.
  • Big Creepy-Crawlies: The last part of "Sun Bug" discusses how big a single firefly would have to be to match the brightness of the Sun. The answer is a firefly the size of the Solar System, which under its mass would collapse into the largest black hole in the universe.
  • Big "NO!": The pilot in this segment doesn't want to fly a Cessna around different planets and moons in our solar system. The rest of the post makes it clear why it's a potentially awesome and very bad idea.
    Alt Text: i do not want to go to space today
  • Bizarre Alien Biology: "Green Cows", or how much food cows would need if they were photosynthetic.
  • Black Comedy: Pretty much every one of these involves some way whatever it is could kill you or make something that's really Squicky. And it's full of jokes.
  • Blown Across the Room: Discussed as part of a list of movie tropes that couldn't happen in real life.
  • Blunt "No":
    • From "Train Loop":
      Gero Walter: Could a high-speed train run through a vertical loop, like a rollercoaster, with the passengers staying comfortable?
      Randall: No.
    • Then he turns it into a Zig-Zagging Trope by Moving the Goalposts until the answer is less definite.
    • "Stirring Tea" has another Blunt No.
      Will Evans: I was absentmindedly stirring a cup of hot tea, when I got to thinking, "aren't I actually adding kinetic energy into this cup?" I know that stirring does help to cool down the tea, but what if I were to stir it faster? Would I be able to boil a cup of water by stirring?
      Randall: No.
    • And again in "Pyramid Energy":
      Michael Marmol: If we could convert the energy to build the Great Pyramid, would it be enough to send a rocket to the Moon and back?
      Randall: No.
    • In the book, one of the "Weird (and Worrying) Questions" sections has someone ask if it's possible to create a tornado by spinning a hammer, like Thor does in the movie. Randall doesn't even bother elaborating on the "NO".
      • Even better, Cueball is just standing there facepalming while a woman stands nearby spinning a hammer like an idiot.
    • He has a similar answer to the question of whether you could stop a volcanic eruption by dropping a really big bomb in it as it happens. An erupting volcano is depicted spewing ash into the sky to form the word "no" — with more ash than usual because someone dropped a bomb in it.
    • Later subverted; when the question of whether fire tornadoes exist is submitted, Randall's answer is a Blunt "Yes". Then a brief aside noting that this fact is awesome.
  • Boring, but Practical: "Snow Removal" shows that it's a lot better to just shovel away snow rather than use either a flamethrower or a microwave.
  • Bread, Eggs, Milk, Squick: What would happen if one tried to funnel Niagara Falls through a straw?:
    One would get in trouble with the International Niagara Committee, the International Niagara Board of Control, the International Joint Commission, the International Niagara Board Working Committee, and probably the Great Lakes–St. Lawrence River Adaptive Management Committee. Also, the Earth would be destroyed.
  • Brick Joke:
    • The finale of "Dropping a Mountain" features a surprise callback to "Drain the Oceans: Part II".
    • The finale of "Lethal Neutrinos" refers back to the first article, "Relativistic Baseball":
      Randall: If it's going fast enough, a feather can absolutely knock you over.
      Alt Text of last image: Dude, AGAIN? Can you just pitch like a normal person?
    • invoked A double brick in "WWII Films". Near the beginning, it goes off on a tangent about IMDb's tagging system, noting that in addition to this making the site a Browser narcotic, (direct copy-paste, pothole not included) "many people are using the database to catalog every movie containing a scene that satisfies their particular prurient fascination"; a footnote mentions quicksand enthusiasts as an example. Once the entry gets back on track, near the end it hypothesizes a 10-minute movie about the Anglo-Zanzibar War (which lasted only 38 minutes). The very last image is of someone shooting said movie with a phone camera... and labeling it with a bunch of IMDb plot keywords. The Alt Text extends the list of keywords, and the very last one is "possible victim of quicksand".
    • "Orbital Speed" compared the speed of the International Space Station to a bullet on a football field; the ISS could cross the field in the time it takes for the bullet to travel 10 yards. note  "New Horizons" makes almost the exact same comparison for the titular spacecraft, and an additional comparison for a speeding car; New Horizons reaches the end zone, the bullet wouldn't even make the 10-yard line, and the automobile would have crossed about an inch. note 
  • Buffy Speak:
    • In "Mariana Trench Explosion" the alt text has, over a picture of the affected area from detonating a nuclear bomb underwater to create waves, "a map showing a thing happening in the atlantic ocean and then another thing happening to the east coast of north america".
    • In "Tatooine Rainbow" Randall mentions types I and II of the Binary Sun systems, calling them "circumbinary" and "the other kind".
  • Bullet Catch: "Catch!" explains that this trope might be possible, provided you shoot the bullet upwards so that the bullet stops mid-air, and have a friend catch it there by flying with a hot-air balloon or something.
  • Call-Back:
  • Canada, Eh?: When researching how high up you'd have to be to freeze to death, he finds "The scholarly authorities on freezing to death seem to be, unsurprisingly, Canadians".
  • Captain Obvious: "Faucet Power" has a little tangent to discuss the "eight glasses of water per day" advice and that there doesn't actually seem to be much scientific evidence as to precisely how much water people need to drink — the best answer Randall has found is literally just "if you're thirsty, you should drink some water".
  • Cut Your Heart Out With A Spoon: "Lethal Neutrinos": It's pointed out how ridiculous the idea of being killed by neutrinos is, since they have a ridiculously small chance of interacting with matter and not just passing through you (about a trillion do it harmlessly every second!). Still, if you were about the distance between the sun and Mars away from a supernova, the scale of the supernova is just so big that the neutrinos would kill you if everything else somehow didn't kill you first.
  • Comically Missing the Point:
    • In the first entry, the question is "What would happen if you tried to hit a baseball going 90% the speed of light?" The result is the complete annihilation of the batter, pitcher, ballpark, and everything within a mile radius. But, for what it's worth:
      A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered "hit by pitch", and would be eligible to advance to first base.
    • The entire point of "Sunless Earth". Since explanations of what would happen if the sun suddenly went out were both plentiful and not particularly interesting (basically, we'd all freeze and die), Randall instead wrote a long list of awesome things that we'd be able to do if the sun wasn't there... mediated, of course, by the fact that we'd all freeze and die.
    • The third image of "Snow Removal" has a guy with three aircraft carriers tied behind his car to power a snow-melting microwave emitter get pulled over by a police car. (Must be the same guy who put a GAU-8 Avenger on top of his car in "Machine Gun Jetpack".)
      Cop: Do you know why I pulled you over?
      Driver: Brake light?
      Alt Text: Your blinker is on.
  • Constrained Writing: After being asked what the most inconvenient word to type on an old cellphone would be (tied between "nonmonogamous" and "nonmonotonic", both having seven consecutive letters typed with the "6" key), Randall has some fun with sentences that can only be typed with the left or the right hand (on a standard QWERTY keyboard). He also puts together some sentences that can be typed using only the home row or the top row. He comes up with some very rare sentences (which are also hilarious).
    (left hand) Ferret sex at great rates Alt Text 
    (right hand) Buy my puppy milk, LOL
    (home row) Galahad has a Flash SSD
    (top row) We owe it to you to pepper your puppy
  • Crapsack World: #120 consists of snatches of his blog from a horrifying alternate universe, answering questions such as how many spiders the average human is currently swallowing per second, and the need for modern scuba gear to be operable when immersed in blood.
  • Currency Conspiracy: In "All the Money", it's implied that all US currency is all under the control of an Eldritch Abomination that resembles the Eye of Providence, this being the reason why the symbol is on the $1 bill.
  • Deadpan Snarker: Randall frequently applies his peculiar brand of humor to the entries. For example, from "Short Answer Section II":
    Chad Macziewski: What if you strapped C4 to a boomerang? Could this be an effective weapon, or would it be as stupid as it sounds?
    Randall: Aerodynamics aside, I'm curious what tactical advantage you're expecting to gain by having the high explosive fly back at you if it misses the target.
    • Another example from "Sunbeam":
      Randall: The sky is dark at night [citation needed] because the Sun is on the other side of the Earth. [citation needed]
  • Death by Materialism: In "All the money", you will eventually be killed by the tide of money falling if you don't build a wall around it.
  • Deconstructed Trope: A lot of the entries do this, carrying an apparently simple question to its most extreme Surprisingly Realistic Outcome-style logical conclusion, mostly involving Apocalypse How. An example is "Everybody Jump", a question that's been answered by multiple other places including a ScienceBlogs post. However, while Randall comes to the same conclusion for the basic question ("not a damn thing happens"), he then proceeds to tear into it and prove that it would result in a Planetary/Societal Disruption-grade Apocalypse How because nobody would be able to get home, or eat, and civilization would collapse.
  • Didn't Think This Through: In "All the Money", he notes that if you suddenly had the entire world's money supply, you couldn't actually spend it, because everyone would be pissed off at you for stealing all their money.
  • Disproportionate Retribution: "(U)sing nuclear strikes in response to traffic violations is probably overkill."
  • Don't Try This at Home: Several times. Among the more amusing examples:
    Before we go any further, I want to emphasize something:
    I am not an authority on lightning safety. I am a guy who draws pictures on the internet. I like when things catch fire and explode, which means I do not have your best interests in mind.
    Randall, on this page.

    disclaimer: i am a cartoonist. if you follow my advice on safety around nuclear materials you probably deserve whatever happens to you. [sic.]
    Alt Text of the third picture on this page.

    After reading this article, don't try to drive over speed bumps at high speeds. Here are some reasons:
    • You could hit and kill someone.
    • It can destroy your tires, suspension, and potentially your entire car.
    • Have you read any of the other articles on this blog?
    Near the beginning of this page.
    • A serious, non-ironic one #81 which discusses firing a bullet in the air and attempting to catch it at its highest point. Specifically, don't try to fire a gun into the air at all — people do this at celebrations in some countries and the falling bullets cause hundreds of injuries and deaths every year.
    • In the book, the illustration of someone spraying water at a bullet with the density of a neutron star (on an indestructible plinth, on an indestructible platform, to stop it sinking to the centre of the earth) to create a relatively dense envelope that would make it almost safe to touch has the caption "Do try this at home, and send me the video".
    • When someone asks "what's the worst thing" that can happen in a pressure cooker, Randall's answer begins with "Note: Never try this, for reasons which will become obvious in a moment."note 
      (Note: Before we go any further, I want to point out that much of the US is under extreme drought, fire season is underway, and wildfires—90% of them caused by humans—kill firefighters every year. Please don't try to set pollen on fire.)
  • Dug Too Deep: "Digging Downward" — "What would happen if I dug straight down, at a speed of 1 foot per second? What would kill me first?" Randall concludes that if you're assumed to be protected from the many things that could kill you, then the question becomes unanswerable scientifically, because by this point the scenario is pure fantasy. Which he notes, makes the answer obvious — a Balrog.
  • Earth-Shattering Kaboom: Several of the scenarios put forth end up in the destruction of the Earth, or at least the extinction of all life.
  • Easter Egg: If you remove the dust jacket from the hardback book, you will find a different cover picture, and a map of the world after the oceans have been drained on the inside of the dust jacket.
  • Eleventy Zillion: 2 undecillion isn't a made-up number, but it's large enough that if you're trying to sue someone for that much in US dollars, it may as well be, since there's no possible way for them (not even converting the entire Earth's mass to the most expensive thing ever sold) to actually come up with it.
  • Emoticon: In "Far-Travelling Objects":
    Randall: So, exactly how far has the longest-operating centrifuge traveled?
    (picture of Cueball shrugging his shoulders)
    Alt Text: ¯\(°_o)/¯
  • Everything Makes a Mushroom: The Relativistic Baseball produced one.
  • Explosive Decompression: Discussed when listing things in movies that don't actually happen in real life.
  • Fiction 500: "All The Money" imagines a scenario where you had all the money in the world.
  • Frivolous Lawsuit: 2 undecillion explores what would happen if the guy who filed a 2 undecillion lawsuit actually won. Turns out, he'd never get the money awarded because it's flat out impossible for Au Bon Pain to gather that much money, ever. They wouldn't even get anywhere near the target amount if they were able to convert the Earth's weight into copies of the most valuable item by weight ever sold (the Treeskilling Yellow postage stamp) and somehow sold all of them for the original's selling price.
  • Full Moon Silhouette: "Speed Bump" includes an illustration of a car that lifts off the ground and tumbles helplessly against the Moon. The Alt Text says "BREAKING: Child, Unidentified Creature in Bicycle Basket Hit and Killed by Car".
  • Gatling Good: "Machine Gun Jetpack" eventually escalates from an AK-47 to a Gryazev-Shipunov GSh-6-30, which if properly set up, can jump mountains.
  • Godzilla Threshold: Randall points out in "Cannibalism" that eating people who ate people would be a good way to transmit prion diseases, but they would take a long time to take effect, so your bigger concern would be that you have a 50% chance of getting eaten every month!
  • Gone Horribly Wrong: The splash image and cover of the book depict a Tyrannosaurus rex being lowered into a Sarlacc pit on a crane, excellently illustrating the tone of the blog. The back cover of the book, under the dust jacket, shows the outcome of this scenario: The T-Rex swings to the side of the pit, bites off its harness, damages the support structure of the crane, and runs down the man on the ground. Clever girl.
  • A Good Name for a Rock Band: The Alt Text of the third graph in "Steak Drop" reads:
    a hypersonic steak breaks mach 6 while elsewhere a jam band produces an instrumental album titled 'hypersonic steak 6'
  • Guns Akimbo: Invoked in "BB Gun".
    With all that in mind, let's look at what happens when a crowd of people with BB machine guns try to stop a train. In fact, people have two arms, so let's have them all dual-wield.
  • Hard on Soft Science: The first image of "All the Money", after Randall handwaves away how you got all the money in the world by saying A Wizard Did It. The image is of Rob and Megan, with Rob having drawn a pentacle on the floor.
    Megan: Whatchya doing?
    Rob: Economics.
    Alt Text: Well, yes, I can see THAT.
  • Heads or Tails?: In the question about humans surviving on cannibalism, flipping a coin to determine who eats whom.
  • Hide Your Children: In the question asking "What if everyone in the world gathered in one place and jumped at the same time?" He assumes all 7 billion people in the world were magically transported to Rhode Island and all jumped (affecting nothing) and wonder why we did that and then tried to make their way home. It conveniently and understandably ignores all the children who would be present but possibly be far from their parents and caregivers (hopefully families were transported together) and millions of babies and disabled people who can't jump.
  • High-Voltage Death: In "Electrofishing for Whales", it's noted that larger animals like humans or whales can die from electricity that smaller fish would be either unharmed by or be injured by but survive.
  • Hiroshima as a Unit of Measure:
    • The aforementioned "megayodas".
    • In "High Throw" he uses giraffes as a unit of heightnote .
    • In "Growth Rate" he gives the birth size of the typical baby as a fraction of the diameter of the Death Star's exhaust port (then as a fraction of the length of a womp rat, in the Alt Text of the corresponding image). Multiple Yodas stacked on top of each other are also used.
    • The second footnote of "The Constant Groundskeeper" converts 25,000 square meters into other measurement systems; the last one being "5,300 Shrouds of Turin".
    • Again in "Blood Alcohol", where Randall compares the volume of a beer can (1 pint = 475 mL) with the volumes of a stadium (250 picostadiums) and the Moon (21.5 yoctomoons).
    • Discussed in "All the Lightning" in the book, wherein Munroe remarks on science writers' love of comparing everything to the Hiroshima bomb. Then he mocks it thoroughly in the accompanying footnote (which is transcribed in the trope page's quote page).
  • Icarus Allusion:
    • "Interplanetary Cessna" talks about how the concept could work on Titan (Saturn's sixth moon, not the mythical giants), and worries about the wings freezing and falling apart. Randall figures engineering could solve the freezing issue, and that the real moral of the Icarus tale was not of the limits of humanity, but of the limits of wax as an adhesive.
    • "Into the Sun" claims that Icarus's problem wasn't flying too close to the sun, it was staying near the sun for too long.
  • I Fell for Hours: Averted. As demonstrated in "Free Fall" jumping off the tallest sheer cliff in the world would only result in 26 seconds of air time.
  • I Lied: The Hair Dryer article promised to stop when half the space was unused.
    1.875 gigawatts (I lied about stopping).
  • I'm a Humanitarian: "Cannibalism" discusses what would happen if everyone did this.
  • Impact Silhouette: Discussed in "Hockey Puck".
    "If you're like me, when you first saw this question, you might've imagined the puck leaving a cartoon-style hockey-puck-shaped hole. But that's because our intuitions are shaky about how materials react at very high speeds. Instead, a different mental picture might be more accurate: Imagine throwing a ripe tomato—as hard as you can—at a cake."
  • In Case of X, Break Glass: According to "Sunset On The British Empire", the interior walls of Buckingham Palace have numerous 'In Case Of Emergency, Break Glass' boxes. Each one has a cup of tea in it.
  • Insane Troll Logic: Fermi Estimation can certainly seem like this, but used correctly, it can at least get you in the ballpark of the correct answer.
    A Mole of Moles: I can pick up a mole (animal) and throw it.[citation needed] Anything I can throw weighs one pound. One pound is one kilogram. The number 602,214,129,000,000,000,000,000 looks about twice as long as a trillion, which means it's about a trillion trillion. I happen to remember that a trillion trillion kilograms is how much a planet weighs. ...if anyone asks, I did not tell you it was ok to do math like this.
    Paint the Earth: Based on my impressions from walking down the aisles, home improvement stores stock about as many light bulbs as cans of paint. A normal house might have about 20 light bulbs, so let's assume a house needs about 20 gallons of paint. Sure, that sounds about right.
  • Instant Gravestone: The end of "Rising Steadily" depicts the unfortunate thought-experiment victim as a steadily-rising gravestone after suffocating to death.
  • Just Before the End: "Expanding Earth" is yet another Apocalypse How situation, but it takes a century to actually kill everyone.
  • Kitchen Sink Included: In "High Throw" Randall mentions a British javelin thrower named Roald Bradstock who held a random object throwing competition, "in which he threw everything from dead fish to an actual kitchen sink".
  • Last of Its Kind: The Sun Bug, when it turns into a black hole, would end up as the last black hole in the universe when all of the black holes eventually evaporate due to Hawking radiation.
  • Layman's Terms: Used as a Running Gag in "Flood Death Valley".
    "Death Valley is an endorheic basin[1]   in California."
    "The Salton Sea is fed mainly by agricultural runoff, so it's become saline[8]   and hypereutrophic.[9]  "
  • Lightning Can Do Anything: Apparently a computer that is flashing the BIOS will install Microsoft Bob Gateway 2000 edition if hit by lightning.
  • Literal Metaphor: While explaining why you can't set fire to something with a magnifying glass and moonlight in "Fire From Moonlight", Randall remarks the reason involving "a rabbit hole of optics". Cue image of a literal rabbit hole with a bunch of lenses in it.
  • Logical Extreme: Some of the hilarity in the posts comes from the progressively more ridiculous situations the What If? suggests (the ever-so-popular "What if we tried more power?" being one of them). They're plausible in Real Life, just not humanly (and, in some cases, inhumanly) possible.
  • Ludicrous Speed: Watch Cueball throw a baseball at relativistic speeds. Watch the entire city be destroyed in a nuclear-level explosion.
  • Made of Explodium: A humble water glass in "Glass Half Empty", and perfectly justified by pressure physics.
    Randall: The lesson: If the optimist says the glass is half full, and the pessimist says the glass is half empty, the physicist ducks.
  • Major Injury Underreaction:
    • "Dang." In response to having one's arms torn off as a result of grabbing a flagpole while falling from a building.
    • The narrator gets in on this in "Relativistic Baseball." After describing how the speed of the baseball would cause it to fuse with the atoms in the air, resulting in hitting the batter with a shell of x-rays and superheated plasma while triggering a nuclear explosion, the narration concludes with "A careful reading of official Major League Baseball Rule 6.08(b) suggests that in this situation, the batter would be considered 'hit by pitch', and would be eligible to advance to first base."
  • Mathematician's Answer: Many segments, at least before attending to the spirit of the question asked, begin their answer with something to the effect of "No, because the conditions you're putting the subject through would destroy it long before anything exciting happened."
    • "Relativistic Baseball" answers the question "What would happen if a baseball were to be thrown at 90% the speed of light" by explaining how the resulting explosion would vaporize the batter, pitcher, and entire stadium...and then finished by saying the ruling on the field would be "hit by pitch".
  • Missing Steps Plan:"Pyramid Energy", asking if the energy it took to build the Great Pyramid would be enough to send a mission to the moon and back, uses this in the second image. Said image consists of the pyramid broken down and fed through a box marked "?", then launching a rocket.
  • Money Is Not Power: Having all the money in the world won't save you from being killed when the pile of money collapses. Or from building codes.
  • Moving the Goalposts: Done in "Train Loop" to allow for an interesting answer (as in, other than "no"). "Could a high-speed train run through a vertical loop, like a rollercoaster, with the passengers staying comfortable?" becomes (changes bolded) "Could a modified and reinforced high-speed train with a jet engine on top run through a vertical loop, like a rollercoaster, with the passengers surviving?"
    • Also done in "Digging Downward", where the concerns of heat, pressure, and digging process are ignored one by one until the question "has left the realm of physics and become fantasy", and the digger is eventually eaten by a balrog.
  • Mundane Made Awesome: "Microwaves" starts of with Munroe straight-up telling admitting that you can Google the answer to the question, but since he himself has had this happen so many times, he's going to What-If it.
  • Mythology Gag: Since the illustrative diagrams are drawn in the same style as xkcd, they sometimes feature guest appearances by characters from there. They also feature allusions to the main webcomic.
  • Non-Indicative Name: In-universe, in the Alt Text for one of the images on "Transatlantic Car Rental", Randall thought NATO is an organization formed to defeat the North Atlantic.
  • No OSHA Compliance: In "All The Money", Randall notes that even if you could manage to avoid your money skyscraper killing you, you would be breaking building codes by not having enough bedrock to hold it up. He wonders if Scrooge McDuck ever had to worry about this.
  • "Not Making This Up" Disclaimer: In "The Constant Groundskeeper", while discussing lawn-cutting speeds:
    Randall: In 2010, Bobby Cleveland set a world record for the top speed in a riding lawnmower, hitting 96 mph. This record was set as part of a rivalry with the British lawnmower driver Don Wales. [5]  
    • There's also this description of the lowest elevation to Death Valley.
      The lowest route to Death Valley is probably by traveling up the Colorado River watershed, along the Arizona border past Quartzite, then northwest past Zzyzx, which is a real place.
  • Not the Fall That Kills You…: In "Falling With Helium", Randall quotes a medical paper to this effect.
    It is, of course, obvious that speed, or height of fall, is not in itself injurious ... but a high rate of change of velocity, such as occurs after a 10 story fall onto concrete, is another matter.

    ...which is just a wordy version of the old saying "It's not the fall that kills you, it's the sudden stop at the end."
  • Omnicidal Maniac: Sam Burke wants to dig a hole deep enough to contain the whole atmosphere and make everyone else suffocate.
  • One True Love: Deconstructed in "Soul Mates"; a world where everybody could only be happy with one other person would be much lonelier than ours.
  • Outlandish Device Setting: features the "Hair Dryer" thought experiment. An ordinary 1875-watt hair dryer is sealed inside an indestructible metal box and turned on. Every paragraph, a new power setting is taped onto the dial, increasing the power by an order of magnitude. At its second-highest setting of 187 terawattsnote , the hair dryer is putting out energy comparable to three nuclear explosions every second. After turning the dryer down to 0 and dumping it into a lake to cool it down, the 187-terawatt setting is taped over with 11 petawattsnote . This boils the entire lake into plasma and launches the box and hairdryer into space.
    At 187 megawatts: Just one more, then we'll stop.
    One paragraph later: 1.875 gigwatts (I lied about stopping).
  • Overly-Long Gag:
    • Unit cancellation is weird.
    • In the "Interplanetary Cessna" entry, every one of the 32 result diagrams had an alt text describing the pilot's reactions. Sadly, Randall has removed the image map making alt text for different parts of the image possible (presumably for technical reasons), causing them to be lost; thus, for the sake of posterity, we present all 32 of them here:
      Sun: [fwoosh]
      Jupiter: why did you send me here
      Saturn: i'm not sure this is better
      Uranus: this planet is the george lucas prequel version of neptune
      Neptune: blue is good. stick with blue.
      Earth: it's hard to fly on earth because i don't actually know how to fly this thing.
      Venus: aaaaaaaaaaaaaaaaaaa
      Mars: do we actually have to do this? we have the simulations.
      Ganymede: crap, there's no--
      Titan: wheeeeee! hmm, it's getting chilly.
      Mercury: another one with no atm--
      Callisto: aaaaaaaaAAAAAAAAA
      Io: the ugliest solar system body
      Moon: ok do we really hav--
      Europa: do we have to do all--
      Triton: wait can we--
      Eris: not ANOTHER one with--
      Pluto: ok listen i didn't--
      Titania: i didn't sign up for--
      Rhea: sign up for--
      Oberon: WILL YOU STOP--
      Haumea: STOP THIS FOR--
      Iapetus: not another--
      "Snow White": AAAAAAAA--
      Charon: charon made the cut?
      Umbriel: i don't even know where--
      Ariel: are we almost don--
      2002 TC3O2R: this one doesn't even have a name!Note FROM THE FUTURE! 
      Dione: just let me--
      Tethys: what are you tr--
      Sedna: are you trying to pro--
      Ceres: you could have done just 10. you seriously could have done just 10.
    • All the different things that don't count as sunsets.
    • The first image for "Free Fall" labels the sheer cliff on the side of Mount Thor with "AAAAAAAAAAAAA". The Alt Text for the image?
  • Overly Long Scream: Both of the Mount Thor images in "Free Fall" have one each in the Alt Text, though the second one is the only one with the obligatory "::gasp::".
  • Overly Narrow Superlative: "Great Tree" ends with Randall's "favorite piece of axe-related legal trivia". As the accompanying footnote lampshades, it's not a long list.
  • Parallel Parking: Parodied; in "Transatlantic Car Rental", an image of hundreds of cars stacked on top of each other while sinking into the ocean is given the Alt Text of "Parallel parking".
  • Pinball Scoring: The $2 Undecillion Lawsuit.note  Sun's weight in platinum isn't worth that much.
  • Planetary Relocation: In "Stop Jupiter", Randall largely dismisses the possibility of significantly altering Jupiter's (or any other planet's) orbit by using it for Spaceship Slingshot Stunts, noting that Jupiter was only affected by 10^-21 meters per second when New Horizons did it on its way to Pluto: Jupiter is so huge it would hardly notice if we threw Earth's entire crust at it. He compares it to trying to stop a moving tractor trailer with a thrown tennis ball: " need an awfully big tennis ball."
  • Plant Aliens: The photosynthetic cows in "Green Cows."
  • Pocket Protector: The back cover of the book version warns that it will not stop a bullet, and anyone wanting to use it as armour should buy a lot more copies.
  • Polluted Wasteland: What would happen if you flooded the Death Valley. We know this, because we did it to the Salted Basin in Real Life, by accident.
  • Pooled Funds: Discussed in "All the Money" as something to do if you summoned all the world's currency. You probably couldn't spend it since the entire human race would be too angry at you for stealing all of their money.
  • Pun:
    Eventually, they give up, and the unexplained meteorological phenomenon is simply dubbed a “Skrillex Storm”note  —because, in the words of one researcher, “It had one hell of a drop.”
  • Rage Against the Author: Inverted in "Dropping a Mountain". Randall gets a little annoyed at Black Hat Guy asking "What if we dropped it from higher up?"
  • Ragtag Bunch of Misfits: Invoked in "BB Gun" (Alt Text of second image).
  • Real Joke Name: Randall considers Zzyzx to be this.
  • Recoil Boost: "Machine Gun Jetpack" asks: how much gun do you need to launch yourself into the air? It turns out that an AK47 has a higher thrust-to-weight ratio than the Saturn V rocket, though bringing more than 250 rounds of ammunition would not work well, that putting a GAU-8 Avenger (the tank-killing Gatling gun on an A-10 Thunderbolt ground attack plane) on top of a car would let you break the interstate speed limit in three seconds, and that a Gryazev-Shipunov GSh-6-30 could jump mountains if set up properly.
  • Regional Redecoration: Drain the Oceans shows maps of Earth in various phases of being drained from water by a portal at the bottom of Challenger Deep. The "sequel" follows that up with maps of Mars getting filled with water dumped from Earth.
  • Relax-o-Vision: "Blood Alcohol" featured drawings of squirrels instead of people coughing up blood.
  • Rhetorical Question Blunder: Randall does this to himself in Saliva Pool:
    But it would all be worth it, because at the end of it all, you'd have an Olympic-size swimming pool full of saliva. And isn't that, deep down, all any of us really want?note 
  • Ridiculous Future Sequelisation: "Twitter Timeline Height" considered the prospect of twenty-six The Land Before Time sequels.
  • Robot War: More or less deconstructed in "Robot Apocalypse": Robots with present technology would pose little threat due to their considerable limitations, with the partial exception of advanced cars. They would be able to cause a nuclear holocaust, but would be unlikely to do so, as the EMPs caused by such an event would destroy them as well.
  • Running Gag:
    • "You will not go to space today."
    • "What if we tried more power?" Used seven times.
    • Wikipedia's "[citation needed]" is frequently borrowed to be placed next to obvious statements, or obviously silly statements, or as a bit of Self-Deprecation (see below). But later on (#47 was the first), it's also linked to other kinds of citations or things that sound like "citation". Lampshaded in "Into the Blue":
      Pop-up note: I was so tempted to vandalize this article to put a [citation needed] after every claim that the night sky was dark.
    • From the book: "...I need to know by Friday." As a non-answer to some of the unanswered questions. Here's one of said unanswered questions, just to convey the impression:
      "What is the total nutritional value (calories, fat, vitamins, minerals, etc.) of the average human body?"
    • Illustrations of very large things, like the earth, with the caption, "Actual Size".
    • "If we [insert thing that would kill many people/humanity/Earth] and for the record, I don't think we should..."
    • Blaming whoever submitted the question for the consequences of actually doing the thing asked about.
  • Russian Guy Suffers Most: Mentioned when imagining the consequences of Earth's axis being moved 90 degrees:
    Moscow is extremely hot and very dry, with a climate somewhere between our Phoenix and our Baghdad. Russians, who have been surviving in Russia for centuries, shrug with resignation.
  • Screaming at Squick: Randall's reaction to searching up "star-nosed mole" in A Mole of Moles:
  • Self-Deprecation: From "A Mole of Moles":
    Randall: I can pick up a mole (animal) and throw it.[citation needed]
  • Serial Escalation:
    • A recurring theme, frequently after the question is answered as asked, Black Hat Guy comes in and asks some variation of, "What if we did more?" Several times. Any topic that can be pushed to extremes (that isn't already) will be pushed to those extremes and then some.
    • Another excuse for this has been a cat stepping on the keyboard, adding a few dozen extra zeroes to a quantity of TNT detonated in the Marianas Trench.
      Randall: Stupid cat.
    • "Dropping a Mountain" shows why this doesn't work in real life. When Denali is lifted and dropped from increasing heights, it is taken to the edge of Earth's gravitational well, the highest point an object could fall from, and hits Alaska at 10 km/s. The Black Hat Guy asks to drop it from even higher, which fails because Earth no longer has enough gravitational force to overcome that of other bodies in the solar system. Randall even hangs a lampshade on it.
      Black Hat Guy: What if we dropped it from higher up?
      Randall: Oh. You again.
      Alt Text: I see where this is going.
      • The second time Black Hat Guy says it, the alt text is "Fine, but put your hat under it, first." Then, near the end:
      Randall: And that's that. We've dropped the mountain from as high as it can be dropped, and I hope John-Clark is proud of the resulting devastation. Thanks for reading, and—
      BHG: What if we dropped it from higher up?
      Alt Text: I'M BACK
      Randall: No, that doesn't actually make sense. The Earth's gravitational pull doesn't—
      BHG: What if we dropped it from higher up?
      Randall: Dropping it from higher up won't do anything; there won't be enough force pulling it toward the—
      BHG: What if we dropped it from higher up?
      Alt Text: I WILL NEVER DIE
      Randall: Ok. Fine. You win. We'll try it.
    • "Cornstarch". The kick key phrase in the question is 'unpleasant things', so the author continues to assume that the person experimenting is having fun (and has an infinite amount of spare time and cornstarch), even after the oobleck blocks the drains, overflows the sink, fills the tester's home, blows out a window, and causes the tester to be dumped out onto the lawn in the resultant flood. But if the tester honestly enjoyed spending several months and several hundred thousand dollars making oobleck and destroying their home until the authorities shut off the water supply, technically no unpleasant things happened.
  • Sequel Hook: From "Free Fall", Randall decides that people jumping off a cliff land in a pit of cotton candy, then wonders in a parenthetical if that would work.
  • Shmuck Bait: One of the images for Spent Fuel Pool", which is about which parts of a storage pool for nuclear waste would actually be safe to swim in, has as Alt Text, "Disclaimer: I am a cartoonist, if you follow my advice on safety around nuclear materials you probably deserve whatever happens to you."
  • Shockingly Expensive Bill: You get this if you switch on an 11-petawatt hairdryer. Or run enough energy through a cell phone transmitter to vaporize a snowflake in an attempt to levitate it.
  • The Short War: "WWII Films" tries to determine which war has the greatest length of movies about war:length of actual war ratio, and naturally brings up a bunch of there. None of these quite manage to beat the ratio of World War II, but there are some that he thinks might, though he can't find confirmation.
  • Shown Their Work: Randall Munroe usually walks readers through any math involved in his answers and cites sources for data.
  • Skewed Priorities:
    • In "All the Money": "There are ways to avoid this. You could, say, build a wall around the coins to contain them. Unfortunately, then you might face a problem worse than death: building code violations.
    • "Niagara Straw" is more concerned with the committees one would anger by funneling Niagara Falls through a straw than the fact that you'd destroy the planet if you did.
    • In "Transatlantic Car Rental" (where an audience asks Randall how many rental cars would it take to build a land bridge across the Atlantic), Randall opens by stating that doing so would be a violation of the car rental's agreement. Also, the ocean currents will be disrupted, causing severe climate change, although that is not necessary a violation of the rental's agreement.
  • Square-Cube Law: Used in "Growth Rate" to explain why nine-plus meter people can't actually live.
  • Star Killing: Joked about in one of the "Weird (and Worrying) Questions" sections, where the questioner asked whether it would be possible to build a new star.
    Cartoon of questioner: (holding a device marked "Sun Obliterator") ...I need to know by Friday.
  • Star Scraper: Randall explores a billion story building that one 4-year old suggested. It extends about ten times past the orbit of the Moon.
  • Surprisingly Realistic Outcome: A segment asked if you swam in a spent fuel pool of a nuclear facility, how deep would you have to dive to suffer fatal radiation poisoning? After the physics filled conjecture suggesting that you'd be pretty safe as long as you stayed away from the casks, Randall then asks a real life friend who works at a research reactor what would happen if he tried to swim in their pool.
    Friend's response: "In our reactor? You’d die pretty quickly, before reaching the water, from gunshot wounds."
  • Take That!:
    • When trying to fill the most expensive shoebox, Randall notes that it's difficult to get a handle on the value of diamonds because "<s>the entire industry was built on a scam</s> the gemstone market is complicated".
    • Randall frequently appends obvious statements with a superscripted "[citation needed]" in a dig at Wikipedia's somewhat spurious notability standards.
    • In "Sunbeam" Randall mentions that if you were standing on Earth's dark side when the eponymous sunbeam is hitting Earth, you would die from twilight (i.e. the radiations and x-rays coming from the horizon). Cue image of the DVD cover of Twilight (2008).
  • Tempting Fate: in "Pressure Cooker"
    Question: What's the worst thing that can happen if you misuse a pressure cooker in an ordinary kitchen?
    Randall: The worst thing?
    (Black Hat looks at a pressure cooker with a hand on his chin)
  • There Is No Kill Like Overkill:
    • "What if we tried more power/higher/faster?" is Randall's go-to answer whenever overkill is not achieved. In the Diamond scenario, it ends with the meteor being fired with the speed of the Oh-My-God Particle (that is, very, very close to the speed of light) and the resulting impact destroys the Earth.
    • In "Sunbeam", the entirety of the Sun's power is collected, then fired at earth in the form of a 1m-wide beam. How destructive is such a beam? Well, in Randall's words:
    "If you were standing in the path of the beam, you would obviously die pretty quickly. You wouldn't really die of anything, in the traditional sense. You would just stop being biology and start being physics.
    • In Proton Earth, Electron Moon, Randall warns beforehands that this scenario is the most destructive yet, even compared to the former Earth-Shattering or Earth-Scorching ones. Indeed, it ends with the destruction of the entire Universe.
  • They Knew the Risks: When trying to figure out the farthest from Earth a living thing has ever died, he first discusses the three humans who have ever died in space and then mentioned there were also several animals, who he can't bring himself to look up the statistics for since while the humans knew the risks, they didn't. This proves to be no problem, because Randall takes a third option and reveals the true answer to be microorganisms.
  • Three Laws-Compliant: Parodied by mashing them up with Three Laws of Thermodynamics in "Fire From Moonlight".
    Cueball: The Second Law of Thermodynamics states that a robot must not increase entropy, unless this conflicts with the First Law.
    Ponytail: Close enough.
    Alt Text: The First Law of Thermodynamics states that a robot must not harm a human being, unless not doing so would lead to an increase in entropy.
  • Time Abyss: "Twitter" deals with some truly mind-bogglingly large lengths of time.
  • Tim Taylor Technology: A number of the questions get MythBusters-esque answers amounting to "What would happen? Not very much. But that's no fun, let's ramp up the power until something crazy happens!"
  • Too Dumb to Live: A lot of the scenarios only become deadly or apocalyptic if the theoretical person acts extremely stupidly. Close to a Real Life example with "Tungsten countertop" about a French soldier drinking wine out of a rifle barrel for some reason and being poisoned by the tungsten, though he ended up surviving.
  • Tradesnark™: In "Expensive Shoebox", Randall refers to a particular well-known image editing software as Adobe®©™ Photoshop®©™ CS®™ 5™.
  • The Triple: The first image of "Free Fall" labels the parts of Mount Thor with "East Slope", "Summit", and "AAAAAAAAAAAAA" (pointing at the sheer cliff).
  • Two-Keyed Lock: Parodied in "Global Snow" with the idea that the National Weather Service's snow depth-measuring board is important enough to be double-locked.
    Scientist 1: It's snowing. We'd better go get the board.
    Scientist 2: OK. You'll need to come along since we need two people to turn the keys to access it.
  • Visual Pun:
    • The third image on "The Constant Groundskeeper" shows a cougar chasing a guy riding a John Deere riding mower. Explained by the Alt Text:
      "A cougar chasing down a deere."
    • "Flyover States" in the book includes a slightly difficult-to-decipher visual pun right before a reveal: a drum rolling down a hill.
  • Wave-Motion Gun: The whole point of "Sunbeam"; all of the Sun's output of visible light were concentrated into a laser-like light with a diameter of 1 meter hitting Earth, reducing it into a charred husk.
  • Whale Egg: The deer eggs in "Phone Keypad".
  • What Are Records?: Footnote 6 in "Far-Traveling Objects" alludes to a future incarnation of this trope.
    If you're reading this in the future, hard drive platters were these things that ... oh, never mind, it's not important.
  • What Happened to the Mouse?: Averted, if you know where to look. The cover shows a Tyrannosaurus rex being suspended over Scarlacc Pit. The resolution of that is on the back cover, under the book jacket.
  • Wiki Walk: In "WWII Films", Randall tells us about IMDb tags.
    Randall: To find other strange combinations, try clicking on a tag, then scrolling down to the "Refine by Keyword" section at the column on the right. Have fun.
    Image caption: SIX HOURS LATER... *click click click*
  • A Wizard Did It: Used constantly, which seems a little unusual for a series that is all about Surprisingly Realistic Outcome, but it's justified as so much of the series is about things that really can't actually happen in the first place, so "magic" is used to set up the scenario the question requires (for example, magically accelerating the baseball in Relativistic Baseball, or a magically expanding and contracting firepole in Earth-Moon Fire Pole), and after that the situation plays out completely realistically.
  • Worrying for the Wrong Reason: In "500 MPH":
    In short, the answer to Grey's question is yes—500 mph winds would send you flying through the air. But don't worry about that. Instead, worry about is the thing that created the 500 mph winds. Odds are, that's what's going to kill you.
  • Worth It:
    • According to "Extreme Boating", exposure to the inexplicable "third sound" is worth a horrible death in a sea of liquid helium. Literal in the Alt Text.
    • Also worth it: hiring 40 billion planets' worth of lawyers for a thousand generations to get out of a $2 undecillion lawsuit, because the fees would still be less than the suit.

"Some interesting physical effects would destroy it" summarizes the answers to a large percentage of questions submitted to this blog. (Tungsten Countertop, footnote #2)