What If?: Serious Scientific Answers to Absurd Hypothetical Questions

by Randall Munroe

Right now, the Earth spins faster than the Moon, and our tides slow down the Earth’s rotation while pushing the Moon away from us.3 If we stopped rotating, the Moon would stop drifting away from us. Instead of slowing us down, its tides would accelerate our spin.

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 tubing was so radioactive that if he’d tucked it into a tool belt or shoulder bag, where it sat close to his body, he could’ve been killed. As it was, the water protected him, and only his hand—a body part more resistant to radiation than the delicate internal organs—received a heavy dose.

As the ice sheets withdrew, large chunks of ice broke off and were left behind. When these chunks melted, they left behind water-filled depressions in the ground called kettlehole ponds. Oakland Lake, near the north end of Springfield Boulevard in Queens, is one of these kettlehole ponds. The ice sheets also dropped boulders they’d picked up on their journey; some of these rocks, called glacial erratics, can be found in Central Park today.

Below the ice, rivers of meltwater flowed at high pressure, depositing sand and gravel as they went. These deposits, which remain as ridges called eskers, crisscross the landscape in the woods outside my home in Boston. They are responsible for a variety of odd landforms, including the world’s only vertical U-shaped riverbeds.

The oceans were full of life, but it was simple single-cellular life. On the surface of the water were mats of blue-green algae. These unassuming critters are the deadliest killers in the history of life. Blue-green algae, or cyanobacteria, were the first photosynthesizers. They breathed in carbon dioxide and breathed out oxygen. Oxygen is a volatile gas; it causes iron to rust (oxidation) and wood to burn (vigorous oxidation). When cyanobacteria first appeared, the oxygen they breathed out was toxic to nearly all other forms of life. The resulting extinction is called the oxygen catastrophe.

A million years is a long time. It’s several times longer than Homo sapiens has existed, and a hundred times longer than we’ve had written language. It seems reasonable to assume that however the human story plays out, in a million years it will have exited its current stage.

Without us, Earth’s geology will grind on. Winds and rain and blowing sand will dissolve and bury the artifacts of our civilization. Human-caused climate change will probably delay the start of the next glaciation, but we haven’t ended the cycle of ice ages. Eventually, the glaciers will advance again. A million years from now, few human artifacts will remain.

Our most lasting relic will probably be the layer of plastic we’ve deposi...

A 1-watt laser is an extremely dangerous thing. It’s not just powerful enough to blind you—it’s capable of burning skin and setting things on fire. Obviously, they’re not legal for consumer purchase in the US. Just kidding! You can pick one up for $300. Just do a search for “1-watt handheld laser.”

We don’t know what astatine looks like, because, as Lowe put it, “that stuff just doesn’t want to exist.” It’s so radioactive (with a half-life measured in hours) that any large piece of it would be quickly vaporized by its own heat. Chemists suspect that it has a black surface, but no one really knows.

For example, people worry about leaving disconnected chargers plugged into the wall for fear that they’re draining power. Are they right? Heat flow analysis provides a simple rule of thumb: If an unused charger isn’t warm to the touch, it’s using less than a penny of electricity a day. For a small smartphone charger, if it’s not warm to the touch, it’s using less than a penny a year. This is true of almost any powered device.

In the Clarendon Laboratory at Oxford University sits a battery-powered bell that has been ringing since the year 1840. The bell “rings” so quietly it’s almost inaudible, using only a tiny amount of charge with every motion of the clapper. Nobody knows exactly what kind of batteries it uses because nobody wants to take it apart to figure it out.

The scholarly authorities on freezing to death seem to be, unsurprisingly, Canadians.

But if you’re even more pedantic, it is true. The ocean is colder than space. Interstellar space is very cold, but space near the Sun—and near Earth—is actually incredibly hot!

apricity

this suggests the name will end up being about as long as the total number of stars: The stars are named Joe Biden. I like doing math that involves measuring the lengths of numbers written out on the page (which is really just a way of loosely estimating log10x). It works, but it feels so wrong.

As they enter the atmosphere, the air can’t move out of the way fast enough, and gets squished in front of the object—and compressing air heats it up.

All in all, I wouldn’t stand in the middle of a desert for five weeks to rid myself of colds forever. But if they ever come up with a rhinovirus vaccine, I’ll be first in line.

Traditionally, the optimist sees the glass as half full while the pessimist sees it as half empty. This has spawned a zillion joke variants—for example, the engineer sees a glass that’s twice as big as it needs to be, the surrealist sees a giraffe eating a necktie, etc.

Earth’s most powerful radio signal is the beam from the Arecibo telescope. This massive dish in Puerto Rico can function as a radar transmitter, bouncing a signal off nearby targets like Mercury and the asteroid belt. It’s essentially a flashlight that we shine on planets to see them better. (This is just as crazy as it sounds.)

We have to use an electric motor because gas engines work only near green plants. On worlds without plants, oxygen doesn’t stay in the atmosphere—it combines with other elements to form things like carbon dioxide and rust. Plants undo this by stripping the oxygen back out and pumping it into the air. Engines need oxygen in the air to run.2

Starting from a friendly sea-level pressure, we’d accelerate through the tumbling winds into a 275 m/s (600 mph) downward glide deeper and deeper through the layers of ammonia ice and water ice until we and the aircraft were crushed. There’s no surface to hit; Jupiter transitions smoothly from gas to liquid as you sink deeper and deeper.

But I’ve never seen the Icarus story as a lesson about the limitations of humans. I see it as a lesson about the limitations of wax as an adhesive.

Lastly, we need to know the strength of gravity on Dagobah. Here, I figure I’m stuck, because while sci-fi fans are obsessive, it’s not like there’s gonna be a catalog of minor geophysical characteristics for every planet visited in Star Wars. Right? Nope. I’ve underestimated the fandom. Wookieepedia has just such a catalog, and informs us that the surface gravity on Dagobah is 0.9g.

However, since jet-fuel-laden planes were used as weapons on 9/11, the FAA has tried to limit the number of unnecessarily fuel-heavy flights crossing the US, so most international travelers who might otherwise travel over California instead take a connecting flight from one of the airports there.

It doesn’t take too many helium balloons to lift a person. In 1982, Larry Walters flew across Los Angeles in a lawn chair lifted by weather balloons, eventually reaching several miles in altitude. After passing through LAX airspace, he descended by shooting some of the balloons with a pellet gun. On landing, Walters was arrested, although the authorities had some trouble figuring out what to charge him with. At the time, an FAA safety inspector told the New York Times, “We know he broke some part of the Federal Aviation Act, and as soon as we decide which part it is, some type of charge will be filed.”

If we want to launch a 65-kilogram spaceship, we need the energy of around 90 kilograms of fuel. We load that fuel on board—and now our spaceship weighs 155 kilograms. A 155-kilogram spaceship requires 215 kilograms of fuel, so we load another 125 kilograms on board . . . Fortunately, we’re saved from an infinite loop—where we add 1.3 kilograms for every 1 kilogram we add—by the fact that we don’t have to carry that fuel all the way up. We burn it as we go, so we get lighter and lighter, which means we need less and less fuel. But we do have to lift the fuel partway.

The story of that effort, dubbed Project Orion, is detailed in the excellent book of the same name by Freeman’s son, George. Advocates for nuclear pulse propulsion are still disappointed that the project was cancelled before any prototypes were built. Others argue that when you think about what they were trying to do—put a gigantic nuclear arsenal in a box, hurl it high into the atmosphere, and bomb it repeatedly—it’s terrifying that it got as far as it did.

To make a human, you need to put together two sets of DNA. In humans, these two sets are held in a sperm cell and an egg cell, each of which holds a random sample of the parents’ DNA.

If they have a child, each one will contribute a strand of DNA. But the strand they contribute will be a random mix of their mother and father strands. Every sperm cell—and every egg cell—contains a random combination of chromosomes from each strand. So let’s say Bob and Alice make the following sperm and egg:

In general, if you have a child with yourself, 50 percent of your chromosomes will have the same stat on both sides. If that stat is a 1—or if it’s a multiplier—the child will be in trouble, even though you might not have been. This condition, having the same genetic code on both copies of a chromosome, is called homozygosity.

Other mutations, like the sickle-cell gene on chromosome 11, can provide a mix of benefit and harm. People who have the sickle-cell gene on both their copies of the chromosome suffer from sickle-cell anemia. However, if they have the gene on just one of their chromosomes, they get a surprise benefit: extra resistance to malaria.

A child from a parent who self-fertilized would be like a clone of the parent with severe genetic damage.

So while there are other animals that use projectiles, we’re just about the only animal that can grab a random object and reliably nail a target. In fact, we’re so good at it that some researchers have suggested that rock-throwing played a central role in the evolution of the modern human brain.

In order to deliver a baseball to a batter, a pitcher has to release the ball at exactly the right point in the throw. A timing error of half a millisecond in either direction is enough to cause the ball to miss the strike zone. To put that in perspective, it takes about five milliseconds for the fastest nerve impulse to travel the length of the arm. That means that when your arm is still rotating toward the correct position, the signal to release the ball is already at your wrist. In terms of timing, this is like a drummer dropping a drumstick from the tenth story and hitting a drum on the ground on the correct beat.

physicist who asked me this question, told me his rule of thumb for estimating supernova-related numbers: However big you think supernovae are, they’re bigger than that.

Here’s a question to give you a sense of scale. Which of the following would be brighter, in terms of the amount of energy delivered to your retina: A supernova, seen from as far away as the Sun is from the Earth, or the detonation of a hydrogen bomb pressed against your eyeball?

Applying Dr. Spector’s rule of thumb suggests that the supernova is brighter. And indeed, it is . . . by nine orders of magnitude.

Space is about 100 kilometers away. That’s far away—I wouldn’t want to climb a ladder to get there—but it isn’t that far away. If you’re in Sacramento, Seattle, Canberra, Kolkata, Hyderabad, Phnom Penh, Cairo, Beijing, central Japan, central Sri Lanka, or Portland, space is closer than the sea.

But 8 km/s is blisteringly fast. When you look at the sky near sunset, you can sometimes see the ISS go past . . . and then, 90 minutes later, see it go past again.6 In those 90 minutes, it’s circled the entire world.

To get a better sense of the pace at which you’re traveling, let’s use the beat of a song to mark the passage of time.9 Suppose you started playing the 1988 song by The Proclaimers, “I’m Gonna Be (500 Miles).” That song is about 131.9 beats per minute, so imagine that with every beat of the song, you move forward more than 2 miles.

In the time it took to sing the first line of the chorus, you could walk from the Statue of Liberty all the way to the Bronx.

What happens to the Earth? Not much. It would actually take hundreds of thousands of years for the ocean to drain. Even though the opening is wider than a basketball court, and the water is forced through at incredible speeds, the oceans are huge. When you started, the water level would drop by less than a centimeter per day.

If you set out a cup of warm water on Mars, it’ll try to boil, freeze, and sublimate, practically all at once. Water on Mars seems to want to be in any state except liquid.

Olympus Mons, and a few other volcanoes, remain above water. Surprisingly, they aren’t even close to being covered. Olympus Mons still rises well over 10 kilometers above the new sea level. Mars has some huge mountains. Those crazy islands are the result of water filling in Noctis Labyrinthus (the Labyrinth of the Night), a bizarre set of canyons whose origin is still a mystery.

The Earth’s atmosphere bends light, so when the Sun is at the horizon it appears about one Sun-width higher than it would otherwise.

After the initial jolt, one of the first effects you’d notice would be that your GPS would stop working. The satellites would stay in roughly the same orbits, but the delicate timing that the GPS system is based on would be completely ruined within hours. GPS timing is incredibly precise; of all the problems in engineering, it’s one of the only ones in which engineers have been forced to include both special and general relativity in their calculations.

More active plate tectonics might be good for life. Plate tectonics play a key role in stabilizing the Earth’s climate, and planets smaller than Earth (like Mars) don’t have enough internal heat to sustain long-term geologic activity. A larger planet would allow for more geologic activity, which is why some scientists think that exoplanets slightly larger than Earth (“super-Earths”) could be more friendly to life than Earth-sized ones.

It’s hard to suck in air against the weight of the water, which is why snorkels can only work when your lungs are near the surface.