However, the glass and water are now moving too fast for the vapor buildup to matter. Less than ten milliseconds after the clock started, they’re flying toward each other at several meters per second. Without a cushion of air between them—only a few wisps of vapor—the water smacks into the bottom of the glass like a hammer.
Water is very nearly incompressible, so the impact isn’t spread out over time—it comes as a single sharp shock. The momentary force on the glass is immense, and it breaks.
This “water hammer” effect (which is also responsible for the “clunk” you sometimes hear in old plumbing when you turn off the faucet) can be seen in the well-known party trick of smacking the top of a glass bottle to blow out the bottom.
When the bottle is struck, it’s pushed suddenly downward. The liquid inside doesn’t respond to the suction (air pressure) right away—much like in our scenario—and a gap briefly opens up. It’s a small vacuum—a few fractions of an inch thick—but when it closes, the shock breaks the bottom of the bottle.
In our situation, the forces would be more than enough to destroy even the heaviest drinking glasses.
The bottom is carried downward by the water and thunks against the table. The water splashes around it, spraying droplets and glass shards in all directions.
Meanwhile, the detached upper portion of the glass continues to rise.
After half a second, the observers, hearing a pop, have begun to flinch. Their heads lift involuntarily to follow the rising movement of the glass.
The glass has just enough speed to bang against the ceiling, breaking into fragments . . .
. . . which, their momentum now spent, return to the table.
The lesson: If the optimist says the glass is half full, and the pessimist says the glass is half empty, the physicist ducks.
1Even a vacuum arguably isn’t truly empty, but that’s a question for quantum semantics.
Weird (and Worrying) Questions from the What If? INBOX, #5
q. If global warming puts us in danger through temperature rise, and super-volcanos put us into danger of global cooling, shouldn’t those two dangers balance each other out?
—Florian Seidl-Schulz
Q. How fast would a human have to run in order to be cut in half at the bellybutton by a cheese-cutting wire?
—Jon Merrill
Alien Astronomers
Q. Let’s assume there’s life on the nearest habitable exoplanet and that they have technology comparable to ours. If they looked at our star right now, what would they see?
—Chuck H
A.
Let’s try a more complete answer. We’ll start with . . .
Radio transmissions
Contact popularized the idea of aliens listening in on our broadcast media. Sadly, the odds are against it.
Here’s the problem: Space is really big.
You can work through the physics of interstellar radio attenuation,1 but the problem is captured pretty well by considering the economics of the situation: If your TV signals are getting to another star, you’re wasting money. Powering a transmitter is expensive, and creatures on other stars aren’t buying the products in the TV commercials that pay your power bill.
The full picture is more complicated, but the bottom line is that as our technology has gotten better, less of our radio traffic has been leaking out into space. We’re closing down the giant transmitting antennas and switching to cable, fiber, and tightly focused cell-tower networks.
While our TV signals may have been detectable—with great effort—for a while, that window is closing. Even in the late 20th century, when we were using TV and radio to scream into the void at the top of our lungs, the signal probably faded to undetectability after a few light-years. The potentially habitable exoplanets we’ve spotted so far are dozens of light-years away, so the odds are they aren’t currently repeating our catchphrases.2
But TV and radio transmissions still weren’t Earth’s most powerful radio signal. They were outshone by the beams from early-warning radar.
Early-warning radar, a product of the Cold War, consisted of a bunch of ground and airborne stations scattered around the Arctic. These stations swept the atmosphere with powerful radar beams 24/7, often bouncing them off the ionosphere, and people obsessively monitored the echos for any hints of enemy movement.3
These radar transmissions leaked into space, and could probably be picked up by nearby exoplanets if they happened to be listening when the beam swept over their part of the sky. But the same march of technological progress that made the TV broadcast towers obsolete has had the same effect on early-warning radar. Today’s systems—where they exist at all—are much quieter, and may eventually be replaced completely by new technology.
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.)
However, it transmits only occasionally, and in a narrow beam. If an exoplanet happened to be caught in the beam, and they were lucky enough to be pointing a receiving antenna at our corner of the sky at the time, all they would pick up would be a brief pulse of radio energy, then silence.4
So hypothetical aliens looking at Earth probably wouldn’t pick us up with radio antennas.
But there’s also . . .
Visible light
This is more promising. The Sun is really bright,[citation needed ] and its light illuminates the Earth.[citation needed ] Some of that light is reflected back into space as “Earthshine.” Some of it skims close to our planet and passes through our atmosphere before continuing on to the stars. Both of these effects could potentially be detected from an exoplanet.
They wouldn’t tell you anything about humans directly, but if you watched the Earth for long enough, you could figure out a lot about our atmosphere from the reflectivity. You could probably figure out what our water cycle looked like, and our oxygen-rich atmosphere would give you a hint that something weird was going on.
So in the end, the clearest signal from Earth might not be from us at all. It might be from the algae that have been terraforming the planet—and altering the signals we send into space—for billions of years.
Heeeey, look at the time. Gotta run.
Of course, if we wanted to send a clearer signal, we could. A radio transmission has the problem that they have to be paying attention when it arrives.
Instead, we could make them pay attention. With ion drives, nuclear propulsion, or just clever use of the Sun’s gravity well, we could probably send a probe out of the solar system fast enough to reach a given nearby star in a few dozen millennia. If we can figure out how to make a guidance system that survives the trip (which would be tough), we could use it to steer toward any inhabited planet.
To land safely, we’d have to slow down. But slowing down takes even more fuel. And, hey, the whole point of this was for them to notice us, right?
So maybe if those aliens looked toward our solar system, this is what they would see:
1I mean, if you want.
2Contrary to the claims made by certain unreliable webcomics.
3I wasn’t alive during most of this period, but from what I hear, the mood was tense.
4Which is exactly what we saw once, in 1977. The source of this blip (dubbed the “Wow Signal”) has never been identified.
No More DNA
Q. This may be a bit gruesome, but . . . if someone’s DNA suddenly vanished, how long would that person last?
—Nina Charest
A. If you lost
your DNA, you would instantly be about a third of a pound lighter.
Losing a third of a pound
I don’t recommend this strategy. There are easier ways to lose a third of a pound, including:
Taking off your shirt
Peeing
Cutting your hair (if you have very long hair)
Donating blood, but putting a kink in the IV once they drain 150 mL and refusing to let them take any more
Holding a 3-foot-diameter balloon full of helium
Removing your fingers
You’ll also lose a third of a pound if you take a trip from the polar regions to the tropics. This happens for two reasons: One, the Earth is shaped like this:
If you stand on the North Pole, you’re 20 kilometers closer to the center of the Earth than if you stand on the equator, and you feel a stronger pull from gravity.
Furthermore, if you’re on the equator, you’re being flung outward by centrifugal force.1
The result of these two phenomena is that if you move between polar regions and equatorial ones, you might lose or gain up to about half a percent of your body weight.
The reason I’m focusing on weight is that if your DNA disappeared, the physical loss of the matter wouldn’t be the first thing you might notice. It’s possible you’d feel something—a tiny, uniform shockwave as every cell contracted slightly—but maybe not.
If you were standing up when you lost your DNA, you might twitch slightly. When you stand, your muscles are constantly working to keep you upright. The force being exerted by those muscle fibers wouldn’t change, but the mass they’re pulling on—your limbs—would. Since F = ma, various body parts would accelerate slightly.
After that, you would probably feel pretty normal.
For a while.
Destroying angel
Nobody has ever lost all their DNA,2 so we can’t say for sure what the precise sequence of medical consequences would be. But to get an idea of what it might be like, let’s turn to mushroom poisonings.
Amanita bisporigera is a species of mushroom found in eastern North America. Along with related species in America and Europe, it’s known by the common name destroying angel.
Destroying angel is a small, white, inoccuous-looking mushroom. If you’re like me, you were told never to eat mushrooms you found in the woods. Amanita is the reason why.3
If you eat a destroying angel, for the rest of the day you’ll feel fine. Later that night, or the next morning, you’ll start exhibiting cholera-like symptoms—vomiting, abdominal pain, and severe diarrhea. Then you start to feel better.
At the point where you start to feel better, the damage is probably irreversible. Amanita mushrooms contain amatoxin, which binds to an enzyme that is used to read information from DNA. It hobbles the enzyme, effectively interrupting the process by which cells follow DNA’s instructions.
Amatoxin causes irreversible damage to whatever cells it collects in. Since most of your body is made of cells,4 this is bad. Death is generally caused by liver or kidney failure, since those are the first sensitive organs in which the toxin accumulates. Sometimes intensive care and a liver transplant can be enough to save a patient, but a sizable percentage of those who eat Amanita mushrooms die.
The frightening thing about Amanita poisoning is the “walking ghost” phase—the period where you seem to be fine (or getting better), but your cells are accumulating irreversible and lethal damage.
This pattern is typical of DNA damage, and we’d likely see something like it in someone who lost their DNA.
The picture is even more vividly illustrated by two other examples of DNA damage: chemotherapy and radiation.
Radiation and chemotherapy
Chemotherapy drugs are blunt instruments. Some are more precisely targeted than others, but many simply interrupt cell division in general. The reason that this selectively kills cancer cells, instead of harming the patient and the cancer equally, is that cancer cells are dividing all the time, whereas most normal cells divide only occasionally.
Some human cells do divide constantly. The most rapidly dividing cells are found in the bone marrow, the factory that produces blood.
Bone marrow is also central to the human immune system. Without it, we lose the ability to produce white blood cells, and our immune system collapses. Chemotherapy causes damage to the immune system, which makes cancer patients vulnerable to stray infections.5
There are other types of rapidly dividing cells in the body. Our hair follicles and stomach lining also divide constantly, which is why chemotherapy can cause hair loss and nausea.
Doxorubicin, one of the most common and potent chemotherapy drugs, works by linking random segments of DNA to one another to tangle them. This is like dripping superglue on a ball of yarn; it binds the DNA into a useless tangle.6 The initial side effects of doxorubicin, in the few days after treatment, are nausea, vomiting, and diarrhea—which makes sense, since the drug kills cells in the digestive tract.
A loss of DNA would cause similar cell death, and probably similar symptoms.
Radiation
Large doses of gamma radiation also harm you by damaging your DNA; radiation poisoning is probably the kind of real-life injury that most resembles Nina’s scenario. The cells most sensitive to radiation are, as with chemotherapy, those in your bone marrow, followed by those in your digestive tract.7
Radiation poisoning, like destroying angel mushroom toxicity, has a latent period—a “walking ghost” phase. This is the period where the body is still working, but no new proteins can be synthesized and the immune system is collapsing.
In cases of severe radiation poisoning, the immune system collapse is the primary cause of death. Without a supply of white blood cells, the body can’t fight off infections, and ordinary bacteria can get into the body and run wild.
The end result
Losing your DNA would most likely result in abdominal pain, nausea, dizziness, rapid immune system collapse, and death within days or hours from either rapid systemic infection or systemwide organ failure.
On the other hand, there would be at least one silver lining. If we ever end up in a dystopian future where Orwellian governments collect our genetic information and use it to track and control us . . .
. . . you’d be invisible.
1Yes, “centrifugal.” I will fight you.
2I don’t have a citation for this, but I feel like we would have heard about it.
3There are several members of the Amanita genus called “destroying angel,” and — along with another Amanita called “death cap” — they are responsible for the vast majority of fatal mushroom poisonings.
4Citation: I got one of your friends to sneak into your room with a microscope while you were sleeping and check.
5Immune boosters like pegfilgrastim (Neulasta) make frequent doses of chemotherapy safer. They stimulate white blood cell production by, in effect, tricking the body into thinking that it has a massive E. coli infection that it needs to fight off.
6Although it’s a little different; if you drip superglue on cotton thread, it will catch fire.
7Extremely high radiation doses kill people quickly, but not because of DNA damage. Instead, they physically dissolve the blood-brain barrier, resulting in rapid death from cerebral hemorrhage (brain bleeding).
Interplanetary Cessna
Q. What would happen if you tried to fly a normal Earth airplane above different solar system bodies?
—Glen Chiacchieri
A. Here’s our aircraft:1
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 el
ements 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
Here’s our pilot:
Here’s what would happen if our aircraft were launched above the surface of the 32 largest solar system bodies:
In most cases, there’s no atmosphere, and the plane would fall straight to the ground. If it were dropped from 1 kilometer or less, in a few cases the crash would be slow enough that the pilot could survive—although the life-support equipment probably wouldn’t.
There are nine solar system bodies with atmospheres thick enough to matter: Earth—obviously—Mars, Venus, the four gas giants, Saturn’s moon Titan, and the Sun. Let’s take a closer look at what would happen to a plane on each one.
The Sun: This would work about as well as you’d imagine. If the plane were released close enough to the Sun to feel its atmosphere at all, it would be vaporized in less than a second.
Mars: To see what would happen to our aircraft on Mars, we turn to X-Plane.
X-Plane is the most advanced flight simulator in the world. The product of 20 years of obsessive labor by a hardcore aeronautics enthusiast3 and community of supporters, it actually simulates the flow of air over every piece of an aircraft’s body as it flies. This makes it a valuable research tool, since it can accurately simulate entirely new aircraft designs—and new environments.
In particular, if you change the X-Plane config file to reduce gravity, thin the atmosphere, and shrink the radius of the planet, it can simulate flight on Mars.
What If? Page 10