We all love to point out the ridiculous bad physics in science fiction — it's like an awesome sport that everybody wins. (Except physics.) But the truth is, sometimes you have to violate the laws of physics to create science fiction stories that people want to watch. We asked six great physicists to name their favorite occasions when breaking the laws of physics makes science fiction better, and here's what they told us.
Here are 10 myths about space travel that make science fiction more fun.
Top image: Jamshed Jurabaev, via CoolVibe
1) Faster Than Light Travel
This is really the biggest and most important. As Phil Plait, writer of Bad Astronomy and author of Death from the Skies, tells us:
FTL is a big plot shortcut, of course, since even light takes years to get from star to star. But even when Our Heroes go from planet to planet in the same system, it doesn't take long. Hours maybe.. or whatever the script demands it to be for dramatic purposes. But in reality, planets are far apart. Our fastest probes take years to get from one place to another. Heck, the Moon is our closest neighbor in the entire Universe and it's still three days flight away. Of course, in the future we'll have faster rockets and all that, but still. Unless your whole plot revolve around some slower-than-light ship taking decades or centuries to get to the next star over, you have to use FTL. Without it, you'd have a vvvverrrrrryyyyy looooooooong movie with nothing happening. After all, space is big. That's why we call it that.
2) You can have artificial gravity without spinning the ship.
Notice how artificial gravity "always works as if you were on a movie set?" says James Kakalios, a professor of Physics and Astronomy at University of Minnesota. Pretty much only 2001: A Space Odyssey has gotten this right — you can't have artificial gravity in space without creating spin, to use centripetal force to keep people stuck to the "floor." And you'll notice that on shows like Star Trek, when life support and power are turned off, artificial gravity somehow always keeps working. (With the exception of Star Trek VI, of course.) Image by Hanho Lee via ConceptShips.
3) You can stop and start without worrying about inertia
Spaceships in science fiction seem to reach fantastic speeds almost instantly, and nobody's ever bothered by the inertia, notes Sean Carroll, a physicist at the California Institute of Technology and a contributor to the Cosmic Variance blog. You never see crewmembers being pushed backwards by the sudden massive acceleration — even though they are flung about when a weapon hits them.
4) Ships traveling at faster than light can communicate with other ships or planets
How exactly do these radio or other signals go fast enough to reach something that's traveling faster than light? Instantaneous communication across light years should be impossible in any case, but it's twice as impossible for objects traveling at superluminal velocities, notes Kakalios, the author of The Amazing Story of Quantum Mechanics and The Physics of Superheroes. Image by Matt Codd via Concept Art World.
5) Objects in space are bunched together
Science fiction movies and TV shows never accurately represent just how big and well, spaced out, space is, says Carroll:
Things are far apart in space. If you took your spaceship through the asteroid belt, you wouldn't even see an asteroid unless you really knew where you were looking. There's very little reason for ships to stay really close together, like the fleet in Battlestar Galactica. And if there were battles, you'd expect the combatants to stay as far apart as possible, and whichever ship had the longer-range weapons would have a huge advantage. But they would look really tiny on a TV screen.
Image: Sacrifice of Angels by Hathawayp4 at DeviantART
6) You can communicate with aliens
This isn't really a physics myth, but it's the one that jumps out at Amy Graves, a physics professor at Swarthmore College. She especially loves it when people come up with a convenient explanation for this, like Star Trek's Universal Translator or the Babel Fish in Hitchhiker's Guide to the Galaxy. Or the dictorobitron from Plan 9 from Outer Space.
7) Ray guns can actually disintegrate someone
The amount of energy required to cause someone or something to disappear, or even to blast a hole in someone, is completely insane, says Kakalios. "A cubic centimeter the size of a sugar cube has on the order of a million million atoms. A person has more," he explains. "If you want to disintegrate that person — blast them away — you need to provide so much energy, the atoms are shaking when they absorb this energy. They're shaking so violently, you break their atomic bonds, so the atoms go flying apart." But it's pretty much impossible to provide energy at a faster rate than the heat can be conducted away through the rest of the person, or object. "You're trying to fill a bathtub that's got a big open drain, and the faucet is not going fast enough to overwhelm the drain." Death rays and blasters are usually small and hand-held, but have an enormous power supply that can create a "short burst" of power, enough to blast a hole in a wall — but in practice, the energy would just be absorbed by the rest of the wall. Image by Matt Codd via Concept Art World.
8) Cheap energy is readily available
Speaking of ray guns, those power packs are usually the most unrealistic part of the whole scenario, says Craig J. Rodger, a physics professor with the University of Otago in New Zealand. A civilization that develops FTL travel, ray guns, and other "serious gadgets" will "need vast amounts of energy, the ability to store it, and use it quickly," says Rodger. This usually means a lot of "handwaving" about fusion plants, or microfusion power packs.
9) You can travel at the speed of light and no time passes elsewhere
If you do manage to travel close to the speed of light, the time dilation effects should be huge, says Kakalios. To the point where a few days traveling at light speed should mean that hundreds of years for the rest of the universe. When DC Comics had Supergirl appear in the 31st century in Supergirl and the Legion of Super-Heroes, and everybody was asking how Supergirl had traveled forward in time 1000 years, Kakalios actually emailed writer Mark Waid, suggesting that Supergirl could have been chasing a Dominator at light speed for a few days. That, by itself, would cause 1,000 years to pass. Waid responded that that was way better than what he'd come up with on his own, which was a rogue Zeta beam. This is something that science fiction stories "have to get wrong," says Kakalios, "unless you specifically wanted to fold time travel into the future into your story." And if you go backwards to your destination at light speed, it's not like the odometer rolls backwards — you just go further forward in time. Image by Layne Johnson via Concept Ships
10) You can travel in space without dying of radiation sickness
Maybe with really huge spaceships this isn't an issue, says Rodger — maybe the Galactica is just massive, and everybody lives in the center of it. But otherwise, you're going to have a huge challenge dealing with "the hot protons and neutrons coming from the sun. It's pretty hot out there," says Rodger. And it's probably a lot hotter outside the Heliosphere — some galactic cosmic rays get in through the Heliosphere, but we know at least some flux gets diverted, because the amount of galactic cosmic rays hitting us goes up and down with the solar cycle. You'd either need magical shields, a super-dense and heavy ship, or nanotech that repairs the cellular damage in real time. (And the heavier the ship, the bigger the problems with energy use.) Image: Dark Nova Fleet Battle Redux by Breandan_OCiarrai at DeviantART
"The bottom line," Says C. Megan Urry, the Israel Munson Professor of Physics and Astronomy at Yale University, "is that although many topics in astrophysics are ideal for science fiction settings, really, I think the universe is stranger and more wonderful than anything authors could imagine in their heads!"