Pity sci-fi writers: they’ve got to come up with yet another Cowboys In Space movie or TV series. This means that all the things we take for granted in our daily lives have to be transferred into whizzy spaceships crossing vast distances without incurring any of the real-world problems that would render the script unworkable.
So script writers create deus ex machina solutions: wormholes, faster-than-light travel, subspace communications, perhaps even a species of docile super-unicorns that can violate all the laws of physics in order to ensure the protagonists can get home in time for dinner.
The problem is, most people don’t bother to acquaint themselves with physics. They read about wormholes in a sci-fi novel or see a CGI wormhole in their favorite space costume drama and assume the script writers (who’ve likely not even mastered basic calculus) know what they’re talking about.
Unfortunately, reality is far less willing to accommodate the needs of lazy scriptwriters than most people seem to assume.
Let’s start with faster-than-light travel, otherwise known by the acronym FTL (as in “activate the FTL drive, lieutenant!”).
This is basically a non-starter. Einstein’s Special Theory of Relativity, which resolved the fundamental discrepancy in Maxwell’s equations of electro-magnetism, showed clearly that (i) only things with zero rest mass can travel at the speed of light; and (ii) nothing at all can travel faster than the speed of light, which is approximately 300,000 kilometers per second.
Furthermore, if you try to accelerate anything that has a rest mass, you need more and more energy as you approach the speed of light (again, because of those pesky Einstein equations). If you had something the size of your typical sci-fi spaceship (and let’s face it, those non-NASA-spec things are huge) you’d need the energy of millions of supernova just to reach 99% of what you were aiming for. In other words, just a teeny bit impractical even if you conjure up impossible energy sources like crystals and special unicorn poop.
Could Einstein’s equations be wrong? Sure. Provided we live in a totally different universe with totally different physical laws. Otherwise, forget about it. Relativity has been independently confirmed in a variety of different ways hundreds of times. It’s a damned good description of how things work at large scales.
Talking of Einstein, guess who came up with the idea that sci-fi writers perpetually refer to as wormholes? Yup, Albert himself, along with a colleague called Nathan Rosen. They modeled the special case that would lead to two entangled black holes being connected by means of a very odd sort of spacetime (the so-called bridge). At this point, everyone who had a Cowboys In Space plot they wanted to pitch began to salivate because here was a solution to the problem of zipping around the galaxy in under 6,000,000 years. Because, let’s face it, even the most handsome action hero isn’t going to look great after all that time.
Unfortunately, the script folk didn’t bother to acquaint themselves with the actual equations. Had they done so, they’d have put the vodka back in the fridge and the cocaine back in its baggie because the equations show very clearly that any E-R bridge that could possibly be formed (by highly implausible trickery, by the way) would have to expand faster than even light could traverse it.
This doesn’t violate the axiom that nothing can travel faster than the speed of light because it’s the spacetime within the bridge that’s expanding and we already know that spacetime can expand faster than light can traverse it. That’s why our observable universe has a radius of 46 billion light-years but the total universe is certainly much larger.
So if you could create a wormhole by manufacturing a pair of entangled black holes (and this would be the most amazing trick ever!) and if you could avoid being torn to pieces as you approached the black hole (pretty much the second most amazing trick ever…) then you’d simply end up trapped inside the Einstein-Rosen bridge, unable ever to traverse it to reach the other black hole.
Oh, and if by unicorn poop magic you did reach the other black hole, you’d still be stuck because nothing, not even light itself, can escape from the gravity of a black hole.
So scratch the wormhole as a practical option for whizzing about the galaxy in a retro-styled spaceship.
The final desperate last gasp of the sci-fi enthusiast is the notion of warping spacetime around a ship, so that technically it doesn’t have to move faster than lightspeed but can still traverse distances faster than lightspeed.
First of all, there’s no theory to support this idea. Furthermore, as we learn more about quantum field effects, it seems highly likely that trying to warp spacetime in this way would be impossible because of the effects of potential energy. Plus, the energy required to achieve this magical warping of spacetime would have to be immense: think the energy contained in several galaxies because even super-massive black holes don’t warp spacetime to the degree necessary for a Alcubierre drive to work. And no one has a clue how to isolate the whizzy spaceship from the effects of all that distorted spacetime. Think of a huge vice-grip squeezing a raw egg.
Not really such a great an option for Captain Cowgirl and her crew, unless they love the idea of being omlettizised.
I know it’s no fun to let reality spoil the party, and script writers are always going to need more unicorn drives for their space novellas. But the rest of us should take the time to look at the equations and their derivations before getting overly excited about how we’re going to colonize space using things that we already know to be completely out of the question. It’s like imagining we’re off to the stars by using really, really big elastic bands to power our space catapults.
Meanwhile, there are some really interesting stories that could be written, using phenomenon we have every reason to believe are genuine, if only sci-fi writers would bother to educate themselves with a little basic physics and cosmology.
But then, we’d be unable to laugh at movies like Gravity and Interstellar, which hilariously get absolutely everything wrong.