Is faster than light travel possible?
Some fumblings by a science fiction author.
Space operas need faster-than-light travel for practical reasons. The distance between stars is so huge that unless your story takes place over centuries (which I’ve seen some books successfully do) there’s no possibility of space travel, let alone space empires. Yet we all “know” faster-than-light travel is impossible
But why is that?
I’m not a physicist, but I sort of understand relativity. So here is my possibly wrong attempt at explaining it.
The key with relativity is to understand there is no privileged reference frame. Imagine, if you will, one camera that is mounted on the universe that is perfectly stationary and it comes with one clock that decides what happens when. This is the world according to Newtonian physics.
According to both special and general relativity, this is not the case.
The problem is that it appears you can create any camera-clock at any place in the universe, and physics will work exactly the same. If you fire a laser from Earth (as it spins, orbiting the Sun, orbiting Sagittarius A*, which is itself moving through space) the light will travel at exactly c—299,792 kilometers per second. If a spaceship traveling at 0.5c away from you fires at Earth, light will travel at exactly c. And in fact, we on Earth and the spaceship will measure both laser beams at traveling at exactly c, but who fired first is impossible to determine, since what our clock-cameras say will not agree, even if physics works the same in both.
It’s hard to bend your mind around in the abstract—I’m not quite able to do it, either. But let’s talk about GPS. Every day, because the GPS satellites are traveling at high speeds relative to us, the clocks on the satellite tick 7 microseconds slower than a Earth-based clock due to special relativity. The satellites are farther from Earth’s gravity well than we are, so according to general relativity, they run 45 microseconds faster than clocks on Earth. The software and hardware are designed to handle this 38 microsecond difference, but the problem is only because we want clocks to sync up on Earth. From the perspective of the GPS satellites, time is running the same as it always does, and Earth clocks are the slow ones.
Relativity, Causality, FTL travel. Pick two.
The even stranger thing is that what the GPS satellite thinks “now” is on Earth is not the same as what we think “now” is on Earth. In fact, what we think “now” is on Earth is not what “now” is on Mars, Alpha Centauri, or anywhere else in the Milky Way.
So let’s say the warship from before shoots an FTL missile at Earth. Let’s say from its perspective it crosses a 100 lightsecond difference in 1 second. Everything is fine from its perspective. It launches “now” and one second from “now” it hits. But from our perspective, it launches in the future and arrives in the past, because “now” means something different for us.
Normal physics avoids this simply by banning faster-than-light travel. And so far, no FTL effects have been observed… well, maybe observed is an important word there.
But suppose you got in a spaceship with unlimited fuel and kept accelerating. As you approached the speed of light, your ship would need to expend more and more energy to get closer and closer. In fact, no matter how much energy you expended, you would still need infinite energy to actually reach light speed. Since the universe does not contain infinite energy, causality is safe… for now.
You can see how this immediately causes all the issues with time travel. Some SF novels just embrace that and have time travel all over the place. Others discard Relativity, and insist on one-clock camera, a privileged “now” that everyone is forced to agree on. A few brave authors dump FTL travel altogether; John C. Wright’s excellent Count to a Trillion has no FTL travel except by minds at least the size of galactic clusters.
Is it possible to rescue FTL travel, though, with “real” physics?
Warp speed!
If you could warp space in front of you, then you wouldn’t break physics per se. Thus the famous Alcubierre drive, hypothesized by an actual physicist. But you still end up with time travel in the end, or breaking relativity.
The critical issue, however, is that construction of the drive requires negative energy. Antimatter does exist, but it’d perhaps be better called contra-terrene. An antimatter particle still has positive energy, and it releases it in a spectacular explosion of energy when contacting identical matter. But negative energy is something else: it would be the lack of energy, and matter falling into it would simply cease to exist, like how money in your bank account ceases to exist when paying off a debt.
There are many, many cans of worms opened by negative energy existing. But physicists aren’t entirely sure if it doesn’t.
Cans of Wormholes
Another possibility is constructing wormholes, which are also not forbidden by general relativity. And if everyone agreed on the same “now”, then there would be no problem. But if aliens from Tau Ceti can build a wormhole from their planet, based on their “now”, and we built a wormhole from our planet, based on our “now”, going through both wormholes would land you in the past from someone’s perspective.
However, some researchers speculate that wormholes would naturally end up preventing changing the past, due to reasons I cannot understand from not being a researcher.
Wormholes, too, may exist! It’s possible that the quantum foam contains wormholes, which could potentially be grown big enough to go through. However, once again, this process requires negative energy, which may or may not exist.
Hyperspace?
A convenient, easily-access hyperspace will probably remain science fiction. However, what if space has more dimensions than we believe?
Imagine, if you will, an ant on a basket ball. From its perspective, it is standing on a flat ground. However, were it to tunnel through the ground, it would find additional space in a higher (to it) dimension.
Thus physicists have speculated about our universe being merely the surface (or brane) of a bigger spacetime continuum. Like any good SF author, I stole this idea for my own stories (particularly the Witch-Queen series) and without, of course, understanding the math behind it.
Quantum teleportation
In the even more mind-bending world of quantum mechanics, it’s impossible to know both the position and momentum of a particle. But, Einstein (who was not a huge fan of quantum mechanics) suggested a simple experiment along with Podolsky and Rosen. Entangle two particles so that they have the same position and velocity. Measure one’s position and the other’s velocity. Heisenberg is now spited.
Well, it turns out that Heisenberg has the final laugh, because if you measure one, it will affect the other, even faster than the speed of light.
This is super weird, and I’ll admit I don’t have the chops to really talk about it. But what I do know is that you can’t quite transmit information this way, because you have to transmit the measurements on your side to the other side, slower than light, in order to figure out what actually happened. Still, relativity and quantum mechanics have yet to be reconciled.
What if we dump relativity?
Of course, it’s possible relativity itself is wrong. But the reason physicists are attached to it (unlike SF authors) is that it’s elegant and makes sense. Somehow, the same math works whether you’re at the center of the galaxy or on the surface of the Earth, and so we on Earth can research what we might find at the center of the galaxy.
But suppose you are an SF author, and just want giant space empires with the requisite way cool space battles. It’s possible to sort of save relativity if you have multiple, but non-overlapping, privileged reference frames. Once you overlap, however, you get time travel.
What if we just want real physics?
However, relativity does come with some perks. While time will pass the same for you if you’re traveling close to the speed of light, space will contract before you. In fact, if you have the energy to constantly accelerate, you can cross from one edge of the galaxy to the other within your lifetime. As you approach the speed of light, time will seem to have stopped for you from Earth’s perspective, but from your own perspective, time is just traveling as it normal is. When you arrive, however, the world behind you will have been changing for tens of thousands of years.
What I think, for realz.
But what do I think about FTL travel?
It depends on three simple questions.
Are there aliens?
Are they fallen, like we are?
Does their method of salvation require the Church on Earth to evangelize them?
I don’t know if any of these are true, but if they all are, I would strongly believe that scientists will one day figure out a method of FTL travel. Otherwise, I don’t think even interstellar travel is practicable, but who knows?
In terms of the deposit of faith, we don’t have any reference to aliens per se. St. Augustine and St. Thomas Aquinas examined the possibilities of what we would call aliens: centaurs, dogmen, monopods, ultimately concluding that they, too, would be men in a theological sense.
However, if we turn to private revelation, we have a tiny bit of information. Eben Alexander, during his NDE, saw alien civilizations, so there’s that. (However, I don’t believe any NDEr has seen aliens in Heaven or Hell.) But NDEs haven’t been ruled on by the Church, as fascinating as they are for both believer and skeptic.
Among Catholic visionaries, Mother Eugenia had a vision of God the Father, who dictated a text in Latin to her, which she understood and wrote down despite not knowing Latin. In this message, which was approved by the local bishop, the Father talks about creatures which people knew nothing of, that he wished to bring into his fold. This vision occurred in the 1920s, at which point the Earth was pretty dang mapped out.
That, too, hasn’t been ruled on by the Church as a whole, though given the DDF is now working through their massive backlog it’s not impossible that we might get an answer sooner or later. Even with approval, it’s only private revelation, and not binding on anyone.
First contact would open the need for answers to those question, and, hey, maybe it will happen. I don’t know, though, so I don’t really know whether FTL travel is possible or not. I guess one day we may find out.