There are ways to get around the light speed limit. Alcubierre drive has a spaceship sit in a spacetime bubble that goes faster than c, but within its local spacetime the spaceship itself doesn’t exceed c. It’s similar to galaxies outside our observable universe appearing to move faster than c, but it’s really the creation of new spacetime that’s pushing them. The only hurdle with this is an engineering one, though it is a pretty major one, considering the energy required to bend spacetime like that.
If a superluminal event were observed it would depend a lot on the details of an event. If it were a particle that somehow exceeded c, we could come up with excuses as to why that sort of thing can only happen at an atomic level. If something like a baseball were launched faster than c, that would be more difficult to explain, but it would nonetheless have physicists very excited.
If you have a device that can allow you to travel from Proxima Centauri to Earth in a day, then you can also use that device to travel to the Crucifixion, or to the age of dinosaurs. This is true regardless of how your device works: It could be a wormhole, or a warp drive, or a magic carpet for all the mathematics cares.
If, in one reference frame, your device transports you from point A to point B and gets you there before light could have arrived, then there exists some other reference frame where the exact same journey took you back in time. And according to the theory of special relativity (which has been tested extremely extensively, and has passed all tests with flying colors), all reference frames are equally valid.
Sorry, i just don’t see how this follows. But if it did follow from Special Relativity, then that would mean that this would prove that Special Relativity wasn’t quite correct, wouldn’t it?
Think of it this way: According to relativity, space and time are the same thing. Where space leaves off and time begins varies depending on your frame of reference. Look at an event one way and you see spatial effects. Look at it a different way and you see temporal effects.
Imagine a rocket travelling close to the speed of light. To an observer on Earth the rocket is moving very quickly through space. Also, time on the rocket is passing very slowly. But to an observer on the rocket the rocket feels stationary and time is passing normally. The rocket is clearly moving, but in one frame that movement is mostly through time and in the other frame the movement is mostly through space.
An object travelling faster than the speed of light is exactly the same as an object moving backwards in time. Which effect you see depends on the reference frame you observe it from.
And therein lies the problem - if you can construct an apparatus to send a beam of light backward in time, it will arrive before you switch the apparatus on, and you could then decide not to.
Want more fun? Make the light a very powerful laser, and have it shoot and destroy itself one minute previously to its being activated. As long as you don’t turn it on, everything is fine…but what if you do?
You can also create similar problems with wormholes. Let’s say when you drop something in wormhole A, it emerges out of wormhole B, 10 seconds earlier. Aim wormhole B in the direction of wormhole A. Shoot a pool ball into wormhole A, so that it emerges from wormhole B 10 seconds earlier, hits its previous self, and prevents it from going through wormhole A. And thusly, the causality becomes undone.
Just because it seems counterintuitive to you? Intuition is a bad measure to apply to relativistic physics (or quantum mechanics, for that matter). It’s a fundamental consequence of time dilatation, which has been experimentally verified, and is in turn a direct consequence of the speed of light being constant in all frames of reference, which has both been experimentally verified and is explicitly predicted by Maxwell’s electrodynamics.
Picture two spaceships equipped with instantaneous communication devices, A and B, receding from each other in opposite directions from a common origin (so that both were in the same place at t = 0) at some substantial fraction of c (let’s say v = 0.866c, because that way we get a Lorentz factor γ [= 1/√(1 - v[sup]2[/sup]/c[sup]2[/sup]) for those playing along at home] of roughly 2). Then, viewed from A, the clocks on B are all slowed by that factor, thus, after ten seconds have elapsed in the rest frame of A, the clocks on B have registered only five. So let’s send an instantaneous signal from A to B at t = 10s in A’s rest frame. It arrives on B five seconds after they departed from the origin; so far, not so troubling. But then, they decide to tell A that they’ve received the message, so they send a signal using their instantaneous communicator. Now, from B’s perspective, it is equally valid to say that A is the moving ship, and thus, that their clocks are running slow – thus, the signal they send five seconds after the start arrives at A after 2.5 seconds have there elapsed since they took off – which means that they receive the ‘message received’ message 7.5 seconds before they even decide to send the original message!
Ah, I think you’re forgetting the premise of this thread: that we have proof of a super-luminal event. So theories like this are, as a consequence, not correct.
That doesn’t actually follow – we can observe galaxies receding with superluminal speed from us now, and special relativity is still correct. Also, wormholes and Alcubierre type drives are possibilities for attaining FTL speeds well within the framework (as far as is known) of relativity.
Well, we already know that relativity isn’t absolutely correct because it doesn’t play nicely with quantum mechanics. Both theories will probably eventually be supplanted by a more all-encompassing explanation.
But according to the conditions of your OP there’s only one superluminal event, which means they’re pretty rare. So relativity would still be a pretty good approximation for how most of the universe works most of the time, just like Newtonian mechanics is still a pretty good approximation for things that aren’t too big or too small or moving too fast.
It’s important to note that just because Newtonian mechanics made incorrect predictions in certain extreme circumstances, Einstein couldn’t just disregard it. In situations where things aren’t too big or too fast, relativity and classical mechanics return the same result.
So you can’t just say “What if we throw relativity out the window, what then?” Any new theory that encompasses your superluminal event must also encompass the observations that we’ve made that agree with relativity. And that means that time travel will be possible.
I’ve said this before in other threads: There are two different theories of relativity. The Special Theory of Relativity, which we’re discussing here, is perfectly consistent with quantum mechanics, as well as with everything else we know or suspect is true, and with all observations anyone has ever made. The General Theory of Relativity is more powerful, but it’s also more precarious: It is not consistent with quantum mechanics, and may be subject to any of a variety of modifications. I’d eat my hat, complete with all of the buttons and pins stuck to it, if the Special Theory of Relativity were ever overthrown, but I’d only be moderately surprised if the General Theory of Relativity were subsumed by something else in my lifetime.