GabrielGABFonseca wrote:No matter how hard you try, every single FTL method will create paradoxes.
You can even use clever tricks to avoid it from yours and your target's Reference Frames, but there will always be another frame of reference, somewhere, where it will be breaking causality.
It sucks.
That's only true for "true FTL". To understand what I mean, think of jump space from Babylon 5. Now imagine that jump space is literally just a higher-energy dimension of real-space (
the fifth dimension or whatever) that only happens to have shorter distances
because it's higher-energy state has caused space-time warping
somewhat analogous to that of space-time close to a black hole: the physical paths are shorter, and literally nothing else. Travelling through that does not necessarily create paradoxes, because not only can
you travel through jump space, but
so can causality, so it
appears to you that you've traveled faster than light, and you have
arrived faster, but only because you took a shortcut. Two equivalents might be useful:
1) You are in a space ship, beside a space station. The station fires a laser at a mirror in orbit around Pluto, and your ship
goes into FTL. You arrive at Pluto before the laser, turn around, and return to other side of the station. You beat the laser back, but when it does arrive, it is received by a detector on the side of the station that you returned to. This can break causality, because you
might have used a method that allows you to travel faster than the "causality cone".
2) You are in a space ship, beside a space station. The station fires a laser at a mirror in orbit around Pluto, and your ship
starts accelerating with ordinary thrusters. You maneuver around the station, to the other side, before the laser reaches Pluto. You beat the laser to the detector, but the laser still is received by the detector on the side of the station that you maneuvered to. This cannot break causality, because you
explicitly did not use a method that allows you to travel faster than the "causality cone".
Every causality violation system falls into scenario 1, but there can be "FTL" systems that fall into scenario 2 instead, the trick is just that causality has to be allowed to pass by that same system. There are consequences to this, of course: I haven't run any math, but just as an example, thinking about it has lead me to suspect that if wormholes are actually traversable in the real universe, then there must be some sort of inertia preservation mechanism going on (thought experiment: you have both ends of a wormhole following an identical ballistic path, but they're 180 degrees out of alignment, so that anything that goes in one end will be travelling the opposite direction when it comes out the other; how is momentum conserved?), which I assume would manifest itself in wormholes either having mass (in which case I would expect perfectly elastic collisions in the example case), or forcing a reshaping of space-time such that momentum would be preserved seamlessly (in which case I suspect that the example case is impossible, either through forcing the wormhole to collapse, or requiring an energy investment to rotate the wormhole that approximates that of a massive particle reaching the speed of light).
Regardless, not all "FTL" systems can actually be said to violate causality + relativity, because the term is broad enough that some of what it covers should instead
automatically let causality + relativity traverse it like ordinary space-time.