Reposting from /sci/, because /sci/ seems to be dead and maybe we could discuss potential ways in which FTL propulsion devices could work.
So, according to relativity, you either have causality, or you have FTL. Since throwing causality out of the window is something hard to conceive, since it would involve reformulating everything related to logic and throwing intuitivity out of the window which we already did with relativity, but whatever, we just decided to throw FTL under the train, probably because it's easier to ignore something we know nothing about, because of course relativity is correct.
But what if relativity is not correct? As in, it could be an incomplete theory that applies to most things within a "narrow" application space, more or less like Newtonian physics are applied nowadays to anything that isn't close to relativistic speeds. We know relativity does work according to many experimennts, but we don't know whether tachyons going FTL would have relativity applied to them, probably because nobody has ever seen tachyons and therefore can not test. Mathematically speaking, though, you should be able to describe the movement between two points as having infinite speed (teleportation), but this is not compatible with the way we think spacetime works, because that would open up a whole can of worms regarding time travel and event synchronization between different time frames.
So, is general relativity the be all end all theories ever devised where nothing could ever contradict it, or is this plain human "we could never be wrong" arrogance that could be "debunked" or superseded tomorrow?