I've been wondering about this for a long time. Given that special relativity is normally true, can we still prove that causality violation must occur if FTL is found? All proofs I can find, depend on it being absolutely true.
What occurs to me, is engaging an FTL drive might do something like prove the aether really does exist, but normal physics is disconnected from it. This model has a few problems, like for example anything transitioning to FTL ends up with an instantly high velocity relative to the aether.
Question almost matches Can FTL-Communication between two points in the same frame of reference break causality?, but the answers are opposed. The first (and most likely correct) answer doesn't apply; however the second one seems to apply but contradicts the first for that question's scenario.
I can prove the answer is NO by geometry if I make an assumption that we believe is false: attempting to cross a black hole event horizon is instantly fatal. A large enough (and galactic core black holes are large enough) black hole gives an absolutely backwards-pointing light cone that might be exploitable here (FTL drive usually means /can/ escape from black hole event horizon).
EDIT: Darn. Question appears to be meaningless without a particular theory to discuss. I was trying to ask if something similar to Noether's theorem for energy and momentum conservation is known under arbitrary laws of physics, but if I try to harden up the question to allow talking about drawing the parallel I get a contradiction in the question itself.