I understand that the questions behind causality and FTL have been brought up numerous times, and I have read several of the old threads. My question isn't with how is causality violated, it is always assumed that any signal sent would appear to travel backwards in time from one point of reference or another. I don't exactly understand why since all examples given to me always seem to make reference between when the events where OBSERVED after having previously stated that when an event is observed does not imply causality violations. Is there an equation which would explicitly clear up how exactly a signal travelling faster than light would move backwards through time. Please don't use an example with the mirrors because if you were to travel faster than light you would leave the photon behind with nothing for it to bounce off of unless you were to stop and wait for it to catch up. This isn't for if FTL is possible since there are plenty of other much more obvious reasons why it isn't. I am just trying to understand why a signal or ship would move backwards in time.