if time travel were possible, and our present is the past of another universe/generation (time travellers, what you will), then wouldn't people from the future come back to our time and fix certain problems, or come up with some genius invention and become rich now.
and what if two people from the future, say A and B came back to say hitler's time and decided to kill him. but they came back at different times say A came back 2 years before B and hence killed hitler first. but then B travelled back to that same time and killed hitler. would hitler still have been alive for person B to kill. would B be teleported back to the standard time with the standard history which we've recorded, or would the time B is teleported back to be the history which A has now messed up? or would they both just travel back to that same period of time, both kill him according to their frame of reference (dunno if this phrase can be used in this context but it's the best way to describe it), and if so then who do we record as the assassin? A or B, assuming they both killed him according to their frames of reference.