But if, with every decision that has ever been made, the world goes off on a different tangent, there will be trillions of parallel universes (In fact, waaaaaay more than trillions. A number so big it's making my head hurt :ermm: ). So that's one possibility, but quite unlikely if you ask me. That theory would require a 5th dimension, as the space-time is taken up by the path we're on at the moment.
Even with that though, the "Grandfather Paradox" that Mike explained still stands. If you kill your parents, how can you be in the world at all? You can't, so how can you go back in time?
If you ask me, time travel won't ever happen (And I'll punch anyone who claims John Titor is "proof" :turned: ). Time is not the same as the other 3 dimesions we have in this universe, as it only moves in one direction, towards the future. It's nice to think time travel will happen one day, and I suppose it's always possible that new shit will come to light and time machines can be built in ways we can't even conceive. Anyway, we're getting off topic.