If it turns out that time travel is ever realy possible, i think the theory SR pointed out would be the most correct. However, I don't really think time travel is possible, perhaps travel to alternate dimensions yes, but not time travel. Only reason I don't think it is possible, becuase anytime you start to think about it, there are a million situations that cuase endless logic loops.
For instance, the old question of: "What would happen if you kill your father or mother before they concieve you"
I mean, if you kill them, you can never be born, making it impossible for you to kill them, or perhaps you never were born becuase sometime in the future you did kill your parents, but then how are you here now?
If someone put that situation out before, im sorry, I really didn't feel like reading all the posts.