[Afrobean]

Originally Posted by devonin

How do you know they aren't?

Probably because if you believe in a correcting time stream like that, a paradox would be unavoidable, and as Doc Brown put it, it would likely destroy the entire Universe.

If backward time travel is possible, it works on a branching system. If the time stream branches at points of backward time travel, it allows for instances of time dopplegangerisms without introducing the idea of a paradox. The future where the time traveler comes from need not exist in that iteration of time, because it DOES exist in another dimension where he came from.