Question: I'm not going to list this as a mistake since apparently it didn't happen, but George obviously changed his, his wife's, and Biff's future (at least) when he knocked Biff out in 1955. Since right there the timeline would have changed, what are the odds that Marty would still have been in the parking lot driving from the Libyans and going back to 1955? Couldn't Marty have accidentally caused a paradox to destroy the universe?
Phoenix
16th Feb 2004
Answer: Yes, he could have. But some theorize that the function of the universe itself cancels out paradoxes. For example, Larry Niven proposed that time travel can never be developed because by its nature it would constantly cause paradoxes, so natural accidents and twists of fate prevent time travel from being discovered. In this case, it's possible that Marty's life was rewritten to insure that he was in the right place at the right time to prevent a paradox.
Phoenix