Does the physics of Marty’s time travel add up?
It's an interesting game to play, trying to make sense of something someone made up for the purposes of fictional entertainment. However, it does remind me of this exchange:
Maybe out lives have no meaning ...Leonard Hofstadter: 210, and you throw in the Iron Man helmet. Stuart: Are you crazy? That helmet's signed by Robert Downey Jr. Leonard Hofstadter: So? Stuart: Okay, if you're gonna question the importance of an actor's signature on a plastic helmet from a movie based on a comic book, then all of our lives have no meaning!