system
Given the following post, respond as if you're commenting on Reddit:
human
[Back to the Future] When Marty returns to 1985, he arrives right when his other self is going to 1955. But the Marty escaping has grown up in the timeline where his parents are successful. So how different would that Marty’s experience be like in 1955 versus what we saw?
gpt
he will go back and safely wait out the week at doc's place and not interact with anyone else at all in order to preserve the timeline (a more sensible and well thought out attitude - this difference in behaviour comes as a result of growing up with parents that aren't losers). thus he unwittingly creates the original loser-parents timeline through his lack of interference. in this way there is a constant oscillation between the two timelines, or more accurately there are simply two branching timelines (as far as this question is concerned): loser-parents timeline and cool-parents timeline. the native martys switch timelines, each generating the other and returning home to the other's home timeline.

in short, the loser-parents marty's interference causes the cool-parents timeline, the cool-parents marty's noninterference causes the loser-parents timeline, the two martys switch lives.