Shrecknet posted:

BttF is one of the 'big three' of time-travel movie theories/systems (the other two being Terminator and Bill & Ted), and the idea that Marty obliterated his 1985 family by going to 1955 feels absurd. The timestream is ever-adjusting (his photos don't have binary 'marty exists/is annihilated' settings, they fade) and as such, we can infer that what Marty did was simply put his hand in the timestream to divert the water a bit; the fact that there is no Butterfly Effect-style 'Marty went back in time and now Nazi Dinosaurs rule the moon!' is proof enough of this. Since he only adjusted the eddies of the timestream, it's safe to say life proceeded mostly the same, and therefore the family in 1985 is his own.