Hi all--First post for me here.This subject has always fascinated me and reading through this thread made me think about a few things.
I am a layman (woman),therefore I might not understand the finer points and nuances of quantum physics/mechanics.
According to what I understand regarding Heisenburg's Uncertainty Principle (Many-Worlds Uncertainty)and Schrodinger's Cat Paradox,nothing in the movie(s) BTTF is paradoxical because all possible futures/iterations exist simultaneously and every outcome is possible because there isn't just one singular timeline.
According to the many-worlds theory--once a decision is made and an action is employed--all the events play out in a certain way on that particular timeline and the 'observer' there has no knowledge or memory regarding what goes on in any of the alternate/other universes.
The BTTF movies are among my favorites and I have found that if I question things too much that it interferes with my immersion to some extent so I just have to allow for a certain suspension of disbelief.
Having said that--all of this may possibly be moot in the first place,as from what I understand--time travel into the past is not possible/viable,as nothing can exceed the speed of light (yes--I know about neutrinos possibly refuting that,as well as even MORE theoretical tachyons).It's also my understanding that travelling to the past would set up an infinite feedback,which would have dire consequences.
So,there's my two cents.