Originally posted by D.St.:
The movie I was referencing was Back to the Future II, where Marty McFly was able to go see his own future without having been there.
It's been a while since I've seen those movies, but I think it's okay that he could see his own future because, in that future, he had
already returned to the past to screw up the rest of his life. If he had gotten to his future and found that in that future he had disappeared as a teenager and never returned, he then should have been worried.
I had more of a problem with him fading out in the first movie when things weren't going well. If you go to the past and screw up your own creation, you wouldn't simply disappear, because that past is not really yours. The past you knew would still exist as a separate past from the one you're currently in. These stories always assume that there's only one timeline, but that can't be true the way these stories are written. If it's actually possible to change the past (which is arguable), then from the point at which you change it another timeline would branch off into a separate past, leading to a different future. Otherwise, the change you make is
already part of your past and cannot be changed, because your present already has the changes you make in the past factored into it.
Let's assume, however, that you can change the past. If you were then to try to move back into the future, you would be moving along a new timeline and would find a different future from the one you once knew. Your old future would still exist on another timeline. You would just have a very difficult time getting back to it.
I can prove this logically. If there's only one timeline, and you can change your past so that you cease to exist, then you would not only disappear from that past. No, every trace of you would also disappear throughout the timeline. That means that you would never exist to travel back in time in the first place. If you never travelled back in time in the first place, you wouldn't have been able to do anything in the timeline to prevent your existence. For Marty, that means that if he screwed it up so that his parents didn't get together, and he didn't exist, then he would never be able to screw it up in the first place, so his parents would get together anyway as if he was never there (which he wasn't).
But it's still a great trilogy, and I'm willing to ignore problems in stories like this if it's entertaining. However, if you want to see a movie with a premise that is completely and conspicuously logically impossible, check out
Minority Report and try to work out the possibilities. Unfortunately that movie wasn't good enough otherwise to overlook the fact that the movie simply can't happen.
[ June 29, 2004, 11:23 AM: Message edited by: Shaky & Blue ]