Movie example time travel question: when they go back in time to change something?

it's called a paradox, it happens when things like time travel come into play. Basically when they go back and change the thing the entirity of history is changed and we enter an alternate time line in which things continue with the change as if it was normal

you are a very Intelligent person and i think you are right

the easiest thing is called the grandfather paradox and it proves that it is impossible with anything on a macro scale. if you went back in time and killed your grandfather, then your father wouldn't exist, and you wouldn't be born, but, if you weren't borne, you couldn't go back in time to kill him.

Dude, why not change your clothes from a red shirt to a blue shirt and go back in time, like 10 minutes and meet yourself the way you were before you changed and fight yourself. If the blue "you" killed the red "you", you'd be cool cuz the blue "you" continues on. But if the red "you" killed the blue "you", then you'd be in trouble cuz the red "you" is going to disappear in a couple of minutes and travel back in time.

Welcome to the world of time-travel paradoxes. Larry Niven proposed that even if it were possible to invent a time machine, it would never happen, because if someone did, eventually somebody would go back and change the past such that the machine never got invented.

you lost me at "wouldn't that mean" but ive thought about how this would all work, and i think i might know what you mean

Fist off, movie time travel is usually crap. The script writers never take the time to make it consistent with any acceptable theory of metaphysics (at least not in my experience). As a presentist, I believe that the only time is the present, period. Accordingly, there is no past and no future, only now. But this view is not at all inconsistent with what you're talking about. The "going back in time" would have to actually send the traveler into something like a parallel universe which wouldn't actually affect the present from which he/she came (except for the fact that the traveler would be gone). If this be the case then "going back in time" would be pointless if you wanted to change the world for other people. It would be useful, however, if you wanted to change the world for yourself and your changes would affect everyone in that universe. Another possible solution to the many time travel problems could involve abstract times and concrete particular time, but I'm not even going there.

Time travel movies are largely based on story telling and not on anything scientific. Since no one has ever traveled in time, there's no way of knowing for sure. But the scientific community does have two different theories of what would happen: 1. When you went back and tried to change the past, something would continually happen that would prevent you from changing it. (This is what happened in the 2002 remake of "Time Machine," where he went back to save his fiance but she kept getting killed no matter what he did.) 2. You would succeed in changing the past. You would then be in a parallel universe in which everything happened exactly the same as it had in your own universe, except for the thing you changed. So you could then go back to your own time, which would actually be a different universe than the one you were in originally. In your own universe, the changes you made never happened. You just disappeared one day and everyone wondered where you were. (This is what happened in "Back to the Future" when he went back to 1985 and found his dad all successful and Biff was afraid of him now.)