Sorry that this thread has nothing to do with gaming but I had to get this off my chest.
Time travel is one thing that doesn't really seem to be compatible with our experience of time. Time goes straight and doesn't change, so what would happen if it did change.
One theory is that you can't change time its one long line thats unchangeable and absolute. If you go back in time whatever thing that you do to change the timeline will fit into the one timeline even if you set out to do something else (think Harry Potter and the prisoner of azkaban). I don't think that this very solid. It wouldn't be difficult to bring back a nuke and bomb everyone to kingdom come, people who would of previously not been nuked. Another one is that if you change something like say kill your mother before you were born it means that you were never born so you can't of gone back to kill your mother so she doesn't die but then you are born so you do kill her. And so a paradox follows. I on the other hand would say actually no, you wouldn't just disappear and so not kill your mother, you just kill your own mother.
So you go back in time and kill your mother who is pregnant with you so you die and obviously can't kill her. BUT the you that killed her has already been born, YOU don't need to be born again. You and the baby you are two DIFFERENT physically things. Maybe exactly the same in every way, but your still separate so it doesn't make sense that if you kill the baby you, you die too, you'd be completely healthy and fine. as for who would go back in time to kill your mother you've already done that so no-one needs to do it again.
I think of it as the world having a time line (that your now screwing with and changing) and you have also got a time line. So you've in your timeline you've already been born, grown up, gone back in time and killed your mother. Nothings going to change that unless you rewind both timeline at the same time.
Of course this also brings up the problem of what happens to the worlds timeline?
There are two ways I can see of thinking about it. One is you just change it and another is you go into another parallel universe or indeed actually create it. So one you go back change something then go back to the present and everything has changed. And because of your own timeline you've already changed everything and there's nothing you can do to stop it. Because the first world timeline didn't have you going back in time and now you have, you can't undo it, the world will never be the place you left it again because in your timeline you've changed the world timeline. Unless you can change your timeline you can't change that. Still with me, cos I'm not completely sure I am.
The other way of thinking of is that you create a new universe because in this current universe no one has gone back in time (that we know of...(who knows maybe those flying saucers are the just the future us mind fucking the past people)). So when you go back in time you've changed the world which is what a parallel universe is, a world that's slightly different to ours. So you've created your own universe and what ever changes you make will change the future BUT you can never go back to the first universe because when you go forward in time the changes you made will have changed stuff so it will be a different world. And again only if you can reverse both timelines(your and the worlds) can you change this. And another thing to think about is that every time you go back in time you change the world again so you go into another parallel universe. One other thing is what happens to the universes you left behind? What happens to the original first universe?
I've got two things on this too. One is that the simply cease to exist, they just disappear. Because you changed the timeline that universes timeline no longer exists.
Or that universe just continues on and you simply disappear, just vanish into thin air because you've gone to another parallel universe.
Of course this is all made a little redundant if we never actually get to go back in time. Theres the wormhole theory which does actually seem to make time travel possible. Or there going faster than the speed of light or breaking some other speed barrier. Now I know theres some very brainy scientists with massive and powerful computers who say that its impossible to break the speed of light barrier. But thats what we said about the sound barrier, we said it wasn't possible to get stuff that fast because it had too much mass. And yet we did it. Also when we first starting making trains people where worried that all your bones would dislocate and you would die but that didn't happen. Point is science isn't always right, its continually saying things then finding out that its not true (remember the butter/margarine thing?). What makes this time any different. Just because we say its impossible now doesn't actually make it impossible.
Maybe Time Travel is just simply impossible and so its literally incompatible with this existence.
Right I've said pretty much all I want to say about this. It might seem to you to be a bit out of place here and I have no idea if anyone's said any of this stuff before. But thats my take on it so enjoy.