If you somehow managed to build a time-machine, you wouldn't be able to go back in time, or else the machine would disassemble itself, correct?

Then what? You can alter the past resulting in the alteration of the future?

What then, if you successfully went back into the past and stopped the planes from crashing into the twin towers? Would that very event not itself become a part of history, not changing the future, but simply adding to it? Even if you were the only one to know that you went back in time and prevented a catastrophe, what you did is still a part of time. Therefore you would not be altering the future, part of time, but adding to it.

The question then becomes, what determines the order of time? Or does it all happen simultaneously?

I think that if you go back in time, you can change things, but what you did orginially will be overwritten in time by the things you do when you go back. Like say August 10th, 1998 I was swimming at my friend's pool. If I go back to August 10th, 1998, I will have never swum that day, but instead done whatever it was I did when I went back. That way I'm never in two places at once. Then, time will reprogress/overwrite itself via whatever you changed. And when Today comes again, or when I travel back to day, things may have changed.

My other theory is that if I went back in time to when I was four, I'd simply be four again, not eighteen.

Meh, whatever. I don't feel like traveling through time anyway. I think I'll go make a sandwich.

-=-Kante-=-

Or there's the alternate universe theory. At the point you go back in time, the universe splits into two previously parallel timelines. One continues to exist as it was before, with your actions having no effect because you don't exist at that point in that timeline, and in the other your actions alter the course of the timeline and they diverge.

To use an example, it's like if your future self suddenly appeared from the future, kicked you in the nuts and ran away. Obviously your reality (the one where you would otherwise have grown up to come back in time and kick yourself in the nuts) is changed, but there's the other reality that split from yours a split second before your future self appears and which carries on as normal, where you actually do grow up to come back in time and kick yourself in the nuts.

It's like having your cake and eating it too, and neatly sidesteps a hell of a lot of time travel paradoxes.

You couldnt go back in time to kill yourself, because technically your still alive, which means it didnt actually happen, even if you did shoot yourself.

The 2 parallel universe thing seems to work, but wouldnt that mean thered have to be another parallel universe in the first place for it to happen?

Well, there's something called the many-worlds theory in quantum physics which hypothesises that every possible reality exists in parallel universes. I guess in that light you could look at time travel as a kind of large-scale quantum tunnelling between those universes.

I'unno. Makes more sense to me than anything else in this thread.

yes, you got it.

I'unno. Makes more sense to me than anything else in this thread.

I agree.

Also, assuming one could go back to a time in his own universe, anything he does will effect the state of the time that he left, so says the butterfly effect.

But I don't think you would go back to a time in your own universe. Just doesn't seem like it should be possible to me.

If you couldn't figure out a way to jump back a universe instead of forward a universe, you may never return to your own universe.

I think you'd create your own universe

If you couldn't figure out a way to jump back a universe instead of forward a universe, you may never return to your own universe.

That's true, but if there are (to all intents and purposes) infinite alternate universes, there are also presumably (practically) infinite alternate universes where the only differences to ours wouldn't ever be noticeable, such as the location of a single grain of sand in the Sahara desert or the luminosity of a single star 5 billion light years away, or the location or velocity of a single hydrogen atom in a nebula. There's so much that could happen in a universe, all you'd have to do is find one where everything you have direct knowledge of is the same. Or find a universe where the technology to direct your movement through universes exists.

I've read something really similar to that somewhere, the grain of sand analogy bit is lifted directly from it (as far as memory serves). I don't really recall where from, though, I think it's some old (as in 50s or 60s) sci-fi novel of forgotten provenance.

That's true, but if there are (to all intents and purposes) infinite alternate universes, there are also presumably (practically) infinite alternate universes where the only differences to ours wouldn't ever be noticeable,

Except the possibility of there being two Vanhallas in the same universe, unless that Vanhalla went universe hopping too.


I've read something really similar to that somewhere, the grain of sand analogy bit is lifted directly from it (as far as memory serves). I don't really recall where from, though, I think it's some old (as in 50s or 60s) sci-fi novel of forgotten provenance.In the Stephen Baxter novel Ring, (http://en.wikipedia.org/wiki/Ring_%28Baxter_novel%29)the universe is doomed because of dark matter entities known as Photino Birds (you can read more about them and why the universe is doomed in the link). But anyways, at the end the Xeelee create an escape hatch by looping cosmic string and they (pretty much a new species by then) look into it before they jump, he tells them it's constantly changing, but one of them look like the universe in this novel (http://en.wikipedia.org/wiki/Raft_%28novel%29). Then it changes again and they jump without knowing where they will end up.
I thought it was a really good book, but I had already read the first three books of Destiny's Children and Manifold: Time by then, so I was already used to his style of writing. Everyone won't enjoy these books, but I think they are awesome. Book two of Destiny's Children and Manifold: Time deal with some of and go far beyond the ideas in this thread.

Ring is one of my favourite novels, I must've read it ten times. Baxter's imagination and logic are superb, I'd definitely second the recommendation.

If the whole divergent alternate universes thing is true, for every universe containing a universe-hopper there's an alternate one that doesn't. Infinities are peculiar.

Infinites are annoying if you ask me. They are used too often as a way to "answer" questions without working hard to find an actual answer.

*skips most of the thread*

http://en.wikipedia.org/wiki/Novikov_self-consistency_principle

That's my thoughts on the matter.

I posted that thread. But I'am not understanding. I know if some odd man from the future warned me wabout a pending attack I would mark it on my calender..

It depends on the theories and methods you travel back in time. Some paradoxes solve themselves if you believe the multiple universes thing. Its all really useless actually IMO. If time travel ever exists why hasn't anyone visited our time yet?

There are no unidentified people from the future now. That means that nobody in the future is ever coming to our time. That means that time travel will never be possible.

Rainbows: If you really believe in the alternate universe theory, I dare you to try Quantum Suicide.
Also, if the alternate universe theory is correct, that means that we are screwed. Because no matter what accident we get into, or how old we get, there's this slight chance that we don't die that exact moment. So that makes us all almost immortal, no matter how crippled we get. Even if we try to top ourselves, we won't die but just keep suffering.

So I'd rather believe in the theory that objects exist in all their states at the same time, until they are discovered. Kind of like "do trees make a sound when they fall in a forest with nobody around?". It's stupid, but it gives us a chance to die with some dignity.

You can't assume that if time travel were possible someone would have come to our time.

I think it's fairly established that we don't live in an infinite universe, right? Either we will die in a big crush, or in a big "holy crap it's cold in here, but there isn't enough energy to turn up the heat. Fuck".

I don't entirely agree with Back to the Future; the alternate universe that they went into in the I think second movie doesn't really make as much sense as I'd like it to. I agree with the new Doctor Who series; anything you go back and do is part of what happened, what always had happened, what will always be what had happened. Martha Jones started people yelling ‘author’ at plays, the Doctor and what's-her-name caused Mount Vesuvius to erupt, etc. They went back in time, did some stuff, and really didn't change anything because that's what they were always destined to do. The only way to ever ‘change’ things is by creating a paradox one way and resolving it another way (like in ‘Father's Day’ or that one with the Master), but that paradox was always destined to happen, so time was always destined to have been changed... so while it may seem like things changed, they haven't really. So that's what would happen if time travel were possible, but it isn't (as far as we know), so there's no point speculating unless you plan to work for the BBC.

You remind me of my gay friend who is fanatical about Dr. Who.

I don't entirely agree with Back to the Future; the alternate universe that they went into in the I think second movie doesn't really make as much sense as I'd like it to. I agree with the new Doctor Who series; anything you go back and do is part of what happened, what always had happened, what will always be what had happened. Martha Jones started people yelling ‘author’ at plays, the Doctor and what's-her-name caused Mount Vesuvius to erupt, etc. They went back in time, did some stuff, and really didn't change anything because that's what they were always destined to do. The only way to ever ‘change’ things is by creating a paradox one way and resolving it another way (like in ‘Father's Day’ or that one with the Master), but that paradox was always destined to happen, so time was always destined to have been changed... so while it may seem like things changed, they haven't really. So that's what would happen if time travel were possible, but it isn't (as far as we know), so there's no point speculating unless you plan to work for the BBC.
You remind me of my gay friend who is fanatical about Dr. Who. Although I wouldn't base my post on a sci-fi program, but seriously, if you build a time machine you can't go back in time. Unless of course you found the time-machine that's been around since the beginning of time. Which is highly unlikely.