No paradox for time travellers

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No paradox for time travellers
http://www.newscientist.com/channel/fun ... rld/dn7535
THE laws of physics seem to permit time travel, and with it, paradoxical situations such as the possibility that people could go back in time to prevent their own birth. But it turns out that such paradoxes may be ruled out by the weirdness inherent in laws of quantum physics.

Some solutions to the equations of Einstein's general theory of relativity lead to situations in which space-time curves back on itself, theoretically allowing travellers to loop back in time and meet younger versions of themselves. Because such time travel sets up paradoxes, many researchers suspect that some physical constraints must make time travel impossible. Now, physicists Daniel Greenberger of the City University of New York and Karl Svozil of the Vienna University of Technology in Austria have shown that the most basic features of quantum theory may ensure that time travellers could never alter the past, even if they are able to go back in time.

The constraint arises from a quantum object's ability to behave like a wave. Quantum objects split their existence into multiple component waves, each following a distinct path through space-time. Ultimately, an object is usually most likely to end up in places where its component waves recombine, or "interfere", constructively, with the peaks and troughs of the waves lined up, say. The object is unlikely to be in places where the components interfere destructively, and cancel each other out.

Quantum theory allows time travel because nothing prevents the waves from going back in time. When Greenberger and Svozil analysed what happens when these component waves flow into the past, they found that the paradoxes implied by Einstein's equations never arise. Waves that travel back in time interfere destructively, thus preventing anything from happening differently from that which has already taken place (www.arxiv.org/quant-ph/0506027). "If you travel into the past quantum mechanically, you would only see those alternatives consistent with the world you left behind you," says Greenberger.

"This is a very nice idea," says physicist Avshalom Elitzur of the Weizmann Institute in Rehovot, Israel, who also suggests that further work in the area could help to clarify the nature of time itself. "Time is a very mysterious thing."

Makes sense. Since the sign or direction of time is interchangable on a quantum level it's only logical that going 'back' in time would lead you only to conditions that would again lead back to the 'present'.

Though I don't have a formal proof, as I'm sure they do, I've been saying this for years.

There is still profit and gains from watching the past unfold. esp in the fields of science and history.
and think about it, if you could hold still in time while moving then star travel in an instant becomes possible almost regardless of the distances.

I read something similar to this article. It inspired me to write another play based loosely on this new philosophy.

I've always subscribed to the theory that going back in time always splits the timeline. So if you went back in time to kill your grandfather, you'll still have come from the timeline in which your grandfather wasn't killed. But this is a new timeline, and you can kill him, which will only prevent the alternate timeline version of yourself from being born, but the original timeline version of yourself is still there.

I always thought that it was impossible to kill yourself or any of your ancestors via time travel, because, if you did kill them, you would not have been born in the first place, and thus would be unable to go back and commit the murder in the first place.

It's good to know that when someone in the future invents a time machine and comes back to sell it on eBay, no one will be able to use it until the time in which it is originally invented and been used has passed as then it would no longer be the first time jump when it has already happened.

The problem I have with the bonkers theorising of time travel is that the events which are supposedly not able to be prevented are not given any scale.

So, if I had a time machine and went a minute or so back in time and just stood there, I would be occupying space which was occupied by specific particles of air in the future when I travel back. By standing there I am disrupting this event by simply interacting with the air, each particle itself a universe-defining event.

None of this speculating distinguishes between going back in time to rig a lottery draw or simply disrupting where air particles were previous.

The problem I am having trouble understanding is that I am STILL changing events just by being there. The only way this could be different is if everything was like a 'shadow' of the past like in Charles Dickens' A Christmas Carol where Scrooge goes back in time.

It's all cause and effect, only the cause happens 'after' the effect, going back in time takes you to the exact same past, you don't change anything.

Imagine watching a video tape of yourself walking around, now play it backwards, your image is moving back in time, now play it forwards again, the exact same thing will happen as when you first played it, your prescense in the past is really no different than the first time you were there.

What if you pressed record after you rewound?

The universe blows up.

This is what I call the EGO theory of time travel.

Anything you do in the past, you already did and history is dependant on you doing so.