Time Travel

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I don't know much about physics, but I was wondering the other day whether what I was thinking was a popular theory.

If time is like a one dimensional line and it starts at the orgin and it grows like a vector along the line as time progresses, then wouldn't it only be possible to travel back in time since that portion of the vector has already been created. And if you went back in time, the all of the vector after the time you went back to erases. So once you go back in time you can't go back to he original time.

Does that make sense?
 

Ivan Seeking

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In order to return to the point of origin you would only need to travel at speeds near the speed of light. Do this for a few minutes, turn around and come back at similar speeds, and you could arrive at a time decades later [or whatever length of time is required]. This is the effect of time dilation from Special Relativity. Going backwards in time is the tough one. The short answer is that we don't know if travel to the past is possible. Also, even if it is theoretically possible, it may never be practical. We just don't know. Of course it is no small challenge to travel at speeds near the speed of light either - about 186,000 miles per second. The fastest manmade object ever to carry humans was the Apollo 10 capsule, which reached a maximum speed of just under 25,000 miles per hour upon reentry.

Here is some good information.
http://math.ucr.edu/home/baez/physics/Relativity/GR/time_travel.html
http://plato.stanford.edu/entries/time-travel-phys/#10
 
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do you think we will know?
 

Ivan Seeking

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Should I look into my crystal ball? :biggrin:
 
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I think it was Stephen Hawking who showed (in a theory of entropy) that the universe could not reverse itself. What I understand from this is that relatively lightlike configurations can not repeat their past.
 

Ivan Seeking

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Could you be a little more specific?

Are you referring to the chronology protection conjecture?
 
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That sounds about right: http://en.wikipedia.org/wiki/Chronology_protection_conjecture" [Broken]. My informed guess was pretty close, but with more accurate physical description this link explains better what Hawking probably had in mind.
 
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Ivan Seeking

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.... Hawking opined that it seems there is a chronology protection agency, which prevents the appearance of closed timelike curves and so makes the universe safe for historians. He may be right, but to date there are no convincing arguments that such an agency is housed in either classical general relativity theory or semi-classical quantum gravity. And it is too early to tell if this Agency is housed in loop quantum gravity or string theory...
http://plato.stanford.edu/entries/time-machine/#Conc
 

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