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Is Time Travel Impossible?

  1. Apr 16, 2006 #1
    I was reading something about spacetime, and I have a question. Space and time are interwoven with each other and unless my understanding is utterly wrong, as an object's speed increases, time slows down. Thus, time slows with increasing acceleration. As well, the law for all motion under special relativity states that the combined speed of any object's motion through space and its motion through time is always precisely equal to the speed of light.

    So here is my question:

    If time stops when the speed of light is approached, would it not be impossible to go back in time even if we (hypothetically) had the technology to do so? There is not enough motion through time left to go faster than the speed of light, which we would need to go back in time?

    Am I correct? I just wanted to see if I understood this.
  2. jcsd
  3. Apr 17, 2006 #2
    Time travel is a myth. Like the fourth spacial dimension.
  4. Apr 17, 2006 #3
    Oh, I was just asking a similar question - but as far as anyone having a firm idea or theory, so far as I know, no one like Stephen Hawking has made an official declaration one way or another. The discussion so far seems to consist of, "maybe, maybe not...".
  5. Apr 17, 2006 #4


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    One thing i don't understand is why travelling in time would change the "arrangements" of particles. For example, if a glass falls to the ground and breaks to pieces, why would travelling back in time reassemble the glass? One alternative is that the glass doesn't reassemble, i only get to see the light that was emitted throughout the process, giving the impression that the glass is reassembling. In either case i don't understand why that would be.
  6. Apr 18, 2006 #5


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  7. Apr 18, 2006 #6
    Yes, time travel is regarded by many physicists to be theoretically possible. Since space is relative to time, the movement back and forth through space can also be applied to time. Scientists now think that wormholes occur naturally on the quantum level, since a wormhole is a tear in space-time, you could theoretically use it for time travel. The problem is harnessing enough energy to create such a thing.

    Stephen Hawking once said, "If time travel were possible then we would have already been visited by tourists of the furure." Well, in 2000 a guy named John Titor, said that he came from the future. Whether this is true or not is still unknown, but he brought with him predictions, pictures, and science to back him up.

    Then their is the problem of paradoxes. Well, due to recent advances in theoretical physics there is now an solution to that problem, parallel universes. If you went back in time and killed your grandmother, how could you have been born to go back in time to begin with. Well, if you were to do that you would just create a parallel universe. Because physicists now think that everytime the quantum world is faced with a choice, it divides itself into the number of worlds needed to cover every choice, now apply that to the macro level.
  8. Apr 18, 2006 #7
    uhh.. these "recent advances in theoretical physics are not near as recent as you suggest" also the paradox your refering to is known as the grandfather paradox, and is quite well known. also your reference to the "quantum world" seems to me to be no more descriptive of the region you are describing than simply saying the "world"... try using modifiers which will aid your argument.
  9. Apr 18, 2006 #8
    :frown: uhh buddy... there are a great number of dimensions even beyond the fourth, or atleast they are just as easily accounted for as the first three you accept, and therfore cannot be refuted without some evidence against the existance of them.
  10. Apr 18, 2006 #9
    so because i can't prove they don't exist, you're saying that means they must exist? haha. Ok, I lose. I can't prove they don't exist.

    Now it's your turn. Prove that just one extra dimension exists before you go talking about dimensions beyond the fourth. it's easy to draw flying elephants on paper, it's different to see them in real life.
    Last edited: Apr 18, 2006
  11. Apr 18, 2006 #10


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    There are some solutions to the equations of general relativity (the current best theory of gravity) that would allow for the possibility of backwards time travel, such as a spacetime that contains a "traversable wormhole". Many physicists speculate that a theory of quantum gravity would close these loopholes, but of course the leading candidate for a theory of quantum gravity is string theory/M-theory, which features 6/7 additional spatial dimensions. So one way or another, chances are good that you're incorrect.
  12. Apr 19, 2006 #11
    To Avoid Speculation and Warnings.
    How Would I achieve posting a theory that has not been discussed inside Physics of using two Space Ships as a means of producing a Miniature Black Hole that could curl up time by their combined energies inversely?

    I am not an exceptional Mathematician so it will be difficult for me to come up with Mathamatical Formula, I do have a very good Engineer mind with Engineer Math Skills only but not nearly as good as the Gurus.

    It would be ashame to pass up the creative method for developement of a Black Hole using two Ships and not have it evaluated by a Professional with actual Math to prove it can't be done.:bugeye:

    I have a very good down to Earth Imagination bordering on an Imaginative Genius Level but my Logical Side of the Brain needs work.
    Last edited: Apr 20, 2006
  13. Apr 20, 2006 #12


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    Either by fulfilling the requirements and submitting it to the Independent Research Forum, or if you do not have the skills to do that, only by posting your ideas as a set of individual questions and taking note of the answers you receive.

  14. Apr 20, 2006 #13
    I don't think I'm adding much to this discussion, but I'd like to point out something that annoys me greatly: when people say "no you can't travel through time because then you would get the thing when you kill your mum before you get born". The very simple solution to this is to state that there is only one timeline, and therefore anything that you might make happen in the past when you travel back has already happened. Bleh, I need dr. Dan Streetmentioner. Anyway.
  15. Apr 22, 2006 #14
    time travel is impossible. plain and simple. don't waste any brain cells thinking about it.
  16. Apr 22, 2006 #15


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    That statement is premature, given what is currently known about physics. General relativity does allow backwards time travel, and it's an open question whether the loophole will be closed by a theory of quantum gravity. There is certainly nothing logically impossible about time travel.
  17. Apr 23, 2006 #16

    Meir Achuz

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    Help! I traveled into the future, and now I can't get back.
  18. Apr 25, 2006 #17
    I would feel that modifers would not be needed being that i know of no other "Quantum worlds." Furthermore, I have heard it called the Grandmother Paradox, so it depends what you've heard (Correction was unnecessary.) I never made a comment on the rarity of the paradox.
  19. Apr 25, 2006 #18
    Time travel is impossible

    Well, to begin with, you would have to achieve AND surpass the speed of light to make time travel even plausible, and as we all know, that is impossible. Einstein's theory of special relativity, the faster you go to try to catch up to light, the faster it's going to run away from you. So if you're traveling at 570 million miles an hour, it's still going to appear as though it's travelling at 670 million miles an hour in front of you.

    Second, say you did achieve the speed of light, or a signifigant fraction of it, you would see that everybody else is moving slower than you are, so you'd think that are slowing down time, but you'd also appear to be going slower to everybody else observing you, even though you're traveling much faster. Einstein's theory of special relativity, among other fundamental laws of physics, states that it is impossible to travel back in time, or really even to slow time for that matter.
  20. Apr 25, 2006 #19


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    In special relativity, yes. But in Einstein's theory of general relativity (which special relativity is understood as a special case of), there do exist solutions where observers can travel through some twisted region of spacetime in such a way that they never locally exceed the speed of light but still end up in the past light cone of some earlier point on their worldline. See this article by physicist John Cramer, for example; a more detailed discussion can be found in the book Black Holes and Time Warps by Kip Thorne.
  21. Apr 26, 2006 #20
    soapbox talk...

    At odds with your own,eh?...apropos. I'd like to disqualify myself quickly in that I'm layman, but it would seem to be more accurate (historically speaking) to say "Time travel is impossible *with the proveable knowledge we presently have*".
    To bleed the lines a bit, we humans are subject to evolution and many other unknown inputs I believe.
    Perhaps the thread should have been "What proveable basis do we have to support the possibility of time travel so far?", or some such.
    To say 'impossible' keeps the world flat.:wink:
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