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Wormhole mouths

  1. Jan 11, 2015 #1
    Hello, All!

    Could a wormhole take us to a different time, but the same place? (Meaning, is it possible for the two mouths of a wormhole to be separated only by time, and not by (significant) space?

    Thank you very much!
     
  2. jcsd
  3. Jan 11, 2015 #2
    Maybe, but a person needs to know how to keep the thing opened in the first place; I'm not too sure how one'll be able to manipulate where a wormhole will take you in time and or space—probably never going to bring you into the past, but more likely into the future, I'd say.
    As for traveling through space, that's much more probable.
     
  4. Jan 11, 2015 #3

    Matterwave

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    It's very hard in General Relativity to try to specify "the same place", and care must be taken whenever you try to invoke this concept. What constitutes "the same place" is different to different people. So what do you mean by "the same place"?
     
  5. Jan 11, 2015 #4
    I think he means a wormhole with a time-like distance between its ends. In that case there would be frames of reference where they are at the same place at different times.
     
  6. Jan 11, 2015 #5

    Matterwave

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    If a wormhole is to be traversible, it must mean that the two ends are connected by time-like curves...so wouldn't that be every (traversible) wormhole?

    EDIT: added word
     
    Last edited: Jan 11, 2015
  7. Jan 11, 2015 #6

    WannabeNewton

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    Did you mean to say "the same time"? If so then yes. See Morris et al (1988). The conclusion of the paper is that if one has a traversible wormhole wherein one mouth is moving with respect to the other then closed timelike curves form in the wormhole. If not then it would seem the question is trivial as matterwave pointed out.
     
  8. Jan 11, 2015 #7
    Both outside and inside?
     
  9. Jan 12, 2015 #8
    You might want to take a look at a popular science book called Black Holes, Wormholes and Time Machines by Jim Al-Khalili which looks at this sort of thing.

    These two articles also look at the possibility of wormholes as time machines-
    Time Travel and Wormholes: Physicist Kip Thorne's Wildest Theories
    Wormholes: Space Machines and Time Machines

    Taken from the first link-
     
    Last edited: Jan 12, 2015
  10. Jan 12, 2015 #9

    Matterwave

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    So you want to rephrase the OP question to "Is it possible for 1 mouth of the wormhole to be in the chronological future of the other mouth of the wormhole, where causal structure is determined in the absence of the wormhole?" I think this is possible. I'm not sure how rigorous you could make this statement, but at face value, I don't see why not.

    But of course, if you modify it this way, I doubt you are staying within the spirit of the OP. There are time-like curves from here to Andromeda...or to a distant quasar. After all, I would simply have to send a particle there to prove there is a time-like curve connecting these objects' world tubes to the Earth's world tube. I don't know if the OP would consider here and Andromeda to be "the same place" that he means in his question.
     
  11. Jan 13, 2015 #10
    He just need to chose an appropriate frame of reference.
     
  12. Jan 13, 2015 #11

    PeroK

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    By that definition the Bakerloo line on the London underground is a wormhole.
     
  13. Jan 13, 2015 #12

    bcrowell

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    But if you ride the train from one station to another, your wristwatch is still synchronized with the clocks outside, and if you ride the train in the opposite direction you don't end up in the past.

    If there's an external frame of reference where the two mouths are at rest at the same place, at different times, then at some point the past mouth is either going to have to disappear or else it's going to be present at the creation of the future mouth.
     
  14. Jan 13, 2015 #13

    pervect

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    My $.02

    While the OP didn't specify a frame of reference or a coordinate system, there's an obvious choice to specify for him - cosmological coordinates, in which objects moving with the Hubble flow are said to be "in the same place". So lets just make that an explicit assumption in order to answer the question.

    Going back to the original question - I don't think it makes sense to allow the two mouths of the wormhole to be in the same place at the same time (here I mean cosmological time), but it's certainly possible for the two different mouths to be in the same place at different times.

    We also have to consider the connection between the mouths. The connection between the mouths can be in general different from a path through cosmological time, and while the connection through the interior path will be timelike, the connection through the exterior path may be spacelike or timelike in general. I see no reason why the connection cannot be such that you enter one of the mouths, and exit the other mouth at the same place at a different time, as long as you ensure that the two mouths are never at the same place at the same time on a cosmological space-time diagram.

    I'm assuming there isn't any issue with wormholes becoming time machines or the existence of CTC's. If you wish to allow the chronological protection conjecture that CTC's are not allowed, the answer might be different.
     
  15. Jan 13, 2015 #14

    bcrowell

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    You basically can't have wormholes without CTCs. You can't form a wormhole without also having CTCs, because topology change can't happen without CTCs. There's a theorem by Geroch on this, described here: http://arxiv.org/abs/gr-qc/9406053 . Any wormhole is also capable of being turned into a CTC: Morris, Thorne, and Yurtsever, "Wormholes, time machines, and the weak energy condition," Phys Rev Lett 61 (1988) 1446.
     
  16. Jan 13, 2015 #15

    Matterwave

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    This was my hunch, so I have been replying in this thread without regard for CTCs. I do; however, wonder if one can fix this partially by making the wormholes only 1-way traversible? (Surely there's a way to build such wormholes?)
     
  17. Jan 14, 2015 #16

    pervect

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    While I agree that creating a wormhole classically requires a time machine, one of the references you cite, "Wormholes, time machines, and the weak energy condition," suggest that wormholes could be created from "quantum foam" without violating Geroch's theorem.
    Thus, as far as I know the non-classical (i.e. quantum) formation of wormholes is still thought to be possible without time machines, even though classical formation of wormholes does require them.

    As far as turning wormholes into time machines go, there is a possibility and perhaps even a probability that quantum vacuum fluctuations could destroy a wormhole that attempted to become a time machine. My not-very-good understanding of this is from Kip Thorne's popular book, "Black Holes & Time Warps", pg 521

    The literature reference where this is discussed is "Do Vacuum fluctuations prevent the creation of closed timelike curves", Kim and Thorne, 1991, the conjecture that they will prevent the creation of time machines is originally due to Hawking. Thorne seems to believe that this is not only possible but likely. Nobody knows for sure, as the calculation requires an understanding of quantum gravity, so the whole issue is poorly understood as Thorne is one of the first to point out.
     
  18. Jan 14, 2015 #17
    Take a second wormhole for the opposite direction and the problem returns.
     
  19. Jan 14, 2015 #18

    Matterwave

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    In a globally hyperbolic space-time (indeed, even in a strongly causal space time), there can be some notion of "forward in time" given by the "time coordinate" of the Cauchy surfaces which foliate the manifold. Given this notion, perhaps it becomes possible to define 1-way traversible wormholes that only allow travel "forward in time" was my thinking. Perhaps then, we can avoid CTCs. I don't know how to make this rigorous, nor do I know if this would fix any of the CTC problems however.
     
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