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Closed timelike curves

  1. Jul 6, 2011 #1
    do they exist in reality or in nature?
     
  2. jcsd
  3. Jul 6, 2011 #2

    bcrowell

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    We have no evidence that they exist in our universe. There is also a conjecture, which I think is widely considered plausible, http://en.wikipedia.org/wiki/Chronology_protection_conjecture that a spacetime that doesn't already have CTCs can't acquire them.
     
  4. Jul 6, 2011 #3
    so they might not be permitted in the universe?
     
  5. Jul 6, 2011 #4

    bcrowell

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    Unless (a) the chronology protection conjecture is false, or (b) CTCs naturally existed as a feature of the universe starting from the big bang. There are cosmologies like the Godel metric http://en.wikipedia.org/wiki/Gödel_metric that have CTCs and always have had them. Observations of the CMB anisotropy rule out the Godel metric as a model of our universe, but they don't necessarily rule out all possible cosmologies that have CTCs.
     
  6. Jul 7, 2011 #5
    what could possibly rule out ctc's all together?
     
  7. Jul 7, 2011 #6

    stevebd1

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    Closed timelike curves are predicted to exist around the ring singularity in Kerr-Newman metric-

    http://arxiv.org/PS_cache/arxiv/pdf/0708/0708.2324v2.pdf

    though this is technically a hypothesis (CTCs) within a hypothesis (Cauchy horizon) within a theory (black hole/event horizon).

    The CTCs are also within a boundary called the turnaround radius which some predict is supposed to send an infalling object out through a (very hypothetical) white hole-

    http://casa.colorado.edu/~ajsh/phys5770_08/bh.pdf (page 23)

    so even at this level of prediction, there seems to be some level of protection from reaching the CTCs (though a white hole would be just as elusive as CTCs, it's normally best to say that the Cauchy horizon is the barrier of predictability).
     
    Last edited: Jul 7, 2011
  8. Jul 7, 2011 #7

    pervect

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    The Kerr Newman metric is probably unlikely to exist in our universe, though - it's basically idealized and inherently unstable. From what I've read it's so unstable that it can't self-consistently describe a single particle falling into the inner horizon - such a particle would acquire infinite blueshift, infinite energy - and distort the geometry into something that wasn't a Kerr Newman metric.
     
  9. Jul 7, 2011 #8

    bcrowell

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  10. Jul 7, 2011 #9
    does the kerr metric exist?
     
  11. Jul 7, 2011 #10

    PAllen

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    The metric exists, it is an exact solution of the field equations. What pervect stated is that it probably doesn't exist *in our universe*.

    An exact, symmetric, treatment says if 10 hunters in a circle fire toward the center at the same time, you get a metal ball stationary in the center. You want to try this some time? Pervect is saying the Kerr metric is idealized in a similar sense. Presumably, even less likely than the proposed method of manufacturing ball bearings.
     
  12. Jul 7, 2011 #11
    i don't get it exist but it does not exist in our universe? also won't quantum gravity rule out all closed timelike curves?
     
  13. Jul 7, 2011 #12

    bcrowell

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    In mathematics "exists" means that there is a solution to an equation. It doesn't mean that it really happens.

    PAllen's example of the hunters exists as a solution of Newton's laws, but it has never happened on our planet.

    We don't have a working theory of quantum gravity, so we don't know for sure. For speculation on this point, take a look at the articles listed in #8.
     
  14. Jul 8, 2011 #13
    i see so your saying they exist mathematicly that does not mean it exist in reality?
     
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