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Is there Proof of CTCs

  1. Oct 29, 2013 #1
    has anyone conducted a successful experiment proving closed timelike curves via post selection and quantum entanglment.
     
  2. jcsd
  3. Oct 29, 2013 #2

    PAllen

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    There is no evidence at all (let alone proof) that they exist. They are feature of many exact solutions of the equations of general relativity; and there is much evidence for many predictions of general relativity - but not for this feature. All the solutions which have CTCs also have features which make them implausible models for the region where the CTCs are (for example, they occur for rotating black holes that collapse with EXACT axial symmetry; perturb the exact symmetry a tiny bit, and it is known the real spacetime for the collapsed region is wildly different, and it is unknown whether it would have CTCs).

    The upshot of all this is that even as a pure classical theory, it is open to question whether CTCs are a prediction of GR, in the sense of arising from plausible initial conditions.

    If you consider quantum phenomena, nobody has a clue whether they are even a mathematical solution in sense that they are in general relativity. They are precluded a-priori in some approaches to quantum gravity.
     
  4. Oct 29, 2013 #3
    well that got m hopes up but thanks anyway
     
  5. Nov 1, 2013 #4

    K^2

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    Kerr-Newmann metric, describing space-time near a charged rotating singularity, does result in a naked ring singularity for sufficiently high angular momentum and charge. Such an object would allow for CTCs and does not appear to have any special requirements other than getting enough charge into the singularity. So it would seem that whatever physics we are stuck with, it should at least allow for such a thing.

    In principle, nothing stops you from working out quantum effects in arbitrary space-time, including a case with CTCs, but only under conditions that the space-time structure does not depend on whatever it is you are doing with the matter fields, and that's a very questionable assumption. The moment that fails, as Allen said, we simply don't have the tools for working with it.
     
  6. Nov 1, 2013 #5

    PAllen

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    The Kerr-Newman metric is known to not describe the end result of a plausible collapse in the central region because infinitesimal perturbations lead to wild differences. No one knows, at present, the general features of the central region of plausible collapse with angular momentum (let alone charge). In particular, it is unknown whether it would have CTC (it is known it would have some type of singularity, but what type is unknown).

    Further, there is much evidence (though no proof) that a super extremal black hole can not actually form from initial conditions that would be considered physically plausible ( the type with a naked singularity is a super-extremal BH).

    Thus, I stand by the summary of current knowledge in GR: Even in classical GR it is an open question whether any possible evolution from plausible initial conditions can lead to CTCs. Thus, they are not a known prediction of GR as a theory of physics.

    This is in contrast to BH horizons and singularities, where theorems make robust statements that these occur for plausible collapse scenarios. [edit: Just to clarify, the validity of Kerr or Kerr Newman for the external region after a sufficient time from initial collapse is reasonably well established. What is altogether unknown is the nature of the interior for realistic collapse; and that it is generally accepted that it would be very different from the Kerr or Kerr-Newman interior].
     
    Last edited: Nov 1, 2013
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