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BICEP 2 and Penrose

  1. Jun 11, 2014 #1
    If inflation is proven by BICEP 2, then what happens with Penrose's proof that infaltion assumes unprobable initial conditions?
     
  2. jcsd
  3. Jun 12, 2014 #2

    bapowell

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    BICEP2 has not proven inflation -- nothing will ever prove inflation. In science the best we can do is 1) falsify a theory or 2) find corroborating evidence for a theory. But, to your point -- supposing that substantial evidence is found in favor of inflation, this means that either the initial conditions/configuration were simply improbable, or that we don't understand the physics underlying the initial conditions well enough. Such arguments regarding initial conditions extend way beyond Penrose, and have been a bone in inflation's closet of skeletons for many years.

    As a somewhat related aside that bothers me, scientists like Steinhardt who wish to discredit an entire theory because the initial conditions are difficult to actualize I think are throwing the baby out with the bathwater -- it's OK not to understand precisely how inflation got started. Currently, inflation does not constitute a well-structured theory as much as a broad paradigm describing early universe physics. This is an important difference.
     
  4. Jun 13, 2014 #3
    First off Bicep 2 results look like they are increasingly ocming into doubt:
    https://www.physicsforums.com/showthread.php?t=753482
    even if the results do hold up there still needs to be further investigation to see if it confirms inflation or not. As Bapowell said nothing in science is proved (but confirming evidence can be found).
    There have been claims that inflaiton needs very unlikley iniitial conditions, Penrose is someone that says that. but there are also claims to solve this problem, Im not sure proof is again an appropriate word. see here for example:
    arxiv.org/abs/0708.3288‎
    There is alreayd evidence for inflaiton with or without BICEP 2 but I think it is not so strong that we cant entertain alternatives to inflation. If the evidence does get to that point then we will have to accept it and try learn more about what happened before inflation .
     
  5. Jun 13, 2014 #4
    Suppose that inflation in any form is not correct. Then, what things inflation explains could be explained by other theories, such as CCC?
     
  6. Jun 13, 2014 #5

    bapowell

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    String gas cosmology, although kind of odd, purports to explain the density perturbation spectrum and solves the horizon problem. Ekpyrosis and other cyclic models can generate perturbations as well during a prior contracting phase (some of these models, like ekpyrosis, assume away some of the traditional problems of big bang cosmology, like flatness). There are some approaches based on loop quantum cosmology that purport to resolve many of the issues that inflation addresses.
     
  7. Jun 13, 2014 #6
    Is penrose interpretation of BICEP2 valid?
    And...
    if Conformal Cyclic Cosmology is wrong, then what happens with the experimental data (the concentric circles on CMB)?
     
  8. Jun 14, 2014 #7

    bapowell

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    The concentric circles discovered by Penrose have not been corroborated by actual CMB experts that actually understand how to do that kind of analysis. Penrose, despite his genius, does not. CCC is borderline fringe at this point.
     
  9. Jun 14, 2014 #8
    are you taking
    http://arxiv.org/pdf/1302.5162.pdf
    into account?
     
  10. Jun 14, 2014 #9

    bapowell

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    Yes. Penrose and Gurzadyan don't know how to do CMB analysis.
     
  11. Jun 14, 2014 #10
    well, but could you name a cosmological theory outside of...
    --> CCC
    --> Inflation
    --> MOND, MOG, Variable speed of light, LQC, etc
    --> Cyclic Branes
    ????
     
  12. Jun 16, 2014 #11
    For what its worth I was at a conference in Oxford to discuss CCC. The presentation by Gurzadyan was not well recived as Bapowell has pointed out. However another study by a Polish team did seem to be go down better with the critics. I'm not saying they accepted it either but here is the link in case you want to read it:
    http://arxiv.org/pdf/1307.5737.pdf

    I should add I dont think LQC is not necessarily an alternative to inflation. They generally include inflation in their models. Some papers even try and predict how many efolds as a result of the bounce ( but I think they still have to have an inflaton field put in):
    http://arxiv.org/abs/1301.1264
     
    Last edited: Jun 16, 2014
  13. Jun 16, 2014 #12
    Heres a new one proposed by Turok and Stenihardt ( of Ekpyrotic fame):
    http://arxiv.org/abs/1307.8106
    string gas cosmology is another, pre big bang string duality is another. There are probably many more. MOnd is more trying to explain dark matter without dark matter , its nto as far as I know a theory of the very early universe.
     
  14. Jun 16, 2014 #13
    well some models of MOND don't use dark matter

    some MOND models however have dipole dark matter.
     
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