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A Is gravity a quantum phenomena or not?

  1. Apr 14, 2017 #1

    ftr

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    You Heard me.:smile:

    Seriously, I have seen some so called low effective theories of gravity, so if they are any good why aren't they taken to be as established theories, since all other ones seem to be valid in some energy scale anyway. Although I do admit that I dislike this adding one more field on top of others to describe a new phenomenon while everything should be derived from some basic entity.


    As an example
    https://arxiv.org/pdf/hep-th/0211072.pdf

    P.S. I know of the graviton argument, but higgs was not discovered for many decades either.
     
  2. jcsd
  3. Apr 14, 2017 #2
    Hi ftr:

    I am not an expert, and I am sure what you are asking. I am guessing you want to know the current status of not-quite-theories concerning the unification of GR with QFT.

    From a few conversations about black holes here on the PFs, I have learned that there are a few partial unifications that have some usefulness, but not yet any complete unification. A partial unification has been developed which includes that math for Hawking radiation. I think you might find the thread below of some interest.

    Regards,
    Buzz
     
  4. Apr 14, 2017 #3

    atyy

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    Yes, gravity is a quantum phenomenon, and the low energy effective theory is established and standard.

    The paper you linked to is one such paper.

    https://arxiv.org/abs/1209.3511
    The effective field theory treatment of quantum gravity
    John F. Donoghue

    https://arxiv.org/abs/1702.00319
    EPFL Lectures on General Relativity as a Quantum Field Theory
    John F. Donoghue, Mikhail M. Ivanov, Andrey Shkerin

    https://arxiv.org/abs/1105.3735
    Theoretical Aspects of Massive Gravity
    Kurt Hinterbichler
    "The real underlying principle of GR has nothing to do with coordinate invariance or equivalence principles or geometry, rather it is the statement: general relativity is the theory of a non-trivially interacting massless helicity 2 particle. The other properties are consequences of this statement, and the implication cannot be reversed. As a quantum theory, GR is not UV complete. It must be treated as an effective field theory valid at energies up to a cutoff at the Planck mass ..."
     
  5. Apr 14, 2017 #4

    ftr

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    So what is this talk about reconciling QM and gravity. Do physicist have Aphasia.:smile:
     
  6. Apr 14, 2017 #5

    atyy

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    For those who understand that we have a good low energy effective theory of gravity, what is meant that there is no good theory of gravity at high energies.
     
  7. Apr 15, 2017 #6

    ftr

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    Thanks atty, but it does not add up. Like I said many(all) theories are scale specific, if what you say is true somebody would have gotten the Noble and the theory would be the last chapters of QFT textbooks, wouldn't you say?
     
  8. Apr 16, 2017 #7

    ftr

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    BTW, atyy, I showed Sabine this thread and this is what she said(literally!)

    "Of course it's not accepted as an established theory because there's no experimental evidence."

    I am really surprised that nobody has an opinion on this fundamental issue here on PF.(aside from you/Buzz)
     
    Last edited: Apr 16, 2017
  9. Apr 16, 2017 #8

    atyy

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    Sabine is wrong (if she said that). There is experimental evidence - it's called general relativity.

    More likely, you misunderstood her. Here she says the effective theory is fine (around 1:50-2:10):
     
    Last edited: Apr 16, 2017
  10. Apr 16, 2017 #9

    ftr

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    As you can see there is even no consensus about low energy, let alone BH which will be impossible to test, period.
     
  11. Apr 16, 2017 #10

    atyy

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  12. Apr 16, 2017 #11

    ftr

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    Actually I have the book for a few months now but never noticed those two pages. I think she is careful not to say it is wrong but it is "not established".

    I am still not sure what is going on since conflicting statements are made and it is not clear the context of those statement. But I hope more people jump in.
     
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