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Quantum Gravity Progress

  1. Feb 8, 2016 #1
    I speak as an novice in this matter.

    Has progress been made in reconciling quantum field theory with general relativity?

    I know that there are theories which show reconciliation but none that seem to be verifiable empirically.

    Gravitons seem, from a practical viewpoint, impossible to detect.

    Just like to know in what ways empirical verification is going.

    Thanks
     
  2. jcsd
  3. Feb 8, 2016 #2

    DrChinese

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    Depends on what you mean by progress. I am not aware of any experiment that indicates that gravitons exist. There are experimental ideas in this regard, but none that have much come to fruition. One of the ideas being decoherence due to gravitational interaction, which would indicate gravity is a quantum force.

    http://arxiv.org/abs/0910.2322

    And a different scheme:

    http://arxiv.org/abs/1511.01237
     
  4. Feb 12, 2016 #3
    I have not been up to date on this but has the supposed detected existence of gravitional waves be an arguement that gravity is a force?

    In another vein my own feeling is that gravity is not a force because it involves an inherent contradiction:

    I do not know if this analogy means anything, but I'll give it anyway.

    Bertrand Russell noted that a self-referential statement has no meaning.

    Very basically (in classical mechanics) a force is a push or a pull in a medium (space) at a duration (time).
    Updating this crude statement slightly a force is a push or a pull in the medium of the spacetime continuum.
    Acknowledged this is not the way to view forces in particle physics, but stay with this.

    In general relativity (gravity) the discussion is from mass/energy to the deformation in the spacetime continuum.

    Break it down further. We are discussing a deformation of the spacetime continuum in the medium of the space time continuum.

    Is it possible to see this as a self-referential statement and therefore has no meaning? Gravity is not a force

    This is a little like painting on white cardbord with white paint of exactly the same hue. Everything is exact, and nothing can be seen.

    Another analogy for this is that while standing you try to pull yourself upwards by pulling on your legs.

    Spacetime to spacetime-self referential, no meaning.

    This has always bothers me that gravity which changes the medium upon which it operates can be seen as a force in QM.
     
  5. Feb 12, 2016 #4
    Does the recent news about the LIGO detector data concerning the black hole merger help in regards to proving or disproving the theory that gravitons may exist?
     
  6. Feb 12, 2016 #5

    DrChinese

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    No change on that front.
     
  7. Feb 12, 2016 #6
    one can see the following for connecting the observation of gravity waves and its significance ;

    the fluctuations of quantum fields as seen by late comoving observers are significantly influenced by the history of the early Universe, and therefore they transmit information about the nature of spacetime in timescales when quantum gravitational effects were non-negligible. We discuss how this may be observable even nowadays, and thus used to build falsifiability tests of quantum gravity theories.
    The Quantum Echo of the Early Universe Ana Blasco, Luis J. Garay, Mercedes Mart´ın-Benito, and Eduardo Mart´ın-Mart´ınez
    http://arxiv.org/pdf/1501.05682.pdf
     
  8. Feb 12, 2016 #7
    I heard that gravitational waves detection would disprove, or make a lot of problems to string theory. Is it true?
     
  9. Feb 12, 2016 #8

    jtbell

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    Where?
     
  10. Feb 12, 2016 #9
    ,,The BICEP2 results will also send some string theorists back to the drawing board, says Frank Wilczek, a theoretical physicist and Nobel laureate at MIT. String theory posits that elementary particles are made of tiny vibrating loops of energy. Efforts to combine string theory with cosmology have led to inflationary models that generate gravitational waves with energies much lower than the level detected by BICEP2, he says.

    Theoretical physicist Eva Silverstein of Stanford says she disagrees that string theory-based models of inflation are in any sort of trouble. “There is no sense in which we are forced to start over,” she says. She adds that in fact a separate class of theories that involve both axions and strings now look promising.

    Linde agrees. “There is no need to discard string theory, it is just a normal process of learning which versions of the theory are better,” he says. “All of us, not just string theorists, should go back to the drawing board, but not because we failed, but because we learned something very important and now we should use this knowledge to make further steps.”
    from http://www.nature.com/news/gravitational-wave-finding-causes-spring-cleaning-in-physics-1.14910
    Maybe i misunderstood it.
     
  11. Feb 12, 2016 #10
    What do you mean by quantum force?
     
  12. Feb 12, 2016 #11
    Wrong experiment. In fact the results mentioned in that 2014(!) article aren't caused by primordial gravitational waves.
    Source: http://news.discovery.com/space/astronomy/bicep2-gravitational-wave-discovery-deflates-150130.htm
     
  13. Feb 12, 2016 #12
    ,,The BICEP2 results will also send some string theorists back to the drawing board , says Frank Wilczek, a theoretical physicist and Nobel laureate at MIT,, So, he was wrong?
     
  14. Feb 12, 2016 #13
    I don't know exactly which specific results he was talking about. If it was the gravitational waves, the issue is non-existent.
     
  15. Feb 12, 2016 #14
    Thank you very much for answer.
     
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