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Unifying Gravity

  1. Mar 29, 2014 #1
    Do we have any theories to unify quantum gravity to gravity?
    What is the opinion on this?

    What about gravity to the other 3 forces?
  2. jcsd
  3. Mar 29, 2014 #2
    Gravity disappears?

    Is it true when we apply quantum mechanics to gravity, it disappears and so does space?

    Does this mean quantum gravity disappears too?

    If so, does this imply quantum gravity and gravity are linked? possibly to be unified?
  4. Mar 29, 2014 #3
    The main option that attempts to unify gravity with the other fundamental forces is superstring theory.

    The fundamental forces with the exception of gravity, were unified under the standard model of particle physics.

    A theory of quantum gravity would describe gravity, so no unification of the theories would be required.
    Last edited: Mar 29, 2014
  5. Mar 29, 2014 #4


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    Where did you get this idea from?

    It is most certainly false.
  6. Mar 29, 2014 #5
    So quantum gravity exists because natural gravity as most know it exists?

    So, if gravity disappeared quantum gravity would too?
  7. Mar 29, 2014 #6
    From Lawrence Krauss's book
  8. Mar 29, 2014 #7
    Or more accurately one of his lectures.
  9. Mar 29, 2014 #8
    The term 'quantum gravity' refers to a theory that describes both the standard model of particle physics (that's where the word quantum comes from) and gravity. It's not a seperate force.

    At the moment we don't have a working theory of quantum gravity. It's still being researched.

    Gravity isn't going to disappear but if it did then the research on quantum gravity would surely stop because we'd have bigger problems to worry about!
  10. Mar 29, 2014 #9

    I don't think it is any time soon, LOL

    I'm just wondering theoretically what this all means.

    So, when we hear 'quantum gravity' what is meant is the standard model plus gravity.

    But, I'm confused, because how do we know that the gravity that pushes on the big stuff is the same gravity working on the small stuff?

    And does it push that too?
  11. Mar 29, 2014 #10
    The force due to gravity has always been measured to be proportional to mass and the mass of an object is the sum of the masses of its parts.

    The effect of gravity has been measured on individual particles so we have no reason to doubt it.

    We don't know what happens when gravity becomes very very weak. It's believed to be quantised and that's where it gets tricky.
    Last edited: Mar 29, 2014
  12. Mar 29, 2014 #11
    Ok, so gravity then works on the big and small.

    But the other three forces seem to work on only the small, that seems weird. And gravity also seems to affect light and be a property of space itself? curvature?

    the other three forces are not like this?
  13. Mar 29, 2014 #12
    Oh, also- the virtual particles follow quantum laws right? I've heard that. Just double checking.

    So, does this mean, quantum laws...the same as the natural laws?

    And is it fair to say these natural laws are just our description of what particles are doing and not necessarily an absolute in and of itself? Meaning the particles behaved and so we see this behavior and call it laws...not that these laws were first and made the particles act this way?
  14. Mar 29, 2014 #13
    All forces work on the big and the small. Just take all the forces on the smaller parts of a bigger object and add them up.

    Our best theory of gravity describes it as a space-time curvature. The other forces are usually just treated as acting in space and time.
  15. Mar 29, 2014 #14


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    There need to be some clarification here.

    There is something called quantum field theory (QFT). Within this formulation, we have successfully described the electromagnetic interaction, the weak interaction, and the strong interaction. So as is natural with human tendency, we think, hey, since gravity is a "force" as well, there should be a way to describe it using QFT as well.

    So that, naively, is what is meant as trying to find a quantum picture of gravity. It is trying to describe it in the analogous way as QFT. Whether we will be successful or not is a different matter.

  16. Mar 29, 2014 #15

    Simon Bridge

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    He is almost certainly speaking poetically.
    Which lecture?
  17. Mar 29, 2014 #16
    I think that she is thinking of the breakdown of general relativity when applied to things on a quantum level.
  18. Mar 29, 2014 #17


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    Two different threads have been merged because they are both based on the same topic by the same OP.

  19. Mar 29, 2014 #18


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    In this forum, we require a more extensive and detailed source than that. So you might as well learn about it now. If you cite a book, please write down the author, title, and page number exactly. If you cite a lecture online, provide the exact URL and where approximately is this particular source.

    This forum, while it may be an open, public forum, has a stricter quality control. However, it also gives you an idea on how scientists operate and communicate, whereby one of the things we do is we justify what we say with appropriate and clear sources, if this isn't something standard and well-known. Thus, we try to instill the same philosophy and practice among the members participating in the physics discussion here.

  20. Mar 29, 2014 #19
    I'm looking for the source, thanks. Just trying to clear up misinformation from books and online so I can understand all this.
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