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Other Approaches to Quantum Gravity

  1. Feb 29, 2012 #1
    Our major candidates for quantum gravity are as you know String Theory and Loop Quantum Gravity.

    Loop Quantum Gravity is about the spacetime curvature as a priori.
    String Theory is about the Flat Spacetime as a priori (although I'm not sure if the 6 compactified dimensions are considered Flat Spacetimes).

    Personally. I don't like both of them. LQG will rise and fall depending if the hunch is right that spacetime is really curved. And String Theory kinda contrived, and the non-perturbative version AsD/CFT doesn't even describe our universe due to the negative curvature.

    Does anyone know of a web or papers that summarize in not so technical way the other approaches and their strengths and weaknesses? Or maybe if you know them, just give a brief assessements like their strengths and weaknesses based on your opinions. Thanks.
  2. jcsd
  3. Feb 29, 2012 #2


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    Other approaches that come to mind are:

    Asymptotic Safety http://arxiv.org/abs/0709.3851

    Causal Dynamical Triangulations http://arxiv.org/abs/1105.5582

    Steinacker's interpretation of the IKKT model, originally proposed for strings http://arxiv.org/abs/1202.6306

    Group field theory http://arxiv.org/abs/1112.3270

    Tensor field theory http://arxiv.org/abs/1112.5104

    Both GFT and TFT have some relation to LQG.

    Gu and Wen's condensed matter approach http://arxiv.org/abs/0907.1203

    Markopoulou's quantum graphity http://arxiv.org/abs/1201.3398

    Vidal's note about LQG and tensor network algorithms in condensed matter http://arxiv.org/abs/0907.2994

    Swingle's note about AdS/CFT and tensor network algorithms in condensed matter http://arxiv.org/abs/0905.1317

    Horava-Lifgarbagez gravity http://arxiv.org/abs/0901.3775

    Also there are efforts in string theory to get a non-perturbative model that works in positive curvature spacetimes like the Twistor Matrix Model http://arxiv.org/abs/1112.5210

    BTW, string theory does have models for positive curvature spacetimes http://arxiv.org/abs/hep-th/0301240
    Last edited: Feb 29, 2012
  4. Feb 29, 2012 #3
    Wow so many. Thanks. I think Weinberg is right we may arrive at the final theory maybe at least year 2050. But then don't forget the possibility that even quantum gravity can be another Effective Field Theory of something else. Any paper along this line?
  5. Feb 29, 2012 #4


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    All the above approaches except Asymptotic Safety and Causal Dynamical Triangulations (CDT) assume that gravity is only an effective field theory of something else. LQG, Asymptotic Safety and CDT assume that gravity is not an effective theory.
  6. Feb 29, 2012 #5
    What? Really? I thought Quantum Gravity is the end goal. Why do they think there is "something else?
  7. Mar 1, 2012 #6
    I think you misunderstood what I was asking. I was not asking if gravity is an effective field theory. I was asking if quantum gravity is an effective field theory. I think it is indeed in AsD/CFT because gravity here is only an illustration and there is neither strings nor planck scale as these are actually in the boundary. I was asking if there are others like this.
  8. Mar 1, 2012 #7
    What, no entropic gravity? :))
  9. Mar 1, 2012 #8
    There are so many quantum gravity models, each identifying with the author name. Do you know know the best way or journal to create a new QG theory under my name. So instead of saying "Gu and Wen's condensed matter approach" or Horava-Lifgarbagez gravity. It's my own name with so and so approach so others would quote it's mine when mentioning it? Maybe I can sneak it into arxiv even with no plan to publish it in a real journal? Maybe that is enough to claim ownership of the model?

    Maybe there are like 50 plus QG models with only 15 discovered. So it's cool to add some your own like "create you own QG" in light of the very possibility that string theory and LQG will come into dead end someday. Then they have to go back to beginning.
  10. Mar 1, 2012 #9

    Vanadium 50

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    This is getting silly.

    You don't get to have an opinion about an approach to quantum gravity until you have studied quantum gravity. Or quantum field theory. Or quantum mechanics. Or calculus.

    If you want a theory named after you, you need to do the groundwork first.
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