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Gravitons ?

  1. Jun 3, 2005 #1
    gravitons ??

    is the inertial mass proportinal to the gravitational mass in the graviton theory of gravitation ? I ask this because I can see easily how GR imply that the two masses must be equal since spacetime curvature acts at everypoint in the body. But with gravitons I cant understand how a particle field can get to everypoint of the body with equal strength. For example electric fields and waves only affect the surface of materials the inside is almost unaffected by the electric fields acting on the bodys perimeter. How is this problem solved in string theory and other theorys that try to use particles as force carriers ?
     
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  3. Jun 3, 2005 #2

    selfAdjoint

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    You shouldn't think of gravitons as one particle at a time, but as a flood of particles zipping through every point of the object and collectively generating gravitational/inertial effects. The superstring graviton is claimed to satisfy the same equations as Einstein's curvature, so it would have the same effects re: the principle of equivalence.
     
  4. Jun 3, 2005 #3

    marcus

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    But the claim is challenged, isn't it?
    http://arxiv.org/abs/gr-qc/0409089
    From Gravitons to Gravity: Myths and Reality
    T.Padmanabhan
    19 pages

    "There is a general belief, reinforced by statements in standard textbooks, that:

    (i) one can obtain the full non-linear Einstein's theory of gravity by coupling a massless, spin-2 field... self-consistently to the total energy momentum tensor, including its own;

    (ii) this procedure is unique and leads to Einstein-Hilbert action and

    (iii) it only uses standard concepts in Lorentz invariant field theory and does not involve any geometrical assumptions.

    After providing several reasons why such beliefs are suspect -- and critically re-examining several previous attempts -- we provide a detailed analysis aimed at clarifying the situation.

    First, we prove that it is impossible to obtain the Einstein-Hilbert action, starting from the standard action for gravitons in linear theory and iterating repeatedly. Second, we..."

    A good time to recall the contribution that Thanu Padmanabhan made to this discussion last year.
     
    Last edited: Jun 3, 2005
  5. Jun 3, 2005 #4
    Does this mean that gravitons arent absorbed by the material in anyway?
     
  6. Jun 3, 2005 #5

    selfAdjoint

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    Oh no, they have to interact; by "zipping through" I meant some woud get so far before interacting and some less far, but all regions of the object (remember it's "mostly empty space") would get particles. To call this absorption though, I have my doubts. I would expect that a quark for example would interact with a graviton, and change its course and then emit another graviton, and so on.
     
  7. Jun 3, 2005 #6

    dextercioby

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    What about cohomologically deforming Pauli-Fierz into Hilbert-Einstein via BRST techniques...?I've seen some articles by M.Henneaux on this.

    It has to go the other way,too.I dunno what this Thanu Padmanabhan claims.

    Daniel.
     
  8. Jun 3, 2005 #7

    selfAdjoint

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    What part of impossible did you disagree with? If Padmanabham is correct not BRST nor anything else will save the graviton. 'Course I tend not to take what physicists call proofs very seriously, but even so, accept, refute, or get out of the way.

    My own comments on gravitons are always contingent on the SST claim being correct, and I do always remember Padmanabham's paper.
     
  9. Jun 3, 2005 #8

    marcus

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    I remember now, it was you who called it to our attention! in the thread
    String Gravitons yield GR. NOT
    that you started September last year.
    https://www.physicsforums.com/showthread.php?t=44414

     
    Last edited: Jun 3, 2005
  10. Jun 4, 2005 #9
    I haven't read any courses about current particle theories but it seem to me that any theory with particles interacting with materials would have imply that the shape and type of material place a role. Like the neutrinos zipping through earth they zipp through different material and different shapes with different efficiency even though they are so tiny. Gravitons on the other hand must interact pretty much since gravitation is very strong compared to neutrino pressure. Perhaps the extra dimension in string theory helps to conserve intertialmass=gravitationalmass ?
     
  11. Jun 4, 2005 #10

    selfAdjoint

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    You are certainly correct about the interaction, although note that gravity is by far the weakest of the four forces. Its large scale effects are due to the fact that it has only one sign, unlike electromagnetism, and is long range, unlike the strong and weak forces. So it can span large distances and accumulate without any negative "charges". Then from its weakness the idea of a strong interaction is somewhat diminished.

    I don't know what you mean about shapes. Elementary particles are pointlike; their dimensions are not important in their interactions. There are of course crystals, but I think gravity is better thought of as acting at the subatomic level. Somehow gravity must interact with the "gluon sea" whose binding energy supplies most of the mass in our macroscopic world.
     
  12. Jun 4, 2005 #11
    I mean that I think that non-geometric theory of gravitation must imply that gravitation mass should be dependent of the shape and composition of bodies. Eg. an object should be able to give gravitational shadow to another if it is explained with a particle theory however weakly interacting it is. What do you think of this belief ?
     
  13. Jun 4, 2005 #12

    selfAdjoint

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    It's no good. First, there is no sign of any gravitational shadow. Second your idea of particle interactions in still too naive. You seem to think the gravitons are like little baseballs. Probably you would do better not to think of gravitons at all, since after all they are not firmly predicted, and go back to spacetime curvature as the source of gravity.
     
  14. Jun 5, 2005 #13

    Haelfix

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    Padmanabhans paper is more or less incorrect, and never made it to publication. His actions were not gauge invariant under his own prescription, and as such he draws wrong conclusions.

    Fundamentally, the papers problem was he linearized gravity too much, so he had no way of ever retreiving the Einstein Hilbert action (a manifestly non linear action)

    The correct way to quantize a spin 2 gauge invariant particle is found in Veltmann's paper in the 70s or by one of Weinbergs papers.
     
    Last edited: Jun 5, 2005
  15. Jun 5, 2005 #14
    Ok, its just that that all other particle theories give rise to 'shadowing'. Even if the particle is as quantum mechanical as it can be and still remain a particle It must obey some sort of solution near 'things' and those solution I believe must be dependent on shape and decomposition of the 'thing'. Always different solutions for different potential and so on.

    Even if we can get the einstein equations that still dont tell us that gravitational mass is equal to inertial mass, that will have to come as an axiom if not proved some other way.
     
  16. Jun 5, 2005 #15

    Haelfix

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    No its not an axiom, its determined experimentally.
     
  17. Jun 5, 2005 #16

    marcus

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    Thanks, this is good to know! I was wondering, since it raised issues that never seemed to get settled, how it would play out. Is there an easy way to find out, after 6 months or so, if an arxiv preprint has not gotten published?
     
  18. Jul 7, 2009 #17

    malawi_glenn

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    Re: gravitons ??

    Can you please stop asking this question in all threads etc. you can find? Spamming is not okay.
     
  19. Jul 17, 2009 #18

    MTd2

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    Re: gravitons ??

    It was finally published last year! :)

    Journal reference: Int.J.Mod.Phys.D17:367-398,2008
    DOI: 10.1142/S0218271808012085
     
  20. Jul 17, 2009 #19

    MTd2

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    Re: gravitons ??

    BTW, it has now a nice number of citations, not from the authors of collaborators.

    http://arxiv.org/cits/gr-qc/0409089

    I also found this article:

    http://arxiv.org/abs/0906.0926
    Bootstrapping gravity: a consistent approach to energy-momentum self-coupling
    Authors: Luke M. Butcher, Michael Hobson, Anthony Lasenby
    (Submitted on 4 Jun 2009)

    Abstract: It is generally believed that coupling the graviton (a classical Fierz-Pauli massless spin-2 field) to its own energy-momentum tensor successfully recreates the dynamics of the Einstein field equations order by order; however the validity of this idea has recently been brought into serious doubt [1]. To remedy this confusion, we present a graviton action for which energy-momentum self-coupling is indeed consistent with the Einstein field equations. The Hilbert energy-momentum tensor for this graviton is calculated explicitly and shown to supply the correct second-order term in the field equations. A formalism for perturbative expansions of metric-based gravitational theories is then developed, and these techniques employed to demonstrate that our graviton action is a starting point for a straightforward energy-momentum self-coupling procedure that, order by order, generates the Einstein-Hilbert action (up to a classically irrelevant surface term). The perturbative formalism is extended to include matter and a cosmological constant, and interactions between perturbations of a free matter field and the gravitational field are studied in a vacuum background. Finally, the effect of a non-vacuum background is examined, and the graviton is found to develop a non-vanishing "mass-term" in the action.
     
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