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Confused about the graviton

  1. Jul 11, 2009 #1
    Hello PF community!

    While reciently reading another thread this paper was posted as a link: http://arxiv.org/ftp/cond-mat/papers/0602/0602591.pdf

    now about 5 pages in it stated that the authors found a wave length and mass for a graviton????

    I did not even know they were proven to be real. I saw that the initial number was complex and almost did not post my questions but a bit later on I saw that they converted it into a real number! I am just asking how that is possible and how long has it been known that gravitons actually do happen?

    Fyi: I have a basic understanding of calc and below so I realize I can not fully understand the paper or most of the physics for that matter, so please help me out here. Thank you in advance. Also I am typing this on an iPhone so I am sorry for any mistakes in spelling or word choice here.

    Thanks again!!
     
  2. jcsd
  3. Jul 11, 2009 #2
    Well I can tell you right now that the graviton is still theoretical. It's proposed mass is zero, but they seem to be arguing over whether it would gain mass through the Higgs mechanism..? (at least, that's what I gathered from the last paragraph) Someone better educated could help.
     
  4. Jul 11, 2009 #3
    I should also add that if I am correct about what they are proposing, they have not read Einstein's Relativity papers. Gravitational waves travel at c. Gravitons travel at c. Ergo, gravitons, if they exist, are massless.
     
  5. Jul 11, 2009 #4
    If you were alarmed that the authors say the graviton has non-zero mass, then I am surprised that you are not alarmed that they say photons have mass as well!

    Fortunately, they are talking about photons/gravitons in a medium, in particular a superconductor, where these massless particles behave as if they effectively had mass. In superconductors there is something called the meissner effect, which is the fact that superconductors expel magnetic fields i.e. magnetic fields cannot penetrate the superconducting surface currents. In a real superconductor the magnetic fields may penetrate a few nanometers into the surface, as they decay exponentially to zero. One way to characterize the hyper-rapid decay of the magnetic field is by ascribing a "mass" to the photon, but what this mass really describes is the effective environment the photon is moving through.

    As an analogy, imagine something very lightweight like a ping pong ball being moved underwater. Because the ping pong ball has to drag water with it when it moves, it has effectively aquired a larger mass. This new mass actually describes the ball and the water it drags around it, just as the photon "mass" in the meissner effect describes the photon + its environment.

    What the authors are doing in this paper is working out the implications of the gravitational analogs of the well understood electromagnetic properties of superconductors. Gravitomagnetism appears in an approximation to general relativity, and in this approximation gravity looks a lot like electrodynamics, so it seems like a natural subject to investigate.
     
  6. Jul 11, 2009 #5
    Yes, they are talking about gaining mass through the Higgs mechanism, i.e. symmetry breaking and goldstone bosons, although to repeat they are talking about symmetry breaking inside of a superconductor, not in a vacuum, and so the common knowledge that photons and gravitons are massless and travel at speed c in vacuum is totally untouched by this paper.
     
  7. Jul 11, 2009 #6
    Hmmm... interesting. That makes much more sense now. But in what sense would a graviton ever behave like a photon in a superconductor?
     
  8. Jul 12, 2009 #7
    Ha! I knew I missed something big. And yea I was so distracted I didn't even pickup on the Photon. Thank you Civ for clearing this up; it makes much more sense. So do you think that we could use this magnetic field theory to approximate what happens in real space on a much much smaller scale? Sort of like the difference between moving something through air and through the water. I was thinking the Higgs mechanism / field and this Superconductor field... ?
     
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