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Quantum gravity

  1. Feb 23, 2009 #1
    If quantum gravity exists, then gravitons are responsible; however, it seems to me as if a body of matter would need to be consuming energy/mass (as the sun does) to create gravitons, because of the Conservation Theory. Have I overlooked something? Almost certainly, but I cannot find it. Any help is much appreciated.
  2. jcsd
  3. Feb 23, 2009 #2


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    Recall that electrons do not "consume" mass nor charge in producing photons.
  4. Feb 23, 2009 #3
    If you describe electromagnetism or gravity in terms of virtually exchanged massless bosons, then those bosons can not strictly be on-shell. They are (maybe very slightly, but in any case) virtual. The classical force arises from the interference between no boson exchange and (at least one) boson exchange.
  5. Feb 23, 2009 #4
    So wouldn't that also break Conservation Theory? After all, the photons can't be popping out of nowhere. Mass and energy can't be created or destroyed, but only change form, right?
  6. Feb 23, 2009 #5
    Wrong (sorry :smile:). You can not enforce conservation laws to better than Heisenberg inequalities.
  7. Feb 23, 2009 #6
    Oh, okay. Thanks.

    (Just so you know, when I made my second post I hadn't seen yours; I wasn't ignoring you = P)
  8. Mar 8, 2009 #7
    k i might be way off and my pysics background is limited , if light creates a gravitational
    field then does this mean that a graviton is inside the photon.?
  9. Mar 8, 2009 #8


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    No, any more than the fact that accelerated electrons can emit photons means that the photons were inside the electron to begin with.
  10. Mar 9, 2009 #9
    It seems to me that since the photon is massless, it has no gravitational influence. But these people seem to be much more educated than me. = P
  11. Mar 9, 2009 #10
    the photon is massless but still creates a gravitational field . Newtons 3rd law.
    if light can be bent in a gravitational field then the light has an equal but opposite reaction. and another way we can show that light creates gravity is that if we had
    matter and antimatter in a sealed can with mirrors when the matter and anti matter collided they would produce photons and the gravitational field would still be there it wouldn't dissappear.
  12. Mar 10, 2009 #11
    massles particles have energy...they can do work.....and from Einstein we know that mass and energy are different aspects of a common entity...both produce gravitational effects and respond to them...hence light is bent in a gravitational field ....as was initially the proof of general relativity by Arthur Eddington....that made Einstein a household name...
  13. Mar 10, 2009 #12
    Well, what do you expect from someone whose IQ is smaller than their age?:tongue:
  14. Mar 10, 2009 #13


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    Four-momentum is exactly conserved at all points in Feynman diagrams (even including loops) :smile:
  15. Mar 10, 2009 #14
    Yes, that's true. That does not change anything to the answer I provided though ! The size of quantum fluctuations, as described by Feynman diagrams, can be estimated from the Heisenberg inequalities. This is done at the level of Halzen and Martin textbook for instance.
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