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Qed and gravity

  1. May 23, 2004 #1
    If a graviton has energy presumably it curves space-time.A virtual
    photon has energy and presumably it curves space-time.So can a
    graviton affect the motion of a virtual photon through space-time and
    vice-versa? If so, can the gravitational field be quantized
    independently of the electric field?
    Does there have to be a field operator that gives two probabilities
    for each point in space: one probability for creating particles for
    the gravitational field and another probability for creating particles
    for the electric field ?
    The electric field has been quantized independently of the
    gravitational field but was this just the inevitability of "adjusting"
    equations in QED?
  2. jcsd
  3. May 23, 2004 #2
    For me these are interesting questions you are asking. Can we look at light cones here?
  4. May 23, 2004 #3


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    Why stop at electromagnetism? The quantum vacuum also contains virtual weakons which have energy and gravitate as well as the virtual gluons and quarks of QCD. So all the forces and matter particles can be virtual as well as observable, and would contribute to the energy of the vacuum, and thus to gravity. So yes, a complete theory that unifies the forces and quantizes gravity is going to have them all interacting with each other.
  5. May 23, 2004 #4
    Essentially what I am saying is this: maybe it isn't possible to quantize gravity independently of the other fields and QED was lucky to get away with it.
    And perhaps qcd isn't a perfect theory for the same reason.
    The standard model assumes that the forces are not unified now in the low
    energy conditions of the universe, at present, but this doesn't necessarily mean they are independent of one another?

    Gravitons and photons will interact only slightly over large distances because
    they don't curve spacetime significantly and can be widely separated in space, but at their point of origin near a particle they could interact significantly. Photons would affect photons ,gravitons would affect gravitons and there would be graviton-photon interactions too.
    If gravitons have mass would it be reasonable to model their
    effect on photons usng the idea that the expected deflection of a photon is twice the Newtonian prediction for one photon and one graviton.Is the relativistic deflection of a photon always twice the Newtonian deflection regardless of distance and energy density?
    QED probably gets away with not considering gravitational redshift of photons because electric charges have the same magnitude and so a photon redshifted as it is emitted by one charge will be blueshifted back to its
    original frequency as it gets absorbed by another charge.
    Also the lamb shift is a phenomenon at 10^-10 metres and photons in QED that have interacted in complex ways at smaller distances would have time and space to rearrange themselves and behave as flat space QED says they should.I reckon gravity can't be quantised because the electric field hasn't been quantised properly yet!

    What did you have in mind with light cones?
    Last edited: May 24, 2004
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