Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

QFT/GR whats the problem? I can't see one

  1. Aug 13, 2010 #1
    Hi,

    Im just wondering why Quantum Field Theory is incompatible with General Relativity. From my current understanding they seem to be compatible. I must be missing a crucial piece of information. Please help :-)

    Talyl
     
  2. jcsd
  3. Aug 14, 2010 #2
    Ok, we have potentials and particles. Why cant you have a discreet amount of a field?
     
  4. Aug 14, 2010 #3

    diazona

    User Avatar
    Homework Helper

    One of the most commonly quoted reasons is that general relativity is non-renormalizable. In other words, the procedures used to prevent certain calculations from giving infinite results don't work for GR. I'm not (yet) familiar enough with the topic to explain that offhand, but maybe someone else can fill in the details.
     
  5. Aug 14, 2010 #4
    Yea I have heard about this renormalisation problem too. Ill go and see if I can read up on it and come back with a post.
     
  6. Aug 14, 2010 #5
    Hi,

    So the problem with general relativity is that its perturbativly non-renormalisable. You can see this just from power counting arguments since newtons constant is dimensionful. This means that when you add counter terms to the action, to cancel the divergences from loop diagrams, these will general not have the same form as the original action. This doesn't stop one treating gravity as an effective field theory though; as long as you only consider process with typical energy E<<M_pl where M_pl is the planck mass QFT/GR are perfectly compatible.


    http://en.wikipedia.org/wiki/Effective_field_theory

    One should also note that the breakdown of perturbative QFT at the Planck scale does not necessarily imply that a non-perturbative formulation of gravity as a QFT is impossible.

    http://arxiv.org/abs/0709.3851
     
  7. Aug 14, 2010 #6
    Besides the one mentioned , non-renormalisability of Gen Rel., there appears to be some other difficulties.

    One is that in QFT the time component has, at least in part, an absolute (Newtonian) character as opposed to the full dynamic (space)time of Gen Relativity.
    See here for example: http://www.sciencedirect.com/scienc...serid=10&md5=ea2de960d543c63799c7fbefc113ff0a
    I'm not so sure this problem has been successfully circumvented , even in Quantum Gravity.
    However, that is not exactly my area of expertise.
    ...
     
    Last edited: Aug 14, 2010
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: QFT/GR whats the problem? I can't see one
  1. What am I seeing? (Replies: 2)

Loading...