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

The Dirac Field

  1. Oct 25, 2003 #1
    I have a question about the Dirac field. If as quantum field theory states , every point in the Universe is filled with "virtual" photons , and if these "virtual" photons in turn give rise to electron-positron pairs , which being components of matter and anti-matter collide and annihilate each other giving rise in the process to a real photon , how are the conservation laws met ? The creation of a real photon implies real energy , which in turn implies its absorption by an electron which means more energy. How does everything balance out ?
  2. jcsd
  3. Oct 25, 2003 #2
    Virtual interaction vertices always conserve energy-momentum. They're just off-shell (in that the relation E^2 = (mc^2)^2 + (pc)^2 isn't obeyed). Virtual processes in vacuum never give rise to real photons, unless you're thinking of something like the Hawking effect, in which case the real photons extract real energy from the real gravitational field.
  4. Oct 26, 2003 #3
    The process of creation of a real photon does take place in a process known as "polarization of a vacuum " . A photon is transformed into a virtual electron-positron pair , which is annihilated and transformed again into a photon. The members of this virtual pair (electron - positron ) during their lifetime may generate virtual photons and consequently new electron - positron pairs , which annihilate themselves to create a real photon , ann so on. Correct me if I'm wrong about this.
  5. Oct 26, 2003 #4
    Vacuum polarization is a virtual correction to the photon propagator, but it doesn't manufacture real photons out of nothing. A real photon can virtually split into an electron-positron pair and then re-form into a real photon as it propagates, and likewise a virtual photon's propagation can be dressed by vacuum polarization, but it does not produce real photons out of vacuum.
  6. Oct 27, 2003 #5
    Yes..do a search for H.E.Puthoff in Xarchive pre-prints.look for:

    Polarizable-Vacuum (PV) representation of general relativity.

    There are conditions where the PV acts as an active field in response to a hidden variable elswhere in the Universe. VP can appear from an un-observed location, as if they have just 'popped-in' so to speak.
  7. Oct 27, 2003 #6
    I have not read Puthoff's work. I do know that he is widely regarded as a crank, and that I have not heard of any physicists other than his collaborators who think his results concerning energy extraction from the vacuum are credible. I also know that an earlier proposal to obtain gravity from vacuum effects was shown to be badly wrong by Carlip. None of this encourages me to spend time checking his results. You , of course, are welcome to do so, but perhaps your time would be better spent learning conventional quantum field theory.
  8. Oct 27, 2003 #7
    Wisdom noted, I do not subscribe to the notion:energy extraction from the vacuum , and I am studying conventional QFT, if one can describe Quantum Fields as being conventional!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook