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Virtual Photons

  1. Feb 3, 2009 #1
    Hey all, I am an undergraduate taking a particle physics class and we just learned that the EM force was caused by charges "spitting" virtual photons back a forth. In like second grade we learned that the EM force was dependent on the two charges involved (keeping this simple) and the distance between them. Now, if you somehow created a device that could detect, lets say, half of the virtual photons between two given charges, wouldn't the EM force between the two of these charges decrease without changing the charges or the distance between them? (I was told that once you detect a virtual photon, you promote it to a real photon and it no longer plays a role in the EM force between charges.) I think I know just enough about this to be dangerous. Thanks for your time!
    Last edited: Feb 3, 2009
  2. jcsd
  3. Feb 3, 2009 #2


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    Virtual photons are not detected, they are mathematical concepts/entities when you do perturbative expansion in quantum field theory.
  4. Feb 9, 2009 #3
    Perhaps best to say that virtual photons are the ones that you don't detect. The distinction is more of a practical one since photons themselves are "mathematical concepts/entities when you do perturbative expansions in quantum field theory". Forgetting this leads to problems like IR divergences and the inability to understand classical light (for which coherent states are necessary -- what is a photon if absorbing it does nothing?)

    The idea you are after is related to the Casimir effect, and I invite you to read, say, the wikipedia article on the subject, and ask for clarification if you want. If you're feeling brave you can read up about Glauber states as well. But only if you can quantize the harmonic oscillator in your sleep.


    So yes, your thinking is dangerous, but as long as you realize that you'll be fine =)
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