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Thread: Nature of light in QED

  1. #1
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    Nature of light in QED

    It's my understanding that in classical electrodynamics, light is a travelling wave that requires no medium to propagate, contrary to sound waves, for example.

    I don't know much about QED (Quantum Electrodynamics), but I think there photons are used in the description of light. My question is:
    is light a wave according to QED, and if it's so, does it require a medium to propagate?

  2. #2
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    Quote Originally Posted by iron4 View Post
    It's my understanding that in classical electrodynamics, light is a travelling wave that requires no medium to propagate, contrary to sound waves, for example.

    I don't know much about QED (Quantum Electrodynamics), but I think there photons are used in the description of light. My question is:
    is light a wave according to QED, and if it's so, does it require a medium to propagate?
    In QED light is described in terms of photons (quanta of the electromagnetic field). There is an excellent series of lectures (to a non-technical audience) by Feynman that explains how this works. Also available as a book (called QED).

    http://www.vega.org.uk/video/subseries/8

  3. #3
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    Modern QED describes light as a set of excitations of an underlying field. The maths for this gets complex, fast, so one of the more common ways to break it down is via perturbation theory. In that interactions are treated as interactions between discrete entities - particles such as photons. So I guess the answer to your question is that light is describes in terms of particles for convenience, but in terms of fields more fundamentally.

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