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Feynman's approach to precision QED

  1. Jan 9, 2016 #1
    Feynman's approach to precision QED calculations, see his book "Quantum Electrodynamics", was shown(?) to be equivalent to the method of quantum fields. Both methods get the right the get the right answers to some problems.

    What quantum problems does Feynman's method (there is a name for that I guess) not work or work as well when compared to the method of Quantum Fields?

    Thanks for any help!

    The book, much of which can be read (edit, some of which can be read),

    https://books.google.com/books?id=xt-Vvhloo8YC&printsec=frontcover&dq=feynman+quantum+electrodynamics&hl=en&sa=X&ved=0ahUKEwiDgseIoZ3KAhULGj4KHQBHCwgQ6AEILTAD#v=onepage&q=feynman quantum electrodynamics&f=false
  2. jcsd
  3. Jan 11, 2016 #2


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    I don't know the book, but I guess you mean perturbation theory. It works well if the coupling strength is weak. That is true in QED and for the weak interaction, and it works reasonably well for QCD at high energies. It fails for low-energetic QCD processes.

    Perturbation theory uses a series that is not convergent - if you would keep calculating higher and higher orders, at some point the results would become less precise again. We are far away from that limit, however, so this does not play a role in today's calculations.
  4. Jan 12, 2016 #3
    Thanks mfb, need time to refine my question, the dentist calls.
  5. Jan 12, 2016 #4


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    If I understand what Spinnor is asking, there is no difference. They are equivalent. There are many important instances in which QED differs from classical electromagnetic fields (e.g. quantum tunneling which is a purely quantum phenomena not found in classical electromagnetism), but QED is a quantum field theory.
  6. Jan 14, 2016 #5


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    Are you referring to "Old-Fashioned Perturbation Theory"? (In this approach, Feynman diagrams are different from the usual approach taught in schools nowadays, several OFPT may correspond a single "model" Feynman diagram). It is completely equivalent to the modern approach.
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