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Electrodynamics question and maybe quantum/classical misunderstanding

  1. Feb 25, 2010 #1

    I have a question. I have being trying to get my hands on any QED book i can cause i love it! but once i found out that the electric and magnetic fields were actually quantized as photons, and that the force between charges is mediated by light, i asked myself a question which i have been unable to answer...

    if charges are radiating an electric field in the form of photons (not the 1/r one, the 1/r^2 one) which are responsible for the forces between charges, then how come there is not a spectrum of radiation separate from the radiative field (the 1/r) that is responsible for the force between charges? And if there is, and i haven't been able to find documentation (sad day), can you point me to the paper so i can read and be happy :smile:

    thank you
  2. jcsd
  3. Feb 25, 2010 #2


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    Those photons that are responsible for the electromagnetic forces (as you say) are not real photons but virtual ones. You cannot detect radiation due to them because you cannot detect them - thats why they are called virtual. For more on virtual particles check wikipedia or other threads on this forum. There are numerous threads about the subject.
  4. Feb 25, 2010 #3
    I was under the strong impression that virtual photons were the photons that traveled short space-time distances, and that after about the width of say an atom, they were just normal photons. right?
  5. Feb 25, 2010 #4


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    No.. Check Wikipedia and other threads
  6. Feb 25, 2010 #5
    Yes, QED says the electromagnetic fields are quantized as (virtual) photons. But I think the actual imaging of this(like the exchange of photons) is very difficult.
    Because the QED has the strong "mathematical" properties even in the things other than the "virtual particles". (So I wonder what the things such as the small Lamb shift actually mean.)

    I want to know how you understand the difference between the Schroedinger equation(nonrelativistic) and the Dirac equation (or the Maxwell equation) of the relativistic form.

    For example, the Schoedinger equation wavefunction of the ground state hydrogen which includes the de Broglie's waves is stable and the electromagnetic waves (photons) is not emitted.

    First, the idea of the probability density of the electron like this hydrogen atom is peculiar to the Schroedinger equation (S.E.), (though the Coulomb force is one of the non-relativistic approximations).

    So how the stability of the (de Broglie's) wavefunction in S.E. can be explained by the QED?
    Of course, the idea of the de Broglie's wave is used also in the Dirac equation.
    But the idea of "probability density" like hydrogen atom in S.E. is not used in Dirac eq.
    If we can't use this relativistic equation, we can't explain the phenomena as below.

    The 2S1/2 state electron moves "faster" than 2P1/2 electron because it can be closer to the nucleus, which causes the relativistic energy difference by the electron's velocity.
    On the other hand, only 2P1/2 electron has the spin-orbital interaction, which causes the interaction energy difference.
    The origins of these two energies are completely different, but their values are completely the same due to the Dirac equation.
    (But to be precise, this Dirac equation of the hydrogen contains the nonrelativistic approximation Coulomb force.
    So I am very confused about the difference between the relativistic and nonrelativistic.)

    (See also this thread)
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