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How is the Coulomb force transmitted?

  1. Mar 24, 2010 #1
    Hi everybody, I'd like to pose a few questions that I've had for ages. I haven't found any answers except "read some Quantum Field Theory" so I'd appreciate an explanation in layman's (or in "science educated but not at all expert") terms.

    Suppose we have two small charges, one positive and one negative in some macroscopic distance. They attract according to Coulomb's law.

    In classical physics, as time goes by, they move together and then collide (if their initial velocity is zero or lies in the line connecting the charges' centers) and what happens next depends on several things (eg if they are metal spheres with equal charge they can exchange electrons and be both neutral, if they are insulated they continue to attract etc) but this does not concern me in this question.

    What concerns me is what is the current understanding of this phenomenon:

    1. I know that the carrier of the EM force is the photon, does this mean that the charges send photons back and forth all the time? Or is it, in macroscopic distances, the form of the EM field that is changing with time, with no individual photons taking part?
    2. I've heard about "virtual photons" called "virtual" because they cannot be detected without cancelling the effect they produce (ie the attraction). But, looking at Feynman diagrams I got the impression that these exchanges happen when the individual particles are close in space.So, if the above is true also in macroscopic scales, ie charges exchange photons all the time, shouldn't there be a "virtual photons density" of some kind for a typical problem? Is there such a density?
    3. Furthermore, if this is the case, how come the charges attract? The exchanged photons carry momentum which should push the charges apart, not bring them together.
    4. Another thing I haven't understood is what happens with the EM field. If the charges are alone in the universe then if the field extends beyond them that would mean that it continually loses energy (radiated to space). Is this the case? If so, if there where only one charge (which still has electric field around it) whould it somehow lose energy as time passes?

    I'm sure I have a lot of misconceptions but I've had these questions for a long time and have yet to find an authoritative answer.

    Thanks for any help.
  2. jcsd
  3. Mar 25, 2010 #2
    virtual photons are just a mathematical concept, a remnant from a perturbation series.

    the answer has thus many answers, all which are conceptual since we can not determine experimentally HOW the force IS mediated.
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