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Photon as force carrier particle

  1. May 15, 2005 #1
    To my embarrassment I realised I do not understand this.

    How does a photon mediate the EM force? If I put two magnets close to each other then there is no EM radiation jumping from the one to the other. So how does the photon carry the particle?

    I know that very magnet has a Magnetic field and that a photon is a little moving quanta of EM energy. Or a EM disruption in the EM field.

    But I fail to understand this. A EM field has nothing to do with photons right? Or do photons only jump over if there is an actual force on a charged object?

    Then, is it possible to observe a EM field through photons?

    Or lies my problem in the difference between an electric field, a magnetic field and an electromagnetic field?
    Last edited: May 15, 2005
  2. jcsd
  3. May 15, 2005 #2


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    Those are virtual photons, not real ones. A virtual photon is basically a mathematical device. It's a name we assign to a factor that repeatedly occurs in the terms of a perturbation expansion in quantum field theory.

    Richard Feynman noticed that one could easily construct or remember the perturbation expansion for a particular process by drawing a series of diagrams which represent the various terms in the expansion. The various lines in the diagram correspond to factors within those terms. A certain kind of line/factor has properties which are similar to some of the properties of a real photon, so for convenience in labeling, we call it a "virtual photon".

    I think most of the conceptual problems that people have with virtual photons are caused by trying to make them more "real" than "virtual."

    In order to have "real" electromagnetic radiation, you need real photons.
  4. May 15, 2005 #3
    So all force carrier particles are virtual particles?

    So one could say all fields are made by virtual photons? These aren't there unless they interact and then they appear real just before their energy is used?
  5. May 15, 2005 #4


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    Nope,not necessarily.They can be in/out states.

    Nope,all fields,at quantum level,are made up of particles we call "quanta".

    Nah,it's more to it.A particle is real iff is on its mass shell,which,in the case of Feynman diagrams means in/out states.

  6. May 15, 2005 #5
    Let me rephrase, all force carrier particles are at some point virtual?

    But quanta are photons?

    The last bit doesn't make sense to me.

    This isn't helping. Are these questions good to ask or am I missing some point? Could someone explain this in some detail? Or is it really all abstract math that cannot be translated into words or concepts?
  7. May 15, 2005 #6


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    Yes,in some diagrams,they are.

    More like the other way around.Photons are light quanta.

    It is abstract math.As for explaining,what level of mathematics & physics education do you have...?

  8. May 15, 2005 #7
    I am not a physics student.

    So quanta are packets of energy and photons are packets of energy in EM form?

    I am not looking for a explanation of the in-detail QM effects. I just want an answer to the original question. That seemed pretty basic.
  9. May 15, 2005 #8


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    That's right. :smile:

    I guess J.T.answered it.

  10. May 15, 2005 #9
    So energy is stored in a field in the forms of quanta and these can become virtual or real photons in some situations?

    Also, how similar are the photons we know as EM radiation and the virtual photons that are EM force carriers? The one is a mathematical construction and the other is visible depending on its frequency. So the last one must be real, right?

    Hmm it seems I really want to know this stuff but my math might not allow it. Could someone give me a page that goes into some of this stuff? I looked at wikipedia and I didn't find anything I was looking for.

    Then I can see how far I can understand this. I don't want to ask someone to type out all kinds of stuff for nothing.
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