QED explanation for charge?

  1. Zak

    Zak 8

    I have read some fairly vague descriptions of charge that say it can be looked at as the amplitude for a particle to exchange a photon.

    For example, when two electrons repel, it is because a photon is emitted from one too the other, which would change the direction of both equally and oppositely due to the conservation of momentum. I believe this photon is known as a 'virtual photon'.

    Firstly, could anyone confirm whether this is at all correct and, if so, how could the same concept be applied to the attraction between two oppositely charged particles?

    Additionally, if charge is the result of photon emission, does that mean that all charge particles are constantly emitting photons in order to always be 'charged'? Would this explain why the electromagnetic force has infinite range?
  2. jcsd
  3. WannabeNewton

    WannabeNewton 5,765
    Science Advisor

    Could you give some references? Paraphrasing often goes awry.

    Charge is simply the conserved quantity resulting from the local (gauge) invariance of the Dirac lagrangian under phase transformations when the electromagnetic interaction is included in the lagrangian.
  4. Zak

    Zak 8

  5. I think their explanation is bogus. You can’t use increased uncertainty in position to exactly position a photon, as they have done.

    I believe that is correct.

    I don’t think you could say that, because now you are talking about real photons. Accelerated charges do emit radiation, and there is still controversy about whether it is acceleration or jerk (change in acceleration) which causes this.

    Look up synchrotron radiation, and the Larmor formula.
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  6. Zak

    Zak 8

    my bad, I meant to say the description wasn't very good.

    So does anybody have a better explanation for why two charges would attract eachother in relation to the photon exchanges between them?
  7. WannaBe’s explanation in post #2 is excellent. That might not be very satisfying to you if you are searching for a deep insight into the cause or origin of charge. The fact is that no one really knows.

    Are you comfortable with that explanation? If so, reflect on what the mechanism might be, by which a photon is emitted from an electron.

    We have a natural tendency to transfer what we think we understand about the macro-world into the micro-world, and the micro-world quiote often punishes us for that. For example electrons don’t fly around the nucleus of the atom like planets in orbit, as was originally thought. In the case of charges “exchanging” photons, that seems to make sense to us for the case of two like charges repelling because that is similar to our everyday experience of contact forces. If we throw a ball at a bottle and knock the bottle over, we observe that method of transfer of momentum and we think it applies to the micro-world of electron and photons. But we really have no justification for that. The micro-world has an entirely new set of rules, and the way in which light interacts with matter is the realm of QED.

    For now, I think a good way to think of it is that charges influence the field, and it is the polarity of the electromagnetic field which determines the direction of the emitting/absorbing photons. It that way of thinking, at least to me, the sample that you have given makes just as much sense for attraction as for repulsion.
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