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How Does QED Explain the Electromagnetic Force

  1. Jun 28, 2015 #1
    From a conceptual point of view, how is it that Quantum Electrodynamics explains the interaction between two charged particles, (let's say two electrons)? I've heard people say that the electrons exchange photons, but how is it that an electron would know when to send off a photon and that it will be absorbed by another charged particle? And how is it that an exchange of photons would be different for two electrons (which repel) and an electron and, say, proton (which attract)? Also, by exchanging photons, would the photons not carry away a little bit of energy, thus causing the electron to lose energy? Thank you for any explanation :)
  2. jcsd
  3. Jun 28, 2015 #2


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    Virtual photons are an attempt to describe the theory in words, that attempt works well in some setups but it cannot answer questions like those you asked. The actual theory (the formulas) can, but then you have to understand the calculations.
  4. Jun 28, 2015 #3
    Basically, if you calculate the differential cross-section for a process like you have described (an electron exchange a virtual photon with another electron) in QED, in the non relativistic limit you will find the Rutherford formula, which is calculated assuming the repulsive Coulomb force. If you do the same with opposite charged particle, you will find an attractive potential.
  5. Jun 28, 2015 #4
    Is there a simple way to explain the following fact, at the level of a reader who has just made his way through "QED The Strange Theory..."

    When a plane wave reaches a cloud of free electrons, they oscillate at right angles to the direction of propagation.

    How does this emerge from QED, (intuitive picture if such is possible)?
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