The electromagnetic field is mediated by photons (energy quanta). Its range is infinite, the interaction only weakens quadratically with distance due to the area of an expanding virtual sphere.

Where do these photons come from? If they are virtual photons emitted by the charged particles, it does not make sense for them to have infinite range (uncertainty theorem). If they are energy packets radiated by the charged particle, where does this energy come from and why is it not depleted? In particular a stationary particle would not radiate Bremsstrahlung.

  • $\begingroup$ Imagine playing note on a musical instrument. How many times can you play that note before that sound is depleted? Sound is simply created out of nothing when particles vibrate in a specific way. Likewise, when you shake a charge photons are simply created on demand. $\endgroup$ – David H Nov 4 '13 at 15:20
  • $\begingroup$ I don't understand how the energy is conserved then. Clearly photons do have energy. What causes two stationary identically charged particles to repel? $\endgroup$ – Klemens Baum Nov 4 '13 at 15:23
  • $\begingroup$ Yes, photons carry energy. When that energy is created, part of the energy of the interacting charges is simultaneously destroyed to compensate. For two identically charged particles, lower energy states correspond to an increased separation. $\endgroup$ – David H Nov 4 '13 at 15:43
  • $\begingroup$ Why the downvotes? This seems a reasonable question to me and the answer is by no means obvious or trivial. $\endgroup$ – John Rennie Nov 4 '13 at 16:27

The picture of two electrons throwing virtual photons at each other is not meant to be taken literally. The Feynmann diagrams you've undoubtably seen are just a graphical representation of a calculation not a literal exchange of a particle. To get some background on this read Matt Strassler's excellent article on virtual particles.

The force between the electrons is indeed mediated by the photon quantum field, but it's not literally an exchange of virtual photons. An electron is an excitation in the electron quantum field. This excitation is continually interacting and exchanging energy with the photon quantum field to create excitations in the photon field (Matt Strassler's article refers to these as ripples). In the absence of any other electrons this energy exchange must average out to zero to conserve energy, though temporary deviations away from zero are allowed by the uncertainty principle. If you bring up a second electron then the interactions of the first electron with the photon field can reach the second electron, and vice versa, and this allows the two electrons to interact with each other.

The transfer of energy in the photon field can be modelled as (an infinite sum of) virtual photons, but it's very different to the excitation of the photon field that we call a real photon. For example virtual photons can travel faster than light.


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