I have a slightly out-of line question:
Consider a single electron (or it's current if you please) The EM field surrounding it will (no doubt) have an EM field energy (T) to go with.
The standard description of interaction is by exchanging a virtual photon. (For simplicity suppose, that only one virtual photon (of arbitrary momentum) can be exchanged)
Question: Is there any way to express the EM field energy "in terms of" virtual photons???
Line A: Every virtual photon has energy-momentum. The EM field energy-momentum is some weighted sum over all virtual photons.
Line B: A photons energy-momentum is very different from the EM field energy, because T ~ FF. But what can be said about the EM T of a single photon?
Line C: Your choice
NOTE: Please note that I own a PhD in physics, so you can answer on any level you like.