Help me understand the virtual particles

[payman]

According to what I have read, virtual particles are those which are intermediate photons in interactions, which cannot be directly observed. If my understanding is correct that would mean that they consist of (in low order perturbation theory), (among other things) u and t channel photons. But electron electron scattering processes are described by such diagrams. That leads me to believe that all electrostatic coulomb force is mediated by virtual photons. Am i therefore to conclude that coulomb force over observable distance is mediated by photons of sufficiently low frequency so as to be unobservabe?

Help would be super.

Regards,
payman

 

[david.sh]

Re: Virtual particles

A virtual photon is an internal photon line, i.e. a propogator.

One measures the presence of a Coloumb potential by the results of the interaction between the source and some charged body. The Coloumb force is the result of a virtual interaction. Two positively charged particles repel by exchanging a virtual photon. I can't trick the system and jump between the two of them and exclaim "hoozah there's a real photon there, look I just detected it", because you'd have just detected it by interacting with the source, assuming you were charged and if you weren't you wouldn't interact with it (the coupling between you and the EM force would be zero, you'd just be a free field).

Non-virtual photons are external photon lines in Feynman diagrams, and are just radiated or absorbed photons.

I'm probably not reading your post right, but are you saying that virtual photons only occur at low orders in perturbation theory? If so, contributions from virtual interactions are less prevalent in the low orders of perturbation theory than in the higher orders.