# What is the spectral energy density of virtual photons around a unit charge at rest?

Given that my previous question, namely "What is the number density of virtual photons around a unit charge?" has no precise answer, here is a more precise wording:

What is the virtual photon spectral density due to the electric field of a unit charge at rest (or, better, its difference with respect to the no-field case)?

Or: How many virtual photons per volume and per energy are found around a unit charge, at a distance r?

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Dear George, "spectral density" surely sounds fancy but it doesn't fix the problem of your question. One simply can't "count" virtual photons in this sense exactly because they're virtual and not "real". You won't ever find any unique answer to such questions. –  Luboš Motl Feb 27 '11 at 16:51
Here is an excellent descrption of virtual particles -in particular, why we should NOT think of them as particles at all. –  FrankH Oct 13 '11 at 13:09

EDIT: If you calculate a field of some charge at some distance $\vec{r}$, it has the only physical meaning - as an external filed in the equations of motion of another charge placed at this point.