Understanding virtual particles

[brianhurren]

what is the correct understanding of a virtual particle? the popular science books would have us believe that a virtual particle magically pops up out of the woodwork, steals some energy and then puts it back before it ( the particl) disappears. Like a thieving employee who steal $100 out of the till and then puts it back in the morning before the boss sees it. the problem I have with this description is I am expected to believe that God, or the Universe turns a blind eye while this is happening. Would a better description be that two particles of oppersite charge interact and the exchange energy. When we calculate from the observed effects of the interaction (transfer of motion perhaps) the amount of energy exchanged adds up to exactly one photon, although an actual photon was not involved in the interaction, so we say that the photon is virtual.

 

[bhobba]

what is the correct understanding of a virtual particle?

They are simply mathematical artefacts of the usual perturbation methods used in Quantum Field Theory.

In particular they arise as a pictorial representation of a so called Dyson series, called a Feynman diagram:
http://en.wikipedia.org/wiki/Dyson_series

They are not in any sense real. Indeed when we use non-perturbative methods they never appear.

Thanks
Bill