I am doing some personal research in this specific area and wanted to ask something related to photons and EM force. are involved. Here is a thought experiment that doesn't add up to observed results, what's the flaw?

Initial assumption: Virtual photons are the carriers for EM force even in static situations.

Initial setup: Two oppositely charged parallel metallic plates are set up like a simple capacitor, inside the plates are an uniform static electric field, fringe fields are ignored.

Based on the force carrier model, exchange of virtual photons are responsible for this uniform electric field. A plate of non-conductive, non-polar material should be capable of blocking any photons.

In this case, the force carriers would be unable to reach their destination and there would be no electric field.

But in reality the electric field passes straight through the non-conductive plate.

Where have I gone wrong?

Cheers Zed.


1 Answer 1


Virtual photons do not pass from one plate to the other. The leave a plate and then return back to the plate and the electron or positive ion they left from - all in a very short time. The only time the leave a plate and do not return is when they have imparted some momentum to another charged particle (imagine a Feynman diagram for two electrons scattering off each other). The other misconception is that the non conducting plate will block the virtual photons. It may be true that the plate would block real photons of certain energies, but virtual photons are not real photons - they can pass through non conducting bodies. On the other hand, the virtual photons will also, sometimes, interact with the plate and cause the atoms of the plate to become small electric dipoles. These dipoles will become additional sources of virtual photons that will will change the electric field between the plates. This is the way dielectrics in capacitors change the capacitance of this kind of capacitor.

The whole concept of virtual photons are really just expressions of how we are able to calculate how a test charge will interact with a electromagnetic field by using Feynman diagrams. It is not a good idea to read too much "reality" into the presence of virtual particles. The results of calculations of the Feynman diagrams is the really meaningful physical result, virtual photons are kind of a hand wavy tool to explain Feynman diagrams.


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