He does specifically ask for the meaning of "mediated" in this context. I didn't need to "guess' that.
Mediated just means "in the middle" i.e. carries or transports the force between charges."It is now understood that those equations tell us that the electromagnetic force is actually mediated by light and that light is an electromagnetic wave". I do not understand the term "mediated" in this context.
There are plenty of explanations of virtual photons on this site, Arnold's FAQ has some good stuff.This is actually something I've been wondering about since my time at university. We were told that "virtual photons" are responsible for all electric and magnetic forces. I understand that photons are the energy parcels of all electromagnetic radiation and I don't think two charged objects send such radiation back and forth between them in order to attract each other. Is there some truth in this concept of virtual photons and, if so, is there some easy way of understanding what they actually are and how they differ from real photons?