[jmcnulty]

Ok, so now I'm confused about what Magnetic field lines are. Many years ago I asked a friend who had a physics degree what Magnetic field lines were made of and gave him an example of those generated by earth propagating through the vacuum of space. His answer involved an interaction between virtual particles and the electromagnetic field. But that doesn't fit with this description of virtual particles.

In the article Strassler says: "A 'virtual particle', generally, is a disturbance in a field that will never be found on its own, but instead is something that is caused by the presence of other particles, often of other fields."

So if a virtual particle (disturbance) can only exist in the presence of another particle, what other particles are involved in the generation of magnetic field lines? I didn't think there were any.