"... one might go to any region in space and measure varying electric potential
etc, but we should not loose sight of the fact that the effect is due to a
moving charged particle somewhere -- not to something independent of such a
charge -- if in fact there "really" are such things as charged particles."
Did someone claim somewhere in this thread that an EM wave is independent of an
accelerating charged particle?
Re the reality of fields or EM waves or particles, I believe that one person's
reality is another person's model of the universe. As a natural philosopher, I
try to understand and to explain and to exploit the relationships between
measurable properties. Whether or not my understanding of nature is "real",
I'll leave to a humanist.