"Going from no field to some field is a change, and that change is what is propagating. It's all that has to propagate for a complete description of what's going on."
That train of thought very likely misses the right track.
It's too easy to think along those lines and confuse the field itself changing or springing into existence with that of an existing field being disturbed.
When we turn ON the electromagnet, the magnetic field suddenly covers a sizeable area where it did not cover in the past when our electromagnet was OFF.
How *fast* did the field cover this new area?
Yet what you seem to be saying is that this "change" in going from "no field" to "some field" is akin to a disturbance in an existing field.
I'm not convinced that's entirely valid or useful. It might be a division by zero event.
Yes, if we have an *existing* magnetic field, then a disturbance in that field should propagate through the field itself at the speed of Light. That's well-known and not under dispute so far as I'm aware.
But what hasn't been conclusively proved or accepted is how fast the field itself covers an area when the field first forms, likewise for when the field ends as to how fast it ceases to cover an area.
Yet what you seem to be saying is that this "change" in going from "no field" to "some field" is akin to a disturbance in an existing field.Exactly! Because consider: an observer at rest with respect to an electrical charge will see an electric field and NO magnetic field, while a moving observer (passing arbitrarily close to the first observer's position) will see both an electric and a magnetic field. The two observers will not agree on whether there is a magnetic field or not; they will, however, agree on the dynamics of locally moving charged particles (i.e., the physics works out the same).
So you see, you can practically never say that any region of space is free from a magnetic field, because the magnetic field in that region will be different for different observers. One man's zero field may be another man's strong field. There can't be anything special about turning on a field; it's the same thing as a change to the existing field. The 4-potential is defined everywhere in space. (Homework: look up the terms "Gauge Principle" and "Gauge Invariance".)
[Geek alert 1: The reason that different observers will see different fields is because of special relativity. From a moving frame of reference, time moves more slowly and space is contracted along the direction of motion. If the field is the same for both observers, the motions of a charged particle can't be agreed upon by different observers. The magnetic force is the force that arises that compensates for the difference in motion between the two versions of spacetime. (It's tempting to call the magnetic force an "apparent force", such as the coriolis force, but it is possible--easy, in fact--to construct magnetic fields that can't be zeroed out by a Lorentz boost.)]
[Geek alert 2: Woah! Wait a second! If the relative distortion of spacetime causes an apparent--no, a real--change in the electromagnetic field for relatively moving observers, why doesn't it do the same thing for the gravitational field? It does. It's called the gravitomagnetic effect. Well, doesn't that just prove what Van Flandern is saying? Isn't that just a different formulation of the same effect? No, because first, unlike the "time delay" canard, the gravitomagnetic effect depends on the speed of the observer and not on the distance from the source, and second, because any "time delay" effects (such as the Poynting-Robertson effect, which really does pertain to the light from the sun) would be orders of magnitude greater than the gravitomagnetic effect.]
(I have used the blue font color to denote scientific ignorance, as is customary on FR.)