D Tibbets wrote:Does the speed of gravity fit into the argument?
Yes. The basic idea is that if gravity causes inertia (Mach's Principle), and is linking gravity sources from across billions of light years, how can we have instantaneous inertial effects caused by gravity? The answer is in Wheeler-Feynmann Absorber theory, which posits waves moving both forward and backward in time, and this theory works for several different kinds of needs. It works in electrodynamics to provide answers we don't otherwise have, about how fields work inside for example, every electric motor. The back reaction from electric and magnetic fields appears likewise to be instantaneous, but we do not note an issue here because if they propagated at c we would not notice this given the small distances inside a motor. Absorber theory says the effects are instantaneous since they're the result of half the sum of the advanced and retarded waves, which are themselves not instantaneous but propagate forward and backward in time.
Absorber theory has trouble when it comes to the self-energy of the electron and this is why Einstein gave up this line of inquiry, and later why Wheeler and Feynman abandoned it. The theory makes good sense and is "elegant" in that it has symmetry no other attempts in electrodynamics have. Time symmetry is a nice thing to find in physics, especially when it solves the problem of instantaneous action at a distance. The trouble was, the electron self-energy issue.
Woodward solved the electron self energy issue. This is what chapters 6 & 7 are all about and IMHO, Woodward deserves an Nobel for this work alone. Time will tell, as physicists work it out, but his solution is again elegant, and truly astonishing.
And it does not hurt to note the utility of the theory proposed. If Wheeler-Feynman and Woodward are all correct, we can have mastery over inertia. We also should expect Cramer and Kastner to be correct in their similar adaptations of Absorber theory, meaning this Transactional Interpretation of Quantum Mechanics, and if this is right, then we have a way forward in looking at quantum gravity. The fact we can't even agree on an interpretation of quantum phenomena, is much of what has held up progress in bringing QM and GR together.
BTW, this is an opportunity for a bright guy to make a name for himself. Design an experiment that would show whether there is a speed c time delay in electromagnetic effects. Since EM is easily turned on and off, there should be a way to test for time delay. The issue would seem to me to be one of measurement when looking at distances divided by c, would require some impressive precision, but there are all sorts of ways to get impressive time measurement precision.say your E field or B field couples across 0.1M, and c is 3E8M/s, so you need sE-9 precision. Seems to me there must be many ways to determine if fields couple at c or instantaneously. Would be a great experiment to do, and maybe not too difficult nor expensive.