On Saturday, May 24, 2025 at 6:28:25 AM UTC-6 John Clark wrote:
On Sat, May 24, 2025 at 3:46 AM Alan Grayson <[email protected]> wrote: Einstein quote: "*The gravitational field has only a relative existence in a way similar to the electric field generated by magnetoelectric induction" * *> What does the sentence emphasized by me, mean? TY, AG* *Electric fields and magnetic fields are relative, one man's electric field is another man's magnetic field and vice versa. * *If someone is at rest relative to a current carrying wire, the magnetic field will be measurable, but what about the electric field? AG* *So in General Relativity there is no such thing as an electric field or a magnetic field, although they can often be useful fictions, there is only an electrodynamic field. In the same way a gravitational field is a useful fiction, it's not fundamental, it's relative. * *I disagree. The gravitational field produces an acceleration, and thus, IMO, is real. It also causes a test particle which is spatially at rest, to accelerate. This, I think, is because the time coordinate is embedded in the geodesic equations of motion, so as time increases, the particle's position must change spatially. But this seems to imply a universal clock which every particle has, or can measure. AG* *An observer in a rocket without a porthole accelerating at 1G will see a gravitational field, but an observer outside would see no such field, he would just see a rocket accelerating in a way that Isaac Newton would understand.* *The equivalence principle can not exactly simulate a gravitational field, since it produces no forces toward a center of mass. I forget what that's called. AG * * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* 4$b -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion visit https://groups.google.com/d/msgid/everything-list/67f97b29-ca5d-4fdd-bb24-dc5dcf18cd9dn%40googlegroups.com.
