On Sunday, May 25, 2025 at 6:08:41 AM UTC-6 John Clark wrote:
On Sat, May 24, 2025 at 10:01 PM Alan Grayson <agrays...@gmail.com> wrote: *>> 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* *If a** test particle is at rest with respect to an uncharged current carrying wire then it is not at rest with respect to the electrons flowing in that wire, and that's what causes the magnetic field. If a negative test particle starts moving in the opposite direction that the electrons in the current are then the relative speed between the test particle and the electrons in the wire will increase, and the distance between the moving electrons will decrease due to relativistic length contraction, so the test particle will observe a stronger negative electrical charge from the part of the wire that is closest to it even though the wire is a whole is not electrically charged. So the test particle will be repelled from the wire because both the test particle and the electrons in the wire have a negative electrical charge.* *But If the test charge is moving in the same direction as the electrons in the wire then it will be attracted to the wire for exactly the same reason, relativistic length contraction, although in this case the part of the wire that is closest to it will seem to have a positive electrical charge. * *So from the point of view of the test particle there is no need to even mention something called a "magnetic field", BUT from the point of view of someone in the same frame of reference as the stationary wire a magnetic field is a very useful fiction. * *> 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.* *Then you're not disagreeing with me, you're disagreeing with Einstein. Who do you think a rational person should bet their money on, you or Einstein? * *I'm disagreeing with anyone, including you, who thinks the EP is an absolute, when in fact it's a relative, an approximation. With sufficiently sensitive measurements, the reality of a gravitational field, or not, can be determined by internal measurements. AG * *> The gravitational field produces an acceleration, and thus, IMO, is real.* *A man in a sealed rocketship without a porthole steps on a scale and notes that he weighs the same as he did when he was standing on the surface of the Earth but, if you ignore tidal effects which you can for something as small as a human, he would have no way of knowing if his rocketship was resting on the surface of a planet similar to Earth or if he was in intergalactic space in a rocketship that was accelerating at 9.8 meters per second squared a million light years from anything more massive than a grain of sand.* *> 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 * *It's called tidal effects, the smaller the size the smaller are the tidal effects, at zero size (a point) the tidal effects are also zero. Einstein's field equations of General Relativity can tell you exactly what pressures and tensions those tidal effects will produce in an object of a given size and shape if it moves from point X to point Y in curved 4D spacetime (also called a gravitational field). * * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* agf -- 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 everything-list+unsubscr...@googlegroups.com. To view this discussion visit https://groups.google.com/d/msgid/everything-list/e84e5d53-bdf3-4050-800b-1c04cdc27d9en%40googlegroups.com.
