On Thursday, March 20, 2025 at 7:28:28 AM UTC-6 John Clark wrote:
On Thu, Mar 20, 2025 at 1:07 AM Alan Grayson <agrays...@gmail.com> wrote: *> As I recall, the gravitational potential is the negative derivative of the gravitational force, but if there's no force in GR, how is that measured? AG* *The gravitational potential energy of an object at a particular location is related to how much slower time runs there compared to infinity where spacetime is flat, let's call that factor X. The weaker the gravitational field is the closer X comes to be equal to 1. On Earth's surface gravity is so weak X is 0.9999999997, so you can simplify the very complex tensor equations in General Relativity to the simple Newtonian equations you learned in high school and you get an excellent approximation. * *However when gravity starts to get strong X starts to approach zero, and at a Black Hole it is zero, so in General Relativity the Newtonian idea of energy, and not just gravitational potential energy, becomes problematic. General Relativity doesn't consider energy and momentum to be two separate things, there is only the "stress–energy–momentum tensor", it is a complete description of how much stuff there is and how it is moving and flowing and exerting pressure or tension. But the result is when gravity becomes very large and space-time has become very curved you can't point to a spot and ask how much gravitational potential energy is there at that point because the question has become meaningless . * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* *Is the gravity wave detected by measuring the vibrating change of the distance between the two separated locations of the detector? If so, how is this a variation of spacetime, instead of just a measurement of spacial differences? AG* -- 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/2264ab04-ab33-4a0b-908f-133351689a65n%40googlegroups.com.
