On Friday, March 21, 2025 at 6:51:18 AM UTC-6 John Clark wrote:
On Thu, Mar 20, 2025 at 11:47 AM Alan Grayson <[email protected]> wrote: *> 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* *LIGO detected the peak to peak displacement that a gravitational wave caused, * *What exactly is waving, space or spacetime, or something else? Variations of time? Time of what? AG* *it does not detect the RMS power in a wave, that's why LIGO's ability to detect gravitational waves only decreases by a factor of 1/r not by 1/r^2 as conventional telescopes that use light or any form of electromagnetic waves do. However gravitational waves with enormously longer wavelengths can and have been detected by variations in time, not space, by using pulsars, a.k.a. neutron stars. They detected a gravitational wave "hum" with wavelengths light-years long that were almost certainly caused by the millions of merging supermassive Black Holes, each being billions of times more massive than the sun, that have occurred since the Big Bang.* *The NANOGrav 15 yr Data Set: Constraints on Supermassive Black Hole Binaries from the Gravitational Wave Background* <https://arxiv.org/pdf/2306.16220> *It is also been propose that when Thorium 229 nuclear clocks are perfected they could be used to detect gravitational waves. * *Breakthrough promises new era of ultra precise nuclear clocks * <https://www.science.org/content/article/breakthrough-promises-new-era-ultraprecise-nuclear-clocks> *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>*2 *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 . * -- 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/d7caa833-80a2-48bf-90cc-3fefcf5ebd43n%40googlegroups.com.
