On Fri, Jun 13, 2025 at 11:01 PM Alan Grayson <[email protected]> wrote:
*>>> GR has many unexplained postulates,* > > > > > *>> Many? General Relativity only has 3 postulates:1) The speed of light > is constant for all observers.2) Gravitational mass and inertial mass are > equivalent.* > *3) Equations expressing physical laws should say the same thing > regardless of what coordinate system is used to describe 4D spacetime, even > accelerating or rotating ones. * > > > *> And bodies in free fall, move along geodesic paths;* > *That fact is a logical consequence of the Equivalence Principle, which is the third postulate in the above. So no additional postulate is required. * > *> and matter/energy causes spacetime curvature. AG * > *The Equivalence Principle (postulate #3) says in effect that gravity is the curvature of 4D spacetime, and if gravitational mass and inertial mass are equivalent (postulate #2) then the logical conclusion is that matter causes spacetime to curve. **So no additional postulate is required.* *>> if you're willing to tolerate a little inaccuracy and wanted to say the > same thing more poetically you could say it only has one postulate. "matter > tells spacetime how to curve". * > > > *> How does matter do that? AG* > *The 4D shape of the resulting spacetime is determined by how the matter/energy is distributed, and its precise shape can be calculated with Einstein Field Equations, which uses 4D non-Euclidean tensor calculus. * > *>> "Spacetime tells matter how to move" comes from the definition of > spacetime. * > > > *> From a definition we get motion?* > *Obviously. If motion doesn't mean a change in spatial coordinates with respect to time then what does "motion" mean? Newton could explain what gravity does (if things are not moving too fast and gravity is not too strong) but he admitted that he did not know what gravity was: * * "I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses"* *But Einstein knew, gravity is the curvature of 4D spacetime in non-Euclidean geometry. * > *>>> Consider the muon. Why does applying the LT cause its half-life to > dilate?* > > > *>>The same exact reason relative velocity causes ANY clock to slow down, > the speed of light is constant for all observers. * > > > > *> Firstly, you have no clue about the form of a muon's clock.* > *Our ancestors didn't know why the sun moved in the sky but that didn't prevent them from using the sun as a clock, and I don't know the exact mechanism the muon uses to keep time, but I don't need to know because I know for a fact that I can use muons to make a clock. And time is what a clock measures. * > *>>And time is what a clock measures. * > > > *> So if there's no clock able to be defined, does this mean time ceases > to exist?* > *Yes exactly. If it was impossible to make a clock, if nothing occurred in a periodic manner, then the concept of time would be meaningless. That's why people say when the universe reaches thermal equilibrium (a.k.a. the heat death of the universe) nothing would be periodic and so time would come to an end. * *And do you have a better definition of time than "what a clock measures"? I don't. * > *> You can't define the form of a muon's clock,* > *As I said I don't know what the muon's internal clock mechanism looks like, but I do know that whatever mechanism it uses it's accurate. And that's all I need to know. * > *> you think the postulates of GR are the final answer to the mystery of > gravity. AG * > *Bullshit! Even Einstein didn't think that, and I doubt if a single living physicist thinks that either!* *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* 8f/ > > -- 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/CAJPayv1e4crt9EYt2nhs3dtmcCrQsRnSb5p3nD_wNAUNS%2Boyzw%40mail.gmail.com.
