On Saturday, June 21, 2025 at 6:53:00 AM UTC-6 John Clark wrote:
On Sat, Jun 21, 2025 at 12:45 AM Alan Grayson <[email protected]> wrote: *>> If the enclosure was large enough, you would be able to detect tidal forces. * *> But you still need accurate measurements (depending on the magnitude of the tidal forces), a fact you earlier denied. AG* *H**uh? I still deny it! It's pretty obvious that if you don't have accurate measurements then you're not gonna be able to tell the difference between gravity produced by a planet or acceleration produced by a rocket regardless of the size of the volume of space you're dealing with. If you don't have accurate measurements an observation will tell you nothing.* You were quite emphatic as I recall that accurate measurements were irrelevant to detecting tidal forces. Of course, the accuracy necessary to detect tidal forces depends on the experimental situation. If the path of two test masses falling toward the bottom of the enclosure is short, in-accurate measurements will still affirm the EP. Some statements of the EP are not approximations, such as that all objects fall at the same rate under the influence of gravity, but not the equivalence of gravity and acceleration despite the equality of gravitational and inertial MASS. AG *>>I have no idea what Wheeler's colleagues think about this issue, nor does it really matter.* *>> Because you know far more about General Relativity than all the professors who have spent their entire careers studying it?* *> More abuse from you.* *That was not rhetorical, it was a legitimate question that, given the circumstances, was an entirely reasonable thing to ask. And I'm still waiting for an answer. You said you're not interested in what Physics professors at major universities who have spent their entire careers studying General Relativity have to say on the subject of General Relativity. Why is that? If it's not because you believe you know more about General Relativity than they do then what is the reason? * I never made the claim you allege. I just meant that relativity has some unresolved issues IMO, and that's clear, so I don't need to ask any university professors for their opinions when strong advocates of relativity can be found on this web site and others. For example, an observer measuring the muon's half-life will get one value in the lab and another value when in motion with respect to the muons, while in the frame of the muon no such change is observable. This is the result of the LT, in order to keep light speed frame invariant. But how this can occur remains baffling. Same with time dilation and length contraction. The moving observer sees changes relative to his frame, which we can call APPARENT, yet somehow this is confirmed by measurements, while in the frame of the object being measured, there is no dilation or contraction. * > **I think it leaves a lot of unresolved issues to claim that geometry alone explains motion for free falling objects, without specifying exactly how geometry interacts with material objects.* *But Einstein's field equation of General Relativity does exactly that! The equation is: * *G_μν = (8πG/c⁴)T_μν* *Left of the equal sign is the Einstein Tensor which describes the shape of spacetime which is geometry. And right of the equal sign is the Stress-Energy Tensor which describes the matter density, the energy density, the pressure, the stress, the tension. and the momentum flux; which are all material things. And "specifying exactly how geometry interacts with material objects" is what you asked for!* *> The equation does no such thing. It just tells you how to calculate one quality, curvature of spacetime, when you know the other (energy / matter distribution). * *You said you wanted something "specifying exactly how geometry [the left-hand side of the equation] "interacts with material objects" [the right-hand side of the equation]. Einstein's equation gives you exactly what you asked for. * *> It doesn't specify any physical process for the calculation it describes. AG * *Are you equally dissatisfied with Newton's most famous equation F=ma? What physical process causes force to accelerate mass? Newton didn't say, but he did say what a force could do to a mass. * I reiterate my opinion that Einstein's equation just tells us how to calculate unknowns of interest, but doesn't offer any physical model of exactly how, say, mass/energy results in curvature of spacetime. F=ma needs additional theory to be really understood, and it likely comes from classical E&M, where one body impacting on another produces an acceleration due to local EM fields which are repulsive. IOW, the interaction of the force and the acceleration are local, but in GR there are no forces, so acceleration from spatial rest seems to be an unsolved problem. AG BTW, Brent was mistaken in his claim that my question, "Why does it move?," doesn't assume 4D spacetime. I referred to spatial rest to mean 3 or the 4 coordinates of spacetime, like when you're sitting on your butt, but time, the 4th dimension, continues to advance. Also, when I used the condition "at rest", I meant at rest on the Earth, or any other frame one might choose. AG *>> Speaking of philosophy, can you tell me of one new philosophical problem that General Relativity introduced that Newtonian physics didn't already have? I can't think of one. * *> Sure, that's easy; time dilation, length contraction, muon clocks, the fact that spacetime has curvature, etc. Oh, I can anticipate your response. These phenomena have nothing to do with "philosophy". AG * *No, t**hat's not my response at all! The phenomena you mention in the above are all new and profound philosophical discoveries, they are also all very odd and non-intuitive. But odd is not the same as paradoxical, so all philosophers came to peace with Relativity by about 1925 except for a few in Germany, and they did so for antisemitic reasons not scientific or philosophical reasons. * *However Quantum Mechanics was an entirely different matter, that really did open up a philosophical can of worms, and even today after more than a century there's no consensus about what it all means. The only thing everybody agrees on is that like it or loathe it Quantum Mechanics works, but I can't think of any modern philosopher who has a problem with relativity.* *Actually Einstein solved a major philosophical problem that Newton admitted his theory had. Newton had a big problem with action at a distance. He thought it was crazy that the sun could influence the movement of the Earth, which was millions of miles from it, without influencing anything in between. Newton tried very hard to figure out how forces could operate with no mediating mechanism but he failed. In Newton's book Principia Mathematica, the most important book in scientific history, he made a confession: * "Hitherto I have not been able to discover the cause of those properties of gravity from phenomena, and I frame no hypotheses." *And in a letter to a friend Newton said: * *"That one body may act upon another at a distance through a vacuum, without the mediation of any thing else, by and through which their action and force may be conveyed from one to another, is to me so great an absurdity, that I believe no man, who has in philosophical matters a competent faculty of thinking can ever fall into it."* *And in another letter Newton said: * *"Tis unconceivable that inanimate brute matter should (without the mediation of something else which is not material) operate upon & affect other matter without mutual contact, that gravity should be innate inherent & essential to matter so that one body may act upon another at a distance through a vacuum without the mediation of any thing else"* *Einstein solved the problem by providing the underlying mediating mechanism Newton was looking for, and it turned out to be spacetime. Einstein could explain exactly how matter affects spacetime and just as important how spacetime affects matter.* The fact that the presence of matter/energy warps spacetime is a POSTULATE of GR, which you can take as brilliant intuition of physical reality, but not as a physical model of how that occurs. AG *You might complain that Einstein's explanation is not fundamental enough and you want something even deeper, * Yes, although I definitely appreciate GR, I would like something deeper, but when I say something about the insufficiencies of GR and Relativity in general, I never get a sympathetic hearing, but mostly mockery from the True Believers. AG *but to do that we would have to find out what space and time are made of, and nobody knows what that could be, and they may not be made of anything. Space and time may be made of nothing but fundamental stuff, they may exist at the bottom level of reality. * *Or maybe not. Nobody knows. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* %+( -- 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/ebdd12f4-1257-4ad1-9445-b910f57f6456n%40googlegroups.com.
