On Sunday, June 22, 2025 at 6:57:09 AM UTC-6 John Clark wrote:
On Sun, Jun 22, 2025 at 1:27 AM Alan Grayson <[email protected]> wrote: *>> 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.* *What the hell? Accurate measurements are absolutely necessary if you want to detect ANYTHING! If your measurements are lousy then you will not be able to detect tidal forces, and if you can't detect tidal forces then you can't tell the difference between being stationary on the surface of a planet and accelerating in a rocket through empty intergalactic space. * *In a recent post, here's where you claimed accurate measurements were irrelevant to detecting tidal forces:* *>> The sensitivity of the instrument is not the issue, no matter how sensitive it is if you pick a small enough region of space it will not be able to tell the difference,* *> Indeed, it IS the issue. The enclosed observer must drop two test masses and determine any tendency for them to converge. So if the region is small enough, and the measurements sufficiently approximate, tidal forces, if they exist, won't be detected. AG * *There is a limit on the precision that any real instrument can have because it will always produce an error, let's call it Ω, that is greater than zero. So no matter how small Ω is, I can always produce a finite region of space in which your instrument cannot detect a difference between gravitational mass and inertial mass. And regardless of how large a volume of space you're interested in, provided it's not infinite, I can produce a large but finite sphere of matter that produces a gravitational field that your instrument cannot distinguish from acceleration. * *So, in this scenario, the experiment can be done so that tidal forces will not be detected and one can conclude the EP holds. But this is obviously contrived, and depends on NOT having no definite idea what "local" means. AG* > *If the path of two test masses falling toward the bottom of the enclosure is short, in-accurate measurements will still affirm the EP.* *Correct. And if you increase the accuracy of your instrument but I reduce the size of the enclosure then the equivalence principle will still be affirmed. The limit of this sequence will be an instrument with perfect 100% accuracy and a volume of zero size (a point), and the equivalence principle will STILL be affirmed. * *> Some statements of the EP are not approximations, such as that all objects fall at the same rate under the influence of gravity,* *The reason all objects fall at the same rate under the influence of gravity is because gravitational mass and inertial mass are equivalent. And that is the Equivalence Principle. * *I'm not sure how this conclusion is reached. AG * *>> 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? * *I never made that claim. You're putting words in mouth! University professors are usually too busy to deal with issues I raise, so I go to other allegedly knowledgeable individuals, such as Brent, who has a Ph'D in physics from the University of Texas at Austin, one of the foremost universities with a focus in physics. AG * *If it's not because you believe you know more about General Relativity than they do then what is the reason? * > *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* *I don't have a PhD in General Relativity from a major university, and I don't think anybody else around here does either, so I pay very close attention to those that do. They know far more than I do about it, and what they say plays a very important part in forming my opinions about what issues are unresolved in General Relativity. However you have used a very different method in forming your opinions, but I can't figure out why. If it's not because after reading about general relativity for 15 minutes you think you know more about the subject than brilliant people who have spent a lifetime studying the subject, then how did you form your opinions?* * > 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. * *20 years before Einstein was born Maxwell used his electromagnetic equations to calculate the speed of light, and it agreed perfectly with the experimental determination of the speed of light. however those equations did NOT say what that speed was relative to, they just said that was the speed of light. At the time many thought that was a major flaw in Maxwell's idea, but Einstein thought it was Maxwell's greatest triumph. * *If you believed what Maxwell's equations are telling you and the speed of light really is the same for all observers, then Einstein proved in 1905 that the logical consequence is time dilation and length contraction; if they did NOT occur then there would be a true logical paradox. * *While I agree that for the velocity of light to be frame invariant, from a logical pov we get time dilation and length contraction. That's the conclusion of an observer in the rest frame observing a moving clock. But the observer in the frame of the clock, does not measure these phenomena. So what I find baffling, as the muon case shows, is how an apparent observation of an observer at rest wrt a moving clock, translates into real measurable phenomena. AG* *So if you understand Special Relativity then you shouldn't be baffled, a unlike General Relativity you don't need a firm grasp of 4D non-Euclidean tensor calculus to understand it, high school algebra is sufficient. So you shouldn't be baffled but it's still understandable to be in awe of it all. * *> 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,* *You could say exactly the same thing about Newton's equation F=ma, in fact you could say the same thing about ANY equation in physics. * Yes, I can say that, and I do, but in the case of classical E&M, it was known before QM that electrons occupy the outer regions of atoms, so F can be understood as repulsive field interactions which create a force preventing penetration into a material object. Of course, QM is more exact, but classical E&M provides a physical model for understanding F. AG * > 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.* *When you touch a marble with your finger, why is a force applied to the marble? To really get to the bottom of that question you need more than classical physics, you need Quantum Mechanics. It's not because of electromagnetism which can be attractive or repulsive or zero if there is no electrical charge, and atoms have no electrical charge, and both your finger and the marble are made of atoms. * *The real reason is because atoms have electrons in their outer layer, and electrons are fermions (that is to say they have half-integer spin) and so must obey the Pauli Exclusion Principle which says that two fermions cannot be in the same quantum state. On the other hand bosons such as photons (that have integer spin) do NOT need to obey the Pauli Exclusion Principle, in fact in some circumstances they prefer to be at the same quantum state. In 1917 Einstein used that fact to discover the principle of Stimulated Emission, which is the operating principle behind the LASER, which is an acronym that stands for Light Amplification through Stimulated Emission of Radiation.* *But why is the Pauli Exclusion Principle true? Because Quantum Mechanics demands that it be true. What demands that Quantum Mechanics be true? I don't know. * *> 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* *On a space-time diagram you are always moving at a constant speed, the speed of light. When you're sitting on your butt all your speed is in the time dimension, but when you get up and start walking a small part of your speed is in a spatial dimension, so your speed in the time dimension decreases slightly. And that is called time dilation. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* da; -- 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/c50b8e8d-ed28-4453-80b2-4708ab0710e5n%40googlegroups.com.
