On Thursday, June 19, 2025 at 9:45:07 AM UTC-6 John Clark wrote:
On Thu, Jun 19, 2025 at 10:07 AM Alan Grayson <[email protected]> wrote: *>>>>> I gave the example of the SS orbiting the Earth. AG* *>>>> And as I explained in another post that you evidently have not bothered to read: * *>>> Evidently? I indeed read it and I pointed out your error, which you completely forgot and correctly below. AG* *>> Where is the error in the below? * *> This is getting retarded. What you have below is correct. What you wrote a few messages ago was in error. Your error was your claim that free fall motion is like moving along a straight line in flat space. I suppose, loosely speaking I could agree. AG* *A free fall through 4D non-Euclidean curved spacetime IS like moving in a Euclidean straight line through flat 3-D space in that an observer couldn't tell the difference because gravitational mass and inertial mass are equivalent. * *>> 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. * *What has the latter fact to do with whether tidal forces can be determined; that is, that gravitation and acceleration are indistinguishable? Earlier you seemed to think this was key, but if true the argument is subtle, and merely saying it's so, is insufficient as a argument. AG * *> If a man is 6 ft tall, and you put him into an elevator of volume 1 cubic inch, will he be able to measure the convergence of two test particles he drops???* *Well, I do agree with one thing you said, "this is getting retarded". I was getting tired of your strawman equivalence principle, * *An example of your abuse. AG* *so I asked Claude to give me the full definition and this is what he said: * "The *full, rigorous equivalence principle* has several forms, but the most precise is the *Einstein Equivalence Principle*, which states: 1. *Weak Equivalence Principle*: All objects fall at the same rate in a gravitational field (regardless of their composition) 2. *Local Position Invariance*: The outcome of any local non-gravitational experiment is independent of where and when it's performed 3. *Local Lorentz Invariance*: The outcome of any local non-gravitational experiment is independent of the velocity of the (freely falling) reference frame The key word here is *LOCAL*. The equivalence principle was never meant to apply globally - it *specifically* applies to small enough regions of spacetime where tidal effects become negligible. Einstein himself was well aware of tidal effects. He knew that if you made your "elevator" big enough, you'd eventually detect the slight differences in gravitational field strength and direction across the elevator. That's exactly why the principle is formulated as a *local* statement. Think of it this way: in any small enough neighborhood of spacetime, you can always find a coordinate system where gravity "disappears" locally. But "small enough" means small enough that tidal effects don't matter for whatever experiment you're doing." *I agree. "Local" resolves this issue. AG * *>> The second law of thermodynamics is an approximation, but not only is it a superb approximation it is also the most important principle in physics. * *> It's not an approximation IMO,* *Then your opinion is dead wrong because the second law of thermodynamics is an approximation , and there is no doubt about it. * *If I recall correctly, the Second Law states that the entropy of closed system never decreases. Where is the approximation or a counter example? AG * *>>>>The external force is provided to the object by your fingers, when you let go that external force suddenly stops and then just as suddenly the object starts following a geodesic path to the ground (not the sun) and then the force of the ground switches the object back to following a non-geodesic one which is the reason why it doesn't continue on to the center of the Earth. But during all of this you have continued to experience a force through the bottom of your feet. So you never stopped following a non-geodesic path and that's why the object is now on the ground and not still between your fingers.* *>>> why is that path geodesic? AG* *>> Both Newton and Einstein would give the same answer to that question. General Relativity and Newtonian Physics have one thing in common; they both say objects that are not experiencing a force always follow a path that is the shortest distance between two points, the only difference is in Newtonian physics were talking about flat 3-D Euclidean space (in which the geodesic is a Euclidean straight line with all the properties you were taught in high school) but in Einsteinian physics we're talking about curved 4D non-Euclidean spacetime where the geodesic is NOT a Euclidean straight line.* *> Is that a postulate of GR?* *It's a postulate of both General Relativity and of Newtonian physics that things that are not acted upon by a force move in a geodesic, a straight line is just the particular geodesic you get in flat Euclidean space. * *Earlier, I'm pretty sure you denied it was a postulate. More important from my pov, is why it moves from being spatially at rest if there are no forces acting in GR. AG* *> In GR, why does the test particle move when it is released from an external force while in a gravitational field, and take a geodesic path?* *You've asked that question before and I've answered that question before. I'm not going to give a new answer until you ask a new question. * *> You keep claiming the path is geodesic in GR, but can't say why. AG* *It's the same reason **the path is a geodesic in Newtonian Physics for any object that is not being acted upon by a force. * *> lately you seem a bit retarded.* *That's** two "retarded" in one post. It's always the same with you, whenever a new topic comes up you start by asking questions that are friendly and sometimes even interesting, but then after just a few exchanges you get personal, things get really nasty, and the conversation degenerates into an insult contest. * *You're the one who starts the abuse but are unaware of it. AG * * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* urn -- 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/b72e80cc-5ff7-4c6b-860a-126547dc4ef0n%40googlegroups.com.
