On Thursday, June 19, 2025 at 5:38:47 AM UTC-6 John Clark wrote:
On Thu, Jun 19, 2025 at 1:47 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 *You know of course that in flat 3D Euclidean space a straight line is a geodesic. Don't you? * *"No force is being applied to the space station but it is not following a Euclidean straight line because it is not in flat Euclidean space, it is in curved 4D non-Euclidean spacetime and is following a geodesic path. In curved 4D non-Euclidean spacetime the shortest path between any two points along the space station's orbit is the space station's orbit itself."* *>> 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. * 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??? Sure, you can't always show the gravity and acceleration are equivalent, because they are not. AG *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. * *And if in your thought experiment you want to conjure up an instrument that has infinite precision even though that would be unphysical then, if you're playing fair, you should allow me to conjure up a sphere made of matter that is of infinite size even though that is unphysical.* *> This is Einstein's error;* *When somebody on the Internet claims to have found an error that Einstein made that nobody had noticed before my built-in bullshit detector goes off. It goes off a lot. My bullshit detector may not be perfect but it has served me pretty damn well over the years. * I have no idea, nor do I care if anyone else has claimed that the EP is just an approximation, not truly a principle. AG *> mistaking an approximation for a principle. 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, whereas the EP is. The latter appears to be true in some cases, and not in others, depening on the space allowed for the experiment and the accuracy of the measuring device. AG *> ** if an object which is falling toward the Sun is restrained by an external force and then let go, why does it move according to GR* *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? 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 keep claiming the path is geodesic in GR, but can't say why. AG *>> I will say that if you're standing on the Earth's surface then you can NOT be in an initial state * *> For simplicity, imagine standing on a non-rotating Earth as the initial condition. AG* *That won't help, you would still be following a non-geodesic path because a force is still being applied to the bottom of your feet. * Sorry, but lately you seem a bit retarded. I know the path is non-geodesic in that case. Nowwhere did I deny that. I was answering your question of what "spatially at rest" means. I figured if the Earth is rotating, you could claim a person standing on the Earth would have his spatial coordinates change. AG *That's why even if its rotation stopped you would still not fall to the center of the Earth. * *John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* gaa -- 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/134dccc0-3102-4a21-a842-7da69e8c647en%40googlegroups.com.
