On Thu, Jun 19, 2025 at 4:16 PM Alan Grayson <[email protected]> wrote:
*>> 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?* > *If the volume of space is so small or the gravity producing object is so large that tidal forces are negligible then gravitational mass and inertial mass are indistinguishable. And if standing on the surface of the Earth and accelerating in a rocket in intergalactic space is indistinguishable then the Equivalence Principle is true. * > *> Earlier you seemed to think this was key,* > *It is. * > * > but if true the argument is subtle,* > *I think the argument is obvious.* * >> I was getting tired of your strawman equivalence principle, * > > > *> An example of your abuse. AG* > *Abuse? Saying somebody is giving a strawman argument is not equivalent to saying that somebody is retarded. Twice. In the same post. Especially when it really is a strawman argument. * *>> 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 * > *Then what on earth are we arguing about?! I've been using that word constantly. * *> If I recall correctly, the Second Law states that the entropy of closed > system never decreases.* > *The word "never" in that **statement of the second law is itself an approximation of the formal definition of the second law, to be precise it should have said "almost never". There are an astronomical number of different ways an egg can be broken, but there is only one way an egg can be unbroken, so statistically it's astronomically more likely you will see an egg being broken rather than see a broken egg becoming unbroken. That's why when you look at a movie that is being run backwards, actions look ridiculous, but the actions don't look like random white noise because they are still following the laws of both Newtonian and Einsteinian physics. * *If you want to understand where the arrow of time comes from you've got to understand the science of thermodynamics, and the foundations of that science is in logic and the mathematical properties of probability. That's why I can imagine a universe in which the law of the conservation of mass/energy is untrue, or quantum mechanics or relativity is untrue; but I can no more imagine a universe in which the second law is untrue than I can imagine a universe in which 2+2=5. * *>> 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.* > *I'm pretty sure I said it's because the Principle Of Least Action is true, and the best I could do to explain why the Principle Of Least Action is true is just to say that nature wants to be lazy and I don't know why nature wants to be lazy. I'm also pretty sure I said that every iterated sequence of how or why questions either goes on forever or terminates in a brute fact. * * John K Clark See what's on my new list at Extropolis <https://groups.google.com/g/extropolis>* aps > > > -- 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/CAJPayv0EH_R3PTGy8pCUcf3FO5O-BwBfM-EdoMEgArbXXch-SA%40mail.gmail.com.
