On Tue, Jun 17, 2025 at 12:19 AM Alan Grayson <[email protected]> wrote:
*>> If you are in freefall then you experience no gravity, so from your > perspective your local spacetime is flat and things move in a path that is > the shortest distance between two points, a Euclidean straight line. But > from my perspective standing on the Earth's surface you are being affected > by gravity and are moving through spacetime that is curved and > non-Euclidean. The Equivalence Principle says both points of view are > equally valid, but the only way that could be true is if I see you moving > in a path that is the shortest distance between two points in 4D > non-Euclidean space, and that is a geodesic.* > > > *> Thank you. I have some questions about your "proof". First, why is the > shortest distance between two point on a curved manifold a geodesic,* > *Because my iMac says the definition of a geodesic is "the shortest <https://www.google.com/search?sca_esv=891adaa60c792029&sxsrf=AE3TifNlaDohvZKQrKRfFnVqzaTRPgJz8A:1750155207900&q=shortest&si=AMgyJEtTt81ZwKfSOowD-Pgs8NXgiVGejrXAY764JTDkuS7qT2k5Ll-KWt5SUNIz-ZQ5LVt3dW6nW9a0hqswv-Sfse4vokjcmQnxvcQXRYco2_MSTlh9c10%3D&expnd=1&sa=X&ved=2ahUKEwiZ29-bnPiNAxV_SjABHa4zIE4QyecJegQIQRAR> possible line between two points on a sphere or other curved surface".* > *> and second, perhaps more important, how can your proof depend on a > principle, the EP, which depends on an imprecise measuremen of tidal > forces? AG * *The Equivalence Principle is about local space where tidal forces are too small to detect. For human sized objects tidal forces can be safely ignored unless they are close to a black hole or a neutron star, and molecules are so small tidal forces don't become important until after they have passed through a black hole's Event Horizon and are approaching the singularity at the center. Einstein certainly didn't ignore tidal forces, his field equations can tell you exactly how strong they will be and in which direction they will stretch and compress things. * *>> If you are holding an object and standing motionless on the Earth's > surface then you and the object are still following a path through 4D > non-Euclidean spacetime because both of you are still moving through time, > but that path is NOT a geodesic because a force is being applied to the > bottom of your feet. When you release the object its spacetime path > suddenly changes to that of a geodesic while your path remains > non-geodesic. * > > > *> The logical necessity of that sudden change to a geodesic is not yet > convincing. * > *Why not? When you're holding the object both of you are on the same path through 4D non-Euclidean spacetime, but when you let go the force that the object felt suddenly stops, so just as suddenly it starts following the path of a geodesic. But you are still experiencing a force on the bottom of your feet so you, unlike the object, are still on a non-geodesic path. And objects that are not on the same geodesic path through 4D non-Euclidean spacetime are moving relative to each other. * *> You claim it's related or caused by the EP, but the object suddenly > shifting to that geodesic motion "knows" nothing about the EP and free fall > in a gravity field.* > *When you were a kid playing with marbles did you wonder how the marble knew to move when you applied force to it with your finger even though the marble was never taught Newtonian physics? * *> As I wrote, and I think you agree, time doesn't exist because clocks do, > but because there are things HAPPENING in the universe;* > *The word "happening" can't be defined without implicitly or explicitly employing the concept of time. A clock doesn't have to be based on a periodic phenomenon (although from an engineering point of view it makes construction much easier and results in a more elegant device) but it does have to be based on a phenomenon that is predictable. If the universe consisted of nothing but random white noise then building a clock would be impossible and time would become a meaningless word. Some people think that is the state our universe is heading for, but I think it's too early to make such a bold prediction because we don't even know what 95% of the universe is made of. Time will tell.* *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/CAJPayv3cotPoc5903PaiLfm87DZMdJfF2YGUF_aLrF3UFREuhw%40mail.gmail.com.
