On Sat, Feb 16, 2019 at 7:07 PM <agrayson2...@gmail.com> wrote: *1) Using the EP and the example of an accelerating elevator, it follows > that light takes a curved path in space (not space-time). * >
No, it's spacetime. If a photon of light has moved from one side of an elevator to the other then it has moved in BOTH space and time because, although it's the fastest thing there is, light does not move at infinite speed. Light, just like everything else, always needs time to move through space. You can't change your position in space without changing your position in time. > Wasn't this known by virtue of Newtonian gravity? > That depends on if light had mass or not; if it didn't, and there was no experimental evidence to indicate that it does, then Newton would say light wouldn't curve at all near the sun, if light does have a rest mass but was just too small to be detected then Newton would say light would curve but only half as much as Einstein said it would. But to Einstein it doesn't make any difference if it has a rest mass or not light must must curve in a gravitational field. So no curvature or slight curvature of light by the sun would be consistent with Newton but only large curvature was consistent with Einstein. And large curvature was exactly what was found in the eclipse of 1918. So Einstein won and Newton lost. > 2) Assuming a geodesic is the shortest distance between two *spatial* > points on a curved surface, does it follow from the EP that free falling > bodies move on geodesics, and if if so how? > Yes Einstein says everything is always following a geodesic path through spacetime unless it is acted on by a force, and to Einstein gravity is not considered a force. So if you jumped out the window you'd follow a geodesic path through spacetime but just standing on the floor you are not because the floor is exerting a upward force on your feet. If spacetime were flat that force would let you to float off the ground but at the surface of the Earth Spacetime is curved so you can't, and we call that spacetime curvature "gravity". It takes light 1/19,184,132 of a second to move 60 feet 6 inches from pitcher's mound to home plate on a baseball field, Earth's gravity is 32 feet per second per second so in that time something near the Earth surface would drop by D=1/2 *AT^2 =16*(1/19,184,132)^2= 2.7*10^-15 inches, that is the amount the spacetime curvature a baseball field deviates from perfect flatness, it's about the same amount of curvature as a sphere with a radius of one light year would have. That's pretty flat but if it were absolutely flat baseball would be a VERY different game. *3) Concerning the above questions, how does "space-time" enter the picture > since it seems the questions can be asked without referencing space-time. * > As Einstein's teacher Hermann Minkowski said about his former student's theory: "*Henceforth space by itself, and time by itself, are doomed to fade away into mere shadows, and only a kind of union of the two will preserve an independent reality*." John K Clark -- 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
