On Mon, Feb 18, 2019 at 5:30 PM <[email protected]> wrote: *> Sure, but why does this obvious fact force us to merge space and time in > one concept, aka a manifold?* >
If you want to meet me in Manhattan you're going to have to give me 4 numbers (aka dimensions); 2 of them will give me the street corner, another one will tell me what floor to get off the elevator, and the fourth will give me the time of the meeting. > *> Also, why is it that Newton's law of gravity is not Lorentz invariant, > yet it seems to work in all inertial frames? TIA, AG * > Newton's law of gravity only approximately works, although the approximation is quite good provided the speeds involved are not too large and the spacetime curvature (aka gravity) is not too great. Newton's world was not Lorentz invariant because there was no limit on how fast you could go, so the laws of physics would look different depending on how fast you were going; if you could move at the speed of light in a closed elevator you could tell you were moving because a beam of light would look frozen in violation of Maxwell's Equations which says light always moves at the same speed. Therefore if things are Lorentz invariant you can't move at the speed of light in a closed elevator. By the way, when Maxwell came up with his theory some thought the one flaw in the idea was that the speed of light that the theory produced with did not say the speed relative to what. But Einstein realized that Maxwell's greatest flaw was really his greatest triumph. *> So how does GR explain motion? That is, how does curvature of space-time > result in motion? AG* > Motion is how a change in time relates to a change in space, if spacetime is flat a given instance in time corresponds to a particular point in space, if spacetime is curved that same instance in time would correspond to a different point in space. *> What would baseball look like without that tiny curvature? AG * > Imagine a baseball game played on the International Space Station. 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 [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
