On Fri, Jan 4, 2019 at 1:03 PM <[email protected]> wrote: > On Thursday, January 3, 2019 at 8:58:14 AM UTC, Bruce wrote: >> >> On Thu, Jan 3, 2019 at 12:00 PM John Clark <[email protected]> wrote: >> >>> On Wed, Jan 2, 2019 at 5:50 PM Brent Meeker <[email protected]> wrote: >>> >>> *> That's like saying if two people drove different cars from L.A. to >>>> New York and their odometers registered different distances then one of the >>>> odometers must have measured miles differently than the other...ignoring >>>> the fact that they took different routes.* >>>> >>> >>> No it's more like you claiming the odometer which measures miles is >>> telling you the time which is measures in seconds. Or it's like saying the >>> readings on any odometer that went from L.A. to New York is a invariant and >>> so will always give the same reading regardless of the path took, even >>> though they *don't have the same reading*. In other words its nonsense >>> >>> >>> >> The spacetime distance d is *not* the proper time, the >>>>> spacetime distance is an invariant, it's the same for all observers, but >>>>> proper time is *not* invariant; >>>> >>>> >>>> * > Sure it is. It's path dependent, but it's an invariant of a given >>>> path. * >>>> >>> >>> Obviously!! If you take the same path through spacetime then you've not >>> only traveled the exact same distance through time but moved the exact same >>> distance through space too, otherwise it wouldn't be the same path through >>> spacetime. But Einstein told us something much more interesting than X=X, >>> If we travel between event A and event B by different paths we'll disagree >>> on the distance through space that was required and disagree on the >>> distance through time that was required but we'll both agree on the >>> distance through spacetime we traversed; that's why it's a invariant and >>> that's why it's useful. >>> >>> >>>> *> The "spacetime distance" between two timelike events is the length >>>> of the longest proper time path between them.* >>>> >>> >>> Brent, this is getting silly. If d^2 = r^2 - (ct)^2 is the formula >>> for spacetime distance (*AND IT IS!*) then there is no way on god's >>> green earth the proper time can be the spacetime distance, one is a >>> invariant and the other isn't and the two things don't even have the same >>> units. I really don't know what else I can tell you except that there is no >>> disgrace in being wrong but there is disgrace in refusing to admit >>> error or learn from it. >>> >> >> So learn from this! >> The 't' in your formula above is the coordinate time, not the proper >> time. Learn the difference! The proper time is defined as the time kept by >> a perfect clock travelling on a geodesic. And a geodesic is the path along >> which the rate of time is constant. >> > > *If time is what is read on a clock, who, what, where, is the observer who > reads coordinate time, or the clock recording coordinate time? TIA, AG * >
For the observer sitting at rest in the one location, his clock reads both coordinate time and proper time. For an observer in motion, his clock reads only proper time, not coordinate time. In JC's formula: d^2 = r^2 - t^2, d = t if and only if r = 0. (natural units). Bruce -- 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.
