On Friday, January 4, 2019 at 2:08:39 AM UTC, Bruce wrote: > > On Fri, Jan 4, 2019 at 1:03 PM <[email protected] <javascript:>> 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. >
*Still a little murky. Does coordinate time ever differ from proper time? TIA, AG * > > 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.
