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. 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.
