Re: A Geometrical Proof of the Non-invariance of the Spacetime Interval

[Bob LaMontagne <rlamont@POSTOFFICE.PROVIDENCE.EDU>]

David Rutherford wrote:

> No, I'm referring to the fact that the assigned locations of the two
> events "breakfast", in F and F', don't coincide in space, at the time of
> lunch, not that the assigned locations of breakfast and lunch don't
> coincide in F'.

They never coincided "in space" in the two systems in the first place. The
breakfast was an event in spacetime - the same event in both F and F'. It just so
happened that the origins of the spatial and temporal coordinates in F and F'
coincided (and were all = 0) when that event occurred (maybe by design - but
that's irrelevant). At many later times, both F and F' can recall that breakfast
as occurring at x=y=z=t=0 and x'=y'=z'=t'=0, regardless of where the origin of
their spacetime coordinate systems are at at those later times. The breakfast
still occurred at the same spacetime point in both systems. There is no way to go
back to that point in the future, one cannot return to past spacetime locations.
But that is not a problem because the coordinates of that single point in
spacetime that defined breakfast are forever x=y=z=t=0 and x'=y'=z'=t'=0. One
cannot ask - Where are those points now? They don't exist "now".

Bob at PC
Sorry if this is a little opaque - I'm writing this between appointments and I
don't have time to fine tune it.