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

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

David Rutherford wrote:

> Bob LaMontagne wrote:
> >
>
> > Place observer F' in the trailer of a moving truck - no windows. F' dills a hole
> > in the floor of the trailer and drops a stone throgh the hole. A minute later F'
> > drops anopther stone. Since F' is unaware of his motion, he would say the
> > "distance" between the stones was 0.
>
> Assuming that the observer in F' drops the stones from a flying trailer,
> high above the ground so that the stones drop straight down without
> hitting the ground, and neglecting air resistance, yes you are right.
> He would say the "distance" between the stones in the x-direction is
> zero.
>
> > But F, of course, gets an entirely different
> > answer. They could only agee on a common value for the distance if they somehow
> > communicate with each other and become aware of their relative motion. Whether
> > it's Galilean or Relativistic transformations is irrelevant.
>
> No, observers in F would also say the "distance" between the stones in
> the x-direction is zero.

Oops - obviously should have checked my spelling before hitting <send> :-)

Anyway, I really don't understand your last statement. Let me make the example more
specific. The F' people in the trailer drop a stone. When it hits the floor it shakes
dirt loose from the bottom of the trailer and it falls on the ground (F frame). Later,
F' drops another stone on top of the first and again dirt is loosened and falls to the
ground. F' measures a distance of 0 between the stones (they lie on top of each
other). F measures about a mile between the patches of dirt. How does this fit with
your last comment? (Again, your example was Galilean - but same idea in Relativity.)

Regards
Bob at PC