[ExI] End of Story? Re: QT and SR

Lee Corbin lcorbin at rawbw.com
Fri Aug 29 03:01:50 UTC 2008

Serafino writes

> Sometimes the relativistic rocket is explained as
> a SR effect. Or it seems so. See in example
> chapter 13.4.2, in the link here below
> http://www.ph.utexas.edu/~gleeson/NotesChapter13.pdf

Very nice chapter. Unfortunately, at the moment I'm
struggling trying to remember just why the spacetime
interval is defined as dt^2 minus dx^2, though I really
should give up and go look at Taylor and Wheeler's
wonderful classic "Spacetime Physics", unfortunately
very overpriced at 

> Maybe the reason is that, for small speeds, physics
> in a uniform gravitational speed and physics in an
> accelerated reference frame are the same.

I believe that ultimately it may be possible to entirely
derive GR from SR, with no more help than the 
Equivalence Principle. (Though it may very well be
that this Principle suffices entirely on its own!) For
example, suppose that a ring or ringworld is rotating
at high speed, and a centrifugal force is developed.

We next imagine that there are two clocks, one 
stationary just outside the ring, and the other moving
on the inside of the ring. By SR, after one revolution
there will be different readings on the clocks because
one of the clocks has been in motion (really!) and one
has not. (And you can tell *which* by recalling that
one is in an accelerated frame and one is not.)

(Of course, Serafino, you have seen all this many
times before, but a number of readers have not.)

But by the Equivalence Principle, the clock inside
the ring may as well be in a uniformly accelerating
spaceship (no experiment localized inside a laboratory
on the inside of the spaceship can possibly discern
any difference). Therefore the GR effect of the latter
is entirely explained by the SR effect of the former,
and it's possible that Einstein went right from there
to considering that the EP should cover gravity too!


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