Re: Special Relativity

[David Bowman <dbowman@TIGER.GEORGETOWNCOLLEGE.EDU>]

Regarding John Clement's further comments on the twin paradox
problem:

> While correct it requires that you ignore what happens during the
> turnaround.  In other words the solution is not complete.  To
> complete the solution requires GR.

No it doesn't.  Real gravity, i.e. spacetime curvature, doesn't come
into the problem at all.  SR is perfectly sufficient to analyze what
happens at the turn around.  We can do it by having a section of the
problem where the moving twin undergoes a uniform local
acceleration w.r.t. a sequence of locally coincident comoving
inertial frames, and then take the limit of the acceleration going
to infinity while the duration of the acceleration goes to zero.

> The fact that SR will not change
> the results significantly does not alter the incompleteness of the
> SR solution.

Completing the solution requires nothing beyond SR.  It *does*
require something beyond a Lorentz transformation though, but the
needed theoretical framework is wholely within SR.

> It seems simple to say that one must change
> timekeeping to the new frame, but I suspect from the point of view
> of the beginning student this is a large leap.  Indeed just
> understanding a spacetime diagram would be a large leap for such a
> student.  As a result they might still tend to see it as
> paradoxical.  One can certainly speculate as to what the moving twin
> observes during the acceleration, but this is not properly predicted
> by SR.

Sure it is.  It can even be done multiple ways within SR.

David Bowman

This posting is the position of the writer, not that of SUNY-BSC, NAU or the AAPT.