Tom Roberts wrote:
> Phil wrote:

> > One of the problems I have never resolved is the difference between
> > curvature and accelerations in flat space-time.
>
> They are completely different concepts, and their physical affects are
> quite different as well.

So much for the Equivalence Principle or equating acceleration with
gravitation locally, of.course.  <shrug>

> Note, please, that "acceleration" when used by itself is ambiguous in
> GR. There are 3 commonly used meanings:
>   a) proper acceleration. This is the acceleration of an object in
>      its instantaneously comoving inertial frame

In GR, the only proper "something" is the proper time which is
nothing more than the absolute value of the spacetime divided the speed
of light in vacuum.  A good hypothesis is to allow the acceleration to
be observed the same using one's coordinate system and with proper
unit translation, of course.  The reason for this is not to manufacture
BS like (b) and (c) below.

>   b) 4-acceleration. This is a 4-vector defined by dV/d\tau, where
>      V is the object's 4-velocity and \tau is its proper time
>
>   c) coordinate acceleration. This is just dv/dt, where v is the object's
>      coordinate velocity in some system of cooridnates, and  is the time
>      coordinate.

I smell BS here.