"Tom Roberts" <tjroberts137@sbcglobal.net> wrote in message
news:Hgg7l.10252$D32.2723@flpi146.ffdc.sbc.com...
> Mike wrote:
>> Imagine that
>> you are in an inertial frame, and a star zips by. The light emitted
>> from the star takes some time to reach you, so there is a small
>> discrepancy between where the star is, and where it appears to be.
>> Is the gravitation force on you in the direction that the star
>> actually is, or in the direction that the star appears to be?
> 
> Let me assume:
>  a) the star is also moving inertially
>  b) all other objects are far enough away that their gravitation
>     can be neglected
>  c) the star is "small" (e.g. a few solar masses or less)
>  d) the observer ("you") remains well outside the surface of the star
> 
> Then a measurement of the gravitational acceleration from the star will
> point directly to its current position in your inertial frame. The light
> you observe from the star comes from its retarded position [#], of course.
> 
> In Newtonian gravitation this is obvious (gravity is instantaneous). In GR
> this is due to a remarkable property of the fields: there is a velocity
> dependence that cancels the effect of the retardation (in this case the
> cancellation is exact, because of (a-d) above).
> 
> [#] The light you observe at time t was emitted from the
> point on the star's trajectory that intersects your past
> lightcone for time t; this is necessarily earlier than t.
> 
> 
> Tom Roberts

Dork Roberts proves yet again that he doesn't understand the Principle of
Relativity. The star as described doesn't move, you do.