Re: [asa] geocentricity

Quoting George Murphy <gmurphy@raex.com>:

 Of course it's true that the earth exerts a gravitational influence on
the sun as well as vice versa, so that what we usually call a
"heliocentric" frame is (when we're doing precise celestial mechanics)
one in which the CM of the solar system is at rest. But there is no
"must" about using this frame or any other. General relativity really
is general - you can use any space-time coordinates you wish (subject
to some modest conditions about continuity & differentiability).

_______________

I have a question concerning the limitation of reference frames. If the
Earth is taken as not rotating, then stars and ultimately galaxies end
up moving at velocities far exceeding the speed of light. However, we
can also calculate the speed of stars and galaxies relative to a
stationary Earth. Thus there is a way to exclude at least one possible
reference frame. It seems then that all conceivable reference frames
are not possible. Am I missing something?

Keith

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Received on Sat Jul 7 09:07:52 2007