[mrjesse]

Said grey_whiskers:--This part of the post explicitly said, that the coordinate system was chosen for ease of use, not because one was "true" and the other "false".

Replied LeGrande:That is correct. They are equivalent. There is no absolute frame of reference. The only thing that is fixed is the speed of light. Time and distance are variables.

But when there is a third body in motion (for example, light) then we can measure and calculate angles and distances between all three -- and now being orbited and spinning are no longer indistinguishable.

-Jesse

[LeGrande]

But when there is a third body in motion (for example, light) then we can measure and calculate angles and distances between all three -- and now being orbited and spinning are no longer indistinguishable.

Light is not a third body, that was Einsteins point. You can't use light to determine your absolute velocity, there is no aether (or fixed velocity for that matter). Did you miss my example of the people floating in space with radar guns?

The use of a third body for reference only changes the point of reference, which can be very helpful and it can simply be an arbitrary point, it doesn't have to be a 'body'. Did you not look at the Merry go Round animation that I linked to?