Summary.
The conclusions to be drawn from all these arguments are,
-
All frames of reference are equivalent, provided we are willing
to include possible gravitational effects (in non-inertial or accelerated
frames forces will appear which are indistinguishable from gravitational
forces).
-
Space-time is a dynamic object: matter curves it, and the way in which
it is curved determines the motion of matter in it. Since all bodies are
affected in the same way by the curvature of space and time the effects
of gravity are independent of the nature of the body. Changes in the distribution
of matter change space-time deforming it, and, in some instances, making
it oscillate.