I don't know general relativity yet, but I have a few questions for which I would like Yes/No answers. Let S be an inertial reference frame with its origin in a relatively empty region of space. Let S' be a concentric frame which rotates with constant angular velocity. A free particle in this region obeys the law of inertia, and therefore moves in a straight line with constant [tex] v [/tex] in in the S system. The dynamics of this particle in the S' system can be calculated by performing a Galilean transformation from S to S' (assume [tex] v << c [/tex]). This is what I know about general relativity: 1. It's equations work in all frames of reference (or at least all physically reasonable frames such as S and S' above) 2. The acceleration/gravitational field in any frame of reference is ascribed to the mass distribution. Now for my questions: 1. Now, does this mean that in the S' frame, the acceleration field must be ascribed to the rotating celestial sphere? 2. If so, under the assumptions above ([tex] v << c [/tex], and no nearby masses), will the resulting dynamics of a free particle be the same as the one calculated by the principle of inertia with Galilean transform above? 3. Was any assumption about the mass of the celestial sphere or average mass distribution of the universe used in the GR calculation? Also, I don't know exactly what Mach's principle is. If it has nothing to do with this, just ignore that part of the title and answer the questions anyway.