Samuel M Barr says:
"you are absolutely wrong, Mark! All experts in General Relativity would agree that in GR acceleration is an absolute concept. The concept of an "inertial frame" is a crucial one in GR. An inertial frame is a non-accelerating frame. One can tell by local measurements whether one is in an inertial frame or not. This is non-controversial. Anyone who knows GR understands this. It is true that Einstein was led to GR by Machian ideas, and according to Mach's ideas acceleration is relative. But it is generally agreed by that the theory Einstein actually came up with is NOT Machian. Though he was inspired by Mach's ideas, Einstein's theory does not actually realize Mach's principle of the relativity of acceleration. "
An inertial frame is a non-accelerating one in general relativity (or any other theory), yes. BUT YOU CAN MAKE ANY FRAME IN THE UNIVERSE A REFERENCE FRAME. and the rest of the universe will accelerate around it and account for the forces which makes the frame you chose a fixed frame. This is the general principle of relativity.
General relativity describes the system (in this case the universe) relative to the rest of the universe from the perspective of the reference frame. Thus relativity.
Mark Wyatt
Dr. Barr:
Are you basically saying you accept general relativity, but not its strong principle?
How do you explain this statement from Einstein with no relativity of rotation? Is our argument over semantics?:
"The struggle, so violent in the early days of science, between the views of Ptolemy and Copernicus would then be quite meaningless. Either CS could be used with equal justification. The two sentences, 'the sun is at rest and the earth moves,' or 'the sun moves and the earth is at rest,' would simply mean two different conventions concerning two different CS." -- Einstein and Infeld, The Evolution of Physics, p.212 (p.248 in original 1938 ed.)
CS obviously = coordinate systems
How about:
Max Born in his famous book,"Einstein's Theory of Relativity",Dover Publications,1962, pgs 344 & 345 says:
"...Thus we may return to Ptolemy's point of view of a 'motionless earth'...One has to show that the transformed metric can be regarded as produced according to Einstein's field equations, by distant rotating masses. This has been done by Thirring. He calculated a field due to a rotating, hollow, thick-walled sphere and proved that inside the cavity it behaved as though there were centrifugal and other inertial forces usually attributed to absolute space.
Thus from Einstein's point of view, Ptolemy and Corpenicus are equally right."
Mark Wyatt