Sabine on Special Relativity.

[Gmetric]

[SkyHiker]

At minute 15 I think she makes a mistake by stating that the water in the rotating bucket goes up because it moves in a circle and, therefore, is accelerating. It does not at all move in a circle in the bucket's coordinate frame, only in the observer's frame! That's the point of Mach's principle, which she missed. The water is at rest, and the gravitomagnetic effect of the rotating universe creates the force that keeps the water up - a true centrifugal force, not a virtual force. Am I missing something here? I don't think so.

Also, her statement that acceleration is absolute is only correct if you don't believe in Mach's principle. By minute 15 that was already clear, of course. While Mach's principle is usually about rotating frames it also applies to linear acceleration as pointed out by Sciama. Mach's principle almost certainly fits in with general relativity, as indicated by Einstein/Lense/Thirring, Brill/Cohen and later GEM based articles, so there is no need to assume that acceleration is absolute. At least not without refuting those results.