Physics - Mach's Principle V

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Physics - Mach's Principle V

Page 221 Mach emphasized that physicists never have access to time. All they can ever do is measure one motion with respect to another or, more generally, one physical change with respect to another.

Mach 1962: "It is utterly beyond our power to measure the changes of things by time." Although time does not exist, in the context of classical (non-quantum) Machian physics we may still assume that the universe in its history occupies a unique continuous sequence of configurations. Each such configuration may be called an instant. There are instants, but there is no time. A history is a string of such instants.

Page 235 Time could be based on millisecond pulsars. The current millisecond pulsar is at least as stable as all the atomic clocks on earth. As Joe Taylor and Thibault Damour note (1991, Astrophysical Journal 366: 501), the differential acceleration between the solar system and the binary pulsar in the field of the Galaxy exactly mimics emission of gravitational waves, so to interpret the binary-pulsar data the galactic gravitational field must be modeled. Now certainly the millisecond pulsars that you refer to may well become the most useful actual clocks from which to read out time, but if there are several of them there's no doubt it will be necessary to model the Galaxy – and, in fact, to some extent the universe as a whole because of the role that quasars play in determining frames of reference – in order to extract a meaningful time from them. There is a very nice paper by G.M. Clemence in the Reviews of Modern Physics for 1957 in the issue that's got the proceedings of the Chapel Hill relativity conference. It's the every first article in that issue; it's on astronomical time, on ephemeris time, and Clemence asks; What is a clock? His answer is: "A clock is a mechanical device which is continually calibrated against ephemeris time."

Page 275 Mach's Principle requires that velocities are measured relative to the matter in the universe.

Page 277 Thirring (1918) showed that a rotating shell drags the inertial frame located at its center.

Page 288 In Mach's Principle we are looking to give meaning to the requirement that inertial motions be determined by matter.

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