Mach’s Principle and Elementary Particles

Abstract

There are at least three different formulations of this principle which is named after Ernst Mach. The most specific is in terms of the Foucault pendulum which, according to the principle [1], moves in a constant plane with respect to the fixed stars, rather than to the absolute space, as Newton had thought. The second formulation, obviously closely related, but more general than the first, is the statement by Mach, that all motion is motion relative to other bodies [2]. Finally, one may consider the statement that inertia depends on the other bodies in the universe, as Mach’s principle, although it was formulated in this general form by Einstein [3]. The three formulations emphasize different aspects of Mach’s principle, and therefore require different criticism. It is clear that rotational motions considered in the first formulation will appear differently when the theory of relativity is taken into account; one need only recall the problem of the rotating disk. According to Newtonian ideas, two Cartesian coordinate frames in rotation relative to each other are “metrically” equivalent, since simultaneity has the same meaning for both observers, and distances of simultaneous events will thus be expressed in the same way. But the two observers are not dynamically equivalent, since in one or in both frames inertial forces will appear. A priori, one could think of two specific coordinate frames; one in which the Foucault pendulum remains in a constant plane, and another one in which the fixed stars remain at rest and it seems quite remarkable that these frames are in fact identical.

Lecture given at the VI. Internationalen Universitätswochen f.Kernphysik, Schladming, 26 February–11 March 1967.