On Absolute and Relative Motion

The most acute observations on the physical significance of the law of inertia and the related concept of absolute motion are due to Mach. According to him, in mechanics, just as in geometry, the assumption of an absolute space and, with it, an absolute motion in the strict sense is not permitted. Every motion is only comprehensible as a relative motion, and what one normally calls absolute motion is only motion relative to a reference system, a so-called inertial system, which is required by the law of inertia and has its orientation determined in accordance with some law by the masses of the universe.

Most authors are today in essential agreement with this point of view, as expressed most recently by Voss¹ and Poincaré² in particular. A different standpoint is adopted by Boltzmann,³ who does not believe he can simply completely deny an absolute space and, with it, an absolute motion. Here, however, I shall proceed from Mach's view and attempt to add some further considerations to it.|