Abstract

Mach has long been an important figure in the history of relativity, but the nature of his role has remained controversial. This essay contributes to this discussion by connecting Mach’s critical philosophical perspective more fully to his diverse experimental research and pedagogical contributions to mechanics, and charting his changing presentations of these over some time. In particular, linking Mach’s early research in sense perception and psychophysics to his conceptual critiques of mechanics offers new perspectives on relativist physics in general and Einstein’s debts to Mach in particular. Mach’s early work on the Doppler effect, together with studies of visual and motor perception explored subtle interrelations between physiology, physics and psychology, and offered new approaches to physiological space and time. These informed the critical conceptual attacks on Newtonian absolutes that Mach famously outlined in The Science of Mechanics in 1883, as well as his positive account of the fundamental laws of physics in terms of experimental propositions and definitions. Mach’s critiques helped form a foundation for later work in electrodynamics in which he did not participate. Yet revisiting Mach’s early work will suggest he was still more important to the development of new approaches to inertia and gravitation than has been commonly appreciated. In addition to what Einstein later called “Mach’s principle,” I argue that a thought experiment on falling bodies in Mach’s Science of Mechanics also provided a point of inspiration for the happy thought that led Einstein to the equivalence principle.