Einstein and Mach: Creating History and Philosophy of Physics as a Discipline

The year 2016 marks not only the 100th birthday of Einstein's first comprehensive review paper of the general theory of relativity and his first (faulty) prediction of gravitational wave solutions . The year also marks the 100th anniversary of Ernst Mach's death. Many may know the name only because of Mach's scale of faster-than-sound velocities (Mach 1, Mach 2, Mach 3…). But Mach was also a historian and philosopher of science who had a decisive influence on Einstein's way of thinking about physics.

Mach's influential book, "The Science of Mechanics; a critical and historical exposition of its principles", helped his appointment to a specially created chair in "the history and philosophy of the inductive sciences" at the University of Vienna in 1895. Mach combined careful and critical historical work on the development of physics with deep reflections on its conceptual foundations. As Don Howard recently pointed out at the 2016 Vienna Conference celebrating Mach, around 1900, every literate German-speaking reader of Mach would have recognized the book's subtitle as an allusion to the method (not the content) of biblical hermeneutics: the aim was not just to use and summarize the science of mechanics but also to interpret it while studying its history, and to uncover its truly fundamental principles.

While working as a patent clerk in Bern, Einstein studied Mach's history of mechanics with his reading group – the self-mockingly named Olympia Academy. Doing so was an eye-opener; he was particularly impressed with Mach's criticism of Newton's concept of absolute space. Mach sided with Leibniz against Newton, arguing that the motion of a body was to be defined only relative to other bodies, rather than with respect to absolute space. Equally important for Einstein was Mach's idea that whether a body moves free of forces or not was also a relative matter. This provided a strong impetus for generalizing the relativity principle from inertial motion to all kinds of motion --- thus, for the general principle of the relativity of motion that Einstein used in the construction of the general theory of relativity. Indeed, in 1918 Einstein remarked that up until then (i.e. up until three years after the formal completion of the theory) he had not carefully distinguished between what he now called Mach's principle on the one hand, and the relativity principle on the other. In the next post of this series, we will see how Einstein came to disentangle these principles, and how he fought hard to keep Mach's principle as one of the fundamental pillars of relativity theory even after the principle came under pressure by work on solutions of Einstein's gravitational-inertial field equations.

Follow this link to see Einstein's obituary for Ernst Mach, reproduced as Document 29 in Volume 6 of the CPAE. Here is a direct link to our English translation of the obituary.