Ori Belkind, The Cohn Institute for the History and Philosophy of Science and Ideas, Tel-Aviv University.
The Principle of Relativity: A Philosophical Examination
According to the restricted Principle of Relativity, the laws articulated relative to different inertial reference frames, that move with uniform relative motion, are the same. The Principle of Relativity was made a cornerstone of Einstein’s theory of relativity, and has been incorporated into contemporary physical theories via the Lorentz Transformations, which seem to be a fundamental part of our dynamic theories. Since the beginning of modern physics, philosophers and influential physicists assumed that the Principle of Relativity stems from some metaphysical or epistemological restrictions on possible theories. In the famous discussion between Leibniz and Clarke, the (classical) Principle of Relativity was used by Leibniz to argue that space cannot be absolute, and that the Principle of Relativity must be the consequence of the relative nature of motion. During the early 20th century, positivist philosophers such as Schlick and Reichenbach argued that the Principle of Relativity reflects both the relative nature of motion and the conventional nature of physical knowledge, which is subject to arbitrary coordinative definitions, namely different selections of sets of measuring rods and clocks that form the foundation of the measurement practice. Finally, in 1908 an influential interpretation of the Principle of Relativity was introduced by Minkowski, who argued that we can think of the Principle of Relativity as a symmetry of a four-dimensional space-time manifold, in analogy with how we think of Euclidean symmetries in 3-dimensional space. We can think of the relative nature of motion, the underdetermined nature of physical knowledge, and of spacetime symmetries as three philosophical attempts to explain the origin and the nature of the Principle of Relativity. I argue that none of these attempts is ultimately successful. Furthermore, I articulate some initial thoughts regarding a possible philosophical account of the Principle of Relativity, according to which the Principle stems from the fundamental nature of paradigmatic motions, a view I term “Primitive Motion Relationalism”.