"What is Truth?" Einstein on Rods and Clocks in Relativity Theory

• Applicant: Professor Marco Giovanelli, Ph.D.
• Subject Area: History of Philosophy ; History of Science
• Term: from 2012 to 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 218862409

This project offers a historical and philosophical investigation of Einstein's vacillating attitude towards the role of rods and clocks in relativity theory. It is conjectured that one can distinguish at least four phases in Einstein's attitude toward this issue: (A) 1905-1916: Einstein used rods and clocks as unstructured entities, to provide physical meaning to coordinates in special relativity. However, in order to implement this operationalist epistemological model into general relativity, Einstein and his contemporaries were forced to free themselves from the burden of a series of prejudices concerning the role of coordinates in physics; in particular from the idea that the gravitational field is a field in a in and coordinate system, just like the electromagnetic field (B) 1917-1926 Einstein was forced by several interlocutors to recognize that this operationalist epistemological model is incompatible with the project of a unified field theory. Einstein started to emphasize that, in the final theory, rods and clocks should be treated as solutions of the fundamental equations, and not introduced 'by hand' (C) 1926-1930. As a consequence, Einstein was induced to rethink the role of geometry in general relativity. Einstein realized that, once rods and clocks were treated as physical systems just like any other, the distinction between geometrical and non-geometrical variables would be dropped. Geometry would lose its privileged status; the final unified field theory should not be thought as a geometrization, but as unification of the gravitational and electromagnetic field (D) In his late years Einstein consolidated his two-stage epistemological strategy, distinguishing between a provisional attitude towards rods and clocks as empirical indicators of the gravitational field and a principled one in which they are treated as material structure like any other. The project concludes that the role of rods and clocks in relativity theory is essential to understand the evolution of Einstein's conception of the relationships between theory and experience on the one hand and between geometry and physics on the other. As Einstein put it jokingly towards the end of his life, it is no less than "Pilate's famous question: 'What is truth?'"

• DFG Programme: Research Grants