"What is Truth?" Einstein on Rods and Clocks in Relativity Theory
History of Science
Final Report Abstract
RaC has provided a historical and philosophical investigation of Einstein’s opportunistic attitude towards the role, principled or provisional, that rods and clocks play in relativity theory. The issue has attracted a great deal of scholarly attention in the last fifteen years, among historians of science, historians of philosophy and philosophers of physics alike. Nevertheless, RaC argues, the importance of the rods-and-clocks issue in Einstein’s thought has not been fully appreciated. With the question of rods and clocks in relativity theory—as Einstein once put it jokingly—no less than Pilate’s question to Jesus ‘What is truth?’ is at stake. RaC distinguishes several phases in Einstein’s attitude toward the rods-and-clocks issue, the major ones being: 1905-1916. Einstein assumed that there are individual parts of a theory that can be directly coordinated with the behavior of physically existent objects used as probes. A theory can be said to be ‘true’ if such objects behave as predicted. In special relativity, as in classical mechanics, the fundamental geometrical variables, the coordinates, are measured with rods and clocks separately from the other non-geometrical variables, say, the electromagnetic field. In general relativity, coordinates are no longer directly measurable independently from the gravitational field. Still, the line element ds is supposed to have a ‘natural’ distance that can be measured with rods and clocks. 1917-1926. Einstein was forced by several interlocutors to recognize that this epistemological model was incompatible with his project of a unified field theory. Such a theory would eliminate the opposition between the gravitational and electromagnetic field, on the one hand, and matter and field, on the other hand. The distinction between rods and clocks and other material systems would become questionable. Einstein conceded that such a distinction was provisionally necessary for the current state of physics, but that in principle a theory should construct rods and clocks as solutions to its equations. The fundamental geometrical structures of the theory cannot be defined separately, but only the theory as whole can be said to be ‘true or false.’ 1925-1930s. As a consequence, Einstein was induced to rethink the role of geometry in physics. The major achievement of general relativity was usually considered the geometrization of the gravitational field. A unified field theory was supposed to geometrize the electromagnetic field as well. 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 become meaningless. The final unified field theory should be thought not as a geometrization, but as a unification of the gravitational and electromagnetic field. 1930s–1950s. Einstein’s field theoretical program was criticized on epistemological grounds. The gravitational and electromagnetic fields, it was argued, are nothing but useful fictions for predicting the behavior of physical probes (rods and clocks, test particles, etc.). It is thus meaningless to speak of elementary particles as regions of high field density since. There are in fact no probes smaller of such particles that can be used to verify this claim. In response to these positivistic objections which served as a guiding principle in the emergence of the new quantum theory, Einstein developed a form of rationalistic realism. The unified field theory-project attempts to understand the mathematical structure the gravitational-cum-electromagnetic field as an independently existing entity, and not just to describe what we observe. As it turns out, the rods-and-clocks issue is entangled with all major themes of Einstein’s epistemology. RaC has, therefore, the ambition to use it as a fil rouge to provide a still missing overall, systematic investigation of some of the major themes of Einstein’s philosophy of science. In doing so, each chapter follows one of such issues through both, the development of theoretical physics and philosophy of science in the early 20th century. In particular, it will be shown how essential philosophical questions emerge within physicists’ practice: Is physical spacetime simply what is measured by rods and clocks, or does it exist independently of its being probed? Are geometrical representations in physics essential or mere analogies? Should a theory be able to describe the physical processes that serve as its means of verification? If this is the case, what does it means that the theory describes something that is ‘out there’? RaC’s methodology is a combination of the following approaches: (a) a historical-critical approach to the philosophy of science, which concentrates on the conceptual biases that that have to be broken to assure scientific progress (b) a dialogical approach to the history of science which insists in the responsiveness and addressivity of scientific arguments (c) an integrative approach towards the relationship between history of science and history of philosophy of science, which sees the emergence of philosophy of science as part of the history of science itself . The results of this investigation aim to contribute not only to Einstein’s scholarship but also to the historical literature on the development of early 20th-century physics and philosophy of science and the technical literature on the philosophy of spacetime theories. For these reasons, this research might be located in three different but overlapping fields of contemporary philosophy of science: (a) integrated history and philosophy of science (&HPS), the idea that it is not only possible but also useful for a philosopher of science to do good history of science (b) history of philosophy science (HOPOS), which focuses on how the interaction between science and philosophy determined the development of philosophy of science itself (c) the philosophy of physics and in particular the philosophy of space and time, an analysis of physics’ assumptions about space and time, and how they have been revised in the face of changing empirical circumstances.
Publications
- “‘What is Truth?’ Einstein on Rods and Clocks in Relativity Theory.” Habilitation. Universitat Tubingen, 2018
M. Giovanelli
- “Lorentz Contraction vs. Einstein Contraction. Reichenbach and the Philosophical Reception of Miller Aether-Drift Experiments.” In: Proceeding of the Fourth International Conference on the Nature and Ontology of Spacetime. Ed. by A. Stefanov and M. Giovanelli. Montreal: Minkowski Institute Press, 2017, pp. 125–155. ISBN: 978-1-927763-47-6
M. Giovanelli
- “‘Physics Is a Kind of Metaphysics’. Emile Meyerson and Einstein’s Late Rationalistic Realism.” In: European Journal for the Philosophy of Science 8 3 (2018), pp. 783–829
M. Giovanelli
(See online at https://doi.org/10.1007/s13194-018-0211-y) - “Einstein’s Philosophy of Science.” In: Stanford Encyclopedia of Philosophy. Ed. by E. N. Zalta. Fall. 2019
M. Giovanelli and D. Howard
- “Nothing but Coincidences. The Point-Coincidence Argument and Einstein’s Struggle with the Meaning of Coordinates in Physics.” In: European Journal for the Philosophy of Science (2020)
M. Giovanelli
(See online at https://doi.org/10.1007/s13194-020-00332-7) - “‘Like Thermodynamics before Boltzmann’. On Einstein’s Distinction between Constructive and Principle Theories.” In: Studies in History and Philosophy of Science. Part B: Studies in History and Philosophy of Modern Physics 71 (2020), pp. 118–157
M. Giovanelli
(See online at https://doi.org/10.1016/j.shpsb.2020.02.005) - “‘Geometrization of Physics’ vs. ‘Physicalization of Geometry’. The Untranslated Appendix to Reichenbach’s Philosophie der Raum- Zeit-Lehre.” In: From Philosophy of Nature to Physics. Logical Empiricism and the Natural Sciences. Ed. by S. Lutz and A. T. Tuboly. London/New York: Roudlege, 2021, pp. 224–261. ISBN: 978-1-138-36735-7
M. Giovanelli
