The History and Foundations of Quantum Physics

Over the last six years, a central research question addressed in Department I was the process of reorganization and reinterpretation of mechanical knowledge in the course of the quantum revolution from 1900 to 1930. This process was triggered in part by conflicts between theoretical expectations and experimental results, but also, importantly, by the difficulty of integrating recently established physical theories such as electrodynamics and thermodynamics into the mechanical worldview. These borderline problems of mechanics necessitated a reorganization and re-evaluation of those controversial concepts where mechanics overlapped with more recent physical theories. Central to this process of re-evaluation was not only a large amount of uncontroversial empirical knowledge accumulated over a long period of time, but also the persistence of certain theoretical structures and methods. Theoretical physicists were confronted with critical decisions about which concepts and theoretical structures could be maintained in the emerging theory and could thus serve as a guide for the development of the theory.

As in the case of relativity, which was studied extensively from 1994 to 2005, in the quantum revolution high-level and abstract structures survived, although frequently with a new physical interpretation. Unlike the case of relativity, a consensus about the physical reinterpretation of the abstract structures was not easily attained. Famous dissenters, such as Einstein and Schrödinger, while accepting the new theoretical structure, disagreed about its meaning and its connection to the traditional mechanical worldview. Later on, the establishment of quantum field theory, including unification with the theory of relativity, has turned out to be at odds with the traditional demands on an interpreted physical theory. These disagreements have persisted up to this day, even though quantum mechanics by all counts is a highly successful predictive theory.

The research project on the history and foundations of quantum physics ran from October 2006 to September 2012 .It was a joint initiative with the Theory Department of the Fritz Haber Institute, originally funded for five years by the Strategic Innovation Fund of the President of the Max Planck Society. It was extended by another year in view of the substantially broadened publication program, which was already outlined in the previous report and is described in detail below.

The project has arrived at a deeper understanding of the genesis and the development of quantum physics, using the tools of historical epistemology that have been developed in Department I. The project thus focused on the long-term history of the process of knowledge restructuration, stressing the continuity of practices and structures. Unlike the relativity revolution, the development of quantum physics was a communal effort whose nature cannot be captured by a biographical approach that focuses upon a few central figures: careful attention must be paid to the broader community of researchers and to the network that allowed them to achieve what no single researcher could do alone.

This challenge necessitated a large-scale collaborative research project, unusual in the history of science not only in its size, but also in its interdisciplinary character. Bringing together researchers with diverse backgrounds, the project achieved a comprehensive account of the quantum revolution. The work drew upon extensive archival records of correspondence, manuscripts, and notebooks.

The research results of the project are in the final stages of publication and will appear in an open access format in three volumes in the Studies series of the Max Planck Research Library for the History and Development of Knowledge. As the central publication of the project, a working-group volume describes the development of quantum mechanics as a long-term process of theory change (editors: Christoph Lehner, Christian Joas, Jürgen Renn). It emphasizes the continuity of scientific methods and structures through the fundamental changes in the mechanical world picture since the nineteenth century. This book bundles the individual research results of the members of the group into a coherent whole, at the same time achieving a legible survey of the development of quantum mechanics and filling a void between thematically focused technical accounts and popular presentations that do not represent the current historical state of the art. The second volume (editors: Massimiliano Badino, Jaume Navarro) analyzes early textbooks of quantum theory and their role in establishing and promoting the theory. It explores the ways in which physics textbooks reacted to the novelties of the emerging quantum physics and how scientific revolutions affect the pedagogical process of knowledge transmission. The third volume (editors: Giuseppe Castagnetti, Jürgen Renn) addresses the role of scientific institutions and networks in the development of quantum theory. It consists of case studies of the major centers where the development of quantum physics took place.

While the project in its original form ended in September 2012, two connected dissertation projects are still ongoing: The radiation theoretical strand of quantum research was investigated in studies of the long-term history of optical dispersion (Marta Jordi Taltavull) and of the development of the correspondence principle (Martin Jähnert), both of which were essential for the formulation of matrix mechanics. The Department will also continue its research on the history of quantum physics in several smaller projects, including a collaborative project on the History of Self-Organizing Processes in Physics and Chemistry Seen through the Nobel Prizes: Complexity, Reduction, and Emergence; a collaboration with the foundation for the Lindau Nobel Laureate Meetings; and a collaborative project together with the University of Haifa and the Hebrew University, Jerusalem, on Probability in Classical and Quantum Mechanics.