Erwin Schrödinger and friends at the "baptism of the 'wave packet'," June 21, 1931. Reprinted with permission of Ruth Braunizer.

# Genesis of Quantum Mechanics

## History and Foundations of Quantum Physics: The Genesis of Quantum Mechanics

### Other involved Scholars:

This group of studies is concerned with the genesis of modern quantum mechanics, which was established in the mid-1920s as a foundational theory of modern physics involving substantial conceptual modifications compared to classical physics. The research program aims at analyzing how these conceptual changes emerged from a transformation of the knowledge of classical physics.

Research activities on the development of wave mechanics (Christian Joas, Christoph Lehner, Jürgen Renn) are dedicated to the historical roots of wave mechanics and in particular to a study of the research notebooks of Erwin Schrödinger. A detailed account of Schrödinger’s formulation of wave mechanics, using the notebooks extensively for the first time, has been published. The study of Schrödinger’s research notebooks continues with a focus on the further development of wave mechanics and Schrödinger’s debates about the interpretation of quantum mechanics.

Walther Bothe studied the wave-particle dualism of light both from the experimental and from the theoretical side and contributed to the understanding of energy fluctuations of black-body radiation. His little-studied work is analyzed in a collaboration between a physicist and a historian (Dieter Fick, Horst Kant). Another study about the connection between experiment and theory in wave mechanics focuses on Charles G. Darwin’s electron diffraction experiments and his work on a wave equation for the electron (Jaume Navarro).

An investigation into the early history of Bose-Einstein condensation and the emergence of quantum statistics has been carried out (Daniela Monaldi). It analyzes the emergence of new concepts related to the new quantum-mechanical formalism, e.g., the concepts of indistinguishable particles and of cooperative phenomena.

Pascual Jordan’s 1927 transformation theory, an early unification of wave and matrix mechanics relevant for the development of quantum field theory is studied in another collaboration between a physicist and a historian (Anthony Duncan, Michel Janssen). Pascual Jordan was the earliest visionary of the possibilities of quantum field theory as a “theory of everything.” His role is examined in a study on the rather unknown early development of quantum field theory from its first appearance in the 1925 Heisenberg-Born-Jordan paper until its crisis in the 1930s because of the problem of infinities and rising skepticism about its fundamental character (Christoph Lehner, Michel Janssen).

The redefinition of traditional mechanical notions, such as angular momentum, and the development of new types of symmetry arguments is the subject of a study on selection rules and symmetry arguments in quantum mechanics (Arianna Borrelli). From late 1926 onward, group-theoretical considerations were employed to interpret spectroscopical selection rules in terms of symmetries, which in turn came to be connected to a new, specifically quantum-theoretical notion of conservation law. Eventually, both in quantum mechanics and in quantum field theory, selection rules – i.e. the failure of specific events to take place – came to be regarded as the observable signature both of symmetries and of conserved quantities.