Weimar Physics: Sommerfeld’s Seminar and the Causality Principle

The development of quantum mechanics in the period 1920–1927 posed challenges to the understanding of causality and its incorporation into the new dynamics. Though aware of these challenges to the classical concepts of causality and to the conservation laws of energy and momentum, Arnold Sommerfeld and the members of his seminar never wavered in their commitment to the conservation laws because of their belief in the “preestablished harmony” between mathematics and physics that Felix Klein, David Hilbert, and Hermann Minkowski had championed. I survey these developments and trace how the concept of causality was reformulated in scattering theory by Gregor Wentzel, Enrico Fermi, and Giulio Racah.