Stöltzner, Michael: Vienna Indeterminism and the Problems of Quantum Mechanical Causality

Vienna Indeterminism and the Problems of Quantum Mechanical Causality

In my paper, I sketch a debate between physicist-philosophers at Vienna and Berlin about the idea that the basic laws of nature are genuinely indeterministic. It had started long before the advent of quantum mechanics, but would chiefly influence how both sides reacted to the crisis of the Bohr-Sommerfeld quantum theory and the quantum mechanics of Heisenberg and Schrödinger. The debate involved two different readings of Boltzmann’s legacy statistical mechanics and two different answers to how causality and ontology ought to be combined.
“Vienna Indeterminism”, as I shall call the first tradition, characterized two generations of physicist-philosophers connected to the Vienna Institute of Physics, among them Franz Serafin Exner, Erwin Schrödinger, Philipp Frank and Richard von Mises. It involved the acceptance of the highly improbable events admitted by the second law of thermodynamics, an assent to Mach’s definition of causality in terms of functional dependencies, an empiricist shift of the burden of proof on the determinist’s shoulders, and the adoption of the relative frequency interpretation of probability. Max Planck and his student Moritz Schlick initially rejected all of these creeds and held in line with the Kantian tradition that strictly deterministic laws represented an indispensable basis for probabilistic theories.
While the Viennese, after 1926, felt themselves confirmed by the newest physics, Schlick had to take a strictly verificationist tack to reconcile his views on probability with the failure of his Kant-inspired notion of causality. Thus he compensated his qualified acceptance of indeterminism with an emphasis on the limits of language ensuing from Heisenberg’s uncertainty relations. Unlike Planck, he did not consider quantum mechanics as a transitory, or incomplete, theory of atomic phenomena.
In view of claims made by some historians that scientists’ abandonment of determinism and causality in the 1920s was caused (Paul Forman), or at least enhanced, by external factors, among them the anti-scientific Weimar milieu and Bohr’s power politics (Mara Beller), a reconstruction of the philosophical debates between Vienna and Berlin requires historical contextualization. My argument is threefold. First, philosophical ambitions were widespread and often serious among German physicists, even though the allegiance to philosophical schools was low. The challenge arising from the cultural milieu thus also concerned the physicists’ philosophical ambitions and not just their social prestige. The opposition commonly made between the rationality and the historical contingency of physicists’ stance on causal matters misses the point. Second, this philosophical discourse followed influential role models and took place in widely-read journals, most prominently Die Naturwissenschaften. It became an important factor for the emergence of scientific philosophy. Third, since the physicist-philosophers were not strictly indebted to philosophical schools, they could form strategic alliances that emphasized one philosophical aspect considered pivotal at a time while other features, often expressing severe disagreements of fact, were played down. This process can be witnessed at the end of the discussion between the Viennese and the Berliners in the mid 1930s. Being confronted with a plethora of “metaphysical” misinterpretations and having taken the linguistic turn, Frank and Schlick developed a logical empiricist interpretation of Bohr’s complementarity. It brought them into opposition with Schrödinger’s quest for a modified ontology of quantum mechanics, although Schrödinger continued to be a staunch advocate of indeterminism.