Between Classical Physics and Modern Physics: Franz Exner and the relationship between determinism and indeterminism

• Grant number: 25/08972-9
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: October 01, 2025
• End date: September 30, 2028
• Field of knowledge: Humanities - Philosophy - Epistemology
• Principal Investigator: Silvio Seno Chibeni
• Grantee: Rafael Velloso Luz
• Host Institution: Centro de Lógica, Epistemologia e História da Ciência (CLE). Universidade Estadual de Campinas (UNICAMP). Campinas , SP, Brazil

Abstract

The objective of this project is to analyze whether the Austrian physicist Franz Exner (1849 - 1926) truly achieved a synthesis of the thought of his counterparts Ernst Mach (1838 - 1916) and Ludwig Boltzmann (1844 - 1906) in his work Vorlesungen über die physikalischen Grundlagen der Naturwissenschaften (1922), and, if so, how this synthesis is structured. A further investigation will examine the role of the indeterministic conception in Exner's thought and the nature of the indeterminism it represents, particularly whether it aligns more closely with the "classical" conception of indeterminism or the indeterminacy adopted by quantum mechanics. A review of physics at the turn of the 19th to the 20th century reveals a prevailing historiographic perspective asserting the occurrence of a crisis, ontological, epistemological, and methodological, during the transition from classical to modern physics. This crisis has been cited as the catalyst for a schism, with proponents of classical physics asserting its irreconcilability with modern physics. However, a thorough examination of the seminal Austrian physicists of that era reveals that certain physicists exhibited a reluctance to accept this notion of a division, particularly due to their allegiance to indeterminism, as exemplified by Exner. This stance can be ascribed, at least in part, to the recognition that indeterminism and acausal theories had already been incorporated within the domain of physics, having been developed and contested by prominent figures such as Boltzmann and Mach. According to contemporaneous scholars, including Erwin Schrödinger (1887 - 1961) and Philipp Frank (1884 - 1966), as well as commentators (Cassirer, 1956; Stöltzner, 2003; Stadler, 2019), Exner synthesized the ideas of Mach and Boltzmann, while also championing indeterminism and acausality even before the advent of Quantum Theory. In this sense, Exner can be interpreted as a transitional figure between what is considered a "classical" physicist and a "modern" physicist.