Between Heisenberg and Feynman: Ettore Majorana's Reflections on the Meaning of Quantum Theory

Abstract

Ettore Majorana is undoubtedly one of the most important figures in 20th-century Italian science. His contributions to nuclear physics and Quantum Mechanics (QM) included innovative ideas, and the search for Majorana-type neutrinos remains an ongoing experimental research question. However, very little is known about his perspective on the significance of the quantum state, the philosophical implications of the then-new mechanics, and the relationship between QM and other sciences. This chapter aims to address this gap. In more detail, here I present the standard interpretation of Majorana's view on the quantum state, according to which the Italian physicist anticipated the physical content of Feynman's path-integral formulation of quantum theory. In what follows, I critically examine this position and propose an alternative understanding of Majorana's beliefs on the nature of the quantum state and the wave function. Finally, I briefly discuss his reflections concerning the major conceptual revolutions introduced by QM, notably, in his view, the impossibility of extending the objectivity and determinism of classical mechanics to the quantum realm, and their consequences for the relation between physics and the social sciences, disciplines that Majorana deeply studied before his disappearance.