Recovered Schrödinger Manuscript from 1944 Explores Hidden-Variable Models in Quantum Mechanics
A three-page handwritten response by Erwin Schrödinger to a 1940s debate over determinism in quantum mechanics has been rediscovered after 80 years among his papers at the University of Vienna.
What happened
University of Geneva researcher Flavio Del Santo discovered an unpublished manuscript by Erwin Schrödinger dated November 1944 in which the physicist constructed a hidden-variable model to explore whether deterministic assumptions could reproduce quantum mechanics predictions. The manuscript was Schrödinger's response to a debate initiated by British mathematician Edmund Taylor Whittaker in 1943, who argued that hidden properties of quantum systems (such as light passing through a polarizer) could determine outcomes in ways inconsistent with standard quantum theory. When Del Santo analyzed Schrödinger's model mathematically, he found its predictions for polarized light agreed with quantum mechanics. Del Santo suggests Schrödinger may have abandoned the work after learning of physicist Heinrich Pelzer's challenge to Whittaker's reasoning. The paper documenting this finding, titled "Schrödinger's Unpublished Hidden-variable Model in the 1944–45 Debate Over the 'Collapse of Determinism'," was posted on arXiv on October 14, 2026.
Context
The manuscript reveals Schrödinger engaging with a foundational question in quantum theory: whether observed randomness reflects a fundamental feature of nature or stems from unmeasured underlying properties. This debate had been seemingly settled by mathematician John von Neumann's 1932 mathematical argument against hidden-variable explanations, but resurfaced in the 1940s through Whittaker and others. Schrödinger's willingness to construct a detailed hidden-variable model despite his known deterministic outlook demonstrates his engagement with competing interpretations of quantum theory. The hidden-variable debate would continue through the 1950s and 1960s as physicists sought to determine whether quantum events might be governed by deterministic processes beneath probabilistic appearances. The recovery of this manuscript provides historical evidence of how leading physicists approached fundamental interpretive questions about quantum mechanics during a critical period in the theory's development.