A long-overlooked manuscript written by Erwin Schrödinger more than 80 years ago shows the Nobel laureate pushing back against claims that the universe is inherently unpredictable, while simultaneously maintaining his own belief in fundamental randomness.
The three-page handwritten draft, titled “Collapse of Determinism,” was uncovered in the Erwin Schrödinger Archive at the University of Vienna’s Austrian Central Library for Physics. A historical study by physicist Flavio Del Santo, posted to the preprint server arXiv, provides the first transcription and detailed analysis of the undated document, ScienceAlert reported.
A wartime clash over causality
The manuscript dates to late 1944 or 1945, a period marked by sharp scientific disagreement over quantum mechanics. In 1932, mathematician John von Neumann published what was widely viewed as a definitive mathematical proof establishing that hidden variables—unseen parameters that could restore strict cause and effect to particle behavior—were impossible. Although mathematician Grete Hermann identified flaws in von Neumann’s reasoning in 1935, her work was largely ignored at the time.
The controversy flared again in wartime Britain and India. British mathematician Edmund Taylor Whittaker delivered a 1943 lecture arguing quantum mechanics had destroyed classical determinism. In January 1944, Indian physicist Satyendra Nath Bose told the Indian Science Congress that scientists had abandoned deterministic natural laws. When mathematician Henry Piaggio summarized Bose’s arguments in the journal Nature in July 1944 under the headline “Collapse of Determinism,” it sparked an exchange among researchers who questioned whether hidden variables were truly dead.
Whittaker presented what he framed as a straightforward demonstration using light polarized through a filter. He posited that if each photon carried a hidden property restricted to two values to decide whether it passed or reflected, altering the filter’s angle could not reproduce observed transmission rates.
Schrödinger’s counterexample
Schrödinger saw a flaw in Whittaker’s assumptions. According to Del Santo’s analysis, Schrödinger questioned why any hidden variable had to be limited to just two values. Instead, he proposed assigning each photon a continuous value between zero and one, distributed evenly through the light beam.
By combining that assigned value with the angle of the polarizer, Schrödinger created a mathematical model that reproduced Malus’ law, matching the statistical results predicted by quantum theory. He went further by introducing a deterministic mathematical rule that altered the hidden value after each measurement, preserving the necessary distribution for subsequent filters.
“Experimental evidence + logical deduction can never prove that either the deterministic or the indeterministic view is impossible,” Schrödinger wrote in the manuscript, ScienceAlert reported.
Despite drafting the model, Schrödinger never published it. Del Santo noted that Austrian physicist Heinrich Pelzer published a mathematically similar single-polarizer construction in late 1944. Schrödinger may have felt the critical point had already been established publicly, although that remains an unconfirmed hypothesis.
A nuanced view of reality
The study clarifies that Schrödinger was not seeking to prove that nature actually runs on clockwork hidden variables. Instead, he intended the model as a counterexample against absolute claims that determinism was impossible.
Schrödinger had argued since the 1920s, influenced by physicist Franz Exner, that physical laws could be fundamentally statistical. In the newly analyzed draft, he wrote that “the strongest plea in favor of indeterminism is older than quantum mechanics,” ScienceAlert reported.
Schrödinger’s wartime thought experiment did not anticipate later experimental milestones. In 1964, physicist John Bell showed that local hidden-variable theories make testable predictions that differ from standard quantum theory, and subsequent experiments have largely ruled out such local mechanisms.
Del Santo observed that legendary physicists such as Schrödinger, Albert Einstein and David Bohm often held far more nuanced views on quantum philosophy than the rigid stances later assigned to them, leaving the question of determinism as an enduring subject of intellectual inquiry.
