This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Unlike classical physics, quantum mechanics generally cannot tell us exactly what will happen in an individual event. Instead, it predicts the probabilities of different outcomes.
As one of the theory's early pioneers, Erwin Schrödinger played a key role in debates about what this randomness really means. However, part of his contribution has stayed hidden for more than 80 years. In a new study posted on the arXiv preprint server, Flavio Del Santo at the University of Geneva has analyzed an unpublished manuscript by Schrödinger, shedding new light on his thinking.
In a classical event like a coin toss, the result only seems random because we can't measure every force acting on it. Since the early days of quantum mechanics, some physicists have wondered whether quantum randomness works the same way. In these 'hidden-variable' theories, particles carry unobserved properties that secretly determine the outcome of each measurement.
In 1932, however, mathematician John von Neumann published what many took as proof that such properties couldn't exist, and the idea was largely abandoned. The question resurfaced in the following decade. In 1943, Edmund Taylor Whittaker argued that quantum mechanics had destroyed the classical idea of a predictable universe.
To make his case, he imagined particles of light passing through a polarizer: a filter whose orientation determines how much light gets through. If each particle carried a hidden instruction to pass or be blocked, Whittaker reasoned that rotating the filter after the light had already set off toward it couldn't change these instructions. In contrast, quantum mechanics predicts that the fraction passing through should change.
After Satyendra Nath Bose made a similar case in 1944, the question sparked a lively debate in the journal Nature. Among the responses, Heinrich Pelzer presented a model showing that Whittaker's argument didn't hold up. Although he is often portrayed as a champion of determinism, Schrödinger himself joined the debate.
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