A three-page manuscript written by Erwin Schrödinger, one of the architects of quantum theory, has been rediscovered in an Austrian library after sitting unnoticed for more than eight decades, according to Yahoo. Physics historian Flavio Del Santo of the University of Geneva brought the document to public attention. In it, Schrödinger argues that some features of the universe cannot be predicted — a position he says he held before quantum mechanics took shape in the 1920s.
The draft also contains his response to a 1943 lecture by mathematician Edmund Taylor Whittaker, who had claimed that quantum theory had finally overturned classical determinism. Schrödinger's reply, titled "Collapse of Determinism" like several other contributions to the same journal debate, takes issue with Whittaker's reasoning about light and hidden variables.
Why it matters
The find complicates the familiar image of Schrödinger as a thinker uneasy with quantum randomness. Yahoo reports that the manuscript shows the opposite: he welcomed indeterminism and had done so for years. The document also adds a missing piece to a mid-1940s exchange in the pages of Nature over whether hidden variables could exist — a question that goes to the heart of how physicists describe reality.
Determinism, randomness and the hidden-variable question
Classical physics leaves no room for genuine chance. A die may have imperfections that shape how it lands, computer random-number generators usually follow algorithms, and even a coin toss is governed by physical forces that could in principle be calculated. This is determinism: the idea that every classical event follows from the conditions before it, whether or not we know all of those conditions. Yahoo notes that the absolute status of classical determinism has been challenged, but it remains a foundational assumption of classical mechanics.
Quantum mechanics behaves differently. At the scale of particles such as photons and electrons, physicists can only give probabilities. They can compute the odds of an outcome with great precision, but they cannot say what a single particle will do. That gap raises a lasting question: is nature fundamentally random, or are there hidden factors — unknown properties that, if we knew them, would let us predict individual quantum events? These hypothetical factors are called hidden variables.
In 1932, mathematician John von Neumann published what was widely read as a mathematical proof that hidden variables were impossible. His standing in the field was such that work on hidden-variable models largely stopped for more than a decade. Mathematician Grete Hermann found serious flaws in his argument in 1935, but her critique was mostly overlooked, Yahoo reports.
How the 1940s debate revived the argument
By the mid-1940s, two physicists had inadvertently reopened the case for hidden variables by arguing against them. In May 1943, Edmund Taylor Whittaker gave a lecture claiming that quantum mechanics had destroyed classical determinism, and that quantum randomness was real rather than apparent — no extra information could make individual outcomes predictable. In January 1944, Satyendra Nath Bose made a related point at the Indian Science Congress, saying physicists had gained knowledge but lost their faith in deterministic natural laws.
In July 1944, mathematician Henry Piaggio published an article in Nature titled "Collapse of Determinism" that reported on Bose's arguments. Responses followed from physicists who were not persuaded that determinism was finished, and the exchange continued in the journal's pages over the following months. Contributors examined the claimed impossibility of hidden variables, including Whittaker's example involving photons and polarized light.
Whittaker's demonstration used photons passing through a polarizer, a device that filters light according to its orientation. Quantum mechanics predicts what share of photons will get through at a given angle. Whittaker reasoned that if each photon carried a hidden instruction saying whether it would pass, then rotating the polarizer while the photons were in flight would make that instruction useless. From this he concluded that hidden variables could not predetermine the outcome.
Schrödinger had been following the debate and wrote his own response sometime after November 1944. According to Yahoo, Whittaker had assumed each photon's hidden variable could take only two values — one deciding whether it passed through the polarizer, the other whether it was reflected. Schrödinger observed that nothing required the variable to be limited to two values. He asked what would happen if it could take any value between zero and one, then built a mathematical model in which the result depended on both the photon's hidden variable and the angle of the polarizer. With the right rules, the model matched the probabilities quantum mechanics predicts while not requiring each individual interaction to be random.
What to watch
The manuscript is now on the record, and its argument invites closer scrutiny from historians and physicists alike. Watch for further analysis of Schrödinger's model and for how the discovery reshapes accounts of the hidden-variables debate.
