— Werner Heisenberg
Werner Heisenberg was a giant of particle physics, but questions remain about other aspects of his life.
TO MOST PEOPLE German physicist Werner Heisenberg’s major contribution to science is eponymous.
“Heisenberg’s uncertainty principle”, sometimes rendered less elegantly as Heisenberg’s theory of indeterminancy, is one of those quasi-poetic formulations that appeal to readers well beyond the boundaries of formal science, in part because it neatly symbolises the fundamental weirdness of the quantum world.
And while such familiarity guarantees the enduring fame of the physicist, who was born in Wurzburg in December 1901, it also serves to obscure some of the more controversial aspects of his career.
Heisenberg was the son of academic parents and entered the prestigious Maximillians-gymnasium, run by his grandfather, in 1911, graduating nine years later.
He entered the University of Munich in 1920. Two years later, at the University of Gottingen, he met up with another giant of quantum physics, Niels Bohr. After earning his PHD, he travelled to Copenhagen and joined Bohr at the latter’s institute.
The primary issue that concerned both scientists was the evident deficiencies in the existing model of the atom – formulated by Bohr and New Zealander Ernest Rutherford only a few years earlier. Although the model was robust in many respects, it could not accommodate an increasing amount of experimental data.
The key to refining a new model, Heisenberg intuited, was strangely banal. Contrary to existing ideas, he determined that it was impossible to actually visualise an atom. This was not because of any limitations inherent in technology or human perception – it was a fundamental limit of the physical universe.
Hence the famous uncertainty. Electrons, particle physicists agreed, had two properties: location and velocity. Heisenberg’s great insight was to realise that it was impossible to measure both. The more accurately location was determined, the less information was available about speed, and vice versa.
Interestingly, when Heisenberg published his findings, he was quickly contradicted by another physicist with an eponymous claim to fame: Erwin Schrödinger, of undead cat fame.
While the former scientist described electrons as particles, the latter described them as waves. Later it was found that the two apparently irreconcilable models were in fact mathematically identical, and the foundation doctrine of wave-particle duality thus confirmed.
Together, Heisenberg and Bohr became known as the architects of the “Copenhagen interpretation” of quantum mechanics, and travelled widely across Europe and the US.
In 1933, together with Schrödinger and Paul Dirac, Heisenberg was awarded the Nobel Prize. By then, he had returned to Germany – to the University of Leipzig – where he would remain for several years. Unlike many other prominent German academics, he chose not to leave when Hitler came to power.
Although he claimed to be uninterested in politics, his actions suggest otherwise. As a young man he had joined the anti-communist youth league and publicly supported the suppression of a workers’ revolt in Bavaria in 1919.
In the highly charged atmosphere of 1937 he was denounced by the SS, but defended by the organisation’s leader, Heinrich Himmler.
In 1942, he became the head of the Kaiser Wilhelm Institute for Physics in Berlin and worked on one of Hitler’s personally directed projects, centred on nuclear fission. His reasons for doing so have been much debated ever since, and opinions are divided over whether he took the role to further or forestall the development of an atomic weapon.
At the end of World War II, he was arrested by the Allies and imprisoned for six months, after which he was allowed to return to his work. Shortly afterwards, he was appointed director of what soon became the Max Planck Institute, where he remained until he retired in 1970.
In his last years he disavowed many of the ideas underpinning particle physics, suggesting instead that “fundamental symmetries” of the type described by Plato were a more promising avenue of research. He died of cancer in 1976.