Quantum dialectics: How communism shaped quantum theory

[Celerity]

When quantum mechanics posed a threat to the Marxist doctrine of materialism, communist physicists sought to reconcile the two

https://aeon.co/essays/how-soviet-communist-philosophy-shaped-postwar-quantum-theory





The quantum revolution in physics played out over a period of 22 years, from 1905 to 1927. When it was done, the new theory of quantum mechanics had completely undermined the basis for our understanding of the material world. The familiar and intuitively appealing description of an atom as a tiny solar system, with electrons orbiting the atomic nucleus, was no longer satisfactory. The electron had instead become a phantom. Physicists discovered that in one kind of experiment, electrons behave like regular particles – as small, concentrated bits of matter. In another kind of experiment, electrons behave like waves. No experiment can be devised to show both types of behaviour at the same time. Quantum mechanics is unable to tell us what an electron is. More unpalatable consequences ensued. The uncertainty principle placed fundamental limits on what we can hope to discover about the properties of quantum ‘wave-particles’. Quantum mechanics also broke the sacred link between cause and effect, wreaking havoc on determinism, reducing scientific prediction to a matter of probability – to a roll of the dice. We could no longer say: when we do this, that will definitely happen. We could say only: when we do this, that will happen with a certain probability.

As the founders of the theory argued about what it meant, the views of the Danish physicist Niels Bohr began to dominate. He concluded that we have no choice but to describe our experiments and their results using seemingly contradictory, but nevertheless complementary, concepts of waves and particles borrowed from classical (pre-quantum) physics. This is Bohr’s principle of ‘complementarity’. He argued that there is no contradiction because, in the context of the quantum world, our use of these concepts is purely symbolic. We reach for whichever description – waves or particles – best serves the situation at hand, and we should not take the theory too literally. It has no meaning beyond its ability to connect our experiences of the quantum world as they are projected to us by the classical instruments we use to study it. Bohr emphasised that complementarity did not deny the existence of an objective quantum reality lying beneath the phenomena. But it did deny that we can discover anything meaningful about this. Alas, despite his strenuous efforts to exercise care in his use of language, Bohr could be notoriously vague and more than occasionally incomprehensible. Pronouncements were delivered in tortured ‘Bohrish’. It is said of his last recorded lecture that it took a team of linguists a week to discover the language he was speaking. And physicists of Bohr’s school, most notably the German theorist Werner Heisenberg, were guilty of using language that, though less tortured, was frequently less cautious.

It was all too easy to interpret some of Heisenberg’s pronouncements as a return to radical subjectivism, to the notion that our knowledge of the world is conjured only in the mind without reference to a real external world. It did not help that Bohr and physicists of Bohr’s school sought to shoehorn complementarity into other domains of enquiry, such as biology and psychology, and attempted to use it to resolve age-old conundrums concerning free will and the nature of life. Such efforts garnered little support from the wider scientific community and attracted plenty of opprobrium. Albert Einstein famously pushed back, declaring that, unlike quantum mechanics, God does not play dice. He argued that, while quantum mechanics was undoubtedly powerful, it was in some measure incomplete. In 1927, Bohr and Einstein commenced a lively debate. Einstein was joined in dissent by the Austrian physicist Erwin Schrödinger, who devised the conundrum of ‘Schrödinger’s cat’ to highlight the seemingly absurd implications of quantum mechanics. But although both Einstein and Schrödinger remained strident critics, they offered no counter-interpretation of their own. Despite their misgivings, there was simply no consensus on a viable alternative to complementarity.



Complementarity also fell foul of the principal political ideologies that, in different ways, dominated human affairs from the early 1930s, through the Second World War, to the Cold War that followed. Both Bohr and Einstein were of Jewish descent and, to Nazi ideologues, complementarity and relativity theory were poisonous Jewish abstractions, at odds with the nationalistic programme of Deutsche Physik, or ‘Aryan physics’. But the proponents of Deutsche Physik failed to secure the backing of the Nazi leadership, and any threat to complementarity from Nazi ideology disappeared with the war’s ending. Much more enduring were the objections of Soviet communist philosophers who argued that complementarity was at odds with the official Marxist doctrine of ‘dialectical materialism’. Vladimir Lenin, who had led the Bolshevik Party in the October Revolution of 1917, was a dogmatic advocate of the materialist worldview expounded by the German philosophers Karl Marx and Friedrich Engels, authors of The Communist Manifesto, first published in 1848. The world according to Marxism consists of objectively existing matter in constant motion, bound by laws. Such laws govern different levels of existence that we attempt to describe through different scientific disciplines that are not necessarily reducible one to another. For example, sociology – regarded as an empirical science – is not reducible to physics and is therefore bound by its own laws of human social and economic behaviour.

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