Some scientific theories are beautiful in their elegant simplicity. 'How extremely stupid not to have thought of that', Thomas Huxley said when Darwin explained to him his theory of natural selection.
Other theories are so baffling that their beauty often expresses itself in the estrangement from everyday experience. And few theories are stranger than quantum mechanics, the study of the inner world of the atom. As scientists started peering into the atom in the first decades of the last century they found a kind of universe in which the normal rules of physics did not apply. Even the very idea of causality seemed under threat in the quantum world.
Unlike Darwinism, and indeed unlike the other great revolution of 20th century physics, Einstein's theory of relativity, the quantum revolution was the product not of a single mind, but a collaborative work involving some of the greatest thinkers of the twentieth century such as Werner Heisenberg, Wolgang Pauli and Erwin Schröedinger. At the centre of the group was Niels Bohr, whose importance lay as much in his ability to provide an atmosphere conducive to collaboration as in his theoretical work itself. Thanks to Bohr, Copenhagen became the centre of the quantum universe.
At the edge of that universe hovered Einstein. He was revered by all the quantum physicists, but he was also deeply suspicious of what has come to be called the 'Copenhagen interpretation'. 'God doesn't play dice', he said in explaining his lifelong refusal to accept any model of the quantum world that undermined the principle of causality.
Faust in Copenhagen is a group portrait of the collaboration out of which quantum physics emerged. Gino Segrè is a distinguished physicist. His uncle, Emilio Segrè, was a Nobel Prize winner and had, in the late 30s, been part of the Copenhagen group, albeit peripherally. Yet, the physics of quantum mechanics plays only minor role in Faust in Copenhagen. What interests Segrè is the context of scientific discovery, both personal and cultural. This is both the strength and the weakness of his book.
The Faust of the title refers to a skit which younger members of the group organised at the end of a conference in 1932, reworking Goethe's story as a parable about quantum physics. The skit forms a centrepiece of the book, and Segrè returns to it again and again. It is misleading, though, because the book is not about Faustian pacts nor about the dilemmas of nuclear physics. Rather, Faust in Copenhagen provides an engaging glimpse of the process of scientific discovery. Segrè unravels the tensions and conflicts within the group, both personal and scientific, and of the different approaches to the task of making mathematical sense of the weirdness of the subatomic world.
Segrè explores the cultural context too. Quantum mechanics, he suggests, was part of a broader development in which modernism overthrew classical concepts. Quantum theories resulted from the same kind of 'wild experimenting' that also produced James Joyce's Ulysses, Schoenberg's atonalism and Giorgio de Chirico's landscapes. In all these cases 'the outer world, carefully described for hundreds of years, did not seem to match the inner world that was being uncovered'.
It is certainly tempting to see a link between the physicists' rejection of classical notions of causality and determinism and the breakdown of linearity in artistic modernism. The cultural landscape of the early twentieth century may well have helped shape some of the thinking of quantum physicists (though Segrè does not establish that this was the case). The strangeness of quantum mechanics is, however, not a reflection of the cultural context in which the theories developed - it is simply a reflection of the fact that the subatomic world is indeed a strange place.
In stressing the background to the quantum revolution, Segrè tends to neglect the physics. Which is a pity, because the debates about the Copenhagen interpretation - and in particular about causality and indeterminacy - have a resonance far beyond quantum mechanics. From nuclear fission to silicon chips, the quantum revolution has helped transform the modern world. Yet the interpretation of the quantum world developed by Bohr and his colleagues remains controversial and contested. It remains nevertheless a debate about the nature of physical reality. If God doesn't play dice, it's not because he hasn't read Ulysses.