The Man Who Broke Reality: Niels Bohr and the Making of Modern Physics

Niels Bohr did not understand quantum mechanics and neither does anyone else. Indeed, the more we learn of it, the less we seem to know.

And no wonder. How can electrons behave both as particles and waves? How can two atomic particles, separated by millions of miles, act upon each other instantaneously? — if you turn the blue one red, the red one will turn blue, on the spot. Such a thing is an impossibility in the Newtonian world where we live, and yet it is so, if you follow the turtles all the way down. As the great 20th-century theoretical physicist Richard Feynman remarked, “I hope you can accept Nature as she is — absurd.”

Niels Bohr is not a household name in the way that Albert Einstein is, yet there are those — though his biographer Philip Ball is not among their number — who will tell you that of the two, Bohr was the greater scientist. He was certainly the more radical thinker. As Ball writes, “Bohr, more than Einstein, bridges the old world of 19th-century physics and the modern era of computers, spacecraft, nuclear power, and institutional and industrial science.”

Science, however, is not a beauty contest. The present builds on the past, the young learn from the old. Without Einstein’s two papers on relativity, in 1905 and 1915-16, much of modern physics might still lie undiscovered. Isaac Newton himself, who was no shrinking violet when it came to his own worth, acknowledged: “If I have seen further, it is by standing on the shoulders of Giants.”

Bohr, born in 1885, came from a well-to-do Danish family with connections to the Carlsberg brewing company, the immense wealth of which was to help him at certain important junctures in his life. The Bohrs were such a happy lot and lived so comfortably in the world that it is a wonder young Niels survived at all. His mother was from a successful family of Jewish bankers. His father, Christian, an experimental physiologist, was nominated for the Nobel Prize; had he won, it would have been the first score in a Bohr hat-trick, for Niels won the prize in 1922, as would his son Aage in 1975.

Speaking of hat-tricks, it is interesting to learn that Niels was a keen footballer, as was his mathematician brother Harald, who played for Denmark in the 1908 Olympics. It was not all swotting.

Bohr’s theory holds that before the observer trains an instrument upon it, a particle exists in multiple potential states; in other words, there is no definite ‘state of affairs’ until we bring it about by observation

Bohr’s theory holds that before the observer trains an instrument upon it, a particle exists in multiple potential states; in other words, there is no definite ‘state of affairs’ until we bring it about by observation

In 1912 Bohr married Margrethe Nørlund, and yes, reader, they lived happily ever after. Ball gives Margrethe her well-earned due: “‘I just have to speak to my wife,’ Niels would say — not, his colleagues suspected, because there was anything urgent he needed to convey or check out but, merely [in the words of an assistant] ‘to gain from her the strength and inspiration for continuing the work’.”

And what work it was. Quantum theory was founded in 1900, more or less accidentally, by the German physicist Max Planck. It was he who posited that physical bodies, yours and mine included, emit energy not in smoothly flowing waves but in tiny, discrete packets, or “quanta”, like a stream of unimaginably minute bullets. The trouble was, the waves would not go away, and eventually it had to be accepted that at the atomic level, objects behave both as particles and waves. Go figure, but don’t expect to understand it. (See Feynman et al.)

Needless to say, many scientists were chary of the new theory, with its indivisible quanta or packets of energy and its sacrifice of certainty in favour of probability — notions which prompted Einstein’s famous remark that “God does not play dice with the world.” Bohr, however, was much more receptive to novel ideas, though even he acknowledged that the quantum view of reality was extremely difficult to comprehend, never mind accept.

It is surprising to learn that Bohr was not a first-rate mathematician, being less interested in the numbers than in the linguistic challenges presented by quantum theory. Unlike his younger colleague Werner Heisenberg, who declared himself to be in pursuit of “complete precision, [which] can be achieved only by means of mathematical abstraction”, Bohr was an anti-dogmatist. As he once wrote, in a passage cited by Ball in an earlier book, Beyond Weird: “There is no quantum world. There is only an abstract quantum physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature.”

Bohr’s greatest achievement was the development, along with Heisenberg, Max Born and a few others, of what has come to be known as the Copenhagen Interpretation. This recognised for the first time — or perhaps “proposed” is a safer way to put it — that human agency has an effect on the nature of things at the atomic level. Bohr’s theory holds that before the observer trains an instrument upon it, a particle exists in multiple potential states; in other words, there is no definite “state of affairs” until we — we — bring it about by observation and measurement. We look, and something that was not there suddenly is there.

This was one of the aspects of quantum theory in general and of the Copenhagen Interpretation in particular that made Einstein — among others — deeply suspicious. Indeed, Einstein had always found it questionable that reality should obey so readily the rules of a discipline — mathematics — not bestowed on us by the gods but invented by human beings. Now here was a new theory that seemed to say directly that it is we who “invent” the world, in the same way that, as the American philosopher Ralph Waldo Emerson observed in his essay Experience (1844), “it is the eye which makes the horizon”.

All these fascinatingly entangled conundrums recede some way into the shadows when, in the second half of Ball’s narrative, we come to the practical applications of quantum theory. In July 1941 a secret committee of UK scientists issued a report on the progress towards the manufacture of an atomic bomb. Within two years, the report coolly stated, “it will be possible to make an effective uranium bomb which, containing some 25lb of active material, would be equivalent as regards destructive effect to 1,800 tons of TNT and would also release large quantities of radioactive substances”.

None of this would have been possible without the invention, or discovery, of quantum mechanics. Understanding the fundamental physics of the atomic nucleus through quantum theory was essential for calculating how to design and control nuclear reactions. Nature at her foundations might be absurd, as Feynman remarked, but she packs a terrible punch.

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Bohr, along with Einstein, worked tirelessly to warn the world of the peril it had put itself in with the invention of nuclear weapons. In this context, it is well that Ball should remind us that although “they laid some of the conceptual foundations”, the “two most prominent physicists of the mid-20th century, Albert Einstein and Niels Bohr, played no substantial role in building the atomic bomb”. That onerous task was left to others.

Bohr lived a long and immensely rich life. One has only to glance at the headings of the later chapters of this biography to have a notion of the breadth and consequence of his activities: ‘Fission: The Dawn of Atomic Energy’; ‘A Dangerous Occupation: Copenhagen under the Nazis’; ‘A Great God: Bohr and the Arms Race’; ‘The Statesman of Physics: Bohr in the World’.

Margrethe was with him to the end. In November 1962, having attended a meeting of the Danish Royal Academy of Sciences in Copenhagen, he took to his bed, complaining of a headache. “Hearing him call her name, Margrethe rushed upstairs to find him unconscious next to his bed. He did not wake up again.”

The Man Who Broke Reality is comprehensive, authoritative and shrewd, and, like all of Philip Ball’s books, as entertaining as it is enlightening.

The Man Who Broke Reality: Niels Bohr and the Making of Modern Physics by Philip Ball, The Bridge Street Press £30/ Little Brown $30, 480 pages

John Banville is a novelist, playwright and screenwriter. His most recent novel is ‘Venetian Vespers’

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