Of all the great scientists of the 20th century, the Danish physicist Niels Bohr (1885-1962) is perhaps the one whose stock has fallen furthest among his successors. It is common to hear top-class young theoreticians ask, “What did Bohr actually do?”, a phrase I have heard used by physical scientists twice in the past week. Yet the quantum pioneer Werner Heisenberg described him 50 years ago as the most influential theoretician of the 20th century. Heisenberg’s friend Paul Dirac commented that Bohr was “the deepest thinker I ever met”, which is some going.
As Heisenberg and Dirac knew well, Bohr did a lot. Arguably his most outstanding achievement, made in 1913, was to develop Ernest Rutherford’s model of the atom, according to which a typical element’s atoms consists of a tiny nucleus orbited by electrons, and incorporate quantum ideas. Bohr’s insights were revolutionary. They made it possible to do some basic calculations on the workings of the atom, and did much to help scientists understand the chemists’ periodic table in terms of the elements’ atomic structures. Later, Bohr was hugely influential in the development of quantum mechanics and nuclear physics, and was a leading humanitarian, admired almost to the point of idolisation by outstanding thinkers, from the hypercritical Wolfgang Pauli to the rather more humane Robert Oppenheimer, who regarded Bohr as a demigod.
All this makes it puzzling that the scientific community’s markings of the centenary of the Bohr atom have been relatively low-key. In Love, Literature and the Quantum Atom, however, we have a fitting celebration – an accessible, handsomely produced volume that sheds new light on Bohr’s development of his atomic theory. The authors are both experts – John Heilbron, an eminent historian of science, and Finn Aaserud, director of the Niels Bohr Archive, one of Denmark’s great cultural resources.
Heilbron and Aaserud have been greatly aided by the Bohr family’s decision to allow them to see previously closed correspondence between Niels Bohr and Margrethe Nørlund, from 1910 – the year the couple were engaged – to a few months after they married, in 1913. The book consists of a section by Aaserud on the light shed by the correspondence on Bohr’s private life, another on the scientific and psychological background to Bohr’s trilogy on the quantised atom, and finally a reprint of each of the papers. The authors aim to demonstrate that Bohr’s personal life considerably benefited his scientific work at his creative zenith. In their preface, they write that “from a psychological perspective [the ‘Bohr atom’] might be said to belong to both of them”. Heilbron even goes so far as to describe Nørlund as “midwife to the quantised atom”.
When Bohr first met her, he was in his mid-twenties and already seemed destined for great things. On their engagement, his brother Harald – later an outstanding mathematician – asked her if she shared the Bohr family’s view that Niels was “the greatest and wisest human being we have known”. She did, fretting “that she was not good enough or clever enough for marriage to so superior a being”, as Heilbron puts it. Bohr also knew that he was blessed to have met his soulmate, a woman he hoped would one day become a “mother” to his students. But first he had to make his name, and in the autumn of 1911 he left Copenhagen and took a temporary research post at the University of Cambridge, where he hoped to work with J. J. Thomson, discoverer of the electron and one of the world’s most accomplished physicists.
The authors aim to demonstrate that Bohr’s personal life considerably benefited his scientific work at his creative zenith
Bohr wrote to his fiancée every day. “My own little darling…Look into my soul. Look,” he wrote in a letter in December. She was no less affectionate to her “own dearest wonderful Viking”. But the two lovers wrote about much more than their feelings, among other things comparing notes on Shakespeare, Ibsen, Goethe and Kierkegaard. Although an admirer of Thomson, Bohr did not have an especially productive time in Cambridge and was soon itching to leave. By February 1912, he was looking forward to moving to the University of Manchester, where he would be able to work alongside Rutherford, who had recently discovered the atomic nucleus. Evidently confident that his promise as a theoretician was about to bear fruit, Bohr wrote to Nørlund: “My courage is ablaze.”
The move to Manchester was an unqualified success (in Rutherford, Bohr acquired someone he later called his “second father”). A few months later, the Dane wrote the first of his great papers on the quantised atom. Bohr’s powerful vision constituted, in the view of Einstein, “the highest form of musicality in the sphere of human thought”. All the more astonishing was that Bohr had yoked together classical and quantum ideas in a way that he and other physicists knew was logically unsatisfactory but that agreed with several key experimental measurements, such as the frequencies of the light emitted and absorbed by hydrogen atoms. “The input was broken bits, the output a gem,” as Heilbron says, adding, in one of his learned asides: “One thinks of Goethe’s little dog, who lived on broken glass and excreted diamonds.”
Aaserud and Heilbron have given us a fine book, a handsome memento to this centenary year of Bohr’s monumental work. Although I, for one, am not fully persuaded that Bohr’s life partner deserves as much credit for the quality of the trilogy as the authors believe, they nonetheless make a powerful case that her emotional support and intellectual stimulus were very important to him. In the mid to late 1920s, the University of Copenhagen’s Institute for Theoretical Physics became a Mecca for quantum physicists, most of them in awe of Bohr and extremely appreciative of the warm atmosphere that he and his wife took pains to cultivate. Love, Literature and the Quantum Atom helps us to understand better why this formidable husband-and-wife team were so effective.
My only regret is that the authors’ contributions are presented separately – it would have been better, in my view, if these two experts had collaborated more closely and written a unified narrative. As it is, their two sections lead to a good deal of repetition, slightly marring our pleasure in this charming story.
Aaserud concludes his section of the book by asserting that the new insights afforded by the Bohrs’ correspondence are “indispensable” for writing a full biography of the great man. This is true and reminds us that, of all the truly great scientists and human beings of the past century, it is regrettable that Bohr is one of the few whose reputation has not benefited from an outstanding popular biography.
Aaserud and Heilbron have given us a truly delightful book. It is high time that someone wrote his biography to bring his achievements to the attention of the public and to the many physicists who appear to be largely unaware of his intellectual breadth and depth, his huge influence and, above all, his nobility. Aaserud and Heilbron have convinced me that it is not only Niels Bohr who deserves a full-scale, accessible biography – his wife does, too.
Finn Aaserud (top), director of the Niels Bohr Archive, lives “in a flat in Copenhagen with my fellow Norwegian wife, Gro Næs. Our two children, Andreas and Karen, are out of the house now, and we’re learning rather successfully to live on our own again.” It is “a safe city, and a good place to raise children”, with terrible winters and summers that can be “the best in the world – but there is no telling when”.
He was “lucky to have an elementary school teacher, Egil Arntzen, in my little town in Norway, who really cared for us, the first class he taught, during our first seven years of school.”
As an undergraduate, Aaserud “started out as a physicist, but got frustrated by the way physicists construct false history for the benefit of physics teaching. So I turned to the history of science with the support of my physics teacher, Kristoffer Gjøtterud, at the University of Oslo.” From there he went to Johns Hopkins University in Baltimore, where he wrote his doctoral dissertation on the early history of the Niels Bohr Institute.
John Heilbron, professor of history and vice-chancellor emeritus at the University of California, Berkeley as well as honorary fellow at Worcester College, Oxford, lives “in Shilton, a village in West Oxfordshire, with my wife Alison and a lot of books”. Its attractions are chiefly “the quiet (my ‘city’ has fewer than 200 souls), the scenery and the Rose and Crown”.
In his student days, Heilbron was “studious but not scholarly, as I preferred maths (at which I have no particular talent) to other subjects and studied physics for most of my time at university. Late in graduate school I switched to history and learned something about scholarship in Berkeley’s strong history department.”
It was, he says, “a pleasure working with Finn. We have different (and fortunately compensating!) strengths and weaknesses.”