On Sunday I learned of the passing of John Heilbron. What follows is my attempt to pay tribute to one of my intellectual heroes and, for the last four years, my co-author, collaborator, and friend. This essay is not an obituary – there will be many of these in the coming weeks and months written by professional scholars who knew him much better than I ever could. For those interested in learning more about John’s career, his many awards and honorary degrees, see this post on the UC Berkeley website. Instead, this essay is a recollection of the circumstances which brought us together, and the joy I found in working with him.
John’s name might not be familiar to many, but he was entangled in some of the most profound developments in the study of science history, and especially the history of quantum physics. As a graduate student working in chemical physics in the late 1970s I, like some few of my fellow students, started to take an interest in the history and philosophy of my subject. Science is not like other professions. Young scientists are not taught what science is. They are not told how it should be done, or how what they are doing might be justified. These are things they are somehow expected to absorb by getting on with their work, as if through some kind of osmosis. It might be helpful to tell them that philosophers find their questions difficult, if not impossible, to answer with any clarity or simplicity. But, then again, it might not.
And, for students of physical science in which quantum mechanics is an essential foundation, there lurks a potential beartrap. Ten years later, deep philosophical questions about my understanding of quantum mechanics would hit me like a train.
But at the time, I, like others seeking guidance or enlightenment, could do little more than scratch around on the surface. This meant becoming vaguely familiar with two of the most important texts of twentieth-century philosophy of science: Karl Popper’s The Logic of Scientific Discovery and Thomas Kuhn’s The Structure of Scientific Revolutions. Popper is famous for his principle of falsifiability, the ‘demarcation criterion’ that many scientists still use today to distinguish science from non-science. A theory is only considered to be scientific if it makes predictions that can – in principle – be proved wrong. So, astrology is not a science because its predictions are typically so vague they can’t be falsified: they are irrefutable. This is the basis for Popper’s take on the scientific method. Scientists make a series of creative conjectures which they then attempt to refute. They make progress by refining their hypotheses in the light of these refutations, and the process begins again.
But Kuhn thought differently. In the ‘normal’ science of everyday, puzzles are solved and discoveries are made within a network of accepted foundational theories, or what he called a paradigm, which is accepted to be irrefutable. Logically, if scientists stopped what they were doing every five minutes and sought to falsify the basis on which they make their predictions and devise and perform tests, then they wouldn’t get much done. Contrast this with ‘revolutionary’ science, in which all bets are off and paradigms shift, in a process that Kuhn likened to religious conversion or political revolution. Kuhn argued that such revolutionary scientific change involves not just a change in laws, entities, and their mathematical descriptions, but also in the standards by which scientists judge the adequacy of their theoretical explanations. Comprehending Kuhn’s thesis was somewhat hampered by his liberal use of the word ‘paradigm’, which was ‘conveniently undefined’. One reviewer found that Structure contains 21 different meanings for the word.
According to Kuhn, what makes astrology different from astronomy is not the irrefutability of the former, but rather the research tradition of the latter and its role in resolving the puzzles of normal science. Confronted with a failed prediction, the astronomer sets to work, checking the data, re-running the calculations, or re-designing and improving instruments. The astrologer has no such tradition, and resorts to arm-waving. Astrology is not science because astrologers don’t do science.
I didn’t get much further than this. Building the foundations of an academic career left little time for reading and researching around the subject. I completed a doctorate at Oxford and a couple of years of postdoctoral research at Oxford and at Stanford University in California, before returning to England to take up a lectureship in chemistry at the University of Reading. Although I was never blessed with any great ability in mathematics, I learned a great deal more about quantum mechanics, and I take some pride in a couple of research papers I published on the quantum theory of high-energy molecular vibrations.
Then, in 1987, whilst working for a couple of months as a guest researcher at the University of Wisconsin-Madison, the train arrived in the form of an article, by N. David Mermin, in a volume celebrating the centenary of the birth of Niels Bohr. The article told of something called the Einstein, Podolsky, Rosen (EPR) ‘thought experiment’, which dates back to 1935, and some laboratory experiments to probe the nature of quantum reality that had been conducted by Alain Aspect and his colleagues in 1982.
I felt embarrassed. I had come to this really rather late. Why hadn’t somebody told me about all this before? I had allowed my (modest) ability in the use of quantum mechanics to fool me into thinking that I actually understood it. Mermin’s article demonstrated that I really didn’t, and marked the beginning of a 36-year personal journey. I used my share of a prize awarded for one of my research papers to buy a copy of Max Jammer’s The Philosophy of Quantum Mechanics and a few years later published my first book on the subject, titled The Meaning of Quantum Theory. I had begun to appreciate that, to make any headway in improving my understanding of why I don’t understand quantum mechanics, I had to engage not only with its philosophy, but also with its history.
As a graduate student of Kuhn in the early sixties, John had witnessed the birth of Kuhn’s Structure. But before the book was published, Kuhn was invited to lead a wide-ranging project to conduct tape-recorded interviews directly with the founders of quantum mechanics, and microfilm copies of their correspondence and unpublished manuscripts. John was appointed assistant director of the project and he and another graduate student, Paul Forman, joined Kuhn in Copenhagen in the summer of 1962. Bohr provided office space. The project quickly gained a sense of urgency. ‘Death was at work among the principal actors, depriving posterity of the true history of adventures and struggles “so much to the glory of the human spirit.” “[T]he immortality of [the] heroes is at stake”’! The need for urgency was quickly confirmed. Bohr died just a few weeks after interviewing began.’
John remembered ‘the excitement of the project, the lure of Copenhagen, the loyalty and erudition of [Léon] Rosenfeld’ (Bohr’s rottweiler, the ‘square root of Bohr x Trotsky’), ‘the quiet powerful personality of Bohr, the complacent manufacture of memories by [Werner] Heisenberg, the confident reserve of [Pascual] Jordan, and the impersonation of [J. Robert] Oppenheimer by Oppenheimer … who had come to Copenhagen to gather material for an obituary of Bohr.’ The archive assembled by the project became Sources for the History of Quantum Physics, and was quickly put to good use in a study of the genesis of Bohr’s quantum atom, published by Kuhn and Heilbron.
This work caught the attention of philosopher Paul Feyerabend, a former student of Popper’s at the London School of Economics. In a letter to fellow philosopher Imre Lakatos on 19 October 1969, Feyerabend wrote: ‘Heilbron’s thesis is on atomic models and it is very good. Heilbron and Kuhn have written a paper … Again, very good. The Kuhnians are doing very interesting historical work.’ One of the project’s later products was Kuhn’s Black-Body Theory and the Quantum Discontinuity, 1894-1912 (in which he makes no reference at all to paradigms). In the influential Bohr centenary volume I referred to above, John contributed a chapter on Bohr’s early atomic theories.
John would go on to enjoy a remarkable career, best known for his work across a broad sweep of the history of physics and astronomy, publishing engaging biographies of Max Planck, Ernest Rutherford, and Galileo, and returning every now and then to Bohr and early atomic theory in Love, Literature, and the Quantum Atom (with Finn Aaserud), and Niels Bohr: A Very Short Introduction. He served for four years as Vice Chancellor of UC Berkeley and was appointed as a Senior (later Honorary) Research Fellow at Worcester College, Oxford. I greatly admired his work, especially his biography of Planck, to which I would repeatedly refer in further books on quantum mechanics. But I had quit academia at the end of 1988, content to write popular science books in what spare time I could find. The chances of us crossing paths were clearly too small to compute.
Of course, a low probability is not zero probability. A later book of mine, The Quantum Story, first published in 2011, led to an invitation to give a short talk during a one-day conference on ‘the nature of quantum reality’ organised by the St Cross Centre for the History and Philosophy of Physics (HAPP), one Saturday in June 2017. I recall that the playwright and novelist Michael Frayn was in the audience that morning. This was my first encounter with the HAPP centre, and I was captivated by the format – a series of five short talks, closing with a summary, followed by drinks and dinner at St Cross College in St Giles, Oxford. I returned for more one-day conferences on other topics, and in June 2019, I was asked to chair the morning session. The topic was ‘paradigms through the ages’, and the summary was to be delivered by John Heilbron.
Joanna Ashbourn, the Director of the HAPP centre, chose to seat John and I together at dinner. To my everlasting delight, we hit it off. We shared many mutual interests, and mutual respect for Latha Menon, our editor at Oxford University Press. We elected to arrange a follow-up lunch with Latha, after which John and I enjoyed a couple of pints at The Eagle & Child, the pub in Oxford at which an informal literary discussion group called the Inklings would gather in the 1930s and 1940s, and which included J.R.R. Tolkien and C.S. Lewis. We finished with a walk in the gardens at Worcester College.
By October, I had plucked up the courage to approach John via email with a proposal, ‘to revisit the Bohr-Einstein debate, inject it with a goodly dose of historical accuracy, review what others (such as [David] Bohm, and Jammer) have made of it, and use this as a vehicle for exploring the philosophies of both Bohr and Einstein.’ Five days later, John agreed: ‘It would be good to present the original EPR discussion as an argument over physical principles within (for the protagonists) a shared commitment of intellectual (and even social) responsibility. Tracing the deviation of subsequent discussions from the spirit of the original would make a good and instructive and even important story.’
Our collaboration had begun.
There followed aspects of the mechanics of writing and publishing a book that most readers are (rightly) unaware of. John and his wife Alison would spend the winter months in Pasadena, California, returning to their cottage in a picturesque Oxfordshire village in the summer. We bounced drafts of our book proposal back-and-forth across continents, and we tested it with Latha. Oxford University Press is an academic publisher, with rigorous academic standards. By the time our proposal had been reviewed and approved by the Delegates to the Press, a whole year had passed.
Although the subtitle of the book has changed between proposal and proof, the main title has remained fixed throughout. The choice of Quantum Drama was inspired by Bohr’s account of his great debate with Einstein, in which he writes: ‘At the next meeting with Einstein … our discussions took quite a dramatic turn.’
From the outset, we were concerned to ensure that the book would be written in a single ‘voice’. Over time, authors grow into a writing style that is distinctive, idiosyncratic, and (ideally) unique. John’s style tended to be erudite, authoritative, somewhat academic, but also inspired and inspiring, with frequent flashes of bone-dry wit. Let me give you an example. In his own writings, Bohr was notoriously convoluted, obscure, vague, and so barely comprehensible. John summarised Bohr’s written contribution to the 1927 Solvay conference as follows: ‘These rhetorical questions called forth a mighty response from Bohr, which, as we know, was omitted from the conference proceedings because the rapporteur could not follow it. Instead, to thicken its linguistic opacity, the editors printed a French translation of the German article that gave the gist of [Bohr’s] lecture conceived mainly in Danish and delivered in Bohrish at Como.’ In contrast, my style tends to be informal, light, and somewhat breezy, as though a friendly uncle has taken you to one side at a family gathering to explain some obscure point in quantum physics.
There was never a question in my own mind. Although this was to be a ‘trade book’, rather than an academic or semi-academic text, designed to appeal to a wider, scientifically-literate general audience, the ‘voice’ had to John’s – there was simply too much to cherish in it. Of course, I had my own intellectual ambitions for the book – all of which were realised – and I authored my fair share of the words. But as we worked together, I learned how best to unpick John’s language when he assumed too much background knowledge on the part of our readership, I introduced explanations where I believed these were needed, and I learned to make my contributions in a voice that started to approach John’s own. I would frequently encourage him to take a passage I had written, and find a way to ‘Heilbron it’. Sitting here, writing this essay, I’m inclined to accept that my collaboration with John has likely changed my writing style, possibly forever, and for the better.
We worked on through a global pandemic, during which I confounded our progress somewhat by choosing to move 8,000 miles from Reading in England to Cape Town in South Africa, in May 2021. I never let go of my laptop, but in the post-pandemic disarray, supply chains were broken and it took five months for my collection of books and papers to make its way back to me by sea.
As we neared the end of our drama, I suggested we organise a series of online video interviews with some key players from contemporary physics. These were conducted in November and December 2021, and included John Clauser, Alain Aspect, Anton Zeilinger, and Anthony Leggett. I suspect (but did not confirm) that John enjoyed the opportunity to top a history that he had tailed with interviews of the founders. We were of course thrilled to learn of the award of the 2022 Nobel prize in physics to Clauser, Aspect, and Zeilinger (Leggett received a share of the 2003 Nobel prize for his work on superfluid helium). Not least because we had chosen to open our drama with the award, in 1922, of the Nobel prize to Bohr and the reserved prize for 1921 to Einstein. ‘That a century elapsed between the awarding of the highest honour in physics to the founders of quantum physics and formulators of its deepest riddles, and the attribution of the same award to those who did most to expose the true nature of these riddles is a pleasing addition to the symbols of our drama. Foundational work took a long time; recognizing its value took longer.’
We submitted our manuscript in November 2021 and received two extremely positive and extraordinarily helpful academic reviews. John and I set to work once again and the final manuscript was accepted for publication in July 2023, now titled Quantum Drama: From the Bohr-Einstein Debate to the Riddle of Entanglement. Proofs are imminent. The book will be published in April 2024.
I had what proved to be my final chance to meet with John in August this year. We met in Oxford for lunch, and we were extremely happy to be joined by Latha for desert and coffee. It was a thoroughly enjoyable occasion. John appeared sprightly and full of life. And full of ideas for new book projects, which he shared with Latha as they walked back through the town. Although our book was finished, our collaboration was not ended, as the final mechanics of responding to copy-editor queries and proof-reading requires as much care and attention as is needed when writing the words and sourcing the illustrations. I was looking forward to closing out this final stage with him and finding a way we could both celebrate publication day. John would have celebrated his 90th birthday a month before.
As I look back in sadness, I am overwhelmed by a sense of extraordinary privilege and good fortune. I was simply in awe of John’s scholarship, his pursuit of truth without judgement or bias, his facility with languages, his ability to cut through the chaff of a convoluted argument, and his unwavering patience and kindness. John wore his learning and his status very lightly. Throughout our work together he never gave the impression that we were anything other than equals in this endeavour. In fact, in his immediate (jet-lagged) response to my tentative proposal he wrote: ‘I am intrigued by your proposal, though in a collaboration I would be the honored party; but for symmetry and simplicity let’s agree to equal honors.’ He was relentlessly optimistic and encouraging.
To close his obituary of Kuhn, John quoted Kuhn himself. I can find no better words to apply also to John. ‘What I primarily owe him is not from the realm of ideas. Rather it is the experience of working with a man who cared more about arriving at truth than about winning arguments. I admired him most, that is, for the noble uses to which he put a distinguished mind.’
Jim Baggott is a freelance science writer and co-author with John Heilbron of Quantum Drama: From the Bohr-Einstein Debate to the Riddle of Entanglement, to be published by Oxford University Press in April 2024.
www.jimbaggott.com
@jimbaggott