The changing face of London

Fritz London retains a special place in the hearts of all who laboured on the theory of superfluids, which, terrestrially at least, are superconductors and helium. The prize in low-temperature physics named after him is valued far above its financial deserts, partly because it was re-endowed by John Bardeen, from his Nobel windfall, which gives it added sentimental value. There is a London lecture, also an honour seldom refused, which entailed (a few years ago) visiting his home and meeting his charming widow Edith - still, then, an artist of major endowments, and I at least felt a very special warmth and pride on that occasion.

Why is this? As I read this book, I tried to think it out. It is not only the remarkable "John the Baptist" character of his work, providing the phenomenological foundations and the general framework ("order in momentum space") about which later theories of both phenomena would be built. It is, for me at least, that London seems to have made the conscious decision that the intellectual problems of at least these macroscopic phases were deeper and more interesting philosophically than those of the nucleus, the problems that came to engage most of his brilliant contemporaries. I see in him my precursor in philosophical predilections as well as in scientific interest: he may have been the first to feel with me that "more is different".

London was one of the remarkable group of students who coalesced around and were formed in the tremendous creative explosion of the quantum revolution. Born in 1900, he was a close contemporary of Eugene Wigner, Felix Bloch, Hans Bethe, Rudolf Peierls, Nevill Mott, Victor Weisskopf, Walter Heitler, Linus Pauling and Lev Landau, among others. Like several of these people, he had not intended to become a theoretical physicist; in fact, he had already written a thesis and taken a degree in philosophy with the "phenomenologist" Alexander Pfander. This was a school that deplored the extremes of logical positivism in denying theory any role, yet held that the role of theory is constrained strictly by experimental fact. (As far as I could interpret Kostas Gavroglu's explanation - here as elsewhere I yearned for London's original words, which, in my experience, have always been crystal clear.) This seems to have amounted to a prejudice against, rather than a rigid rejection of, strict reductionism, which I see as the Cartesian assumption that everything is in principle derivable from basic theory.

The young philosopher began to dabble in physics, where through contacts with Max Born, Arnold Sommerfeld, and finally as P. P. Ewald's assistant at Stuttgart, he kept being steered away from philosophy and towards the quantum theory. He seems to have independently developed a basic component of the quantum ideas, the Dirac-Jordan transformation theory, but slightly too late to publish. Then he dabbled in quantising Hermann Weyl's projective theory, before settling down in Berlin as Erwin Schrodinger's assistant. Here is where he and Heitler made the first theory of the chemical bond, sorting out the energy levels of the hydrogen molecule, and soon he followed this with a perturbation theory of the van der Waals attraction (the "London dispersion force") and a group-theoretical study of polyelectronic molecules.

The author's discussion of London's work on the chemical bond could have used a little more modern hindsight; as it is, the crucial distinction between Pauling's heuristic use of the Heitler-London scheme, and Robert Mulliken's in principle rigorous molecular orbital methods, is blurred, as is the now understood relationship of the two. London seems to have been frustrated by the complication and difficulty of formulating a more rigorous valence-bond scheme, and to have abandoned a book on quantum chemistry at an almost complete stage. Those of us who have worked on the valence-bond representation will understand his difficulties with this overcomplete, non-orthogonal system. With his rigorist instinct, he probably abominated Pauling's slipshod but empirically successful use of his ideas, making remarks that Gavroglu interprets as more negative than they were meant to be about both Pauling and Mulliken.

The lightning bolts of Kristallnacht and the Nazi decrees of 1933 seem to have caught London unaware; yet within months he and his brother had joined forces in Oxford, and within a year they had produced the phenomenological theory of superconductivity which bears their name and is London's most presently known result.

But Fritz was not to be allowed to settle down at Oxford, as were his brother Heinz and his brother's mentor, Franz Simon (later Sir Francis). His job evaporated in 1935-36, and he was off to another temporary post in France with Frederick Joliot-Curie. This was another fertile period, stimulating a fuller write-up of his superconductivity work, the paper hypothecating Bose-Einstein condensation as the basis for superfluidity in 4He, and the well-known paper with E. W. Bauer on the problem of quantum measurement. Of the latter, more later.

Reading in detail about this period puts in very sharp focus the suddenness and completeness of the exodus of the intellectual heart of German physics. London intended to give his first talk on the new theory in Manchester, where he was at first silenced by criticisms from Bethe and Peierls, who had already arrived and were hard at work. No one who left seems to have slowed down - quite the contrary. What is hard to understand, at this remove, are the minds and consciences of those who stayed: in academia, the nature of the new regime was as clear as the glass broken on Kristallnacht.

To complete the story, after rejecting offers from Leningrad - fortunately - Ohio State University and Jerusalem, Fritz was finally reduced to making his way out of France in 1939 on one of the last possible steamers. He had accepted a job at Duke University, where he remained until his death in 1954. This could hardly be called "landing on his feet"; while the department was of very respectable quality, there were no other theorists for several hundred miles. The indignities of life as an "enemy alien" were not mitigated by the presence of colleagues in the same fix, and at that time the South, even Durham, North Carolina, was a stifling place to live for a cultivated couple like the Londons.

These 16 years were primarily devoted to refining his ideas on superconductivity and superfluidity and presenting them in the two volumes of his major work, and on keeping abreast of the experimental situation, especially in superfluid helium . He participated in the first postwar conferences at which modern low-temperature apparatus and adequate supplies of first liquid He and then 3He began to appear (his brother's first measurements convincing them that indeed it was the Bose character of 4He that leads to superfluidity). But he died of a weak heart in 1954 before either of his subjects had begun to come to resolution; and in all of his short life, he received only one major scientific honour, the Lorentz medal in 1953.

It was, at least to its subject, a strangely incomplete life. Starting with enormous promise, he managed to make only five identifiable contributions, and of these on only one did he convincingly have the final say: the London dispersion forces. (Even these were slightly revised, much later, by Landau, for very long ranges.) Yet what contributions! The chemical bond - the basis of all of chemistry - that part which is not controlled by van der Waals forces, which he also solved; the first correct paper on the foundations of quantum mechanics, severely revising the Copenhagen interpretation; the London equations, and their interpretation - with the first mention of quantised flux; and, finally, the Bose-Einstein nature of superfluidity and the basis of two-fluid models.

Yet why, unlike such contemporaries as Peierls, Weisskopf, Bloch, Wigner, and Heitler - even Laszlo Tisza, Klaus Fuchs and Joseph Rotblat - did he never achieve a stable position in a major university, either in Europe or in America? Why was he totally left out of the war effort in which his contemporaries were involved? (Though politically leftish, that seems not to have been a serious impediment for some of the others; he seems to have been simply forgotten.) One must admit that there is revealed in this book a somewhat prickly, perfectionist personality. He was not willing to follow Pauling in elevating an imperfect theory into a system for chemistry. He condemned, at first, the Ginsburg-Landau phenomenological theory of superconductivity, unwilling to admit that its conclusions agreed perfectly with his own, where both applied. (Yet he was sorely tried by Landau, who never gave him - or his friend Tisza - the slightest credit for their seminal suggestions about superfluidity. It is shocking that I. M. Khalatnikov's book on superfluidity explaining the Landau theory still repeats this grave injustice in supposed loyalty to the master.) But I think that the main problem was that London was simply too far ahead of his time. Time and again he saw the importance of looking at the macroscopic world from the quantum point of view. In the London-Bauer paper, he was even the first to see clearly (despite Gavroglu's misunderstanding the message) that it was in the macroscopic world and the problem of its description in terms of quantum theory that the philosophical difficulties of the quantum theory had their origin. He seems to have early understood the philosophical implications of Paul Dirac's "the rest is chemistry" - that the world of nuclear physics would increasingly become irrelevant to the macroscopic world around us - and he chose the latter to study and understand. In this, he was far outside the direction towards which the fashion of the time was leading and he paid the corresponding price. His contemporaries in solid state theory, on the other hand, mostly eschewed deep problems in favour of mining the many relatively easy, practical, useful results that could be recovered rapidly; again, an occupation he fastidiously rejected.

It is wonderful to have a biography of this fascinating and complex character - any biography. His personal history, and the essence of his life, are lovingly and sensitively portrayed. My only problem with this book is that biography often requires almost a deeper understanding of the science than does the research itself, to bring out its full meaning in relation to its scientific environment; and this seems here to be somewhat lacking.

Philip W. Anderson, Nobel laureate, is Joseph Henry professor of physics, Princeton University.