Julian Schwinger: The Physicist, the Teacher, and the Man

The following sections are included:

• PREFACE

• CONTENTS

The recollections that follow were delivered as the introductory remarks at a special session in memory of Julian Schwinger that took place on Sunday, Sept. 11, 1994 at Drexel University following a symposium on the quantum-classical correspondence. The author of these remarks had the privilege of chairing a session in which the speakers were Walter Kohn, Bryce DeWitt, and Freeman Dyson.

I was lucky to spend three days with Julian Schwinger and his wife Clarice in July 1993, shortly before he got sick with his last illness. We were at the University of Nottingham in England to celebrate the two-hundredth birthday of George Green. Julian was in excellent spirits and enjoyed the festivities as much as I did. He gave two talks, a short talk in response to the award of an honorary degree, and a long talk at the Green celebration. I decided it would make no sense to speak today about my personal memories of Julian, memories which are dim and unreliable after forty years. Instead I will give you the authentic Julian, as we saw and heard him in Nottingham only a year ago. So here are his two talks, first the short one and then the long one. He told me that the short one cost him far more time and effort to prepare. The protocol required him to say what he had to say in less than four minutes. As you will hear, he said more in four minutes than most Commencement speakers say in one hour…

The young theoretical physicists of a generation or two earlier subscribed to the belief that: If you haven't done something important by age 30, you never will. Obviously, they were unfamiliar with the history of George Green, the miller of Nottingham…

Referring back to Abe's remarks I should first like to expand on Abe's reply to Gleick on the so-called "disadvantage" the Schwinger students were supposed to have found themselves at, in the late forties and early fifties. In the book by Sam Schweber that Abe mentions I am quoted as saying (this is off of a tape that I sent Sam ten years ago)…

I am deeply honored by the award that has just been given to me, especially because I am from a generation of physicists sufficiently old to have known Paul Dirac personally and to have had numerous occasions to talk to him and to admire him…

It is a melancholy privilege for me to take part in this symposium in honor of my venerated teacher, Julian Schwinger.

All of us here know that his brilliant scientific insights and methodologies have left deep imprints across the entire spectrum of theoretical physics, both pure and applied. No doubt his most outstanding work was his monumental relativistically covariant renormalization theory of quantum electrodynamics; other areas which he substantially reshaped include quantum gauge theories, whose significance he was one of the first to realize; nuclear physics — beginning with his first papers written as a teenager and in which he offered perhaps the first comprehensive lecture course; the theory of waveguides, a powerful reformulation during World War II in terms of tensor Green's functions and variational principles; scattering theory; particle accelerators; and, very broadly, the structure of elementary particle theory…

The following sections are included:

• Introduction

• Warm-up Exercises
  • The Hohenberg-Kohn (HK) Theorem
  • HK Variational Theorem
  • Kohn-Sham (KS) Equations
  • Generalizations
  • Approximations
  • Density Functional Theory and Molecular Dynamics
  • Applications and Work-To-Do

• Density Functional/Wannier Function Theory for Systems of Very Many Atoms

• Acknowledgments

• References

The following sections are included:

• Introductory Remarks: The Early Years

We're gathered here today to salute Julian Schwinger, a towering figure of the golden age of physics — and a kind and gentle human being. Even at our best universities, people with Julian's talent and his passion for discovery and perfection are rare — so rare that neither they nor the rest of us know how to take best advantage of their genius. The failure to find a happier solution to this dilemma in recent years has concerned many of us. It should not becloud the fact that over their lifetimes, few physicists, if any, have surmounted this impedance mismatch more effectively than Julian, conveying not only knowledge but lofty values and aspirations directly and indirectly to thousands of physicists…

In this talk, I will describe the Julian Schwinger whom I remember as a teacher and friend during the time when I had the closest association with him and which was the formative period in my life as a theorist. This was the period from late 1952 to mid 1957. In order that I can do this, occasionally I also will have to tell you a little about me. At the end of the spring in 1957 I left Harvard and went to Los Alamos for a short time and then I went to the Bohr Institute. When I returned to Cambridge it was to MIT, which although close to Harvard still I didn't meet with Julian very often since it was a time when Julian had a large number of very talented students who wished to have some of his time. Thus it was then that our friendship continued but my close association with him was over. I would not attempt to describe here his research except briefly, even during this short period, so this will be a more personal account of my contact with him. I will divide my remembrances of Julian into my views of him as a superb teacher, as a fantastically creative mathematical physicist, as a preeminent theorist, and as a warm and good friend…

Julian Schwinger was a great scientist and a complicated — therefore interesting — human being. It seems such a short time ago that we celebrated his 60th and 70th birthdays here; likewise for the 45 years ago that I first saw Julian, and the 39 years since Elsbeth and I became real friends with Clarice and him, in Copenhagen. It was only a very few months ago that he sent me (via Clarice of course) what was to be his last, kind, message. During those years a lot of memories have accumulated for me, as they have for many of you. Indeed, several of my older fellow-alumni, notably Bryce DeWitt, Abe Klein and Walter Kohn have given their recollections at another recent memorial occasion. Doubtless there will be many more. Our collective memory will thereby help to perpetuate Julian's memory and that will serve as some consolation to us all…

Although I did not take my degree with Julian, I — like so many others — must count myself as one of his students, first because of his immense influence on the physics of our times, then in my own case because I attended his Michigan lectures of 1948, and most importantly as a result of having enjoyed his friendship for many years after he came to UCLA. I shall say a few words first about the early QED period at Michigan and then about the later source theory period at UCLA…

Earlier, you will recall, I quoted Sam Goudsmit's remarks about Julian, the Nobel Prize and propitious times. In large part because of wartime work on microwaves, work going on even as Goudsmit spoke, the period following the War unexpectedly turned out to be "as exciting as the great days of the 1920's," as Bethe put it. Sam was right. When the time was ripe, Julian at once carried out the work which earned him his Nobel Prize…

I was among Prof. Schwinger's last students, probably the last one from Harvard. For a couple of years I was virtually his only thesis student, and so I had some rare opportunities to interact and socialize with him. I need not dwell on Schwinger's prowess as a physicist, since that is well known. I will instead tell some Schwinger stories — small stories that also involve me. (More than once, Schwinger warned me not to believe every story told about him. But these stories are true.)…

I first heard of Julian Schwinger some 60 years ago. My physics instructor at CCNY, Lloyd Motz, since that time a professor at Columbia University, told me of an extraordinary brilliant and young physicist. Actually at that time Motz and Schwinger published a paper "On the β-Radioactivity of Neutrons." It was one of two papers by Schwinger published during 1935. The other was with Otto Halpern, "On the Polarization of Electrons by Double Scattering." He was only 17 years old. In 1937 at the advanced age of 19 he published seven papers…

This article is a transcription of a talk given at the April 1995 Meeting of the American Physical Society in Washington DC. The talk showed a number of transparencies which reproduced some of Schwinger's published work as well as other relevant journal pages. Some of these transparencies have been incorporated into the text; other transparencies are displayed here as 'figures'.

This is a very personal account of my interactions with Julian during the period 1954–1958, whilst I was a graduate student at Harvard. Julian was my thesis advisor, my mentor, and my professional idol. He continued to be my dear friend until his passing…

Julian Schwinger began the construction of Source Theory in 1966 in response to the then apparent failure of quantum field theory to describe strong interactions, the physical remoteness of renormalization, and the utility of effective actions in describing chiral dynamics. This development did not meet with wide acceptance, and in part for this reason Julian left Harvard for UCLA in 1971. This nonacceptance was quite understandable, given the revolution in gauge theories that was then unfolding, a revolution, of course, for which he had laid much of the groundwork. Acceptance of his ideas was further impeded by his rejection of the quark model of hadrons and of QCD. I will argue, however, that the source theory development was not really so abrupt a break with the past as Julian may have implied, for the ideas and techniques in large measure were present in his work at least as early as 1951. Those techniques and ideas are still of fundamental importance to theoretical physics, so much so that the designation "source theory" has become superfluous. Julian did a great deal of innovative physics during the last 30 years of his life, and I will touch on some of the major themes, including magnetic charge, chiral dynamics, radiation theory, Thomas–Fermi models, theory of measurement, and the Casimir effect, as well as various forays into phenomenology. The impact of much of this work is not yet apparent.

When I enrolled as a graduate student at the University of Chicago in 1946, Schwinger was already a legend. I heard many stories about him. Like the one about his virtuoso performance at the Radiation Laboratory in Cambridge, Massachusetts, and the one about his never coming to work until way after ordinary physicists' dinner time, and many others…

The following sections are included:

• APPENDIX 1 LIST OF SCHWINGER'S DOCTORAL STUDENTS

• APPENDIX 2 JULIAN SCHWINGER — LIST OF PUBLICATIONS

• ABOUT THE EDITOR