EARLY YEARS
I was born on 1 November, 1950 in Visalia, California, a medium-sized town just south of Fresno in the San Joaquin Valley. It was at that time an agricultural community more like the Middle West or West Texas than Hollywood or Beverly Hills. The main highway into town was lined with magnificent walnut orchards and stands of valley oaks. My childhood home backed onto wheat and cotton fields. And when the navel orange crop was threatened by a freeze there was smudge in the air by day and talk of little else. A 10-minute drive in any direction brought one out of the town and into rows of tidy farms with peach orchards, olive orchards, avocado orchards, nuts of all sorts, row crops, and dairies. And above us stood the mighty Sierra Nevada, John Muir's Range of Light, the rivers of which irrigated the land and turned what would otherwise have been oak savannah into the richest farmland in the world. The mountains were obscured most of the time by the haze caused by irrigation and too many automobiles or the dense radiation fog that hides the sun most of the winter in that part of the world. My great Aunt recalled how they were visible most of the summer when she first came there after the great San Francisco earthquake of 1906. But on brilliant winter mornings just after a Pacific storm had blown through there they would be, a blazing wall of white stretching north and south as far as the eye could see, topped by the silhouettes of Sawtooth, Mineral King, and the Great Western Divide.

Both sides of my family landed in Visalia by accident. My mother was the daughter of a local doctor, Irvin Betts, who had come down from San Francisco after medical school "temporarily" and induced my grandmother to accompany him by promising her a return in a couple of years. She always laughed when she told this story. My father had grown up a widow's son in Chico, served as a naval officer in the war, followed his brother into the law, and had come to Visalia fresh out of law school to work in the Tulare County District Attorney's office. There he met and married my mother, and together they raised four children, of which I was the first. Like so many other American families mine had roots that were deep but temporary. We attended church, joined the Boy Scouts, contributed casseroles to PTA pot luck suppers, and celebrated many a Thanksgiving with family and friends, but in the end moved away. My father died in Visalia 18 years ago, and all of us, including my mother, now live elsewhere.

Early on in his career my father left the District Attorney's office and set up a private law practice in town. He worked very hard but was, as one of my uncles later put it, an "artist lawyer", meaning that he was more concerned with correctness than profits and often did work for needy clients for free. As a consequence while we had a roof over our heads, food on the table, and clothes to wear to school we were constantly conscious of being of modest means. Whether caused by this or our home environment generally it came to pass that all of us became quite self-reliant at an early age. I, for example, used to take appliances apart when they broke in an attempt to fix them, which I rarely did successfully, being a kid. I am better at this now. My sister Margaret, who is an attorney, still enjoys doing needlework from scratch. My brother John, a software engineer, prides himself in being able to fix any broken thing. It was through such creative play that I first learned about pump impellers, refrigerant cycles, material strength, corrosion, and the rudiments of electricity, and more importantly the idea that real understanding of a thing comes from taking it apart oneself, not reading about it in a book or hearing about it in a classroom. To this day I always insist on working out a problem from the beginning without reading up on it first, a habit that sometimes gets me into trouble but just as often helps me see things my predecessors have missed.

Another important aspect of our home was respect for ideas. At dinnertime one of my parents, usually my father, would lead a discussion about some controversial matter, such as racial integration of schools, whether John Lennon should have compared himself with Jesus Christ, support of Israel, or the morality of the Vietnam war, and all of us were expected to air and defend our views on these things, even if we did not want to. Over the course of time this gave us a deep respect for ideas, both our own and those of others, and an understanding that conflict through debate is a powerful means of revealing truth. This was, of course, before any of us understood rhetoric and how easily it can be misused. But the need for conflict to expose prejudice and unclear reasoning, which is deeply embedded in my philosophy of science, has its origin in these debates.

My mother, who was professional schoolteacher, was particularly concerned about our formal education and even went so far as to start a private school together with some other parents so that our intellectual needs would be met. They acquired an old two-room schoolhouse out in the country among the walnut groves at the foot of Venice Hill, added some indoor plumbing, and hired a small faculty to teach us a broad curriculum that included such things as Latin and French. I am afraid the money was largely wasted on me because I was not ready to learn French, or much of anything else, at that time, although I did rather enjoy watching the machines shaking walnuts off the trees in the fall. But it was impressed upon me that there was such a thing as good study habits and that I would have to acquire them if I wanted to be a scholar. My mother also had us take piano lessons, and this had a similar effect. I hated those lessons, but I now play regularly for pleasure and have even tried my hand at composing. So mothers everywhere take heart. The indoctrination you administer now may have unanticipated positive effects years later.

I was an extremely reclusive and introverted boy. It was to my parents' credit that they weathered the storm and encouraged my self-motivated study, even though it scared them to death, especially my mother. While still at Venice Hill, for example, I got very interested in how televisions worked, and electronics generally, so my parents bought me a Heathkit color TV, which I soldered together and eventually made work. It was a magnificent thing filled with vacuum tubes. One could probably have heated the living room with it. I found building this kit rather unsatisfactory, actually, because the manual did not explain how the circuits worked but only how to assemble them. So I went back to old discarded black-and-white models, which my father dutifully acquired for me, and began reading about what the various parts did and then testing the theory by removing them one at a time. It was in this way that I learned why it is bad to allow the 10 kilovolts stored on a cathode-ray tube to discharge through one's body. Thank God my mother never knew. I also taught myself how to blow glass using a propane torch from the hardware store and managed to make some elementary chemistry plumbing such as tees and small glass bulbs. The latter I filled with isopropyl alcohol and attached with a piece of surgical tubing to the intake of a cooling compressor I had scavenged from a broken refrigerator. This lowered the pressure sufficiently to boil the alcohol and lower the temperature well below the freezing point of water. I had ambitions of making liquid nitrogen, and could probably have done it with more compressors and some dewars. I also tried to make sodium metal by electrolysis of molten salts. I discovered that common wood lye had the lowest melting temperature of all the available materials, so I melted some in a orange juice can and electrolyzed it using an auto battery charger and an ice pick as the cathode. It worked, except that the sodium lived only a second or two before being oxidized by the surrounding air. It was at this time that I picked up the can to check for corrosion on the bottom and accidentally poured its contents all over my right hand, burning it severely. My father rushed me to the hospital, had it dressed, and then invented a story to tell my poor mother so that she would not have a heart attack. By good fortune the molten sodium hydroxide was so hot that it had vaporized the water in my skin and sloughed off without burning me chemically. My hand recovered fully. My parents would probably never have encouraged these things had they known how foolish and dangerous they were, but it is nonetheless a testament to their belief in the value of self-motivated exploration that they allowed me to cultivate such interests even though I got no credit from them toward college or employment.

In parallel with the development of my interests in technical gadgetry I began to acquire a profound love of and respect for the natural world which motivates my scientific thinking to this day. My maternal grandmother had a mountain cabin deep in the Tule river canyon just south of Sequoia Park, to which we were often invited as a family or as individuals. My grandfather had built it as a kind of hunting lodge before I was born, so it had a very masculine feeling despite being my grandmother's home. It had a big stone fireplace, knotty pine walls, a big cast iron chandelier for light, and a marvelous old Aeolean player piano with plenty of rolls. My grandmother was a complex person, but she loved the mountains and welcomed anyone else who did, including reclusive grandsons. So I spent time there whenever I was able, which was not very much because I had responsibilities at home, and over the course of time came to understand what a treasure it was - the house-sized boulders left in the riverbed by retreating glaciers, the massive ponderosa pines six feet in diameter at the base, delicate mosses and lichens of every imaginable color, the complex geometries of pine cones and oak boughs, the hundreds of fragrant herbs along the riverbank, the quiet rush of the river at night on a cool summer evening, and the vast tracts of wilderness beyond known to no one. I realized that nature is filled with a limitless number of wonderful things which have causes and reasons like anything else but nonetheless cannot be forseen but must be discovered, for their subtlety and complexity transcends the present state of science. The questions worth asking, in other words, come not from other people but from nature, and are for the most part delicate things easily drowned out by the noise of everyday life.

I owe my interest in mathematics to my father, or more precisely the sense that mathematics was something important and mysterious. He knew very little mathematics himself but was always reading about it and encouraging everybody else to do the same. He even mounted blackboards in the hall so that a person could write down a brilliant idea if he happened to be passing by. I remember particularly one day hearing a shout from my father's bedroom and rushing in to discover that he had just discovered Euler's theorem. He did not understand the proof completely, so it appeared to him more astonishing than it does to those of us with technical training, but he had correctly understood its significance and elegance. I did well in my mathematics courses in school but was not that challenged and, truthfully, not that interested either. But through my interests in electron motion in vacuum tubes I discovered a need to describe trajectories of moving particles with equations. So I taught myself calculus. I was terribly proud of this at the time, but I realize now that people at this age are simply developmentally ready to learn such things, which is why calculus is now taught in high school. But I was certainly the only person in my town to have done this, and my father's own interest in mathematics was the underlying cause.

BERKELEY
The experience that firmly placed me on a course toward a professional career in science was the four years I spent as an undergraduate at Berkeley. I entered in the fall of 1968 as an electrical engineer, my parents having prevailed upon me to take the economic facts of life seriously. I had applied to more elite schools but had not gotten in, presumably because my grades were not high enough, and also because I was what we now call an "angular" student, i.e. not well-rounded. My parents were not that disappointed, for they had themselves attended Berkeley, as eventually did my brother and two sisters. Berkeley was as different from the quiet country town of my youth as one could possibly imagine. It was full of coffee shops, politics, book stores, theaters, ethnic restaurants, stray dogs, junkies, street musicians, and fascinating people from every conceivable walk of life. As time passed I became more and more intoxicated with all this freedom and more and more convinced that the university was where my future lay. Here was the place ideas mattered, where everybody was eccentric, where originality was not only accepted but had actual market value. It was easy to get lost in the crowd at Berkeley, particularly in the great lecture courses, but this did not bother me because I had no intention of getting lost in the crowd, and anyway considered it a small price to pay for the freedom to think as I saw fit.

At Berkeley I had my first encounter with real professional scientists. I remember the Berkeley faculty as being particularly visionary and inspirational. In the physics department in particular there was a palpable sense of history going back to Heisenberg, Pauli, and Einstein. I later came to understand that Berkeley has always been a special place in American physics and that many of the greatest physicists in the world, perhaps even most of them, can trace their roots back to Berkeley in some way. It was this faculty that defined for me what physics was and should be, and thereby helped me make up my mind to pursue physics as a career. I came home in the middle of my sophomore year and announced, much to the horror of my parents, that I was switching to physics from engineering. After some discussion they gave in, as well-meaning parents tend to do in this situation, and I remember my father musing afterward that it would probably come out all right because these things usually did. Meanwhile at school I was experiencing such wonderful things as the surprise appearance of Charles Townes, winner of the Nobel Prize for invention of the laser, in one of my large lecture courses to explain simply and accurately how lasers work and how they came to be invented. I took quantum mechanics from Owen Chamberlain, who had won the Nobel Prize several years before for the discovery of the antiproton, and who was happy to discuss all sorts of unrelated things such as whether fusion would ever work and whether one should go East to graduate school. I learned electrodynamics from J. D. Jackson's wonderful book and had many occasions to ask him questions about the subject. I took introductory solid state physics from Charles Kittel, the acknowledged father of the field in which I was eventually to work. I took Goeffrey Chew's advanced quantum mechanics course and learned more about the S matrix than he probably intended. I also had many useful exchanges with Ray Sachs, who helped me learn differential geometry and general relativity on my own and guided me to a thesis. My work with Ray began with the question of whether a charged particle dropped in a gravitational field should radiate light, since the relativity principle said it was actually not accelerating. The correct answer is yes because electromagnetic field knows about the curvature tensor. This line of thought led us to a calculation of the cross-section for scattering gravitational radiation off of a charged particle, the roles of the gravitational and electromagnetic fields in this case being exactly reversed. It was a wonderful time in my life. On commencement day we were addressed by Emilio Segré, sharer of the Nobel Prize for the antiproton discovery and author of a book on nuclear physics that is a delight to read to this day. He took the long view, told us all not to worry too much, and recounted how he and his fellow students in Rome had regularly scanned the obituaries in hopes that a job would become available soon. Many years later when I returned to Berkeley to talk about fractional quantization it was Professor Segré who rushed up after the lecture to ask if the particles we had identified in the fractional quantum hall effect might have something to do with quarks. It was his life's work to ask questions like that, and this was the reason I had found him and his colleagues so inspiring.

My years at Berkeley coincided almost exactly with the worst of the Vietnam war. It is not necessary to recount here the many terrible events of that time, but the political unrest at Berkeley caused ultimately by the war was a major constraint on student life, both intellectually and physically. It was also a real lesson in how people's perceptions of exactly the same facts can be profoundly different. I had no sympathy at all for the disrespect for property and formal education implicit in these demonstrations, but I did think long and hard about the issues raised and, more importantly, about what these events said about politics. Western society has many flaws, and it is good for an educated person to have thought some of these through, even at the expense of losing a lecture or two to tear gas. As to the war, I had no idea what to think about it, except that there were already scattered reports of people in my high school class having come back in body bags. So it came as quite a shock when President Nixon canceled student deferments arguing, correctly in my view, that they were unfair, held a lottery, and picked for me a draft number equal to my age - nineteen.

I remember vividly the day it was announced and the coldness I felt as the full implications slowly became clear. It was common knowledge that theoretical physicists do their best work before age 27, sometimes even earlier. I could not possibly meet this deadline now. There was also the moral question of whether to serve at all. Many people at that time were fleeing the country to avoid the draft, others were faking health problems, and still others were enlisting for long periods in exchange for safety. After stewing over this a long time I decided that I did not think defending one's country was wrong - although the Vietnam war had very little to do with defending one's country - that I could not lie about so important a matter, that I did not want to flee the country, and that I should obey its laws if I stayed. So that was that. I often question now whether this was the right decision, but in any event it is the one I made. But the weight of it bore down on me more and more heavily as my senior year progressed, and at the very end I lost focus, failed a laboratory, and graduated with only a degree in mathematics rather than with the double degrees in mathematics and physics I had actually earned. So I left Berkeley with everything I had come to value in ruins. The only thing I had left was the faith in myself instilled by my parents and the certainty that I had understood what theoretical physics was and was extremely good at it.

MILITARY
At the time I felt that my induction into the military was a giant step backward. It was certainly unfair taxation of my time, but then life is unfair, and getting reminded of this from time to time is perhaps not such a bad thing. I had decided not to become an officer because to do so would have required me to stay in a year longer, and time was critical. So I became an enlisted man and let the system do with me as it saw fit. Skill as a theoretical physicist matters very little in the lower ranks of the army - or perhaps has negative value. It is an interesting fact that during my tour I was never allowed access to computers, radios, or anything else that I might damage through curiosity, or perhaps something more sinister. What matters most is that one blends in. In basic training, which I had at Fort Ord near Monterey, one's identity and past are excised and a new one substituted. All one's clothes and possessions are removed and shipped home. All one's hair is shaved off so that one looks like a concentration camp victim. All people get the same hemorrhoid examination. All people get the same equipment. All people run with this equipment to the firing range. All people get the same cold. All people do the same chin-ups before meals. It was about as different from Berkeley as one could imagine, the suppression of individuality and freedom for the purpose of preventing mischief. In retrospect I consider my induction to have been not so much a step backward as an important lesson in civics, for it eventually became clear that these things I found so abhorrent were the very things required to make a large organization run well under stress. So I learned the hard way that freedom and efficiency conflict, that more of one means less of the other, and that this is fundamental. To this day I break out in a cold sweat every time I hear the term "programmic science", for I know it really means tight bunks, shiny boots, and digging holes that will be filled back up by someone else the next day.

Some time near the end of basic training a computer somewhere decided that I was suited for missile school, so I was ordered to Fort Sill, Oklahoma to learn how to fire Pershing missiles. This was a good deal less stressful than basic training, as the pace was slower, and this part of Oklahoma is laid back and rather beautiful, with rolling brown hills not unlike the ones in California. The Pershing missiles, on the other hand, were not beautiful. They were horrible weapons of war - solid-fuel rockets five feet in diameter at the base, long as a moving van, and capable of throwing a tactical nuclear warhead 500 miles. They were launched from trucks and required a team of 10 men to service and fire. The most interesting thing I learned during this time was how small a nuclear warhead was. The nose cone of a Pershing is only about 18 inches in diameter at the base. I had not been interested at all in nuclear weaponry as a student, and so I had never thought through carefully about their "efficiency". It is sobering thought that these missiles were actually deployed in continental Europe in those days and that on at least one occasion, namely the 1973 Arab-Israel war, there was an alert serious enough to leave the commanding officers trembling.

While at Fort Sill I met, or more precisely was grouped with, the people who were to be my companions for the rest of my tour in the military. They were a very personable bunch mostly from the upper Middle West, Pennsylvania, and Nebraska, and rather like a selection of the smarter students from my high school, except that the contingent from Detroit was rabidly racist, something that I had never encountered before and still have trouble understanding. Getting to know these people was my first of many reminders that the world is full of intelligent, well-meaning people who, for one reason or another, did not attend university but are nonetheless well-read and educated. Out there on the prairie lost opportunities of youth were the rule rather than the exception, and I slowly became disabused of the myth of the Bright Young Thing and have not believed in it since.

After missile school I was ordered to southern Germany, where I spent the remainder of my tour. This assignment was a welcome turn of events, but it was not a vacation, and it was in some respects extremely unpleasant. Most of the locals in my parents' generation were very accepting and helpful, for they were afraid of the Russians and remembered the many kindnesses done to them after the war. They were also prospering economically, which I know from personal experience helps one overlook indignities. But the people my age and younger hated the whole idea of a foreign army on their soil, especially one with nuclear weapons, felt little personal guilt for Germany's past, and felt that the Vietnam war had thoroughly discredited the alleged ethical superiority of English-speaking countries. So we were tolerated but not liked all that much. Also there were terrible morale problems in the unit to which I was assigned in Schwaebisch Gmuend, a small town near Stuttgart, which caused particularly heavy and widespread drug usage. These were largely corrected by a change in command about halfway through my tour, but they were nonetheless extremely scary.

During this time I tried to think about physics, and about university life generally, and I made a point of visiting the nearby technical universities and the great medieval university at Tübingen, but it was hopeless. I had a job to do, my time was too fragmented, and my unit discouraged much contact with university types, this being politically dangerous. Tübingen, in particular, was frowned upon because of the safe house for AWOL soldiers alleged to be there. So I decided to make the best of a bad situation and invest the time studying language. This turned out to be a better expenditure of time than reading physics books, for like most of my countrymen I had an incomplete understanding of how language is a vehicle for ideas rather than the other way around. While my language ability is still poor, I can still remember the day that radio stations began to sound clear, when newspapers began to inform more than frustrate, when I began to get jokes, and when I told my first joke. So in the light hindsight, I judge this time to have been well spent.

At the end of my tour I was released from duty in Europe, as I had elected to travel around a bit as a free man before going home. On the day of my emancipation I celebrated in traditional fashion by burning my boots - although in an especially thoughtful and creative way. I went downtown and bought 3 kilos of saltpetre, mixed it with sugar, and filled both boots up to the brim, fully laced, and lit one off. There was a tremendous pink flame, fierce heat, and dense smoke that began shooting straight up 30 feet as from a volcano as the fire ate down into the boot. Several of the battery officers came running up just as the experiment was ending to see what was left of the sole curling up like a shriveled bug. They had been playing baseball nearby and had thought that a radio unit was on fire. I assured them that the radio unit was not on fire and then proved it by lighting off the other boot.

MIT
I entered graduate school at MIT in the fall of 1974 with a sense of urgency sharpened by my two-year absence from academic life. I was behind all my friends and I was very impatient with any activity not leading directly to fundamental discovery, i.e. taking classes. However I soon found that things were not that simple. Physics graduate schools in America are for the most part set up as a first priority to service federal contracts, not to make fundamental discoveries, and a graduate student career makes no sense outside the context of one of these contracts. Indeed it was, and is, the practice at MIT to admit graduate students directly into research groups on an as-needed basis as a kind of labor pool. It took me a while to fully understand this depressing fact of life, but I eventually did and then proceeded to look for a home in a research group as a means of supporting myself while learning the things essential to achieving my larger ambitions. I had by this time become quite cynical about and suspicious of institutions of all kinds, and I felt that government-sponsored science was no more likely to be immune from economic pressures than business. So I directed my attention toward the branch of physics with the largest number of experiments, namely solid state physics, figuring that this was the best way to cut out the intellectual middleman and go directly to nature. I have since discovered that most good theorists think this way.

It was my good fortune at this time to fall in with John Joannopoulos, a young faculty member who had just come from Marvin Cohen's group at Berkeley. I had heard John talking at a research fair and had noticed that he was the only theorist who seemed genuinely interested in his own work, so I contacted him and asked for a job. Neither of us knew it at the time, but John was to become one a truly great trainer of graduate students, for the list of alumni from his group includes Prof. E. J. Mele at the University of Pennsylvania, Prof. A. D. Stone at Yale, Prof. Karen Rabe at Yale, Prof. D. Vanderbilt of Rutgers, Prof. T. Arias at MIT, Prof. E. Kaxiras at Harvard, Prof. D. H. Lee at Berkeley, and me. His main expertise was in using local exchange methods (c.f. Walter Kohn's 1998 Nobel lecture) to model electronic materials, which in those days meant defective silicon, silicate glasses, and amorphous selenium. I figured at the time that this was a good way to learn the basics, and I knew that William Shockley had started out doing similar things for John Slater at MIT. So I worked for John for a long time and published several papers with him that were not that memorable but kept dinner on the table while I was coming up the learning curve on the vast subject of solid state physics. John's strategy was to give students simple problems they could market right away and then invest enormous amounts of personal time making sure the research was on track. The physics training I got from John emphasized bread-and-butter things such as the basics of semiconductors, tight binding modeling methods, and pseudopotentials. The truly invaluable things I learned from him, however, were not technical at all but organizational: how to mount a research campaign and execute successfully, how to render a big body of work down to its essence, how to package work so that it is interesting and comprehensible to an audience, how to look for new physical content in old results, and how to think experimentally. John took as his highest priority that all his students have a professional niche to live in after graduation, something I now understand to be of paramount importance, for the science will come later if the person has what it takes, but it will never come if the student has no job in the critical years right after graduate school.

One of the terrific aspects of MIT in those days was the enormous variety of experimental work that either took place there or was talked about in seminars by outside speakers aggressively recruited by the faculty. It was motivated by questions that did not interest me that much, such as whether the Kosterlitz-Thouless transition could actually be observed in the laboratory or what renormalization group principles told one about scattering lineshapes. The important thing for me was the experiment itself, how it worked, and whether it might be saying something that the experimentalist himself had overlooked. So I learned about X-ray diffraction, neutron scattering, raman scattering, infrared absorption spectroscopy, heat capacity, transport, time-dependent transport, magnetic resonance, electron diffraction, electron energy loss spectroscopy - all the experimental techniques that constitute the eyes and ears of modern solid state physics. As this occurred I slowly became disillusioned with the reductionist ideal of physics, for it was completely clear that the oucome of these experiments was almost always impossible to predict from first principles, yet was right and meaningful and certainly regulated by the same microscopic laws that work in atoms. Only many years later did I finally understand that this truth, which seems so natural to solid state physicists because they confront experiments so frequently, is actually quite alien to other branches of physics and is vigorously repudiated by many scientists on the grounds that things not amenable to reductionist thinking are not physics.

It was at MIT that I met and married my wife Anita. We used to swim at the same time after work at the MIT swimming pool and were annoyed by the same guy in a leopard suit who obviously thought he was beautiful and talented. So one day I said, "That guy may look tough, but he keeps his suit on in the shower." It was absolutely true, of course, for I could not have made up such a good story. This broke the ice. Anita corrected many of my worst habits, in particular the one of returning to my office after swimming and working until midnight. We would instead go up to Harvard Square for a late-night snack or attend a movie or a poetry reading, the usual staples of student life. Also, Anita's family lived nearby and was quite close-knit and warm, so we used to escape from Cambridge regularly to visit them. They had a wonderful old saltbox house out in Concord with a huge fireplace heating an equally huge kitchen with low wooden beams and an old plank floor. In winter the hearth was always lit and there was always something interesting simmering on the stove. Her father, who was then Dean of Graduate Studies at Lesley College, is a yankee with a wicked sense of humor who had grown up on a dairy farm in Massachusetts and then gone on to a life of scholarship at Yale and Harvard. Her mother had grown up as a doctor's daughter in Palo Alto and graduated from Stanford. Thanks in part to this latter fact, Anita and I were married by candlelight at Memorial Church at Stanford, an interesting turn of events considering what was to happen later. Anita's mother got a bit carried away with this wedding and went so far as to get us onto the New York Times society page. But her father kept things in perspective. One afternoon, totally unprovoked, he held out a wedding gift that looked suspiciously like a dentist's bowl and said "spit please".

BELL LABS
I must have been doing something right at MIT, for at the end of my graduate career there the faculty got together and recommended me for a position in the Theory Group at Bell Labs, the best placement a young theoretical physicist could possibly have gotten. I had wanted to go to Xerox Palo Alto, but a job did not materialize, and in light of what happened later it was probably just as well. Bell Labs had been a kind of holy place of solid state physics since the 1950's when it was built up by Shockley after the invention of the transistor. I had no idea at the time of the significance of this placement, but I did notice during my job talk that everybody understood what I was saying immediately - this had never happened before - and that the audience had an irresistible urge to interrupt, heckle, and argue about the subject matter loudly among themselves during the talk so as to lob hand grenades into it, just like back-benchers do in the House of Commons. Being a combative person I rather liked this and lobbed a few grenades of my own to maintain control of my seminar. I later came to understand that this heckling was a sign of respect from these people, that the ability to handle it was a test of a person's worth, and that polite silence from them was an extremely bad sign, amounting to Pauli's famous criticism that the speaker was "not even wrong."

It was at Bell Labs that I first made direct contact with real semiconductor experts and thus began to fully understand what amazing materials they were and what they could do. I knew a little about semiconductors already, having worked on the theory of silicon-oxide interfaces at MIT and also having intimate familiarity with Marc Kastner's experimental amorphous silicon work there. But a thorough grasp of this great subject was not possible to acquire at MIT or any other university, because no faculty could ever be big enough. I learned about cyclotron resonance measurements of electron masses and the associated disorder broadening from Jim Allen, defect-pair recombination luminescence from Michael Sturge, deep levels from John Poate and Dave Lang, silicide Schottky barriers from Marty Lepselter through Jim Phillips, infrared spectroscopy of shallow donors and acceptors from Gordon Thomas, and transport in the 2-dimensional electron gas from Dan Tsui. The theorists at Bell had all done work in semiconductors at some time or another and were very helpful in the learning process, particularly through their constant give-and-take with the experimentalists. While I was there, for example, Gordon Thomas and Tom Rosenbaum verified the continuous nature of the metal-insulator transition in phosphorus-doped silicon predicted by Phil Anderson and his "gang of four". Don Hamann and Michael Schlüter were doing ab-initio density functional computations for semiconductor surfaces, interfaces, and defects. Patrick Lee was working hard on the field theory of weak localization. I was also familiar with the cutting-edge work in gallium arsenide heterostructures being done at the time through seminars and informal conversations with Mike Schlüter, who was good friends with Horst Stormer. The fact that the two German expatriates at Bell were in the thick of this subject was no accident, for semiconductor physics had been particularly emphasized at that time in the German research establishment, and most of the careful, scholarly work on the subject, particularly the 2-dimensional electron gas, was being done in Germany.

It is a great irony that the work leading to the Nobel Prize this year began in a time of terrible defeat for me personally, as I had just learned that I would not get a permanent job at Bell. John Joannopoulos had recommended that I work closely with Mark Cardillo, who was diffracting neutral helium atoms from semiconductor surfaces as a means of diagnosing their structures, presumably on the theory that my proper niche at Bell would be as a modeler. Unfortunately, Mark was such a good experimentalist and so good at understanding the meaning of his results before I had even seen them that there was little left for me to do but confirm his insight after the fact. Also, there was no profound conceptual issue at stake. By about one year into my appointment I could see the inevitable but was unable to do anything about it. I had actually made a breakthrough in my helium diffraction work - I had discovered empirically by studying atomic beam experiments that the potential felt by the incoming helium atom was a universal constant times the electron density of the target - and was writing it up when Jim Phillips pointed out that the same idea had just been published by somebody else in Physical Review Letters. So it didn't count. The fateful vote on my promotion to permanent status came shortly thereafter, and rumor had it that I had only one supporter. While I had been expecting the axe to fall for some weeks my blood froze when it actually did. Once again my ambitions had been thwarted due to circumstances beyond my control, only this time the damage was much greater and almost certainly unrecoverable. I went home and told Anita, and together we began making plans for what to do. She was not all that unhappy, actually, for she did not like the New York metropolitan area all that much and had had ambitions to live in New England or out West.

It was at this moment that I wrote my first important paper in theoretical physics. I was 32 years old, 5 years beyond the alleged age of senility for theorists. Dan Tsui had come into the tearoom one afternoon with a copy of Klaus von Klitzing's famous paper on the integral quantum Hall effect to see what the theorists thought about it. Everybody was interested, for localization in the 2-dimensional electron gas was a timely topic. The version of it unique to two dimensions called weak localization had been discovered at Bell by Doug Osheroff and Gerry Dolan shortly before my arrival, and there was a raging controversy over the sign of magnetoresistance of these systems in weak fields. Von Klitzing's experiment was in the strong-field limit, for which there was no theory. I remember Phil Anderson's making a mumble about how there was probably a "gauge argument", by which he meant something like the physics of the Josephson effect, and this stuck in my mind. I knew that the enormous accuracy of Klitzing's effect precluded any complicated explanation, I knew from my work with John Joannopoulos what the Hamiltonian appropriate to the problem was, and I knew localization had to be occurring. I also knew how the experiment worked, in particular that the gate voltage on a field-effect transistor fixes the density and not the chemical potential, so that a gap in the density of states as proposed by Ando could not be the right answer. Within a few days I had hit on the idea of replacing a calculation of the current with a derivative of the energy with respect to vector potential, and shortly thereafter I made this physical by imagining an experiment in which the sample was wrapped into a ring. Thus was born what later became known as the "gauge argument" for accurate quantization of the Hall conductance. The upshot of this theory was that localization caused the effect and that the Hall conductance was accurately quantized because it was a measurement of the charge of the object being localized, in this case the electron.

The response at Bell to these events is a fascinating case study in how even well-informed people find a truly new idea difficult to understand and accept. Anderson complains regularly about this problem, and he often cites Planck's complaints about it, so I am in good company. A week later I gave a journal club presentation about von Klitzing's discovery, and finished off with my explanation, which could be given to that audience in two minutes. I got some questions about the experiment, but none about my ideas that were on the mark at all. I remember being challenged over, that well-known fact that all states were localized in two dimensions, something that made no sense at all in light of the experiments I had just shown. I remember giving the right answers, namely that the experiments showed the current theory of localization to be wrong in strong magnetic fields, and that there had to be a band of extended states below the fermi level carrying the current. But they were not convinced, and it was not until Bert Halperin wrote a paper repeating these and elaborating upon them that they were accepted at Bell, by which time I was long gone.

LIVERMORE
By the time I began looking for jobs my fame for this work had begun to spread and I eventually was offered a job at Purdue which I accepted. A few weeks later I un-accepted and took a job at the Livermore lab as a post-doc, an act for which I feel guilty to this day, as Al Overhauser and Sergio Rodriguez had gone out on a limb on my behalf. I had received a call from Andy McMahan months earlier asking if I might want to come out, and on a whim I went for an interview and gave a talk on my quantum Hall theory. By good fortune one person in that audience, Dick More, understood its significance and caused an offer to be generated, even though my interests and training did not match the Laboratory's needs at all. Like most of the physicists at Livermore, Dick was an expert in atomic and plasma physics, but he had been trained as a solid state physicist and had even held Ted Holstein's old position at the University of Pittsburgh. I first turned the Livermore offer down, knowing full well that it was not an academic job. But after Anita and I had discussed it at length, I decided that I felt completely betrayed by the academic establishment and saw no reason to trust it a second time, especially for so little money. She felt the same way, noted that everybody switches careers nowadays, and suggested that we move to California where the economy was strong and just go out on the open market if things went bad at Livermore. So it was decided. We flew back to Newark, and that very evening I put Anita on a plane to San Francisco to look for a place to live. I remember watching her plane take off through a cyclone fence at North Terminal and standing there for a long time afterward with tears in my eyes wondering if I had done the right thing.

Livermore was and is a real industrial laboratory, by which I mean that it considered its job to be maintenance and development of technology for inertial-confinement fusion and nuclear weapons and not the generation of public-domain scientific knowledge. I was hired into what was then known as H-Division, the group responsible for generating equation-of-state and opacity tables for use in design codes. My job description said I was to work on modeling matter at a temperature of about 10 eV and a density of about 1/10 that of ordinary solids, a particularly difficult regime relevant to the X-ray laser program. However, it was the practice in those days to induce people to work on such applied problems by providing them with resources to work on real science as well. This is how Hugh DeWitt's famous Monte Carlo work on the 3-dimensional one-component plasma came to be done, for example, or Ceperley and Alder's excellent numerical work on the phase diagram of metals at zero temperature. So I was encouraged to continue thinking about the quantum Hall effect on the side and even given permission to use my computer account for any calculations that I might need to do. Also, for the first six months I was with Livermore I worked in a trailer known as the "cooler" outside the fence waiting for my clearance to come through. So at least in the short term my decision had been a a good one.

It was while I was in the cooler that I received the preprint from Horst and Dan about their discovery of fractional quantum Hall effect. I remember flipping through to the figure at the back, staring at it for 10 seconds, and realizing that they must have found a many-body condensate with excitations carrying charge e/3, for there was no plausible explanation for the existence of a plateau other than localization of such a carrier. The temperature in the experiment was not that low by modern standards, so the plateau was not that flat and the parallel conductance not that small, but I knew Dan was very careful about localization physics and would have said something if this conductance had not been converging rapidly to zero with decreasing temperature. Also the bare eye could see that the quantization was at least 1% accurate, and there was no reason it should have been even that good unless it was von Klitzing's effect. I quickly telephoned Horst to make sure I had understood correctly and to find out all the little experimental details that never get published in formal papers, including in particular any evidence that the localization was incomplete. There was none. I told Horst what I thought it meant, and he told me they had had a similar idea. Dan had apparently seen the chart recorder plot, measured the field strength of the integral plateau with his fingers, displaced this 3 times to the right to land under the new plateau, and said "quarks".

So the task remaining was to find a prototype for this condensate simple enough to be convincing. I was familiar at the time with the theory of fractionally charged domain walls in 1-dimensional chains, an idea attributed by solid state physicists to Su and Schrieffer but actually going back further to a particle physics paper by Jackiw and Rebbi. I had learned about them from my fellow graduate student Gene Mele, who had worked on them at Xerox Webster. Gene had thought about these "solitons" deeply from every possible angle, knew as a result that they had to be real, and convinced me of it over the course of several meetings. It was actually a hot idea in those days, and there had been much experimental activity attempting to detect these solitons in polyacetylene, usually with light scattering. However, despite claims of success, the matter was never resolved because sample imperfection always corrupted the data and allowed the experiments to be interpreted more than one way. So my first attempt to write down a prototype for the fractional quantum Hall ground state borrowed heavily from the literature of solitons, in particular the idea of discrete broken symmetry on which it was based. I wrote up a theory and sent it in to Physical Review Letters. It was rejected, thank God. The referee, who I later discovered to be Steve Kivelson, observed that the discrete broken symmetry I had written down was actually a continuous broken symmetry and that its pinning on impurities would cause the sample insulate. This was correct, and furthermore I had known about the problem before I sent in the paper and had deceived myself into believing that it did not matter.

It was at this time that I wrote the paper for which I have been awarded the Nobel Prize. Realizing that most people would require more than experimental phenomenology to be convinced I went back to the beginning and began computing the properties of the interacting 2-dimensional electron gas problems by the exact-diagonalization method. For most many-body problems this would have been a foolish thing to do, but I knew from the experiments that the system had an energy gap and that this would protect the calculation and give it meaning even when the number of particles was small. So I solved the problem for one and two particles, then powered up the computers to do three, four, five, and six. Each time the system locked in at particular densities as the pressure on it was increased, and thus exhibited the behavior seen in experiment. There was no sign of any tendency to crystallize, which would have shown up as a near degeneracy in the eigenvalue spectrum. So I knew that the right answer was indeed a uniform fluid with an energy gap. Having seen the behavior with small numbers of particles I began trying to guess the functional form of the wavefunction in hopes of then extrapolating to the thermodynamic limit. One particular functional form, a product of pair factors, caught my attention because it had occurred naturally as a basis element in the numerical calculations and had a particularly large weight in the correct ground state at filling factor 1/3, sometimes as much as 99.9 %. But it was not exact. Also there did not exist any standard mathematical machinery for computing the properties of such a state in the thermodynamic limit. Feeling rather discouraged I went to the library to read up on many-body physics, hoping to find some reason that the state I had proposed would be exact. I was looking through Eugene Feenberg's book on helium and chanced to open up the chapter on Jastrow ground states and there, in front of my eyes, was the functional form I had guessed! It was not exact at all, but rather a well-known variational technique for approximating the ground state of strongly-interacting many-body systems. I eagerly read about the analogy between such wavefunctions and the statistical mechanics of classical fluids and then realized that the fluid analogous to my proposed ground state was the very one-component plasma I had been learning about from Forrest Rogers and Huge DeWitt in the "cooler", albeit in one lower dimension. So I went to them to get guidance on how to compute the properties of this plasma. Once I had mastered the hypernetted chain and semiclassical Monte Carlo techniques and understood their error bars the rest was straightforward. The ground state energy was computed and found to be variationally superior to all known crystals. The charge-1/3 excitations were constructed from this ground state with an adiabatic thought experiment very similar to that used in the integral quantum hall effect. Wavefunctions for these excitations were proposed and their computed variational energies found to match the experimental activation energy for the parallel conductance in the plateau regions. It all fit. So I wrote the new theory up and sent it to Physical Review Letters. It was published there a few months later.

These rather heady events coincided almost exactly with the purchase of our first house and the birth of my first son, Nathaniel. Anita had been near the end of her pregnancy when we closed the deal, and I remember her scooting along the floor painting the baseboards white, the only chore she could do comfortably. Nat arrived a few weeks later in the dark of the morning on one of the rainiest day I can ever remember. We somehow made it to the hospital, where he was delivered by Caesarean with me in attendance. It is quite something witnessing surgery on one's spouse while she is awake. My mother drove up from Visalia when she got the news and was almost annihilated by weather-induced traffic accidents. It was a wild and beautiful day. Thus I became a father and a homeowner at the same time and experienced all the changes in perceptions and priorities that happen to a person at this time in life. Our house was quite small, and in particular had one bathroom that needed its floor replaced twice due to dry rot caused by the children's shenanigans in the bathtub. But in the back was a small creek, a little grove of redwoods, and three wonderful apple trees which kept Anita busy canning apple sauce in the fall. Nat and my second child, Todd, who was born two years later, used to play endlessly back there. The larger environment was also quite rural. On occasion I would take one of the kids in a backpack across the street and up into Briones park to explore the wild oak woods and the herds of horses that roamed freely on the ridges.

We lived in this house many years, but the day finally came when we had to sell out and move to Stanford. I remember the last day very clearly. The moving van had left, Anita was just driving away with the last load of stuff, and Todd and I were left to vacuum up the last bits of dust. The house was echoing, as houses do when they have no people in them. I pointed out to him that this was the sound of ghosts. Here was where my children were born. Here was where we had run madly around the apple trees and smashed the violets. Here was where I had planted the Monterey pine which was now shading the patio. Todd stared at me for a moment and then said with obvious annoyance, "Let's go, Daddy."

STANFORD
My career at Livermore was effectively derailed by the fractional quantum hall theory, for I became so famous on account of it that I had to travel constantly and could not begin learning the classified parts of the Laboratory's business. I am to this day rather poorly educated about nuclear weapons, and I know virtually nothing about laser fusion capsules. The Lab had plenty of money in those days, and the head of H-Division, Hal Graboske, always supported my requests for travel, including once a trip to Denmark, Finland, and the Soviet Union. But the handwriting was on the wall. In 1984 offers began pouring in from universities, and there was a particularly good one from Stanford. Stanford at that time had a terrific solid state physics faculty and was quite a bit smaller, and therefore more malleable, than my old alma mater Berkeley. Also Anita and I were worried about the anti-intellectual attitudes towards the University of California expressed by the state legislature, worries that proved well-founded when a few years later salaries were capped, teaching loads were increased, and the state budget was not passed on time, causing faculty to be paid in IOU's. I had originally turned down all these university offer on the theory that the research environment would be better inside at Livermore where somebody else took care of salaries and research support. But Stan Wojcicki, Sandy Fetter, and Mac Beasley were particularly persistent, and I got sound advice from both Berni Alder and Anita not to let this train go by, so in the end I relented and accepted their offer. Little did I know that in a few years the Cold War would end, the Department of Energy's budget would be squeezed, and the "expendable" public-domain science activities paid for by fat budgets would be the first thing to go. This is a well-known effect in industrial laboratories, as the recent histories of Bell Labs, Xerox, and IBM Research have sadly reminded us. But at this time I accepted mainly because of Berni's advice.

When I moved to Stanford I began to pursue the line of research I have been following ever since, namely trying to understand the larger implications of fractional quantum hall discovery. The historical significance of the effect is a matter of some debate, but my own view is that it sets a precedent for completely trivial equations of motion to generate particles carrying fractional quantum numbers and a concomitant set of gauge forces between them, both of these also being postulates of the Standard Model. Thus I think the trail leads ultimately to big questions about the universe and cosmology. Progress in this direction has been painfully slow because the experiments have not cooperated. Most of the leads for finding other effects in nature analogous to the fractional quantum Hall effect turned out to be false, including particularly high-temperature superconductors, which have been my main materials physics research interest here for the last several years. However, Phil Anderson's idea that the phenomenology of the cuprates might be related to the known behavior of 1-dimensional antiferromagnets, which has a beautiful formal relationship to the fractional quantum hall ground state discovered by Duncan Haldane and Sriram Shastry, is still very intriguing, especially since the particles carrying fractional quantum numbers in the latter system, which we call spinons, are relativistic.

My experience with high-temperature superconductors has been very different from the fractional quantum Hall effect. The problem has been difficult to formulate clearly, and progress has been slow. I do not know whether this is due to an historical paradigm shift or just intellectual incompetence on our part, but I certainly find myself yearning for the good old days when the entirety of a problem could be understood in 10 seconds. It has been my good fortune to have an excellent group of experimentalists at Stanford with whom to work, notably Aharon Kapitulnik, Ted Geballe, and Mac Beasley, known collectively as the KGB, and Z.-X. Shen. I predicted optical rotary activity in bulk cuprate superconductors, which was unfortunately disproved by Aharon, although the symmetry breaking I predicted was eventually found by Laura Greene at the University of Illinois. I also predicted the so-called large pseudogap in the cuprates that was eventually discovered by Prof. Shen in photoemission from samples in extreme underdoping. I have also done some mathematical physics work for which I am very proud, most notably the invention of the Kalmeyer-Laughlin spin liquid vacuum and "anyon" superconductivity, although these things broke with my tradition of going directly to nature for inspiration and are in this sense flawed.

My job at Stanford is rather different from the ones I had held previously in that my own ambitions must take a back seat to the well-being of the students with whom I work. But this actually is not very difficult. My own sons are almost college age now, and my rule is simply to do for my students exactly what I hope someone else will do for my sons when the time comes: I teach them to have faith in themselves and in their own compass, to listen to nature to find truth, to love knowledge for the sake of itself, and to strive for greatness. A few days after the Nobel Prize announcement I got the following wonderful e-mail from Andrew Tikofsky, one of my best graduate students, who is now on Wall Street:

Hi Bob, Ian McDonald, Steve Strong, and I are getting together for a beer near Grand Central Station this coming Tuesday in honor of your prize. You are cordially invited to attend.

From Les Prix Nobel 1998.