A Theoretical Alchemist

C. W. Chu - Hong Kong University of Science and Technology, Hong Kong, and Texas Center for Superconductivity, University of Houston, Texas

An indisputably great physicist. An undeniably great human being. A man in a class of his own. It is indeed a great honor and privilege for me to join the chorus here this evening to sing the praises of Professor C. N. Yang. This is particularly so since I am only a lowly experimentalist in condensed matter physics or solid state physics, which was once called "squalid state physics" by someone.

Professor Yang's impact on the world of physics is far-reaching. His seminal contributions extend from particle physics to statistical mechanics to condensed matter physics. But his influence reaches beyond the world of physics. Both as a physicist and as a human being, his influence on the Chinese communities inside and outside China is immense and unprecedented. He is known to different people by different epithets: one of the greatest physicists of the 20th century, the pre-eminent stylist of the 20th century, a conservative revolutionary, a genius, a magician, a theoretical alchemist, a great physicist with a sensitive big heart, a physics romanticist, a humanist, and so on. As an admirer, a beneficiary and his student-at-large, I would like to take the next few minutes to share with you some of my personal thoughts about Professor Yang and the effects he has had on my life.

To the great majority of scientists, science lacks style, taste and personality, and science should be strictly impersonal. Therefore, it was surprising to read: "In every field of creativity, it is one's taste, together with ability, temperament, and opportunity, that determines one's style and through it one's contribution" - these telling words were written by Professor Yang in his Selected papers 1945-80 with Commentary published in 1983 to celebrate his 60th birthday. He wrote this because he believes "the physical universe has structure, and one's perceptions of this structure, one's partiality to its characteristics and aversion to others, are precisely the elements that make up one's taste." Thus he concludes, "taste and style are so important in scientific research, as they are in literature, art, and music". Indeed, it is easy for a trained ear to tell the music of Mozart from that of Bach as a trained mind to tell the work by Heisenberg from that by Dirac. No wonder Freeman Dyson once called Yang the pre-eminent stylist of the 20th century.

While Professor Yang is an admirer of Dirac, he has developed a style of his own. For instance, Professor Yang, the stylist, uses words precisely and parsimoniously because of his love of exact analysis and formal mathematical beauty coupled with his deep understanding of physics. As a result, his papers are often characterized by a high density of ideas. This was amply demonstrated during Yang's student days. As Professor Edward Teller told it, shortly after Teller and Emil Konopinski (Kayski) published a paper with an unproven statement about the relationship between the angular momentum changes and the angular distribution of the products in a nuclear reaction involving deuterons, Yang showed up in his office and went to the blackboard to prove the statement in just a few minutes. Yang did not want to be a theorist at first. Only later did he change his mind with Teller's encouragement. Teller asked him to write up what he presented on the blackboard as his thesis in the late 1940's. A few days later, Yang appeared in Teller's office with only three sheets of paper. Although they did supply the proof of the relationship, a thesis of such short length made Teller somewhat nervous. Teller suggested Yang extend it to include the case of half-integer angular momentum. A few days later, Yang reappeared with an additional four sheets of paper. It was more than double its original length and it was very good. But Teller was still nervous and told him that University of Chicago normally required a thesis longer than seven pages. A few weeks passed, Yang produced eleven pages. Teller finally said OK and granted Yang the degree. I was told that this is the record for the shortest PhD thesis in physics. Years later in the 1980's, I told my former student, Professor M. K. Wu, who is also here tonight, that "if one day we find a superconductor with a transition temperature above the liquid nitrogen boiling point of 77 K, we should submit a one paragraph paper to beat Yang's record." In 1987, we did discover a superconductor with a transition temperature of 93 K. However, we neither had the courage nor the wisdom to defy the conventional impersonal article format, which includes the objective, experimental method, results and conclusion. As a consolation, I did manage to slip in a couple of sentences describing our emotion at the time of the discovery at the very beginning of the article. I have also been telling my students, " it's Nature's rule to be simple; simplicity is beautiful", which clearly bears Yang's imprint.

Many physicists are often amazed at Yang's ability to seek out problems of significance and solve them long before others can. Some consider Yang a genius. Mark Kac once wrote " In science as well as in other fields of human endeavor, there are two kinds of genius: the 'ordinary' and the 'magician'." Someone could be an ordinary genius only if he or she were to be a few more times smarter. However, a magician genius is someone in a different part of the phase space from where we are, and the working of his or her mind is beyond comprehension. To me, Professor Yang is an ordinary genius at one time and a magician genius at other times. Some of his former colleagues found his work most elucidating and easy to understand. Others were frustrated because before they could understand the problem he raised, Yang had already had the answer. There is a Chinese saying "Since they are so endowed with talent by God, they are beyond the comprehension of earthly people" (自是天生有仙骨,世人那得知其故).

It is easy for me, as an experimentalist, to consider Professor Yang a theoretical alchemist since so many inconspicuous physics topics have turned into goldmines once touched by him. Professor Townes mentioned this morning that twelve Nobel Prizes have been awarded to works related to lasers directly or indirectly. Similarly, many significant contributions leading to the Nobel Prize clearly grew out of Yang's earlier work, as was shown by talks in this symposium. And more will come, I surmise.

Until I formally met Professor Yang in 1969, I thought there were only two kinds of scientists: those who only want to impress others by bragging about what they do and those who only want to pump information by asking what others do. I found Professor Yang belongs to a third extremely small category, i.e. he always generously shares his exciting insights and thoughts with others and at the same time shows a genuine interest in others' works. His amicable demeanor inspires confidence in many young scientists because he always listens to their work carefully and offers helpful suggestions. I am inspired by his forever-young state-of-mind, which acts like a sponge whenever there is something new, be it in science, history, or art.

Professor Yang has influenced me in varying degrees in various important stages of my life. While I have always been interested in science, the award of the Nobel Prize in Physics to Lee and Yang in 1957 made my decision to choose physics as my career much easier. Their award reinstilled self-confidence in the Chinese people, who started to lose confidence in their abilities after witnessing China's repeated defeats in the hands of the western powers in the past century. In the 1960's, many physics students thought particle physics was the only physics worthy of study. However, Yang's elegant work on phase transition, flux quantization and off-diagonal-long-range-order demonstrated that solid state or condensed matter physics is equally challenging and that the significance of a physics problem depends critically on the ability of a physicist to unravel it. As a result, I was among the minority of physics students in the 60's who decided to enter the exciting field of condensed matter physics with gusto.

Later, the time came for me to form a family. I was at that time courting Professor S. S. Chern's daughter, May. Professor Chern would like to know a little about me. So he asked Professor Yang. Professor Yang directed the question to my late mentor, Professor Bernd Matthias. Professor Matthias' answer was, "Paul is bright but May is brighter". This "correct message" changed my personal life and May later became my wife. However, Matthias confided to a friend of mine later that he was merely joking with Yang since he was amazed by how concerned a Chinese parent (Chern) could be about his daughter's social life!

After the discovery of high temperature superconductors in 1987, I received numerous attractive offers from many prestigious universities. The University of Houston thus faced the dim prospect of losing all pledges of support should I leave. Aside from my sense of loyalty to Houston, Yang's advice also played a key role in my decision to stay in Houston. He told me that with enough support and good will, one might draw more satisfaction from building a great center in a less well-known university than in an already well-established institution. So I decided to stay in Houston to build up the Texas Center for Superconductivity at the University of Houston (TCSUH). TCSUH is now one of the world's leading centers for superconductivity researches. Last year, in 2001, I encountered an equally great if not greater challenge, viz. whether I should take up the presidency at the Hong Kong University of Science and Technology (HKUST). HKUST is a young and vigorous university and it is moving up the international academic ladder rapidly. After reading the long list of carefully thought-out reasons from Professor Yang and talking to Professor Sam Ting, I decided to take up this new challenge in Hong Kong while pursuing at the same time my superconductivity research in the US.

At this happy occasion, I would like to thank Professor Yang for his sagacious advice, stanch support and unfailing friendship. But more importantly, I would like to thank Professor Yang for being an inspiration not only to me but also to generations of physicists worldwide. I wish you the best of health, happiness, insight and productivity for many years to come.

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