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1、June 27, 200113:47WSPC/143-IJMPE2-h-yang1INTERVIEW OF C. N. YANG FOR THE C. N. YANG ARCHIVE THE CHINESE UNIVERSITY OF HONG KONGKerson Huang(January 3, 2001)Huang: This is Kerson Huang. It is July 29, 2000. We are in Professor YangChen-Nings office at the Chinese University of Hong Kong. I am intervi
2、ewing him on the subject of statistical mechanics.Huang: Chen-Ning, do you think ergodic theory gives us useful insight into the foundation of statistical mechanics?Yang: I dont think so. It is true that in the early days of statistical mechanics, there was much discussion about ergodic theory. In p
3、articular, it was very useful for mathematicians to launch into this subject; but in the 20th century, statistical mechanics mostly developed in the area of equilibrium statistical mechanics, and ithas taken offreally without much reference to ergodic theory. This does not mean that ergodic theory s
4、hould not be pursued in the future, but I doubt that in the 21stcentury ergodic theory would have much influence on the development of statistical mechanics.Huang: As you know, theres this Boltzmann factoreH,where is one over Boltzmanns constant times the temperature. It turns into the quantum-mecha
5、nical time-translation operatoreitH,if we make the temperature pure imaginary by setting = it. Do you think this is just a mathematical coincidence?Yang: I think it is a coincidence. I myself do not see a deeper physical origin of this “coincidence,” as you call it. But this is of course a deep subj
6、ect. The path integral formalism of Feynman, which I regard as one of the great contributions to physics, indicates that the integral of the phase factor that is, with the i underlies the true meaning of quantum mechanics. It was not the way quantum mechanics was developed, but I think to understand
7、 what quantum mechanics is all about, the deepest way is through the path integral formalism, which deeply1June 27, 200113:47WSPC/143-IJMPE2-h-yang12entangles this exponential phase factor. How that happens to be, in a formalistic way, related to the partition function expression. I do not see eithe
8、r a physical ormathematical significance, or deep meaning. It is of course very important, once one recognizes this relationship, to borrow from each other. Its a very deep subject.Huang: Do you think we will some day have a theory of so-called “complexity” comparable to thermodynamics?Yang: “Comple
9、xity” is a word which has been used and abused in recent years. There were people who thought that complexity will overwhelm the whole of physics. I do not think that is likely to happen. Now, complexity, as relating to such subjects like dynamics, is likely to be a very important subject, both for
10、physicists and mathematicians. But I doubt it will have any importance comparable to thermodynamics. On another level, complexity can have additional meaning, for example, in infor- mation theory and the structure of the human brain. These are mysterious subjects for future development. How that wil
11、l play out in the 21st century I cannot guess. If you call that complexity, if you call the understanding of the structure of the human brain a part of complexity, then I would say that would likely be the one dominant subject of 21st century science.Huang: Do you think a broader understanding of st
12、atistical phenomena will help us in understanding group human behavior?Yang: I hope that we will have some penetration of the understanding of human behavior, both in the individual and in the group; but I think that subject is likely to be much more complicated then the subject of thermodynamics.Th
13、ermodynamics was something that was very difficult for scientists to under- stand, and to tame. But once it has been understood in principle, and tamed, it hasflowered into one of the major areas of understanding of physics in the last century. I doubt that the elegance and depth that characterize s
14、tatistical mechanics of this century, the 20th century, is likely to be matched by the understanding of either individual human behavior or group human behavior in the 21st century. This does not mean that there would be no penetration. Im only saying that I doubt the elegance that characterizes the
15、 statistical mechanics of the 20th century could be matched in that area in the next century.Huang: I believe one of your earliest publications was on lattice models in statistical mechanics1. Can you tell us what attracted you to the subject?Yang: When I was a graduate student in China in the warti
16、me, 1942-44, I hadstudied with Wang Zhuxi on phase transitions, specifically, on such things as beta brass, which was a popular subject in the mid-thirties. So I was very familiar with lattice problems. Then, one day in 1944, I remember distinctly Professor Wang1C.N. Yang, J. Chem. Phys. 12, 66 (1945).June 27, 200113:47WSPC/143-IJMPE2-h-yang13Zhuxi very excitedly told me that the two-dimensional Ising model had been solved exactly by a physicist named Onsager. He and I both stud
