[来源]http://www.s.u-tokyo.ac.jp/koshiba/shukuji_e.html
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X})5XYvA* Masatoshi Koshiba 小柴昌俊 zUq ^ YYNh|
2 I am filled with all sorts of emotions as I stand here to give the commencement address to those of you graduating from the Faculties of Science and Engineering. The reason for this is that I graduated as a physics major of this university at the bottom of my class fifty-one years ago. The late Professor Mitsuo Taketani, who was known for his dislike of the University of Tokyo, gave a speech at my wedding reception. He said, "Despite the fact that the groom graduated from the University of Tokyo, there is some hope for him since he graduated at the bottom of his class." I was told that my wife's parents and relatives were worried about my future. But, since I became a professor here and lasted until my retirement, most people do not believe that I was at the bottom my class. I am rather embarrassed, but to prove it, let me show you a transcript of my record. (figure omitted) Now you see how bad it was. You might wonder why I revealed my poor academic record at the beginning of my talk. It is because this is directly related to what I want to talk about today.
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NXU W )|3BS` "I think therefore I am." This is a statement by the famous French philosopher of science, Descartes. In scientific cognizance there is a distinct surface of demarcation between the subject, which perceives, and the object, which is perceived. Because of the existence of this surface, the results of scientific cognizance have built up over the generations as the common intellectual property of all humankind. Of course, there are types of cognizance in which this surface of demarcation does not exist. "Truth, goodness, beauty" are often given as examples of things to be perceived. For example, in religious enlightenment, which perceives goodness, or when one is intoxicated with pleasure while listening to one's favorite music or observing objects of art, the subject and object are in complete harmony. There are other ways of classifying cognizance. Let us classify it by whether it is passive or active. Now, we have classified cognizance into four types. We can classify what you have been studying as the "passive subject separated type" cognizance. You should be prepared to engage with the "active subject separated type cognizance", which you have never encountered before, whether you go into the real world to work or to graduate school to engage in research. It is not true that just because your academic record is good, things will necessarily go well for you from now on. In this sense, it is more proper to consider today's ceremony as a commencement ceremony rather than a graduation ceremony.
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$ }a O6% There are many successful research projects being conducted at this university. As an example, I want to tell you about an underground experiment in Kamioka, initiated by the Faculty of Science in 1981, and later by the Institute for Cosmic Ray Research of the University of Tokyo. So that you will understand why I started such a project, I want first to tell you very briefly what I have done since my graduation from the university. After two years in the Masters Course, I went to the graduate school of University of Rochester in America to obtain a Ph.D. I was hired as an associate professor at the former Institute of Nuclear Study, probably because of a paper I wrote while I was a research associate at the University of Chicago, in which I pointed out that the origin of cosmic rays is supernovae. An attitude I picked up during those years in America was to point out a mistake to even a distinguished scientist, if what he or she had said was wrong, even in public. I felt that it was the proper attitude for a scientist to adopt. But, in Japan, unless you acted in a deferential manner, you would be ostracized, and I found it difficult to remain at the Institute of Nuclear Study. I thought seriously of returning to America, but there chanced to be an announcement of a position being created for an associate professor in the Physics Department of the University of Tokyo. I applied for it without anybody's recommendation, and luckily I was hired despite my academic record at the time of graduation, and I was able to happily carry on research there until my retirement in 1987.
,5V w^@F 3bYP i^ Now that I was accepting graduate students every year, I had to think of their future jobs. If I had kept on doing the analysis of nuclear emulsions as before, the job market would have been limited. So, I started to do counter experiments in elementary particle physics and cosmic ray physics. At that time, I received a request from Dr. Budker, who was constructing an electron-positron colliding accelerator in Siberia, to come to Siberia and start a collaboration. I decided to have a look at the facility there before I seriously considered participating in the project. However, the elementary particle physics theorists around me said that what the colliding accelerator would reveal could be discovered without the need for experimentation using quantum electrodynamics, and it was entirely unnecessary to take part in a project that would only soak up a large sum of government money. Fortunately, the Department Chair at that time was a first-rate elementary particle physics theorist, and he said, "Unless you do it, you'll never know what may happen," and allowed me to submit a budget request to the Ministry of Education. First-rate theorists are always aware of the limitations of their own understanding, but second-rate theorists seem to be unaware of the limitations of their theories. Unfortunately, Budker had a heart attack around this time, and we had to quickly look for a facility in Europe where we could perform electron-positron collision experiments. Finally, we ended up doing the experiments at the national electron accelerator laboratory in Hamburg, Germany (DESY). This type of experiment has since become the most mainstream experiment in elementary particle physics. Fortunately, the University of Tokyo group was very highly regarded, and we received a special award from the European Physical Society for our experimental work on gluon physics. This type of experiment is being carried out now at CERN-LEP in Geneva by the International Center for Elementary Particle Physics of the University of Tokyo. Under such arrangements, graduate students ready to begin their doctoral theses would join these international collaborations, but the problem was the education of graduate students in the Masters course and undergraduates.
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1 q)j b9e I proposed the idea of holding "Summer Vacation Experiments" to the Physics Department so that undergraduate physics majors could get a taste of scientific research and active subject separated cognizance, and my proposal was accepted. Regardless of their grades, juniors could carry out the experiments that they wanted to do in the research groups of their choice during the summer vacation. This proposal was a great success, and many highly motivated students came to my group. But there remained the problem of providing experimental projects for Masters students and graduate students in their early stage of doctoral work to which they could fully devote themselves.
HQ /D )D d ~#B,+ In the mid-1970s, several Grand Unified Theories, which went beyond the Standard Model of elementary particle theory uniting weak and electromagnetic interactions, and including strong interaction in the unification scheme, were proposed. All these theories predicted that the proton, which had been considered to have an infinite lifetime, would decay over a finite lifetime into lighter particles. Elementary particle experimentalists the world over became extremely excited. Two experiments to search for proton decay were proposed in Japan, and one of them was the Kamioka underground experiment. The idea of observing particles in a massive volume of clear water by photomultipliers from the side in an underground space was hatched in my Chicago days and had been mulled over by me since then. I always impressed two things upon entering graduate students: one was that "We are supported by taxpayers' precious money, and it is unthinkable to buy things from companies at their quoted prices," and the other was "If you want to be a researcher, always have three or four topics of research you want someday to carry out. If you do that, you'll be able to select which information to take and which to ignore from among the massive amount of information now available." The plan to store 3,000 tons of water 1,000 meters underground and to observe the water with 1,000 photomultipliers was realized (KamiokaNDE: NDE=Nucleon Decay Experiment). However, I discovered that a similar design, but on a scale several times bigger than ours, was being planned in America. This would mean that taxpayers' money would be spent on a second-rate one-shot experiment. I really thought extremely hard. With the expected budget, we couldn't compete in terms of size, but if we could improve the measurement resolution of the detector enormously, then we should be able to measure the branching ratios of various proton decay modes, and could pick out which Grand Unified Theory was correct, even though we might not be the first to discover proton decay itself. I wondered if this scheme was possible within the limited budget. Then, I thought that instead of increasing the number of photomultipliers, we should improve the light detection sensitivity of each tube as much as possible. I immediately asked the president and the head of the technical division of Hamamatsu Photononics Company to come to my office, and spent several hours trying to persuade them to take on the development of such a tube. I offered to assign a research associate and a graduate student to this project, and was finally able to get the president to say "yes." The world's largest photomultiplier with a diameter of 50cm was developed one year later. This photograph reminds me of that time when I felt a sense of total elation. But, since I haggled over the price of the new tube, for some time after that the president told me several times that thanks to me the company was in the red to the tune of 300 million yen.
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_z With a 50cm diameter photomultiplier TrCut 2 {E =BFs We spent about a year and a half installing new anti-coincidence counters surrounding the tank, to thoroughly purify the water, along with new electronic circuits and making adjustments to them. It was January 1, 1987 when we started the data taking for solar neutrinos. We had a great stroke of luck immediately afterwards. A supernova explosion signifying the end of a massive star happened 170 thousand years ago in the Large Magellanic Cloud near our own galaxy, and the light and neutrinos emitted at that time finally arrived at earth. Since our KamiokaNDE had been tuned to observe solar neutrinos, it was easy to catch supernova neutrinos with higher energy that that of solar neutrinos, and with clearly defined times of arrival. This shows you the neutrino signals (figure omitted) from the first supernova explosion ever to be observed in the world. There were only 12 neutrino events, but they gave us fundamentally important data regarding supernova explosions.
de=){.7Y T*o!#E. The observation of solar neutrinos proceeded smoothly, and we were able to make astrophysical observations inclusive of time, direction and spectrum. Here is the data (figure omitted). The figure on the left shows the direction from the sun, and that on the right is an n-graph of the sun taken by neutrinos rather than a photo-graph taken by light. These observations and the observation of supernova neutrinos are commonly held to be the foundation of neutrino astrophysics.
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The analysis of cosmic ray neutrino background designed to facilitate accurate observation of various proton decay modes led to an unexpected result. This was the discovery that neutrinos created in the atmosphere by cosmic rays turned into other kinds of neutrinos in flight. This phenomenon known as neutrino oscillation clearly indicated that neutrinos have mass. This figure shows the data. (figure omitted). This is the first clear experimental evidence that the Standard Model of elementary particles had been broken.
W ( 5XcP( Right now Kamioka is the Mecca for neutrino research in the world, and over 150 researchers from the U.S. are engaged in research there, for example. The third generation experiment, KamLAND has been completed, and data taking has started with anti-neutrinos from a nuclear reactor.
Ic2Q<V}oq `PY=B$?{4 Looking back over my life, I think I have been very much blessed with good teachers, good colleagues and good students. It gives me great pleasure that my former students have been the recipients of numerous academic awards.
