fore been at a conference where tion of the Schrôdinger equation), Computational Physics library is so many developing countries had turbulence, function minimization enormous. And there is network been represented, and it clearly (for protein folding, spin glasses, ing, which both solves and intro came as a surprise to him and oth etc.), quantum field theory, and duces many problems, but does ers that it was not only possible stellar evolution. The difference in not obviate the need for centres to carry on computational physics the time-, length-, and energy- of excellence. research in such places, but that scales is impressive. The economic aspects of the it was being done actively. The Communications issues are also research cannot be neglected. The obvious conclusion is that this very important. The usual language future of Computational Physics enormous source of intellectual of Computational Physics, Fortran, will depend on how we interact potential cannot be neglected. has long been recognized as inad with the larger scientific computing Ken Wilson's summary talk cov equate in many respects, especially market, which has a huge industrial ered the major outstanding issues as a vehicle for explaining what a base representing about $ 10 bil for computational science as he program is expected to do. Yet lion per year, and is truly inter saw them and as they were none of the many other languages national. With the technology ad brought out at the conference. His has had widespread acceptance. vancing rapidly on many fronts, first point was: what is quality There are other important as the prospects for Computational research? Or, equivalently, what pects of the publication issue: Physics are apparently limited only research will still be respected four Where should new papers be pub by our own skill and imagination. centuries from now? lished, where and how should pro The great algorithmic challenges grams be published? The list of By Fred James remain : electronic structure (solu journals needed for a complete
At the 'Jackfest' marking the History of the weak 65th birthday of Jack Stein- berger (see July/August 1986 issue, page 29), T. D. interactions by T. D. Lee Lee gave an account of the history of the weak interac tions. Lee was a graduate In 1898 Rutherford discovered people on my track. I have to pub student with Steinberger un that the so-called Becquerel ray lish my present work as rapidly as der Enrico Fermi in Chicago actually consisted of two distinct possible in order to keep in the from 1946, and went on to types of radiation : one that is read race. The best sprinters in this win the 1957 Nobel Physics ily absorbed which he called alpha road of investigation are Becquerel Prize with C. N. Yang for their radiation, and another of a more and the Curies../ Rutherford's pre suggestion that the weak penetrating character which he dicament is very much shared by interaction does not conserve called beta radiation. Then, in us to this day. parity (mirror symmetry). This 1900, the Curies measured the Soon even more runners ap edited version * omits some electric charge of the beta particle peared : Otto Hahn, Lise Meitner, of Lee 's tributes to Steinber and found it to be negative. That, William Wilson, von Baeyer, John ger, but retains the impres at the turn of the century, began Chadwick, Niels Bohr, Wolfgang sive insight into the subtleties the history of the weak nuclear Pauli, Enrico Fermi, Charles Ellis, of a key area of modern phy interaction. From the very start George Uhlenbeck, and many oth sics by one who played a the road of discovery was tor ers. We know that to reach where vital role in its development. tuous, and the competition intense. we are today took nearly a whole A letter written by Rutherford century and a large cast of illus to his mother expressed the spirit trious physicists. Yet probably any * The full version is available as a 'Yellow of research at that time: 'I have Report' No. 86-07 from CERN Scientific modern physicist is only three Information Service. to keep going, as there are always handshakes away from these pio-
CERN Courier, January/February 1987 7 T. D. Lee (left) and Jack Steinberger — two lucky breaks.
question concerning the origin of the continuous spectrum. She rea soned that a nucleus, presumably quantized, should not emit elec trons of varying energy. Could it be that the observed inhomogene- ity was introduced after the expul sion of the electron from the nu cleus? A series of experiments by Ellis and others quickly established that this is not the case. This then led to Bohr's suggestion that per haps energy was not conserved in beta decay. Pauli countered this by formulating the neutrino hypo thesis. Fermi then followed with his celebrated theory of beta de cay. This in turn stimulated further investigation on the spectrum shape, which did not agree with Fermi's theoretical prediction. This led to other ideas, and the confu sion was only cleared up complete ly after World War II, in 1949, by neers (for some perhaps only two) found that because she was a wo C. S. Wu and R. D. Albert. — you shake Jack Steinberger's man she could only work at hand, which shook Fermi's hand, Planck's institute in the basement, which shook all those other hands. and only go in and out through the New horizons (1949-1953) In the mid-1960s, Lise Meitner servants' entrance. At that time, came to New York and I had lunch Otto Hahn had his laboratory in an In 1946, the pion was not with her at a restaurant near Co old carpenter's shop. Lise Meitner known. Fermi and Edward Teller lumbia. When K. K. Darrow joined decided to join him and to become had just completed their theoretical us, Meitner said 'It's wonderful to an experimentalist. For the next analysis of the important experi see young people.' To appreciate thirty years, their joint work shaped ment of M. Conversi, E. Pancini this comment, you must realize the course of modern physics. and 0. Piccioni. I attended a sem that Darrow was one of the earliest In 1908 they found that the ab inar by Fermi on this work. Where members of the American Physical sorption of beta particles through he arrived at the conclusion that Society and at that lunch he was matter followed an exponential the 'mesotron' (the observed par over 70. But Lise Meitner was near law. From that they concluded ticle) could not possibly be the 90. I was quite surprised when beta rays are of unique energy. It carrier of strong forces hypothe she told me how she started her was Wilson, in 1909, who drew sized by Yukawa. Fermi's lectures first postdoctoral job in theory an opposite conclusion that the were always superb, but that one with Boltzmann, a contemporary beta rays are heterogeneous in to me, a young man not yet twenty of Maxwell. That shows us how energy. But soon Hahn and von and fresh from China, was abso recent even the classical period of Baeyer found line spectra, which lutely electrifying. our profession is. again confused the issue. This was One lucky break in my life was After Boltzmann's unfortunate cleared up by Chadwick in 1914, to have Jack Steinberger as a fel death in 1906, Meitner had to find who established the continuous low student at Chicago, because another job. She said she was beta spectrum. he told us that the muon decays grateful that Planck invited her to With the advent of quantum the into an electron and two neutrinos. Berlin. However, upon arrival, she ory, Meitner, in 1922, raised the This made it look very much like
8 CERN Courier, January/February 1987 C. N. Yang — violating mirror symmetry.
any other beta decay, and stimu lated M. Rosenbluth, C. N. Yang and myself to launch a systematic investigation. Are there other in teractions, besides beta decay, that could be described by Fermi's theory? We found that muon decay and capture resembled beta decay. This began the 'universal Fermi interaction'. We then went on to speculate that, in analogy with electromagnetic forces, the basic weak interaction could be carried by a universal coupling through an intermediate heavy boson which I later called W± for weak. Naturally we went to Enrico Fermi and told him of our discov eries. He was extremely encourag ing. With his usual deep insight, he immediately recognized the further implications beyond our results. He put forward the prob lem that if this is to be the univer is never changed through the emis was never published. The full sig sal interaction, then there must be sion and absorption of a photon; nificance of these conservation reasons why some pairs of fer as for the weak interaction, why laws was not realized until years mions should have such interac should one bother to introduce a later. While this might be the first tions, and some pairs should not. long list of mysterious numbers, time that I failed to recognize a For example, why does the proton when all one needs is to say that great idea in physics when it was not decay into a positron and a only a few combinations can have presented to me, unfortunately it photon, or into a positron and two interactions with the intermediate did not turn out to be the last. neutrinos? boson. (Little did I expect that soon In the early fifties, extensive ef A few days later, he told us that there would be many others.) forts were made to determine the he had found the answer; he then Most discoveries in physics are space-time transformation proper proceeded to assign various sets made because the time is ripe. If ties of beta decay and so give an of numbers, + 1,-1, and 0, to one person does not make it, then insight into the underlying mechan each of these particles. This was surely another person will do it at isms. A 1953 experiment on he- the first time to my knowledge about the same time. In looking lium-6 decay seemed to rule out that both the laws of baryon-num- back, what we did in establishing the theoretical idea of the interme ber conservation and of lepton- the universal Fermi interaction was diate boson, and I became quite number conservation were formu a discovery of exactly this nature. depressed. lated together to give selection This is clear, since the same uni rules. However, at that time versal Fermi coupling observations (1948), my own reaction to such were made independently by at The theta-tau puzzle (1953-1955) a scheme was to be quite un least three other groups, 0. Klein, impressed: surely, I thought, it is G. Puppi, and J. Tiomno and J. A. During a recent physics graduate not necessary to explain why the Wheeler, all at about the same qualifying examination in a well- proton does not decay into a posi time. Yet Fermi's thinking was of known American university, one tron and a photon, since everyone a more profound nature. Unfortu of the questions was on the theta- knows that the identity of a particle nately for physics, his proposal tau problem. Most of the students
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10 CERN Courier, January/February 1987 were puzzled over what theta was; the decay angles in the disintegra of course they all knew that tau is tion of hyperons (heavy relatives The modern period the heavy lepton, the charged of the nucléon, carrying strange member of the third generation. ness) I realized how non-conserva At present, there seems to be So much for the history of physics. tion of parity might be revealed if a divergence in the viewpoints of In the early 1950s, theta referred the data were analysed the right theorists and experimentalists. The to the meson which decays into way. experimentalists are full of prob two pions, whereas tau referred Very soon. Jack and his collabo lems, looking for solutions — to the one decaying into three rators (R. Budde, M. Chretien, money problems, managerial prob pions. Experiments showed that J. Leitner, N. Samios and M. lems, scheduling problems, etc. these mesons had different intrinsic Schwartz) had their results, and On the other hand, the theorists parities (behaviour under mirror the data were published even be think they already have the ultimate reflection), but on the other hand fore Yang and I published our the solution and that there is no prob had the same lifetime and the same oretical paper on parity non-con lem. Superstrings may well be the mass. This was the puzzle. servation. There was a suggestion theory of everything (TOE), but My first efforts were all on the that mirror symmetry was being how about calculating things like wrong track. In the summer of violated in hyperon decays, but the Higgs mass, quark-lepton 1955, Jay Orear and I proposed because of the limited statistics, masses, etc? Therefore, instead, a scheme to explain the puzzle no conclusion could be drawn. I would like to go over our experi within the bounds of conventional Nevertheless, except for the high ence and try to extract not the theory. We suggested a cascade standard of Jack and his group, laws of physics, but the laws of mechanism, which turned out to this might have been claimed as physicists. be incorrect. the first indication of parity non- We all know that to do high The idea that parity (left/right conservation. energy physics requires accelera symmetry) is perhaps not con However, on the theoretical side tors. When each new accelerator served in the decay of these parti there was still the question of par is proposed, theorists are em cles flickered through my mind. ity conservation in ordinary beta ployed like high priests to justify After all, strange particles are by decay. In this connection, about and to bless such costly ventures. definition strange, so why should two weeks later, I had the further Therefore it pays to look at the they respect parity? The problem good fortune of having Yang join track record of theorists in the was that, after you say parity is me. This led to our discovery that, past, to see how good their pre not conserved in these decays, in spite of the extensive use of dictions were before experimental then what do you do? Because if parity in nuclear physics and beta results. Looking at the important parity non-conservation exists only decay, there existed no evidence discoveries made in particle phy in theta/tau, then we already have at all of parity conservation in any sics for more than three decades, all the observable facts, namely weak interaction. it is of interest to note that, with the same particle can decay into Several months later followed the exception of the antinucleon either two or three pions with dif the decisive experiments by and the intermediate bosons W ferent parity. I discussed this pos C. S. Wu, E. Ambler, R. Hayward, and Z°, none of these landmark sibility with Yang, but we were D. Hoppes and R. Hudson, at the discoveries was the original reason not able to make any progress. end of 1956, on beta decay, and given for the construction of the So we instead wrote papers on by R. Garwin, L. Lederman and relevant accelerator. parity doublets, which was another M. Weinrich and by J. Friedman When Lawrence built his 184 wrong try. and V. Telegdi on other decays. inch cyclotron, the energy was From then on we entered the thought to be below pion produc The breakthrough (1956) modern period: theta and tau be tion. Therefore, after the cyclotron came the kaon, the transformation was turned on, even though pions In 1956, I had second lucky properties of beta decay were final were produced abundantly, for a break, this time because Jack was ly determined, and the weak inter long time nobody noticed them. my colleague at Columbia. Dis action was unified with electromag- The progress of particle physics cussing with him the definitions of netism in the electroweak picture. is closely tied to the discovery of
CERN Courier, January/February 1987 Galaxy of Physics Nobels at Columbia in March to mark the 60th birthday of T.D. Lee and the thirtieth anniversary of parity (mirror symmetry) nonconservation — left to right S. Chandrasekhar (1983), J. Cronin (1980), I. Rabi (1944), T. D. Lee (1957) andS. Ting (1976).
(Photo Joe Pineiro, Columbia)
resonances, which started at the bution? But as it turned out, when In order to achieve that, we must Chicago cyclotron. Yet even the the energy increases the angular have good experiments. great Enrico Fermi, when he pro -distribution of proton-proton colli We now come to my second posed the machine, did not envis sions no longer remains flat and law of physicists: 'Without theo age this at all. After the unex becomes quite uninteresting. In rists, experimentalists tend to pected discovery of the first nu stead, it was production and decay falter/ cléon resonance, for almost a year dynamics of strange particles that A good example is the history Fermi expressed doubts whether put the Cosmotron on the map. of the Michel parameter, which it was genuine. We could go on and on, and the governs the shape of the spectrum A similar story can be told about same pattern would repeat itself. or the electrons produced in muon the next landmark discovery. When This leads to my first law of phy decay. the Cosmotron was constructed sicists: 'Without experimentalists, It is instructive to plot the exper at Brookhaven, some of the leading theorists tend to drift.' There is imental value of this parameter theorists thought that the most no reason for us to believe that it against the year when the meas important high energy problem will change, nor should we expect urement was made. Historically it was to understand the angular dis too much from our present theo began with zero and then slowly tribution of proton-proton colli rists for the prediction fo the fu drifted upwards; only after the sions, which remains mysteriously ture. theoretical prediction in 1957 did flat even at a few hundred MeV, The density of great discoveries it gradually become 0.75. Yet, it although at that energy the dynam per unit time is quite uniform and is remarkable that at no time did ics of the collision are quite com averages out to about one in two the 'new' experimental value lie plicated ; many different levels are years. Let us hope that this long outside the error bars of the pre all involved. Why should they con standing record of constant rate ceding one! spire to make a flat angular distri of discovery can be maintained.
12 CERN Courier, January/February 1987