sign in sign up
<<
Home , John Stewart Bell, Steven Weinberg

In the Dirac tradition

The late - 'a way of looking at things so they appear not so mysterious'.

It was who cast quantum into the form we now use, and many generations of theo­ reticians openly acknowledge his in­ fluence on their thinking. When Dirac died in 1984, St. John's College, Cambridge, his base for most of his lifetime, institu­ ted an annual lecture in his memory at Cambridge. The first lecture, in 1986, attracted two heavyweights - Richard Feynman (see page 1) and Steven Weinberg. Far from using the lectures as a platform for their own work, in the Dirac tradition they pre­ sented stimulating material on deep underlying questions. (The lectures - 'Elementary Parti­ cles and the Laws of ' by Richard P. Feynman and Steven Weinberg - are published by Cam­ bridge University Press.)

Richard Feynman

When I was a young man, Dirac was my hero. He made a break­ through, a new method of doing tic . However, cles, then to get the new wave- physics. He had the courage to the puzzle of negative energies that function from the old you must put simply guess at the form of an the equation presented, when it in a minus sign. It is easy to de­ equation, the equation we now call was solved, eventually showed monstrate that if Nature was non- the , and to try to in­ that the crucial idea necessary to relativistic, if things started out that terpret it afterwards. Maxwell in his wed quantum mechanics and relati­ way then it would be that way for day got his equations, but only in vity together was the existence of all time, and so the problem would an enormous mass of 'gear . Once you have that be pushed back to Creation itself, wheels' and so forth. idea, you can do it for any spin, as and God only knows how that was I feel very honoured to be here. Pauli and Weisskopf proved, and done. With the existence of anti­ I had to accept the invitation, after therefore I want to start the other particles, though, pair production all he was my hero all the time, and way about, and try to explain why of a particle with its be­ it is kind of wonderful to find my­ there must be antiparticles if you comes possible, for example with self giving a lecture in his honour. try to put quantum mechanics with electrons and positrons. The mys­ Dirac with his relativistic equa­ relativity. tery now is, if we pair produce an tion for the electron was the first Working along these lines will electron and a positron, why does to, as he put it, wed quantum me­ permit us to explain another of the the new electron that has just been chanics and relativity together. At grand mysteries of the world, na­ made have to be antisymmetric first he thought that the spin, or mely the Pauli exclusion principle. with respect to the electrons which the intrinsic angular momentum The Pauli exclusion principle says were already around ? That is, why that the equation demanded, was that if you take the wavefunction can't it get into the same state as the key, and that spin was the fun­ for a pair of spin one-half particles one of the others that were already damental consequence of relativis­ and then interchange the two parti­ there ? Hence, the existence of par-

CERN Courier, April 1988 27 Huntington Vacuum Positioners

LARGEST SELECTION OF and a variety of mounting de­ POSITIONING SOLUTIONS VACUUM POSITIONERS vices providing tilt, rotary, or If your positioning problem Huntington offers the vacuum linear for any flange- cannot be solved by any of the industry's largest selection of mounted source. wide range of devices already bellows-sealed and magneti­ on the shelf at Huntington, tell cally coupled positioning de­ In addition, Huntington has de­ us about it. Whether the solu­ vices for ultrahigh-vacuum and veloped a range of coaxial and tion is an innovative modifica­ high-vacuum applications. multimotion feedthroughs and tion or an entirely new concept, accessories for gripping, hold­ Huntington is ready to help. MULTIMOTION ing, heating, cooling, and PERFORMERS transferring samples within the For information on several The positioning possibilities vacuum environment. newly patented positioning include X-Y-Z precision manipu­ devices and for current prices, lators; rotary, linear, and an­ call Huntington today. gular motion feedthroughs;

Huntington* Laboratories, Inc. • 1040 LAvenida, Mountain View, CA 94043 • (415) 964-3323 • (800) 227-8059 FAX (415) 964-6153 -Telex 592328 -TWX 910 379-6944 • Easylink 62-795443

28 CERN Courier, April 1988 Steven Weinberg - looking for principles with a greater sense of inevitability. tides and antipartieles permits us to ask a very simple question : if I make two pairs of electrons and positrons and I compare the ampli­ tudes for when they annihilate di­ rectly or for when they exchange before they annihilate, why is there a minus sign ? All these things have been sol­ ved long ago, in a beautiful way which is simplest in the spirit of Di- rac with lots of symbols and opera­ tors. I am going to go further back to Maxwell's 'gear wheels' and try to tell you as best I can a way of looking at these things so that they appear not so mysterious.'

Steven Weinberg

'I am very grateful to St. John's College and to the Cambridge Ma­ thematics Faculty for inviting me here to speak in honour of Paul Di- rac. I was much in awe of him when as a student I learned of his great achievements. Later I had the privilege of meeting Dirac a few times, and I still am very much in awe of him. It's really quite a chal­ lenge to give a talk in honour of so great a man, and in planning it I felt we will discover some day in the movement toward greater simplici­ that it would not be appropriate to future ?' ty. It's not that the mathematics speak about anything less than a First of all, let me say what I gets easier as time passes, or that great subject. I am going to jump mean by a final underlying theory. the number of supposed elementa­ over all details, and speak about Over the last few hundred years ry particles necessarily decreases what is for people working in my scientists have forged chains of ex­ every year, but rather that the prin­ own area of physics the greatest planation leading downward from ciples become more logically cohe­ question of all: 'What are the final the scale of ordinary life to the in­ rent ; they have a greater sense of laws of physics ?' creasingly microscopic. So many of inevitability about them. My collea­ Well, not quite. Much as I would the old questions - Why is the sky gue at Texas, John Wheeler, has like to honour Dirac by presenting a blue ? Why is water wet ? and so predicted that, when we eventually transparency on which I have writ­ on - have been answered in terms know the final laws of physics, it ten the final laws of physics, in fact of the properties of atoms and of will surprise us that they weren't I am not going to be able to do . In turn, those properties have obvious from the beginning. that. My real topic must necessarily been explained in terms of the pro­ I don't know if we will ever get be more modest. It will have to be perties of what we call the elemen­ there; in fact I am not even sure 'What clues can we find in today's tary particles : quarks, , that there is such a thing as a set physics that tell us about the shape gauge and a few others. At of simple, final, underlying laws of of the final underlying theory, that the same time there has been a physics. Nonetheless I am quite

CERN Courier, April 1988 29 Hermetisch geschlossen hOte&hOtesse Kein Stopf buchsarger Keine Wartungsprobleme TUNON un metier different. drfferents metiers Tounsme *H6tellerie Relations publiques Salons internationaux Die • Stages pratiques durant sichere la scolarite pres de 100 employeurs Membran de stages en references • Aide au placement Dosierpumpe • Initiation a I'informatique Fur alle umweltgefahrdenden, kritischen Fluide (ubelrie- • transfert entre nos chende,giftige, radioaktive.aberauch sterile oder abrasive). 23 ecoles In vielen Ausfuhrungen fur nahezu alle Betriebsanforderun- gen. Auch mit "Remote-Head". Forderstrome von 5 ml/h bis uber 100 m3/h, Drucke bis 3500 bar. Mit der patentierten LEWA-Sandwichmembran bietet sie ein HochstmaG an Betriebssicherheit. A GENEVE 1967-1988 Weitere Informationen: Broschure D 2-200 bitte anfordern. ECOLE INTERNATIONALE GROUPE PONDE EN 1964 HERBERT OTT AG ENSEJGNEMENT PRIVE Missionsstrasse 22, Postfach, CH-4003 Basel 2, rue Vallin 1201 Geneve Tel.(022) 32.83.20 J Telefon 061 / 25 98 00, Telex 964 562 (hoc) Accelerator Engineers & Technicians

CEBAF, now under construction in Newport News, Virginia, ELECTRICAL will be a 4 GeV, high-intensity continuous wave electron ac­ Construction of a large RF power system, a state-of-the-art ac­ celerator based on superconducting RF technology. The ac­ celerator control system, instrumentation and control for com­ celerator will provide a unique capability for the detailed study plex experimental equipment, and power supplies for conventional and superconducting magnets. of nuclei. MECHANICAL The challenges of building this facility offer great potential for Construction of cryogenic equipment for superconducting professional growth for engineers and technicians in thefol- cavities, superconducting magnets for spectrometers, con­ lowing areas: ventional magnets for beam transport, and other complex ex­ perimental apparatus. CRYOGENICS CEBAF is located in a pleasant mid-Atlantic coastal location Construction of the two largest 2 K refrigeration systems in near Colonial Williamsburg and the Chesapeake Bay. For theworld. Projects include a 5 kW,2 K refrigerator, 1.5 km prompt consideration, please send resume along with salary of transfer line, contamination detection, and acryogenic test history to: Employment Manager, CEBAF, 12070 Jefferson facility for production and R&D testing. Avenue, Newport News, VA 23606.

The Continuous Electron Beam Accelerator Facility An Equal Opportunity Employer, M/F/H/V

CERN Courier, April 1988 sure that it is good for us to search though we could predict how every chaos. And of course it's even for them, in the same way that molecule in a glass of water would more true for sciences outside the Spanish explorers, whey they first behave, nowhere in the mountain area of physics, especially for pushed northward from the central of computer printout would we find sciences like astronomy and biolo­ parts of Mexico, were searching for the properties of water that really gy, for which also an element of the seven golden cities of Cibola. interest us, properties like tempera­ history enters. They didn't find them, but they ture and entropy. These properties I'm also not saying that elemen­ found other useful things, like have to be dealt with in their own tary is more impor­ Texas. terms, and for this we have the tant than other branches of phys­ Let me also say what I don't science of thermodynamics, which ics. All I'm saying is that, because mean by final, underlying, laws of deals with heat without at every of its concern with underlying laws, physics. I don't mean that other step reducing it to the properties of physics has a branches of physics are in danger molecules or elementary particles. special importance of its own, even of being replaced by some ultimate There is no doubt today that, ul­ though it's not necessarily of great version of elementary particle timately, thermodynamics is what it immediate practical value. That is a physics. I think the example of is because of the properties of point that needs to be made from thermodynamics is helpful here. matter in the very small. But we time to time, especially when ele­ We know an awful lot about water don't doubt today that thermody­ mentary particle come to molecules today. Suppose that at namics is derived in some sense the public for funds to continue some time in the future we came from deeper underlying principles their experiments. to know everything there is to of physics. Yet it continues, and The realistic hope of finding a know about water molecules, and will continue to go on forever, as a small set of simple principles that that we had become so good at science in its own right. The same underlie all of physical reality dates computing that we had computers is true of other sciences that are back only sixty years, to the ad­ that could follow the trajectory of more lively today and in a greater vent of the great revolution in every molecule in a glass of water. state of excitement than thermody­ physics which Paul Dirac put in its (Neither will probably ever happen, namics, sciences like condensed final form, the revolution known as but suppose they had.) Even matter physics and the study of quantum mechanics.'

People and things

A.H. Wapstra has been appointed Bill Ash steps down as On people Knight of the Order of the Lion of the CERN Courier's correspondent the Netherlands. From 1970 to at the Stanford Linear Accelerator Julius Wess of Karlsruhe and Bruno 1983 he was Director of the Insti­ Center, where he took over the slot Zumino of Berkeley receive this tute for Research from Lew Keller in 1984, continu­ year's Dannie Heineman Prize for (IKO), now the Nuclear Physics Di­ ing the West Coast tradition of en­ for 'crucial vision of NIKHEF, as well as being lightened but refreshingly informal contributions to the discovery and Professor at Delft Technical Univer­ despatches. He was also the first development of , a sity. correspondent to communicate profound extension of the notion of with us via electronic mail. His space-time symmetry, that may un­ place is taken by physicist and au­ derlie unification of the fundamental Quantum theorist John Stewart Bell thor Michael Riordan, whose book forces'. The two theorists collabo­ of CERN receives an honorary 'The Hunting of the Quark' was rated on this work in the CERN D.Sc. from Queen's University, Bel­ published by Simon and Schuster Theory Division in 1973. fast, Northern . in the US last year.

CERN Courier, April 1988 31