Subject Grouping: Praxis

by George Johnson (published by Knopf in the US: 0679437649, and by Jonathan Cape in the UK: 0224044273).

Murray Gell-Mann befriended me in Paris towards the end of my National Science Foundation postdoctoral junket and lured me to Pasadena. It was the year of the Eightfold Way, smack in the middle of Gell-Mann’s two-decade reign as emperor of elementary particles. His brilliance was so intense that lesser folk, such as myself and my sidekick Sidney Coleman, had to ration our time with him. Not only did Gell-Mann devise the lion’s share of today’s particle lore, but on first acquaintance you would soon learn, through his painfully in-your-face erudition, that he knew far more than you about almost everything, from archaeology, birds and cacti to Yoruban myth and zymology. He once drew a false etymology of avocado, but his errors were so rare as to be cherished.

This book is a brave attempt to interweave two stories. One is the history of particle physics according to Gell-Mann, from the development of quantum field theory to the fall of the Superconducting Super-Collider (which he lamented) and the coincidental rise of string theory (which he championed). The other is a must-read account of the life of a truly fascinating character.

Explaining particle physics to the lay reader is a labour of Hercules. Johnson strives magnificently but doesn’t always succeed. After a long explication of strangeness, he drops the ball by asserting that the Xi hyperon has strangeness +2. His exposition of the quark hypothesis is better: how they were invented and named by Gell-Mann; thought of independently by George Zweig, who called them “aces”, had his paper rejected and soon left physics; how Gell-Mann vacillated for years between the interpretation of quarks as helpful mathematical fictions or as real and observable particles (they are neither); how quarks acquired their “colours”, the change of which from patriotic to primary is given undue significance; and how they have become a crucial part of today’s Standard Model of particle physics.

However, bloopers like “the briefer a particle’s life span, the higher its energy”, “in quantum theory every particle can be represented by a differently shaped wave”, “neutrons and antineutrons [have] different spins” and the allegation that mesons are fermions will annoy physicist readers and mislead others. To explain the meaning of parity violation, Johnson asks how a radio message sent to Martians could tell them which side is the left. Two simple answers are given, but they are said to cheat or to “violate the spirit of the game”. Just what game is this?

Johnson portrays Gell-Mann’s family origins in Galicia and Austria, and his father’s difficult accommodation of life in the US, partly via his introduction of the curious hyphen. We see Gell-Mann evolve from an arrogantly precocious know-it-all, to a preppy pretender at Yale, to an aspiring then renowned theoretical physicist and, most recently, to a wealthy and charming curmudgeon with homes in Aspen, Santa Fe and Manhattan.

We follow his triumphant path through the reductionist subatomic world and his recent return to a childhood fascination with the richer world of “complex adaptive systems” consisting of such marvels as birds, jaguars and (says Johnson) the relationship between biographer and biographee. Along the way we learn how Gell-Mann wooed and wed two remarkable women, reared two difficult children and was almost jailed for receiving smuggled antiquities.

This tale of quarks and quirks is engagingly told, although Johnson often resorts to jarringly undocumentable quotations. He has Gell-Mann saying: “But I do know everything” to his classmates, “Where are the dotted eighth’s?” at a concert, “I would rather starve” to his father’s suggestion that he become an engineer, “The cross-sections are just details” to Dyson, “[Electromagnetism] doesn’t do dirty little jobs for people” to Fermi, and so on. Was Johnson there at the time, like Edmund Morris’s imaginary avatar who follows Reagan about in Dutch?

Much is made of the family’s rejection of their heritage: neither father nor son wished to be regarded as Jews. Gell-Mann once attributed his name to the confluence of two Scottish rivers. I recall another incident when, as we were wandering about Hollywood, Stanley Mandelstam read the Hebrew sign on a butcher’s shop and Gell-Mann immediately corrected his pronunciation of kosher. “I didn’t know you were Jewish,” said poor Stanley, to Murray’s pained “What? Me Jewish?” (Here I adopt Johnson’s conceit.) Why does Gell-Mann do this? Why does he refer to Israel as Palestine, and Jerusalem as the citadel of the Jebusites?

Another recurrent motif is Gell-Mann’s sometimes extreme difficulty in putting thoughts to paper. He was almost unable to complete his one book The Quark and the Jaguar,and he never did write up his Nobel lecture. However, Johnson errs when he relates Gell-Mann’s reluctance to disseminate his discovery of the Eightfold Way. The original version, a well circulated and often cited CalTech report, was created in just a few days.

In summary, I rather like this book. It explains why Gell-Mann is universally regarded as a great scientist, but only occasionally as a pompous prig. It describes his warmth and generosity toward his colleagues (Francis Low, Harald Fritzsch, John Schwarz and Yuval Ne’eman, among many others) and his problems with others (he alienated Zweig, belittled Julian Schwinger, detested Bram Pais, and his friendship with Dick Feynman turned sour). Most of all this book gives a new twist to the classic tale of a poor immigrant’s son from the Bronx making it big in the US.

This review first appeared in the June issue of the American Journal of Physics. Reprinted with permission. Sheldon Lee Glashow, who shared the Nobel Prize for Physics in 1979, has been Higgins Professor of Physics at Harvard since 1979. He is joining the faculty of Boston University as the first Arthur G B Metcalf Professor of Science.

by Howard Georgi (2nd edn) Perseus 0 7382 023 9.

It is fortunate that Howard Georgi has decided to publish a revised and updated version of his famous book Lie Algebras in Particle Physics, the previous edition having appeared in 1982. In this case it may have been a non-trivial problem to decide whether significant changes to the text are pertinent, because, as the author himself points out in the preface to the second edition, “this has been an extremely successful book”. Indeed, many generations of graduate students have learned from it the basic algebraic tools in SU and other such Lie algebras, which are at the core of the Standard Model and all of its conjectured extensions.

Besides a healthy evolution from old-fashioned typewriter fonts to modern LaTeX layout, the present edition includes numerous improvements in the presentation, as well as new material. Perhaps the most important piece of new material is an enlarged introductory chapter on finite group theory. This makes the book a little longer, but much more self-contained, because a lot of the group-theory jargon – such as conjugacy classes, characters and the role of the permutation group and Young tableaux – is introduced in a simple form, where the student can see the nuts and bolts explicitly.

Finite groups appear in many physics problems, so their absence from the first edition was somewhat unfortunate. On the other hand, in its present form the book can be used as a rather complete group-theory textbook for particle physics students.

One of the distinctive reasons for the book’s success had been the introduction of “physics-flavoured” chapters in which the algebraic techniques were put to work in simple yet important topics in high-energy physics. It is those physics chapters that have undergone comparatively major rewriting.

Keeping the essential outline of the first edition, one notes many changes in wording and emphasis, which reflects the author’s desire to suppress anecdotal information – such as the hadron tables of chapter XVII in the first edition, while at the same time making room for more useful theoretical applications. One good example is the description of algebraic constraints on the Higgs mechanism in various common unification models.

To summarize, the book’s contents have been improved while the basic philosophy – introducing the mathematical tools in a way as concrete and “calculational” as possible – is kept almost intact. Prof. Georgi has managed to maintain a fresh and direct “lecture notes” style – something that students and teachers will surely value.

by J Cole, Institut des Sciences Nucleaires, Grenoble, France. Institute of Physics Publishing, Bristol and Philadelphia 0750305126 (illus. hbk 368pp £80/$130).

This book covers statistical models applied to the decay of atomic nuclei with emphasis on highly excited nuclei, which are usually produced using heavy ion collisions.

by Lawrence Krauss, Basic Books, 04650337402.

Cosmology has a lot going for it at the moment. Unprecedented amounts of data characterizing the universe at almost every possible energy and lengthscale make it one of the richest scientific fields around. Theorists scramble to explain all of the disparate results, while experimentalists and observers push the limits of what, only a few years ago, was not thought possible. In the middle of all this activity, Lawrence Krauss’s book Quintessence(a re-edition of his 1989 Fifth Essence) arrives to assess what is going on.

There is a growing trend in astrophysical and particle cosmology to believe (or at least sell the idea) that cosmology is “solved”. Again and again researchers in the field say something like: “things are finally falling into place”,so that we now have a standard  model for structure formation. Often this represents a very theoretical and prejudiced view in selecting which data to believe.

Krauss himself embraces the latest high-redshift supernova results and consequent evidence for a cosmological constant as a confirmation of the “new standard cosmological model” that he developed with collaborators in the mid-1980s. He is not alone in doing this, but such an attitude seriously compromises the evolution of the field.

It is the glaring inconsistencies and the conceptually inexplicable fixes that we should be trying to tackle. For example, we assume that the universe is homogeneous (and we know that the cosmic microwave background is very smooth), but when we look atthe  distribution of luminous matter it is strongly clustered as far as we can see; we believe that galaxies follow the underlying distribution of mass, but when we try to compare catalogues of different galaxies we end up having to invoke biasing mechanisms to make them all consistent.

My view is that cosmology is opening up and complexifying, not closing down and focusing on an existing component theory. Having declared my prejudices when starting this book, the truth is that I enjoyed it a lot. Although Krauss does try to oversell the inflationary cosmology and the derived cold dark matter scenario, this theme does not dominate the narrative. He does a great job of explaining the existence of dark matter, critically assessing the different pieces of experimental evidence and ensuring that he can relate these results with understandable physical principles. Particularly impressive is his description of the cosmic virial theorem (relating the kinematics of systems of gravitating bodies with the overall underlying mass) and his careful attempts to explain freezeout and relic abundances.

Many of the fundamental concepts needed in contemporary cosmology are outlined in the book and I see it as a great source of explanations for a wider audience. It was inevitable that this book would be revised. When Krauss wrote The Fifth Essenceat the end of the 1980s, it was at the end of a decade of fruitless searches for cosmological relics (he relates the story of the “Cabrera Monopole”, which was never properly explained away).

The search for dark matter in the universe really took off in the 1990s, with bolometric and scintillation direct detection experiments being set up all over the world, the microlensing searches producing arguable evidence for clumped baryonic dark matter in our halo and the new weak lensing experiments mapping out the dark mass in clusters. Krauss systematically goes through these different technological advances, explaining why they happened and what scientific returns to expect. I particularly liked his description of the use of bolometric detectors in direct detection experiments, and his clear explanation of the phonon/ionization method used by the CDMS experiments at Berkeley. It conveys the beauty of experimental physics – how clever ideas and masterful work can really transcend physical limitations. Krauss has also done a reasonable job of avoiding the sociological folklore of characters and egos. He succumbs vary rarely, the most notable occasion being in his description of his work on WIMP detection and axions (and he likes Glashow’s quips).

The bottom line is that Lawrence Krauss has been able to give us a glimpse of an open,fascinating problem in physics that is far  from being solved: the existence and essence of dark matter. The book can be read by the layperson but is also useful for scientists and non-specialists in cosmology.