BOOK REVIEW / Quantum leap of model professor: 'The Quark and the Jaguar' - Murray Gell-Man: Little Brown, 18.99 pounds

MURRAY Gell-Man is probably the most important living scientist. Yet outside the small world of high-energy physics he is better known for his contributions to the English langauge than for his theoretical discoveries. It was Gell-Man who in 1963 lifted the term 'quark' from James Joyce's Finnegans Wake ('Three quarks for Muster Mark') to stand for the basic units in his theory of matter. His other coinages include the fundamental property of 'strangeness', which led to his 'eightfold way' of classifying elementary particles and eventually to the theory of quantum 'chromodynamics'.

This taste for whimsical phrases should not obscure the substance of his achievements. With the late Richard Feynman, his colleague at the California Institute of Technology, Gell-Man led the postwar search for the simplicity behind the confusing behaviour of high-energy particles and he was awarded the Nobel Prize in 1969 for his work leading up to the quark theory.

Feynman and Gell-Man were rivals as much as collaborators. In person they cut contrasting figures. Where Feynman was an insistent nonconformist, who flirted with women, Californian mysticism and the bongo drums, Gell-Man was the model of a modern university professor. Always a dominant figure in the physics community, he is now, in his mid-sixties, about as great and good as it is possible for a scientist to be: a founder and leading light of the Sante Fe Institute (a New Mexico think-tank devoted to the study of 'simplicity and complexity'), a director of the huge John D and Catharine T MacArthur Foundation, and much involved with the World Resources Institute, Project 2050, the UN environment programme, and so on.

The Quark and The Jaguar, Gell-Man's first book, is written for a general audience and decribes his many current interests as well as the theories that made him famous. The middle part of the book is devoted to modern physics, but it is preceded by a long section on randomness and complexity in nature, and followed by a discussion of biological and cultural evolution. A final section offers some eminently sensible proposals on how to preserve the diversity that evolution has bequeathed us.

Theoretical physicists are the intellectual aristocrats of science. The problems they face are ill-defined and mathematically intractable. In trying to solve them, they cut corners and fudge like the rest of us, but at a level of mathematical abstraction accessible to only a few. They use intuition and feel to cut through the mathematical clutter and reach a sense of how things ought to behave. It is amazing that these procedures work at all. But the fantasies of theorists like Gell-Man are often triumphantly confirmed by subsequent experiments.

This ability to anticipate nature by sheer brain-power can breed arrogance, and it is not unusual for physicists to view all other intellectual disciplines as so much hot air. Although most of this book covers well-trodden ground in biology and cognitive science, Gell-Man is sparing with references to anyone but his current research associates, almost as if he thinks that nobody made any progress on these topics until he and his colleagues at Santa Fe decided to take a hand. Still, he writes extremely clearly, and the points he covers are of interest in their own right.

The best part of the book is the section on modern physics, where Gell-

Man sketches not only the modern theories of matter that he helped to build, but also his most recent work on the understanding of quantum mechanics. Quantum mechanics is the foundation of all modern physics, but it is an embarrassment to physicists because they can find no mechanism to explain the random jumps that are characteristic of quantum phenomena.

Gell-Man and his most recent collaborators cut through this problem by proposing that the quantum world does not really jump at all. It just seems that way from our limited human perspective. In reality, however, the universe is continually and smoothly branching into different histories. The past as we know it is just one branch on the tree of universal history. There is an infinity of other branches, on many of which human history took a different course, and on even more of which human life did not evolve at all. The nature of each branch is determined by the 'frozen accidents' which separated it from the others, and communication between branches is prevented, in practice but not principle, by their 'decoherence'.

This is heady stuff, but Gell-Man's account of it is curiously muted. Instead of emphasising the oddity of this picture, he presents it as if it were nothing but common sense, and the conventional idea of a unique world- history a mere confusion. One has the impression here of the scientific politician keeping the theoretical visionary on a leash. Successful scientists are those who make their ideas seem obvious, rather than eccentric, and Gell-Man has been as successful as anybody else in modern physics. But there is nothing wrong with eccentricity in popular writing. Gell-Man's unusual mind has led him to an extraordinary vision of the universe. It is a pity he feels a need to hide this under his cloak of respectable normality.