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A Visit to the Particle Zoo

John Huth

Facts and Mysteries in Elementary Particle Physics. Martinus Veltman. viii + 340 pp. World Scientific, 2003. Cloth, $48; paper, $19.

Elementary particle physicists seek to describe the functioning of matter and the fundamental forces of nature in the most comprehensive and unified fashion possible. To achieve this goal, they have had to develop a theory that encompasses extremes beyond normal human experience: things moving at velocities near the speed of light and objects that simultaneously behave as waves and as particles. The result, something called quantum field theory, provides a framework for describing the fundamental constituents of atoms and the forces affecting them. It rests on a great body of experimental work, which has shown, for example, that the irreducible building blocks of matter are quarks and leptons. Quarks make up protons and neutrons; the most familiar lepton is the electron. More-exotic species of subatomic particles are only produced in special circumstances that involve either high-energy cosmic rays or accelerators.

Martinus VeltmanClick to Enlarge Image

Currently, the "holy grail" for which many particle physicists are searching is the mechanism that imparts mass to particles. This quest has engendered some of the largest scientific collaborations ever, among physicists working with huge accelerators and massive detectors, which are required to probe the energy densities needed to explore the mystery of mass generation. A great deal has been learned from such collaborations, but many questions remain: For example, why are there three "families" of quarks and leptons? What is the mechanism that gives particles mass? And why do their masses vary so much?

For an overview of what particle physicists know and what they puzzle over, readers can now turn to Martinus Veltman's Facts and Mysteries in Elementary Particle Physics. The book is written for a lay audience, but even experts may discover interesting tidbits here. Veltman seamlessly combines historical and thematic descriptions of particle physics, an approach that allows the reader to appreciate how experiment and theory interrelate. Interspersed in the text are one-page biographies of many of the luminaries in the field, which include fascinating and sometimes bizarre details. For example, Veltman says that Erwin Schrödinger conceived his key ideas about quantum mechanics after being inspired by an erotic encounter.

Veltman shows how the foundations of modern particle physics lie in discoveries made many decades ago: observations of radioactivity, the constancy of the speed of light and the realization that matter behaves both as a wave and as a particle. After conducting many experiments, physicists have now arrived at a theory that encompasses three of the four fundamental forces of nature: the strong, weak and electromagnetic forces. Veltman describes much of this background in his introductory chapters.

Without the continual leapfrogging of theory and experiment, progress in elementary particle physics would have been impossible. So after considering some of the critical aspects of theory (quantum mechanics, special relativity and how they are woven together in our modern understanding), Veltman turns to the experimental tools of the trade: particle detectors and accelerators. In this section he often focuses on individual efforts, highlighting some that are not widely appreciated, even by many physicists. Examples include the development of so-called storage rings, in which counter-rotating beams of particles are used to produce the high energy densities required to make "exotic" forms of matter: that is, matter not ordinarily found under terrestrial conditions. The seminal idea for this important development came from the Austrian Jew Bruno Touschek, who in 1945 was shot and left for dead by an S.S. officer who thought that the physicist was resisting being sent to a concentration camp. (Veltman explains that Touschek was not in fact resisting Nazi orders; rather, because he was ill and weighed down with books, he simply fell to the ground.) Miraculously, Touschek survived and went on to help develop one of the most powerful tools in modern particle physics.

Veltman himself was an important figure in the development of the understanding of neutrinos. These are neutral, nearly massless particles, which are produced in stars as they burn hydrogen into heavier elements. Veltman and John Bell were two "house theorists" for a series of neutrino experiments at the European Center for Particle Physics. (Ironically, John Bell's contributions in neutrino physics were overshadowed by his work on the foundations of quantum mechanics, which he considered a hobby.) There was an intense and nearly theatrical competition between European and U.S. physicists to make progress in understanding neutrinos, and the resulting research provided important clues to how the weak interaction is unified with electromagnetism to produce a single "electroweak" force.

Veltman and Gerardus 't Hooft developed a mathematical procedure that allows finite results to be derived from the unified electroweak model, which otherwise would generate infinite answers in some situations, which make no physical sense. In doing so, the two men placed important constraints on the very nature of theories that one can even consider before aspiring to test them experimentally. This is a complicated subject for the layperson even to approach, yet Veltman gives readers a window to the goings-on that is remarkable for its clarity.

I found the book to be immensely entertaining, and I recommend it highly to anyone looking for insight into the nature of elementary particle physics. I should caution readers, though, that Veltman does assume some background in physics, roughly at the high school level.

My chief criticism is that the book almost entirely ignores the contributions of women to the field. For example, with the sole exception of Marie Curie, all of the mini-biographies included are portraits of men. This is not entirely Veltman's fault, as the field has been largely dominated by men. He does miss, however, important contributions from people such as Mary K. Gaillard, Emmy Noether and Madame Chien-Shiung Wu. A minor nit-pick is his tendency to make pronouncements on the worth of Nobel prizes (Veltman shared the 1999 Nobel Prize in Physics with 't Hooft for their work elucidating the quantum structure of electroweak interactions); this struck me as hubristic and I found it distracting. But I'm willing to grant Veltman an indulgence on these points, because he has produced an otherwise excellent portrait of a difficult field.—John Huth, Physics, Harvard University

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