Driving forces who live in the fast lane

Facts and Mysteries in Elementary Particle Physics
March 12, 2004

Elementary particle physics began in 1897 when J. J. Thomson discovered the electron. It advanced through the discoveries of protons and neutrons in the atomic nucleus, quarks in protons and neutrons, neutrinos, heavier varieties of the electron and finally, about 20 years ago, the W and Z particles, the heavy cousins of photons.

What is an elementary particle? Martinus Veltman gives a typically pragmatic definition: "We call a particle elementary if we do not know of a further substructure." Less modestly, Veltman claims the epithet fundamental for elementary particle physics. Other advances in physics, for example the discovery and explanation of superconductivity, are, he says, advances in "width" not "depth". Some people would question this distinction. It was the understanding of superconductivity that inspired the theory of the "standard model" of particle physics.

Whatever the definition of particle physics, Veltman's book is a lucid introduction to it. His approach is clear, practical and down to earth. He describes experiment as well as theory, and is usually careful to anticipate readers' possible misconceptions. There are nice line drawings, enhanced by the use of colour. Equations are avoided or may be skipped over. The treatment should be accessible to any sixthformer or undergraduate with a scientific bent and willingness to concentrate and, indeed, to anyone with enough motivation. More experienced scientists will find all sorts of things to interest them.

An unusual and delightful feature of the book is a set of about 90 page-long thumbnail sketches, with photographs, of most of the heroes of the subject. These are often enlivened by Veltman's personal experiences, and afford occasions for his puckish humour. I like the photograph of Steven Weinberg failing to convince the sceptical Veltman of something (I wish we were told what). There are also photographs illustrating experimental techniques. Veltman is careful to give credit where it is due, for instance, to the brilliant but not-so-well-known theoretician Ernest Stuckleberg. Also, he writes: "If there is one group of people that has made all progress possible, it is the group of laboratory directors, accelerator engineers and applied physicists."

Veltman generally combines exposition of physics with a brief history of its development. One episode described in particular detail is the experiment at the European laboratory Cern in 1963 on the interactions of a high-energy neutrino beam. Neutrinos are so unreactive that they can easily pass through the earth. Nevertheless, each day about 15 "events" were seen in which a neutrino interacted with a proton and so turned into other particles. According to Veltman, opportunities were lost in the interpretation of the data gathered. Perhaps Cern's greatest success came 20 years later when the W and Z particles were discovered.

Any popular exposition of particle physics must somehow explain a little about special relativity and quantum theory, as they provide the framework for the whole subject. Veltman deals with quantum theory in about 14 pages, focusing on the two-slit experiment. Relativity takes a similar space, concentrating on the connection between energy and momentum. It is typical of Veltman to take a few pages to "demystify" Einstein's notorious E=mc2.

Another rather abstract idea central to modern particle theory is that of gauge invariance, which is difficult to explain without mathematics.

Veltman avoids it altogether. He derives the right interplay of particles and their interactions from the requirement that interactions should not grow too fast at high energies.

Particle physics is largely done using machines to accelerate particles to high energies. Since the 1950s, the energies attained have (as Veltman illustrates with graphs) increased roughly tenfold every 15 years or so.

The machines have got bigger, increasing in size from metres to tens of kilometres. They have also got more expensive and produced more data (the worldwide web grew out of the need to distribute some of this information).

Since the early 1980s, there has been somewhat of a lull (except for the discovery of the top quark), waiting for new machines to start up and perhaps find the Higgs particle. Anyone who thinks that string theory has, in the meantime, shown the way that particle physics is going gets short shrift from Veltman. Supersymmetry and string theory are "figments of the theoretical mind", he writes.

The only thing I might wish different about the book is that it could have been a little longer, to include for instance CP breaking. This would have fitted in quite well with the general style. Also, Veltman is cautious about accepting the evidence for neutrino mixing, although this (assuming it is right) is one of the more exciting finds of the past few years.

Veltman is a top physicist (he got a Nobel prize in 1999), and he has written an authoritative and distinctive book that will inform and entertain a variety of people.

John C. Taylor is emeritus professor of mathematical physics, University of Cambridge.

Facts and Mysteries in Elementary Particle Physics

Author - Martinus Veltman
Publisher - World Scientific
Pages - 340
Price - £33.00 and £13.00
ISBN - 981 238 148 1 and 149 X

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