Without a beer mat

Asking theoretical physicists to explain their work in layman's terms without using maths or excessive jargon can be a risky business. Few can resist the temptation to reach for the nearest envelope, beer mat or serviette and cover it with formulae. But Gerard 't Hooft, a leading light in theoretical particle physics, copes admirably in this personal and entertaining account of developments in the field since the late 1960s.

His book describes the enormous effort that has gone into developing theories to describe the world of subatomic particles and the known forces in nature, which led to the so-called standard model of particle physics. It does not attempt a historical overview nor is it an introductory textbook, although it does resemble one in some places. It is best enjoyed as a story of the development of theoretical ideas, packed with colourful analogies, lively anecdotes and personal reflections.

't Hooft begins his journey into the subatomic world by demonstrating that the laws of nature at the microscopic level are very different from the ones we are used to in everyday life. He does this convincingly through a series of clear analogies: from asking us to make aeroplanes from successively smaller pieces of paper until we are left with useless shreds, to Gulliver and his travels through the miniature and giant worlds of Lilliput and Brobdingnag.

Once familiar with this concept, we are guided through the laws of physics that are now needed in the subatomic world, where particles are not only tiny, but also travel close to the speed of light. This is the world of quantum mechanics and Einstein's theory of special relativity. 't Hooft began his career in particle physics as graduate student in Utrecht in 1970, a time when a plethora of particles had been discovered in experiments with cosmic rays and particle accelerators. The fundamental theory describing the interactions of the particles that feel the electromagnetic force, electrons and photons, had been hailed as a resounding success, predicting experimental results with stunning accuracy. In contrast, it was known that the theory that had been developed for the weak force, responsible for radioactive beta decay, was on shaky ground. The situation was even worse for the strong force which holds the nucleus together, where a whole range of inaccurate theories existed.

One of the book's most interesting sections is the inside account of how theorists tried and failed to apply the successful parts of the theory of electrodynamics to the weak and strong forces. As time passes, unsuccessful theories are are often forgotten and it is easy to forget the effort invested in them and their value in steering the way towards the solution.

't Hooft confesses that in comparison to his colleagues, he read little and thought lots. So despite running the risk of discovering something that was already known, he also acquired a very deep understanding of the problems. During a visit to a summer school in Corsica he was inspired to combine the work of Benjamin Lee and Kurt Symanzik with that of his thesis advisor, Martinus Veltman, and others. This led to his first major breakthrough, overcoming the technical problems of formulating a fundamental theory of the weak force. Despite the enormous impact this has had on particle physics, he remains extremely modest. A quality, he later reflects, many of today's physicists lack as they rush to claim international recognition.

Less well known is the significant contribution 't Hooft made to understanding the strong force. The American theorist, Murray Gell-Mann, had proposed that particles like the proton are made from smaller building blocks called quarks. Single quarks have never been detected in experiments - they always come in pairs or threesomes - because the enormous strength of the strong force ties them to their friends. But later results from experiments that probed deep within protons suggested that the underlying building blocks did behave like free particles. 'T Hooft was able to develop a theory which explained this apparent contradiction and which has become a cornerstone in the strong force theory. To his regret, he did not follow Symanzik's advice to publish his result and the textbooks now credit others with the discovery.

It is 't Hooft's personal reflections that make this book enjoyable. He recalls what were for him the glory days of physics, between 1970 and 1976, when many pieces in the puzzle fell into place and experimental results revealed that the details of the theory were much more accurate than were ever thought possible. He is also quick to acknowledge that today's understanding of particle physics has arisen through collaboration between experimenters and theorists.

The standard model of elementary particles which was based on these developments, has been phenomenally successful. Almost all of the high-precision measurements made in today's high-energy particle colliders are in agreement with the standard model predictions. Despite this, 't Hooft reminds us, particle physics is far from wrapped up. This mathematical model has been finely tuned to our current observations and may not be a valid description of particles created at even higher energies.

't Hooft believes that the new theories will be logical extensions of the current theory. His review and assessment of some of these extensions to the standard model - supersymmetry, grand-unified and string theories - does become a bit hair-raising at times (he admits that his publisher and friends warned him that parts of the book were almost unintelligible!). He then speculates on the social and scientific implications of an all-encompassing "theory of everything" from which all laws of physics could be derived.

The book provides an interesting insight into the development of particle physics theories in the 1970s which are now taken for granted. 't Hooft's metaphors make complicated ideas seem reasonable and no doubt will appear in many popular articles. My only criticism is that these analogies, likening certain kinds of particles to silly putty and vampires, may suggest that this is a good introductory book for the layman. There is too much jargon and too many new ideas packed into a small book for a beginner. However, for the general reader who has developed an interest in particle physics, physics students and even the professional physicist it is definitely worth reading.

Valerie A. Noyes is a research fellow in the Particle and Nuclear Physics Laboratory, University of Oxford.