Hidden Worlds: Hunting for quarks in ordinary matter by Timothy Paul Smith, Princeton University Press, 拢17.95/$24.95, ISBN 0691057737 Reviewed by Alan Martin
THE physics of the very large and the very small captures the imagination. Astronomy, cosmology and particle physics all draw people to want to understand more about science. But there鈥檚 a catch. Astronomy and cosmology have visual appeal; when reading about them we almost feel we share in the discoveries. Particle physics, however, appears more abstract and less accessible inspite of its crucial role in understanding the early stages of the evolution of the Universe. It is harder to convey the beautiful things that have been learned.
We may be told that the building blocks of matter are quarks of six flavours (up, down; charm, strange; top and bottom) and six leptons (the electron and its five partners). Our everyday world, however, is made of only the up and down quarks and the electron, which arrange themselves into three families, each with very similar properties. Why nature chooses to make one heavier copy of itself, and then a second one that is heavier still, is one of the great puzzles of science. The particle accelerators at Fermilab near Chicago and at CERN near Geneva have (or will have) enough energy to produce all these particles and, more importantly, to see if other types of particles exist, such as the Higgs boson and supersymmetric particles that are postulated and favoured by theorists.
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Hidden Worlds concerns the first family. It steps back from the high-energy frontier to explore how the up and down quarks bind together to form the proton and neutron, the constituents of the nucleus at the centre of the atom. Timothy Paul Smith nicely describes purpose-built lower-energy particle accelerators specially designed to probe how the quarks dance around to form these well-known nuclear constituents. Here the author, a key player in one of these experiments, is on familiar territory. Smith tells how experiments are conceived to address problems, how groups of scientists are formed, funds acquired and measurements made.
Although we have compelling evidence that quarks exist, we cannot seen them directly: hence the title of the book. There is a well-established theoretical framework 鈥� quantum chromodynamics or QCD 鈥� for describing how quarks interact through the exchange of gluons. QCD is based on another attribute of quarks, and gluons, whimsically called colour. It is ironic that QCD is much more difficult to apply at intermediate energies than at high energies. Smith describes how, at present, we have to resort to models such as the constituent quark model, and how experiment may guide our theoretical understanding. As well as flavour and colour, quarks have another attribute, spin. It is in the discussion and manipulation of spin and colour that misconceptions and errors creep into the text.
Smith gives us a series of extremely readable and well- chosen analogies to explain the science. His relaxed style makes for an enjoyable read. Provided the misconceptions are corrected, this could be a useful addition to the popular literature on particle physics.