The Casimir Effect: Physical Manifestation of Zero-Point Energy by K A Milton, World Scientific, ISBN 9810243979 $87/£58.
In 1948 Hendrik Casimir showed that, according to quantum electrodynamics (QED), two parallel conducting plates should exert a force on each other - an effect that now bears his name. This force, according to one of several possible interpretations, is a direct result of the existence of zero-point vacuum fluctuations of the electromagnetic field. In simple terms, as the plates are placed closer and closer together, more and more modes of the electromagnetic field are excluded, with a corresponding reduction in the (admittedly infinite) amount of zero-point energy between them and an associated (and, amazingly, finite) attractive force. Similar effects occur whenever boundaries are placed in the vacuum, and all are collectively considered to be manifestations of the Casimir effect.
Milton's book reviews this remarkable phenomenon from a theoretical viewpoint. Starting with parallel conducting plates, he goes on to extensions to different geometries; partially conductive and dielectric materials in place of conductors; the relation to van der Waals forces; dimensions more and less than the usual 3+1; contributions due to fermion fields; finite temperature effects; radiative corrections; and implications for hadronic physics and even cosmology.
With all these calculations and applications one might imagine that the Casimir effect would be well understood, but hardly anything could be further from the truth. For example, Casimir forces can be repulsive; they tend to expand a spherical shell, which is by no means intuitively obvious and in fact is a bit of a pity. Anticipating a force of the opposite sign, Casimir had hoped that they might supply the Poincaré stresses needed to stabilize a model of an electron as a tiny spherical shell of charge, and even lead to a calculation of the numerical value of the fine structure constant.
If the sign of the Casimir effect for a spherical shell is somewhat surprising, what happens in other cases can be even stranger. Change a spherical shell to a cubical box and it still tries to expand, but make it a long thin rectangular box and it tends to collapse. Go to an even number of space dimensions and the force on a hyperspherical shell becomes infinite. It's all wonderfully bewildering.
Perhaps the most interesting recently recognized manifestation of the Casimir effect - if indeed that's what it is - is the phenomenon of sonoluminescence, in which an acoustically tickled bubble of air in water releases visible light in 100 picosecond bursts. While the jury is still out on what exactly is going on, there are calculations suggesting that this could be due to a dynamical version of the Casimir effect in which vibrations of the bubble excite the QED vacuum. Here, however, the theory is much more difficult to work out, and different approximations lead to wildly differing estimates of how big the effect ought to be.
The Casimir effect is about a lot more than a force between two metal plates, and Milton's book offers a great opportunity to read about it and learn the techniques by which it can be calculated. My one criticism of the book, which is probably not really fair given that the author is a theorist, is that it would be beneficial to have a discussion of the techniques by which the effect is observed in the laboratory. That said, the book is very comprehensive, clearly written and filled with wonderful physics.
John Swain, Northeastern University.
Quantum Electrodynamics by V Gribov and J Nyiri, 2001 Cambridge University Press (Cambridge monographs on particle physics, nuclear physics and cosmology no. 13), ISBN 0521662281, £55/$80.
This short book is based on the lectures of Vladimir Gribov that were given in Leningrad in 1974. It was completed, after his death in 1997, by his collaborator Julia Nyiri and it provides a pleasant introduction to the basics of field theory and quantum electrodynamics (QED). One of the book's strengths is its intuitive and relatively leisurely introduction to quantum field theory (QFT) via the Feynman propagator and diagram approach that is particularly suited to students on their first approach to the forbidding machinery of modern QFT. Indeed, in its treatment of elementary but fundamental topics - such as the construction of the scattering amplitude; the relation between causality, unitarity and analyticity in the Mandelstam plane; and tree-level processes such as the Compton effect or soft electron bremsstrahlung - it can be compared to two of the best older texts on quantum electrodynamics - Feynman's own book of this title and the volume on QED of the Landau and Lifshitz series. Unfortunately it also inherits deficiencies from its origins in the early 1970s.
Though the last two chapters discuss radiative corrections in QED and some aspects of renormalization theory, such as Ward identities, no mention is made of the central topic of the renormalization group, either in its older Gell-Mann-Low form or in the more modern Wilsonian guise within the effective field theory picture. Thus there are no anomalous dimensions of operators or running couplings as encapsulated in beta-functions - apart from what the student may find rather confusing remarks on the "zero charge problem". Without these crucial tools a student is ill-prepared to explore the deeper properties of quantum field theory.
In addition there is no discussion of spontaneous symmetry breaking, the Higgs mechanism, Yang-Mills theory, ghosts, dimensional regularization, anomalies, or the operator product expansion. Therefore none of the physics of the theory of the strong or weak interactions can be discussed. So sadly, despite its pleasing and pedagogical introduction to the basics of QED, it can't compete with modern quantum field theory texts, such as Peskin's "Introduction to Quantum Field Theory", as a full introductory course. However, I can recommend it as an enjoyable basic supplement to more complete texts.
John March-Russell, CERN.
A Century of Physics by D Allan Bromley, Springer-Verlag New York, ISBN 0387952470, $59.95.
Senior statesman of US physics, Allan Bromley, has chosen the centenary of the American Physical Society to offer an illustrated review of the last 100 years of physics. At various times in his career, Professor Bromley has been president of the American Physical Society, the American Association for the Advancement of Science and the International Union of Pure and Applied Physics. He was also founder of Yale's nuclear structure laboratory, and is Sterling professor of the sciences and dean of engineering at Yale. All of these achievements make him very well qualified to present a successful and accessible overview of 20th-century physics.
Pictures are the stars of this book, bringing the highly readable narrative to life. The reader's eyes are spoiled by images such as that of J Robert Oppenheimer and Edward Teller shaking hands, despite their well publicized differences. The great advances in accelerators are brought home by the picture of the original Cockcroft-Walton machine, and the hilarious photo of Isidor Rabi cooking hot dogs on the coil head of the Columbia cyclotron demonstrates not only that cooling technology has improved over the years, but that physicists can have a delicious sense of humour.
What A Century of Physics necessarily lacks in depth, it more than makes up for in breadth. After covering events from the early part of the century, such as the Annus Mirabilis of 1932 and the Manhattan project, Bromley moves on to discuss post-war physics. He covers subjects as diverse as superconductivity and the evolution of computers, and he explains the Standard Model and covers the research activity of laboratories all around the world.
At the end of the book, Bromley draws connections between particle physics research and cosmology. In the book's final breath, he goes back to the start of it all. Ten unanswered questions conclude his report, opening the door to a new century of physics.
Montserrat Capellas Espuny, CERN.
Books received
Quantum Chaos Y2K proceedings of Nobel Symposium 116 Bäckaskog Castle, Sweden, 13-17 June 2000, eds K-F Berggren and S Åberg. ISSN Royal Swedish Academy of Sciences 00318949 (02811847), ISBN Royal Swedish Academy of Sciences 9187308932, ISBN World Scientific 9810247117, £56.
Strings, Branes and Gravity lecture notes from the Theoretical Advanced Study Institute in Elementary Particle Physics 1999 (TASI 99) edited by Jeffrey Harvey, Shamit Kachru and Eva Silverstein, World Scientific, ISBN 9810247745, £91.
Symposium of North Eastern Accelerator Personnel, Oak Ridge National Laboratory, US, 25-28 October 1999, edited by D K Hensley et al. World Scientific, ISBN 9810244665, £58.
Lectures on Quantum Chromodynamics by Andrei Smilga, World Scientific, ISBN 9810243316, £22.