Nothingness: The Science of Empty Space

  • Henning Genz
Perseus Books: 1998 340pp $30, £20.95

If you tried to empty a box, by taking out all the material objects inside it, sucking out the air with a super-efficient pump, and cooling it towards absolute zero to eliminate thermal radiation, what would you be left with? An empty space, but is that nothing or something? If something, the box is not really empty, but if nothing, how could it be said to exist at all? These semantic puzzles about the void or vacuum intrigued the ancient Greeks. Some, like Aristotle, denied that the vacuum was a coherent concept. Others, like the ancient atomists, thought it necessary to allow the atoms to move about and change their configurations.

In this new translation of a German text published in 1994, a theoretical physicist, Henning Genz, has had the happy idea of linking these ancient discussions to the subsequent history of scientific investigation of the vacuum, such as the seventeenth-century studies of Evangelista Torricelli, Otto von Guericke and Robert Boyle, and the nineteenth-century ether theories of electrical, magnetic and optical phenomena. This leads on to modern theories of the vacuum described by quantum field theory, with exotic phenomena such as vacuum fluctuations, virtual particles, the Casimir effect, the mysterious Higgs field — supposedly responsible for spontaneous symmetry breaking of the vacuum state — and much else besides. So the vacuum of modern theoretical physics is seething with activity, and is very far removed from nothing!

While the idea of such a book was a happy one, its execution leaves much to be desired. Genz fails to cover both key issues from history and important recent developments. The history is sloppy, largely reliant on secondary sources. There is no sense of the subtlety of the arguments of the ancient Greeks. Indeed, they are made to look just stupid and ignorant. Nearer our own times, names are misspelt and dates inaccurate — the most glaring howler is the remark that Einstein's paper on the photoelectric effect dates from 1900 (it was 1905). The translation is clumsy and in the bibliography the works of Plato and Galileo, for example, are still cited in German editions.

In explaining the physics, Genz uses no equations (other than E = mc2) and the level of exposition is much below the standard of Scientific American. Some of the cosmological discussion is well done but some of the explanations are quite baffling. I defy anyone to follow the discussion of the Michelson-Morley experiment, where the motion of the source and the motion of the observer are systematically confused. There is some discussion of Mach's principle, but I was unable to discern whether the author thought that general relativity exemplified it or not. There is passing reference to vacuum solutions of the Einstein field equations, but no adequate discussion of their significance.

In explaining vacuum fluctuations, Genz deploys familiar arguments in terms of the creation and annihilation of virtual particles. But the fact that free fields also exhibit vacuum fluctuations shows that interactions are not really the source of the problem, which lies, more accurately, in the fact that the global vacuum is irreconcilable with a local vacuum in relativistic quantum field theory, the direct opposite of the situation in nonrelativistic quantum field theory.

Moreover, Genz gives no discussion of the recent literature on the Bell inequalities and the Einstein-Podolsky-Rosen argument for the incompleteness of quantum mechanics, in the context of relativistic quantum field theory. These exciting developments throw much light on the possible interpretations of vacuum fluctuations in relativistic quantum field theory.

In summary, Genz's project is thoroughly worthwhile, but it is to be hoped that someone better qualified will make a better effort on some future occasion.