A cat and frogs in tiny taffeta pants

In 1944 Erwin Schrodinger published What is Life? in which he discussed the question "how can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?" His conclusion was as follows: "The obvious inability of present-day physics and chemistry to account for such events is no reason for doubting that they can be accounted for by those sciences." Schrodinger's broad-ranging, multidisciplinary book stimulated and influenced many scientists including both Francis Crick and James Watson, and it is the inspiration for molecular microbiologist Johnjoe McFadden. Although Schrodinger was wrong in detail - DNA had yet to be identified as the basic genetic material - he had high-lighted the puzzling physics of life. In homage to Schrodinger, the first chapter of McFadden's book is titled "What is life?" The influence of Schrodinger does not end there - the paradox of his simultaneously dead and alive cat is central to the argument. For McFadden, it is the ability of a system to make its own quantum measurements that provides an answer to Schrodinger's question.

This book has an ambitious agenda. The contents break down into three main topics: neo-Darwinism, quantum mechanics, and finally, life and consciousness. These constitute a huge sweep of science. It is impossible for one person to be an expert in all these fields. Nevertheless, if you have a speculative explanation for the emergence of life and consciousness, how can you get it published? This book is McFadden's answer to this problem. Armed only with quantum superpositions, quantum decoherence and the quantum Zeno effect, he proposes a quantum "anthropic multiverse" to explain the emergence of the first primordial replicator. He then suggests that living cells are distinguished by their ability to make internal quantum measurements and produce directed actions. He ends by speculating that the induced electromagnetic field of the brain could be the basis of consciousness.

There are already many wonderful expositions of Darwinism, but McFadden's account of evolutionary theory - from "black smokers" and "resurrection plants" to Darwin's "gemmules" and Lazaro Spallanzi's experiments on frogs wearing "tiny taffeta pants" - is both interesting and informative. While emphasising the "overwhelming molecular evidence that all modern species have evolved from earlier species", he identifies three problem areas for the neo-Darwinian process: the existence of distinct protein families, the emergence of complex metabolic pathways, and heretical "adaptive mutations" that can be influenced by their environment. One of McFadden's central themes is the contrast between the directed movement of individual particles in biological processes and the random, statistical movement of billions of particles underlying the second law of thermodynamics. Unfortunately, his account of Maxwell's Demon omits its denouement: Charles Bennett and Rolf Landauer have shown that it is not measurement that generates entropy but the erasure of information.

McFadden's discussion of quantum mechanics is a little irritating (but perhaps this is the personal reaction of a rival "populariser"). Nonetheless, his stress on Bohr's concept of "complementarity" is curious - complementarity is not even mentioned in the classic texts on quantum mechanics by Dirac and Feynman. Even Einstein had difficulty in defining what it was, referring to: "Bohr's principle of complementarity, the sharp formulation of which I have been unable to achieve despite much effort I have expended on it." McFadden relies on Heisenberg's uncertainty principle for many of his qualitative explanations. This is fine, but the energy-time uncertainty relation is not on the same footing as those for "conjugate operators" such as position and momentum. These are minor quibbles, although the text would have benefited from more diagrams.

His major purpose in these chapters is to present a detailed discussion of the problems of quantum measurement. Again, though in more emotive language than is comfortable, McFadden gives a fairly accurate account of the present state of affairs - apart from re-locating Cern's Large Hadron Collider accelerator from Geneva to Mont Blanc. "Many worlds", quantum computers and a quantum version of Zeno's paradox are other essential components of the argument. A significant omission is any account of recent experiments by Serge Haroche and Jean-Michel Raimond, who have staked a claim to have "caught decoherence in the act".

The last four chapters contain McFadden's attempt to apply quantum principles to molecular evolution and cell biology. The problem here is his familiar use of quantum decoherence. This is a process about which most physicists would admit to some ignorance, especially in respect of quantitative calculations. For example, I find it difficult to estimate the plausibility or otherwise of the existence of a "quantum peptide chain" as a quantum superposition. I am not comfortable with statements such as "the emergence of the self-replicator nailed the growing peptide chain to a classical reality". Similar remarks apply to his suggestions that life is a quantum cell capable of measurement in the presence of an appropriate environment, and that quantum evolution provides an explanation for adaptive mutations.

The last chapter is an extended speculation about a possible quantum basis for consciousness and he assesses an alternative suggestion by Stuart Hameroff and Roger Penrose for a central role for microtubules as "the neurobiological equivalent of walking on water". Nevertheless, despite my reservations, McFadden has succeeded in putting together an intriguing tale that is reminiscent of Schrödinger's earlier attempt to understand the physical basis of life.

Tony Hey is professor of computation, University of Southampton.