What is life?
We are all patterns, dynamically evolving ones, but patterns nonetheless. There is nothing special about the individual atoms that constitute our bodies. They could all be replaced by other atoms of the same kinds, and neither we nor anyone else would notice the difference. So what is it about our particular arrangement of atoms that makes us alive and our distinctive selves? Indeed, what is life? Erwin Schrodinger addressed this latter question head on in the celebrated set of lectures that he delivered at the Dublin Institute for Advanced Studies in 1943. His classic text What is Life? based on the lectures, was published the following year and seems to have been in print in one form or another ever since. The edition to be reviewed, which also includes Schrodinger's Mind and Matter and Autobiographical Sketches, plus a foreword by Roger Penrose, was first published in 1992 and is now in its 12th reprinting. As Penrose comments, What is Life? must rank among the most influential of scientific writings of the last century. It was written more than a decade before the discovery of the structure of DNA and both Francis Crick and James Watson, who received the Nobel Prize for the discovery, acknowledged the book as an early source of inspiration. Remarkably, however, many of the ideas, paradoxes and open questions raised by Schrodinger are still as apposite today as they were at the time. The book is wide ranging and considers, not just the physical/chemical nature of inheritance, but the nature of life and conscious awareness. Schrodinger opens by introducing the ideas of statistical physics and addresses the question 'Why are the atoms so small? which could, of course, equally well be expressed as 'Why are we so big? His answer is that, given the constant thermal jiggling of the atoms and molecules, and quantum indeterminacy, life can only be stable, governed by reliable physical laws, if the statistical averages are good, which in turn requires that the number of atoms be very large. It is one of his penetrating insights which yields a conclusion that, in retrospect, seems absolutely obvious. Although a lot was already known about heredity, and it was evident that the information to be inherited must be encoded in some way in the genes, it was unclear how that happened. Schrodinger argues cogently that the hereditary information must be carried by a molecule. On the scale of a gene, nothing else would provide the necessary stability. Furthermore, an 'aperiodic crystal' as he describes this molecule, would allow for the encoding of a sufficient number of possibilities with relatively few atoms. The stability of the molecule would derive from quantum mechanics, and mutations could be attributed to rare quantum transitions in its structure. He thus shows that the existence of such a molecule could account for the observations. Of course, it is now well known that his arguments were characteristically well aimed, and that the molecule in question is DNA. How can one define life? There are many different approaches, none satisfactory, but Schrodinger comments,