Still seduced by the final theory

January 25, 2002

Brian Pippard looks for God between the arcs of a double rainbow.

Steven Weinberg is a distinguished physicist who has found time in recent years to write for a more general readership, and his books have been received with enthusiasm. The latest, reprints of articles and talks presented since 1988, is as lucidly written as ever, with a gentle humour that does not hide his strong convictions on science, philosophy and religion. I unreservedly recommend it, not only to scientists but to all who share his beliefs in the contribution that science has made, and will continue to make, to the way we see ourselves and our world. My recommendation is no less whole-hearted for not agreeing with him on some basic issues; they are matters of opinion rather than fact.

The most controversial themes (to my mind) that run through these essays concern human consciousness and religion, and their place in scientific thought. But let us look first at other pervasive themes that have excited antagonism in other quarters and that are introduced because of Weinberg's need to answer critics among scientists and science watchers; these relate to the ever-deeper probing of the fundamental laws of nature and to the part played by reductionism in science. They cannot, of course, be separated; to pursue fundamental laws one must neglect all the frills - the manifold variety of their operations in the everyday world - neglect indeed almost everything except those seemingly dry and mathematically intricate conceptions that physicists believe underlie the reality derived from direct observation. There is no need to stress how essential reductionism has been in the advance of science; Sir Isaac Newton's mechanics and gravitational theories were the springboard for two centuries of discovery, and the same may be said of his optics and what it led to. Yet, those who feel pleasure in learning of each successive refinement in, say, the theory of the rainbow do not in the least ( pace John Keats) forgo their enjoyment of the spectacle itself. They may enjoy it all the more because they appreciate, for example, why the sky is darker between the arcs of a double rainbow. One may argue in the same way that we do not probe the intricacies of Bach's counterpoint merely to be astonished at its intellectual power, but to experience in the music itself an entrancement of mind and spirit. The study of counterpoint is the reductionism of music, holism (as the term is commonly understood) is pop.

Although the central role of reductionism is hardly in dispute among scientists, there is less agreement that it gives special significance to the continued search for fundamental laws. Weinberg and his critics do not disagree on one important point, that you cannot proceed from these laws alone to derive the rules governing the behaviour of complex systems. As soon as more than a few particles interact, the equations that might be used to predict their behaviour from first principles would have more variables than any compu-ter could cope with; other tricks are needed. The normal process is to explain an observed phenomenon within its own set of concepts - superconductors by extending the theory of simple metals, simple metals by applying the quantum theory of atoms, atoms in terms of their constituent particles, and so on down to the deepest accessible levels. At every stage, large or small gaps of comprehension may open up and demand a corresponding exercise of imagination to bridge them; superconductivity was discovered in 1911 but an adequate explanation was only found in 1957, after many ingenious but abortive efforts. In the whole range of science, from string theory to the migratory habits of hippopotami, there are so many tiers of understanding that no one would wish to tackle more than a very few. At almost every level there is a lifetime of profit and enjoyment to be had by those with only moderate skill, as well as intellec-tual challenges that defy the most accomplished imaginations.

Very rarely indeed do the problems presented by complex systems suggest doubts about the fundamental theoretical structure, nor are the ideas and mathematical methods often transferred between one and the other. If many scientists are disquieted at the gene-ral interest excited by discoveries at the subatomic level or, at the opposite pole, in cosmology, the cause is largely resentment at the inordinate expense of the equipment - or, more precisely, a sense of deprivation because too much of the science budget is spent on work that employs a small proportion of research workers and has little impact on the thoughts of others or on technology for the benefit of ordinary citizens. It is easy to sympathise with both sides, even more with Weinberg and his colleagues now that the United States has abandoned its super-colli-der and funding bodies in the east and west begin to doubt whether the big machines give value for money. Yet Weinberg is surely right to see the triumphant history of the centuries-long quest for deep truth as one of the finest of human achievements, not to be lightly discarded. Even if this appeal carries no political weight, it should be remembered that great scientific ventures attract young minds; everyone will suffer if we cannot capture some of the best and then go on to show them the various excitements they may find.

So far, I am entirely with Weinberg. To turn to the points of disagreement, he, in company with many others, entertains Dreams of a Final Theory (the title of his 1993 book). He knows there are eminent (and less eminent) physicists who cannot believe the ultimate secrets will ever be tied into a neat bundle with no loose ends, and he is not so sanguine as to suppose that if it ever happens, it will happen soon. After all, should the fashion of string theory succeed in providing a coherent origin for every sort of force and particle, including gravitons, and we have to reconcile ourselves to entities in ten or more dimensions and by many orders of magnitude smaller than any other postulated object, questions will still remain; why only ten dimensions, and why do the basic equations take their particular form? Those driven to probe at the deepest (or most rarefied) levels will not be satisfied if they cannot show that the structure of our universe is logically and uniquely necessary; and if, like Weinberg, they are of an atheistic turn of mind they will accept no easy escape route signposted God.

It is not, however, only in the heights or depths that we face major obstacles. At the very heart of science and of all experience lies the fact of consciousness, for each of us the one sure reality that Descartes made the foundation of his philosophy. Without conscious thought we can have no science and yet, paradoxically, scientists have agreed to exclude conscious thought from their thinking. It is a source of strength in any branch of learning that it sets reasonable bounds to its ambition, and in science this is achieved by treating only such observations as can be agreed on by all observers and, ideally, repeated until there are no remaining doubts. An individual's thought is not such an observation. It is one thing for me and my friends to agree that we observe together the public manifestation of a private reaction - laughing at a joke, blushing at a faux pas - but I cannot experience the thought that provokes another's behaviour, nor can another experience mine. A symbol in science is the expression of an observable, and preferably measurable fact; or, not infrequently, it represents something unobservable (a wave-function, say, or an electric field strength) that is used to help the analysis but eventually eliminated from the result in favour of observable quantities. There are no symbols referring to private responses. Lacking the necessary language, one cannot imagine analysing the behaviour of a robot and concluding "it thinks"; at best one might find that it responds to every test "as if it thinks". Weinberg seems to believe that a full scientific appreciation of the "as if" aspect of behaviour might well lead in the end to incorporating into science the whole phenomenon of thought itself. I cannot agree. This is not to say that we may not eventually devise a philosophy that includes everything of science that survives criticism and also the central experiences of thought; but if that happens it will not be science but something so transcendent as to eclipse the huge adventure begun by Newton and his peers.

Without the benefit of such a breakthrough, scientists are in no position to affirm or deny the existence of God. We can, of course, point out discrepancies between facts as presented in holy texts and what we assert as a result of observation and theory. But this is a shallow game and Weinberg's concern goes deeper; to quote from his earlier book: "Will we find any sign of the workings of an interested God in the final theory? I think that we will not." The God of Weinberg's argument is interested - not the impersonal, detached creator whom he could hardly regard as separate from the "final theory". With this in mind, one can readily sympathise with him as he contemplates the enormities committed by the followers of diverse creeds, and feels that a universe designed to allow such things was ill designed indeed. But here he is responding as a human being, not as a scientist, and moreover takes no account of the opposite belief, amounting to certainty and held by men and women of the highest principle, in a caring God. What he has to say he says well, and it is worth reading, but it must not be read as the voice of science - science has no voice here. To avoid misconceptions, I must add that I write as a strict agnostic.

In comparison with these serious questions about the aims and limits of natural science, the arguments of some postmodernists - loosely summarised as "science wars" - seem rather trivial. Weinberg has little use for them and applauds the way they were dealt with by Alan Sokal's satirical paper, "Transgressing the boundaries", in the journal Social Text . He appreciates that this was much more than a naughty hoax, and contains sound analysis of the gulf between scientists and sociologists. Issues such as these are dealt with in several of the chapters and provide additional reasons for reading and enjoying the book.

Sir Brian Pippard is emeritus professor of physics, University of Cambridge.

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