The problem which quantum gravity addresses is the apparent gap separating two of the fundamental ideas of modern science: Einstein's theory of general relativity, which deals with matter on the largest scale (planets, solar systems, galaxies) and matter on the smallest scale (atoms and subatomic particles). Smolin has been closely involved in the attempt to reconcile these two seemingly disparate descriptions of the world, and this book is in part a personal account of his search, though it is also a general survey of where the subject stands today. As Smolin remarks in an Epilogue, one of his motives in writing is to explain why this work is worth while. It's essential to do this, he says, because funding for cosmological research will ultimately only be forthcoming if the public is convinced that it matters. On this evidence, it certainly does.
Smolin confronts the question of how science relates to religion head-on in his first chapter, whose theme is that there is nothing outside the universe. "This is not to exclude religion and mysticism, for there is always room for these sources of inspiration for those who seek them. But if it is knowledge we desire, if we wish to understand what the universe is and how it came to be that way, we need to seek answers to questions about the things we see when we look around us. And the answers can involve only things that exist in the universe." Having set out his position in this way, he then goes on present a masterly account of present-day thinking about his subject. This involves the reader in a fairly demanding intellectual journey that takes in, among other topics, black holes and string theory. All these are highly mathematical subjects, but Smolin manages to explain them using hardly any equations. Non-mathematical readers will have to take it on trust that translating these ideas into words hasn't resulted in too much distortion or over-simplification, but Smolin is confident that such a translation is possible. He is a skilled popularizer, in the best sense of that term, as readers of his earlier book, The Life of the Cosmos, will already know.
It's as well that Smolin writes so clearly, because the idea that he leads up to at the end of the book is dramatically counter-intuitive. Most of us are familiar by now with the notion that Einstein showed that our everyday three-dimensional space is not exactly Euclidean on the large scale, but Smolin explains that, according to quantum gravity theory, it need not have been three-dimensional at all. The fact that it has this characteristic is, apparently, serendipitous. This is a consequence of another idea: that space, like matter, is not continuous but has an atomic structure. The central insight to which modern theorizing about quantum gravity tends thus involves a radical rethinking of our most basic ideas about the world.
Since near-Euclidean space is only one of a myriad possible geometric arrangements of space that might have existed, the fact that we live in such a world requires to be explained. Here we find ourselves facing another aspect of the by now familiar Anthropic Principle: why is the universe so improbably arranged as to make life possible? The quantum theory of gravity is not yet complete, but, if it is successfully built, it may explain why the universe has to be as it is. If it doesn't, Smolin says, "then the mystic who said that God is all around us will turn out to have been right. But if we find a scientific explanation of the existence of space, and so take the wind out of the sails of such a theistic mystic, there will still remain the mystic who preaches that God is nothing but the power of the universe as a whole to organize itself. In either case the greatest gift the quantum theory of gravity could give the world would be a renewed appreciation of the miracle that the world exists at all, together with a renewed faith that at least some small aspect of this mystery may be comprehended." Smolin here appears to favour a form of pantheism, much like that advocated by Spinoza.
This is actually a rather dangerous area for scientists to get into. A few years ago we were constantly reading claims that modern physics and ancient mystics, especially those of Far Eastern provenance, were all saying the same thing. The alleged resemblances, however, were often rather superficial, and didn't stand up to serious criticism. I think that Smolin has avoided falling into that trap. He has written a most stimulating book, one that will appeal to people who seek to preserve a sense of the numinous without venturing beyond the boundaries of science. But transcendentalists will no doubt remain unmoved, for no amount of scientific argument will persuade them that God is not totally outside the universe.
%T Three Roads to Quantum Gravity
%A Smolin, Lee
%I Weidenfeld and Nicolson
%G ISBN 0-297-64301-0
%P viii + 231 pp
%K Physics, cosmology