There have been many books on cosmology in recent years but this is one of the best. Timothy Ferris, a seasoned science writer, presents an up-to-date and very readable account of what we know, and don't know, about the universe; he also explains the reasons that have led cosmologists to their present views.
A recurrent theme, which we first encounter almost at the outset, is the correlation between the very large and the very small. The relativity specialists and the particle physicists seem to be coming together, their joint efforts promising to give rise to a unified theory of the universe. Thus the universe may (or may not) have originated from a singularity (a black hole), while the strings postulated by superstring theory may also be, in some sense, black holes.
Ferris presents a particularly good account of dark matter, that puzzling component of the universe which seemingly has to exist to account for the observed behaviour of galaxies yet which no one has identified convincingly. It is surely astonishing that, after all the work that has been done by astronomers, we still don't know what most of the universe is made of. This leads naturally to a discussion of the large-scale structure of the universe.
Although the divisions are somewhat artificial, astronomers have identified five levels of structures larger than galaxies: groups, clusters, clouds, superclusters, and supercluster complexes or walls. A sharp distinction can be drawn between clusters and all larger structures, but at a larger scale than clusters the nomenclature becomes somewhat subjective. Some cosmologists think that this structuring goes on for ever, at larger and larger scales; in other words, they suggest that the universe has a fractal geometry. However, Ferris says that this appears unlikely. How did all this structure arise as the universe developed? As usual there are no firm answers, but dark matter once again appears to be involved.
Ferris has a lot to say about the notion of inflation: the theory that the universe expanded exponentially during the first fraction of a second of its existence. He believes that this may be one of the most fruitful ideas in modern cosmology, partly because it provides elegant solutions for various cosmological puzzles or paradoxes. Actually, inflation comes in various flavours. 'Ordinary' inflation goes fast enough, but 'chaotic' inflation proceeds immeasurably faster: it provides a radius of the universe so huge that a complete university library would be needed to list all the zeros in the number describing its dimensions.
Towards the end of the book we come back to the relation between the very large and the very small. This inevitably requires Ferris to present an account of quantum indeterminacy. Many people have tried to do this in non-mathematical terms, but Ferris's method is as good as most. Instead of talking about 'real' properties of the electron such as spin, he uses arbitrary terms, calling the possible electron states sour/sweet and hard/soft. This works rather well. As for interpretations of quantum strangeness, he leans towards David Bohm's 'hidden-variables' theory, though he acknowledges its problematic nature.
There is a tendency for descriptions of cosmology to slide away into philosophy or even theology, and Ferris doesn't shirk this. The theme emerges in a long chapter on cosmic 'evolution'. There is a sense in which the universe may be said to evolve, but what connection, if any, does this have with biological evolution as described by Darwin? Is there such a thing as progress, or is it all in the eye of the beholder? These are deep questions, but it's good that Ferris is prepared to discuss them. Further deep questions are confronted in the final chapter, in which Ferris looks at the cosmological anthropic principle in its several versions and asks if there is any evidence that we are in some sense designed into the universe. The conclusion seems to be: yes, possibly.
This question, finally, brings us face to face with theology, which Ferris touches on in an afterword. Physicists who tackle this theme often appear philosophically and theologically naive, with a view of God that they seem to have acquired at Sunday School; Ferris's discussion is a lot better than this. He insists that the science of cosmology tells us nothing at all about God. Whether you believe in God, disbelieve, or are agnostic (as Ferris tells us he is himself), you cannot legitimately support your arguments from modern cosmology, nor will you ever be able to do so.
I would certainly recommend this book to readers who know little or nothing about modern cosmology, but I would also recommend it to those who have read a fair amount already. It doesn't provide much information that cannot be found elsewhere, but it brings a lot of material together in a convenient compass and it does so clearly and elegantly; Ferris is an excellent writer.