Robert Lambourne welcomes a lucid account of the latest theory of the origin of the universe.

Despite its name, the big bang theory does not suggest that the universe began with an explosion at some point in space. There was no initial “kerpow !”

The universe produced by such a singular event would have a centre and would still be expanding outward from that special point. In contrast, our universe, though certainly expanding, appears to be doing so in a uniform fashion. On a cosmic scale, distant galaxies are spreading out evenly from every point, not just streaming away from a single location. There is expansion, but it has no unique centre.

The real success of the big bang theory is in showing how a complicated universe such as ours could develop from an earlier, plainer state that had the simplest credible composition and the same high temperature and density everywhere. The theory’s greatest shortcoming is that it provides no real explanation of the origin of this improbably uniform initial state. The conventional assumption used to be that the universe just started out that way - unlikely as that may seem.

The need for such a clearly unsatisfactory assumption was removed in the early 1980s when the classical big bang theory was augmented by cosmic inflation. According to this widely accepted proposal, tiny regions of the very early universe have a natural tendency to expand at a rate far greater than that supposed by the conventional big bang theory. If this happened, the whole of the visible universe - everything we can currently observe - might have originated in a microscopically small region of the very early universe. The uniformity of the big bang’s initial state would then no longer be a mystery; prior to inflation our universe would have been contained in such a small region that its uniformity would have been quite natural.

Now, in The Inflationary Universe, the originator of inflation theory, Alan H Guth, explains how he made his discovery and tells what it was like, as a young untenured academic, to find himself at the centre of a revolution in cosmological thinking.

The story is an exciting one, since in addition to solving the riddle of uniformity, inflation also answers a bigger question: “Where did the matter comprising our universe come from?” The quantum processes that are supposed to cause inflation also lead to the formation of matter, making the universe, as Guth puts it, “a free lunch”.

Guth has always had a well deserved reputation as an outstandingly clear lecturer. His lucidity, often cited as one of the reasons for the rapid acceptance of inflation, is displayed to great effect in this outstanding work of popular science. Eight of its first nine chapters are devoted to the background needed to appreciate properly inflation, general relativity, particle physics and the cosmic microwave background radiation. All of these topics have been covered in other popular works, sometimes in more detail, but rarely so well. Guth’s reflective style is ideally suited to his demanding subject matter. The treatment is as simple as it can be, but no simpler.

Even better are the four chapters that follow. These form the core of the book. They set out the circumstances that led to the breakthrough, and the announcement of the observational evidence that supports it. Guth himself had such a flimsy background in cosmology that he hardly seems to have recognised the magnitude of his achievement. Realisation must have come in a rush, though, when Murray Gell-Mann, the Nobel prize-winning physicist, greeted one of Guth’s earliest presentations of inflation with the exclamation “You’ve solved the most important problem in cosmology!” Guth ends his book with three chapters devoted to more recent work on inflation. These are necessarily more skimpy and less satisfying than the earlier chapters, but they do have the merit of leaving the reader with a clear impression of the current status of inflation, and of the important observational tests to which it is likely to be subjected over the next 10 years.

The Inflationary Universe is not an easy read, but it is exceptionally well written and will reward serious study. The book has been long awaited by those familiar with cosmology. Now that it has finally arrived it seems set to become one of the classics of popular cosmology.

Robert Lambourne is acting head of physics at the Open University