An Infinity of Worlds - Will Kinney ***

There is something rather odd about this book on cosmic inflation. Will Kinney assumes a considerable amount of foreknowledge in the reader - for example, he uses electron volts as a unit of energy without unpacking the concept and throws in everything from 'the unification of strong and electroweak forces' to 'the Hawking radiation of black holes' as if these are topics with which the reader will be comfortably familiar, no explanation needed. The problem with this is, if you know that much, you are probably pretty clued in on the basics of cosmic inflation too, so I'm not sure who the target reader of this book is. This is not helped by a series of light cone-based diagrams that convey nothing much at all.

Inflation is a strange subject. It's a patch to fix the Big Bang theory so it can cope with the way that the universe is unexpectedly homogenous and flat (in the sense of (not) curved space), a patch that has limited evidence to back it up. Kinney emphasises where inflation makes confirmed predictions, but also notes that it has its failings - it's the kind of topic where speculation tends to be piled on speculation. An Infinity of Worlds does quite a good job of explaining the nature of inflation, but, as tends to be the case in books on this topic, it is less successful on making symmetry breaking and eternal inflation accessible and comprehensible.

Kinney sometimes throws aspects of current theory into the mix without justifying them. So, for example, a lot of the early discussion in the book is based on the cosmological principle without saying why we should assume the cosmological principle holds. It's just given as a sort of cosmological axiom. The book is also strangely selective in what it questions. We read in the preface that Kinney 'has chosen to give short shrift to theories of modified gravity…' - but it seems odd to treat dark matter in this way when the whole basis of the book - inflation - is described as 'a highly speculative idea'. The degree to which dark matter is also speculative and only partly matches observation, yet is built into the assumptions, really ought to have been included.

Overall, then, some interesting content, but An Infinity of Worlds is unlikely to satisfy either the beginner wanting to understand inflation from scratch, or someone who has already read widely and wants a more hands-dirty exploration of inflation's nuts, bolts, context and failings.

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Review by Brian Clegg - See all of Brian's online articles or subscribe to a weekly digest for free here