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The Cosmic Microwave Background - Rhodri Evans ****

In the preface to this book, Rhodri Evans describes cosmology as ‘understanding the beginning, evolution and nature of the Universe’. Probably every culture in human history has made a stab at doing this. What sets modern cosmology apart, however, is that it’s based on physical observations rather than metaphysical speculations. In a nutshell, that’s what this book is about – a chronological history of observational cosmology from the renaissance to the present day.

The first chapter describes how careful observations by successive generations of astronomers gradually built up an accurate picture of the structure and scale of the solar system, followed by the extension of the cosmic distance scale to other stars in the Galaxy. The second chapter deals with the rapid progress made during the early decades of the 20th century in understanding the structure and dynamics of the Galaxy, the distances to other galaxies, and the expansion of the universe. A lot of the material in these first two chapters will be familiar to many popular science readers, but it serves as a useful reminder and scene-setting for the rest of the book.

It goes without saying that observations of stars and galaxies are relevant to cosmology. It’s less obvious that low level, high frequency radio noise is too. Yet it turns out that the Cosmic Microwave Background (CMB) is critical to our understanding of the universe – so critical, in fact, that it features in the book’s title. It makes its first appearance in Chapter 3, and remains at or near centre stage for the rest of the book.  Originally predicted as an observable consequence of the Big Bang hypothesis, the CMB was detected experimentally in 1965. As well as supporting the Big Bang model, it provides a unique insight in the structure of the very early universe. When the COBE satellite (the subject of Chapter 4) detected spatial fluctuations in the CMB in 1992, Stephen Hawking described it as ‘the scientific discovery of the century, if not of all time’!

The last three chapters cover all the most recent developments in observational cosmology, from space missions like WMAP and Planck to the search for gravitational waves and cosmic neutrinos. There’s ‘the most surprising astronomical finding of the century’ – the discovery in 1998 that the expansion of the universe is speeding up rather than slowing down, leading to the suggestion that as much as 75% of the universe might consist of an unknown form of ‘dark energy’. Even more controversial was the announcement in March 2014 of ‘B-mode polarization’ in the CMB – supposedly evidence for an inflationary phase that occurred when the universe was just a trillionth of a trillionth of a trillionth of a second old!

This is a popular science book that is eminently suitable for general readers. The emphasis is almost entirely on observations, not theory – which should come as a relief to most people, because theoretical cosmology is notoriously mathematical! Any worries that the reader is expected to have some kind of mathematical knowledge is dispelled early in the first chapter, when the author spends a page and a half carefully explaining what an ellipse is. As with any good popular science book, there is almost as much about the people who made the discoveries as about the discoveries themselves. There are even accounts of Captain Cook in Tahiti and Captain Scott in Antarctica – both of which, surprisingly enough, played a peripheral role in the history of our understanding of the universe!

The reason I want to stress that this is a popular science book is that, from a quick glance, it doesn’t look like one. The fact that it comes from an academic publisher (Springer), that it has abstracts at the start of each chapter and no index at the back, and that sections and subsections are numbered hierarchically, all make it look like a rather dry postgraduate text. But that’s not the case at all, and it would be a shame if these little quirks put off a non-specialist reader who might otherwise enjoy it. The fact is that it’s as readable and engaging an introduction to observational cosmology as you could hope to find. The book’s only fault is its price, which at £31.99 is twice what it ought to be.

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Review by Andrew May

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