Splinters of Infinity - Mark Wolverton ****

Many of us who read popular science regularly will be aware of the 'great debate' between American astronomers Harlow Shapley and Heber Curtis in 1920 over whether the universe was a single galaxy or many. Less familiar is the clash in the 1930s between American Nobel Prize winners Robert Millikan and Arthur Compton over the nature of cosmic rays. This not a book about the nature of cosmic rays as we now understand them, but rather explores this confrontation between heavyweight scientists.

Millikan was the first in the fray, and often wrongly named in the press as discoverer of cosmic rays. He believed that this high energy radiation from above was made up of photons that ionised atoms in the atmosphere. One of the reasons he was determined that they should be photons was that this fitted with his thesis that the universe was in a constant state of creation: these photons, he thought, were produced in the birth of new atoms. This view seems to have been primarily driven by religious beliefs, posing an ongoing creation in opposition to the decline of the universe into heat death championed by British physicists such as James Jeans and Arthur Eddington.

By contrast, Compton believed that cosmic rays were produce by atomic decay and consisted of charged particles, which he initially thought were primarily electrons, originating from the outer reaches of the atmosphere. In principle it was possible to distinguish between the two theories by checking whether there was a variation in cosmic ray levels as you headed from the equator to the poles: the path of charged particles would be influenced by the Earth's magnetic field, but photons would not.

Wolverton gives us chapter and verse of the many (many) expeditions to detect cosmic rays around the world, using increasingly sophisticated technology, and deploying the detectors on everything from round the world cruise ships to record-breaking balloon ascents. He also, more than is commonly the case in such books, brings in commentaries from (US) newspapers. As Wolverton points out, while today we may be more aware of Shapley and Curtis's debate, back then the cosmic ray debate garnered far more publicity and interest from the public, in part because it was spuriously tied in with the concept of nuclear power and the imaginary potential for practical use of cosmic rays as an energy source.

The very name 'cosmic rays' (coined by Millikan) has a wonderfully 1930 science fiction feel to it, but what makes the whole thing more interesting is the clash between two major scientists that did at times become quite heated. While Millikan was without doubt a significant scientist, he comes across as a major self-publicist who regarded cosmic rays as his domain - at some points even refusing to acknowledge the work of Compton and others, and clinging on to his theory long after it became unsupportable. If anything, Wolverton is rather kind to Millikan, toning down the negative aspects of his personality and self-centred view of science.

The biggest problem with this book is that for chapter after chapter the content can be summarised as 'more of the same'. We get lots of details of the various expeditions, pronouncements and how the newspapers covered them (with hilarious bias from the Los Angeles Times in favour of local boy Millikan). This detail is very welcome in giving a clear picture of the long, drawn out nature of this scientific argument, and how small incremental gains in data gradually changed the picture of what cosmic rays were - but it can feel a little hard work reading it all.

My other smaller complaint is that some of the references outside of the central characters and the US can seem a little adrift, particularly to a non-American reader. After mentioning J. J. Thomson, we are told that 'fellow Britisher Ernest Rutherford discovered...' - although New Zealand was not a fully independent country at the time, I wouldn't apply the term 'Britisher'. Similarly, it feels odd to describe James Jeans - a  Lancastrian whose main academic ties were to Cambridge - as having an 'Oxford accent'. This does reflect a newspaperish approach to the writing style throughout.

This is a genuinely interesting dive into a little-remembered scientific debate, leavened by much reporting from US newspapers. The slow resolution of the nature of cosmic rays reflects the realities of many scientific endeavours in opposition to the 'sudden dramatic discovery' school of science writing. And the contrasting personalities of Millikan and Compton make for an interesting reflection of the human nature of science. All in all, a worthwhile contribution to the popular science canon.

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