Here's a thought. Every second of the day, a hundred trillion neutrinos pass through your body – fortunately without effect. It's like drinking alcohol-free lager. Indeed, during your life, perhaps one neutrino will interact with an atom in your body, says astrophysicist Ray Jayawardhana in this absorbing, elegant history of the hunt to find the neutrino.
The particle – which has virtually no mass – may be "pathologically shy", he says, but it is also happens to be of immense importance to science for "whenever anything cool happens in the universe, neutrinos are usually involved". Today we use them to study supernovae and the births of black holes and to understand how matter first formed in the universe. Our past reliance on electromagnetic radiation – from radio waves to light to gamma rays – to study the heavens is now being supplemented by neutrino astronomy.
For good measure, studies of "the poltergeist particle" turn out to have practical potential. Some scientists plan to use neutrino detectors to pinpoint nuclear reactors that might be making illegal weapons-grade plutonium. Others want to use them to send and receive signals underground or through water.
The trick, of course, is to find ways to detect these elusive little entities, which – given the rarity of their interactions with normal matter – is not an easy business. Indeed, researchers have had to go to great pains to pinpoint neutrinos, constructing detectors deep underground so that spurious signals triggered by cosmic rays – which constantly batter Earth's atmosphere – do not produce false readings in their instruments.
The end result has been the creation of an array of extraordinary devices in some of the planet's most remote places: IceCube, which is made up of several thousand photo-detectors buried a mile beneath the south pole; the Super-Kamiokande observatory, which consists of a tank of 50,000 tonnes of ultra-pure water built beneath Mount Kamioka in Japan; and the Sudbury neutrino observatory, which is situated more than a mile underground in Creighton mine, operated by Vale, in Sudbury, Ontario, Canada.
To date, these detectors have spotted only modest numbers of neutrinos. Nevertheless, these observations have been of enormous importance, showing that when huge stars erupt as supernovae, they emit vast amounts of neutrinos in ways that have precisely confirmed astronomers' theories about the nuclear reactions involved in these stellar explosions. Future observations should provide further insights.
The neutrino was originally postulated, in 1931, almost as "a form of scientific witchcraft", says Jayawardhana. "When scientists couldn't account for energy that went missing during radioactive decay, one theorist found it necessary to invent a new particle to account for that missing energy," he adds. The theorist was the physicist Wolfgang Pauli.
Many other scientists were dubious – including the Nobel laureate Paul Dirac and British astronomer Sir Arthur Eddington – because every effort to detect neutrinos invariably produced negative results. Then in 1953, two US scientists, Frederick Reines and Clyde Cowan, showed – in an experiment they dubbed Project Poltergeist – that gamma ray bursts observed by their instruments must have been caused by neutrinos colliding with atoms inside their detectors. The neutrino had been uncovered. Reines was eventually given a Nobel prize in 1995. Cowan had died 21 years earlier.
It is an intriguing story, deftly told by Jayawardhana with commendable brevity and clarity. The Neutrino Hunters is comprehensive without being overburdened with detail or weighed down with too much theory, while the book's neat pen portraits of the men and women who tracked down the poltergeist particle give it added depth. Think of this as a great ghost story and a thumping good piece of science writing rolled into one.
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