Of all the particles detected so far by physicists, neutrinos are the most difficult to find. This is not because they are rare – far from it. Billions of neutrinos produced in nuclear reactions deep inside the sun pass through each square centimetre of your skin every second. But that’s the trouble: they pass through just about everything. In 1930 the physicist Wolfgang Pauli postulated the existence of neutrinos to explain anomalous features of nuclear interactions and was so confident that they would never be detected directly that he promised a case of champagne to anyone who could do the trick. In 1956, when neutrinos were indeed detected, he made good his promise.