The remarkable history of the discovery of neutrino oscillations

The experimental observation of neutrino flavour oscillations took place some 30 years after they had been first proposed, and even then came about principally as a result of an anomalously low value in the measurement of the electroweak mixing angle, resulting in the possible validity of the minimal SU(5) grand unification scheme and the prediction of proton decay. In turn this led to underground experiments which failed in their original objective, but were to discover – purely as a background – the oscillatory behaviour of neutrino flavour, due to a fortuitous fourfold coincidence in the values of the neutrino mass differences, the Earth’s radius and magnetic field and the tiny value of the Fermi constant.