A half-century with solar neutrinos (Nobel Lecture)

The Sun derives its energy from fusion reactions in which hydrogen is transformed into helium. Every time four protons are turned into a helium nucleus, two neutrinos are produced. These neutrinos take only two seconds to reach the surface of the Sun and another eight minutes or so to reach the Earth. Thus, neutrinos tell us what happened in the center of the Sun eight minutes ago. The Sun produces one-third as many neutrinos as predicted by the standard solar model of particle physics. The author's pioneering work proved that nothing was wrong with the experiments or the theory; something was "wrong" with the neutrinos, in the sense that they behave in ways beyond the standard model.