text: Pontecorvo was never able to prove his theory, but he was on to something with his thinking. In 2002, results from an experiment conducted 2100 meters underground at the Sudbury Neutrino Observatory proved and supported Pontecorvo's theory and discovered that neutrinos released from the Sun can in fact change form or flavor because they are not completely massless. This discovery of neutrino oscillation solved the solar neutrino problem, nearly 40 years after Davis and Bahcall began studying solar neutrinos.