The discovery of the positron experimentally confirmed that the electron had a positively charged counterpart of the same mass. It vindicated a theoretical implication identified by J. Robert Oppenheimer in 1930 and helped establish the existence of antimatter as a physical possibility.

Theoretical Prediction

On February 14, 1930, J. Robert Oppenheimer completed “On the Theory of Electrons and Protons,” a paper drawing on Paul Dirac’s equation for the electron. Oppenheimer argued that the equation implied a positively charged particle with the electron’s mass. It could not be a proton; he identified the predicted particle as an anti-electron, later known as the positron. Dirac credited Oppenheimer with recognizing this implication of the equation.

Experimental Confirmation

In 1932, experimental physicist Carl Anderson proved that the positron existed. His result confirmed the particle Oppenheimer’s calculations had indicated two years earlier: an antimatter counterpart to the negatively charged electron, with the same mass and the opposite charge.

Reception and Significance

The prediction had not initially persuaded even leading physicists. Wolfgang Pauli rejected it, and Niels Bohr was also incredulous. Anderson’s experiment transformed the proposal from a disputed theoretical inference into an experimentally established discovery. Dirac subsequently suggested that a new kind of particle with the electron’s mass and opposite charge might exist, and he received the Nobel Prize the following year.