The equation also implied the existence of a new form of matter, antimatter, previously unsuspected and unobserved and which was experimentally confirmed several years later. It was validated by accounting for the fine structure of the hydrogen spectrum in a completely rigorous way.
It is consistent with both the principles of quantum mechanics and the theory of special relativity, and was the first theory to account fully for special relativity in the context of quantum mechanics. In its free form, or including electromagnetic interactions, it describes all spin- 1⁄ 2 massive particles, called 'Dirac particles', such as electrons and quarks for which parity is a symmetry. In particle physics, the Dirac equation is a relativistic wave equation derived by British physicist Paul Dirac in 1928.
