It has been said of Paul Dirac (1902-1984) that he was able to conjure laws of nature from pure thought. His method was not experimental, but instead theoretical. He conceived the existence of the positron, the antiparticle of the electron. He also predicted antimatter, purely on the basis of certain equations and on the need for it to exist, long before actual observation confirmed it.
Dirac was a gifted mathematician, not at all diminished by his quirky and eccentric personality. He was given to long silences and strange statements, although by all accounts he was good-natured and courteous to friends and colleagues. Albert Einstein said of him: “This balancing on the dizzying path between genius and madness is awful.” Nothwithstanding, as a mathematician and theoretician Dirac’s intellect and contributions to twentieth-century physics were immense.
Dirac focused on theoretical aspects of quantum mechanics, taking as his perspective that the underlying reality is mathematical. He became deeply involved in Werner Heisenberg’s quantum mechanics, introduced in 1925. Dirac’s great innovation was a non-commutative algebra for calculating atomic properties. (Non-commutative means that there exists an a and b such that a times b is not equal to b times a. Hamiltonian quaternions are examples.)
This was the background for his relativistic Theory of the Electron, published in 1928 and followed by a theory of holes, which may be variously described as absence of an electron or presence of a positron. Dirac’s description of the positron preceded its actual discovery in 1932 by Carl Anderson. Its existence was proved in 1933 by Patrick Blackett, who described pair production and annihilation. Thus, Dirac characteristically anticipated the existence of antimatter as a concept in the domain of pure thought before it was actually detected.
Dirac’s greatest achievement was his wave equation, which updated Erwin Schrödinger’s quantum equation and made it relativistic. Thus, Dirac can be seen as reconciling Albert Einstein’s relativistic theory of the very large with Heisenberg’s quantum mechanical theory of the very small. These two domains have yet to be thoroughly synthesized, but Dirac laid the foundation over 80 years ago.
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