Abraham Pais (born 19.05.1918) is an American theoretical physicist, a member of the National Academy of Sciences (1962). He was born in Amsterdam. He graduated from the University of Amsterdam (1938) and the University of Utrecht (1941). In 1946 — 63 he worked at the Institute for Advanced Study in Princeton (as professor from 1950 —). From 1963 he has been professor at Rockefeller University. His work is in nuclear physics, elementary particle physics and quantum field theory. In 1952 he explained (independently of others) the slow decay of strange particles by putting forward the idea of their associated production, which was later confirmed experimentally. In 1955, with M. Gell-Mann, to describe the properties of neutral kaons he introduced the concept of “mixed” particles, or states K01 and K02, which are superpositions of K0 and K0~, and with O. Piccioni he proposed a thought experiment in which the properties of neutral kaons should show themselves clearly (the Pais — Piccioni experiment); he predicted oscillations in a beam of neutral kaons and the regeneration effect. He developed the principles of the economy of constants (1954) and of the hierarchy of interactions (1958). In 1964, the SU(6) symmetry scheme. A corresponding member of the Royal Netherlands Academy of Arts and Sciences, the R. Oppenheimer Prize (1979).