Hungarian-American physicist who studied in Berlin before moving to Princeton in 1930, where he later became professor of theoretical physics. His main contribution was in applying group theory to quantum mechanics. He was among those urging the U.S. to build an atomic bomb, and he made some important contributions to the Manhattan Project.

In 1927, Wigner concluded that parity is conserved in a nuclear reaction. In other words, the laws of physics should not distinguish between right and left; or between positive and negative time. This held as a central tenet of physics until 1958, when Yang and Lee showed that certain types of reaction involving the weak force, such as beta decay do not conserve parity. Wigner also investigated the strong nuclear interaction which binds neutrons and protons in the nucleus, and showed that it only acted over short distances.

He gave his name to the "Wigner's friend paradox," a variant on the Schrödinger's cat paradox. The "friend" is a human observer who replaces the cat in one of the thought experiments on quantum reality. He suggested that the entry of information about the quantum system collapses the quantum wave and reduces the hybrid state (where the "cat" is both alive and dead) to a simple cut-and-dried system.

Wigner shared the 1963 Nobel Prize in Physics with Maria Goeppert Mayer and Hans Jensen. In his later years, as an elder statesman of science, Wigner contemplated the complexity that is modern physics by stating, "Physics is becoming so unbelievably complex that it is taking longer and longer to train a physicist. It is taking so long, in fact, to train a physicist to the place where he understands the nature of physical problems that he is already too old to solve them."