German theoretical physicist Werner Karl Heisenberg (1901-1976) was one of the leading scientists of the 20th century. He did important work in nuclear and particle physics, but his most significant contribution was to the development of quantum mechanics. He is best known for his uncertainty principle, which restricts the accuracy with which some properties of atoms and particles--such as position and linear momentum--can be determined simultaneously. Heisenberg studied physics at the University of Munich.

Werner Heisenberg Credit:AIP

In 1925, Heisenberg invented matrix mechanics, the first version of quantum mechanics. In subsequent work with German physicists Max Born and Pascual Jordan, he extended this into a complete mathematical theory of the behavior of atoms and their constituents. In 1932 he was awarded the Nobel Prize for physics. He remained in Germany during the Nazi period and became director of the Kaiser Wilhelm Institute, also heading the unsuccessful German nuclear weapons project. In 1958, Heisenberg became director of the Max Planck Institute for Physics and Astrophysics. He spent his later years working toward a general theory of subatomic particles. Heisenberg's work has had important influences in philosophy as well as physics. Some of his own works, such as Physics and Philosophy (1962) and Physics and Beyond (1971), deal with philosophical issues.