German theoretical physicist best known for his work on the quantum theory, including matrix mechanics and the uncertainty principle, for which he was awarded the 1932 Nobel Prize for Physics.
The son of a professor of history, Heisenberg was educated at the universities of Munich and Göttingen. He subsequently spent two years in Copenhagen working with Niels Bohr before returning to Germany in 1926 to take up an appointment as professor of physics at Leipzig. There, in the mid-1920s, he developed a formalism, known as matrix mechanics, that provided a plausible basis for quantum mechanics. This insight was followed by the uncertainty principle, according to which it is not possible to determine exactly and simultaneously both the position and momentum of elementary particles. No improvement in instruments or techniques can overcome what is a theoretical limitation on the knowledge we can gain of the material world. This remains a fundamental tenet of modern physics.
With the outbreak of World War II Heisenberg was called to Berlin to direct the German nuclear programme. Although he had defended Einstein against attack from the Nazis, and had himself been investigated by the secret police, as an ardent nationalist he was convinced that it was his duty to fight for his country. In 1941 he visited occupied Copenhagen and contacted his old teacher and colleague, Niels Bohr, to warn him, so Heisenberg later reported, that Germany could make an atomic bomb. However, Heisenberg's team made little progress in overcoming either the theoretical or the industrial problems implicit in such a programme. Whether the lack of progress was due to the banishment of the best physicists to England and America because they were nearly all Jewish, or to a reluctance of the remaining ones to provide the Nazis with such a weapon, remains a matter of dispute. Heisenberg's role in the affair is still controversial; when he first heard of the Hiroshima bomb he is said to have dismissed it as 20 000 tons of high explosive.
After the war Heisenberg helped to establish the Max Planck Institute for Physics, serving as its director, first at Göttingen and after 1955 in Munich. Although he campaigned strongly against the Adenauer government's failure to back the construction of nuclear reactors, Heisenberg also made his own position clear on nuclear weapons, declaring in 1957 that he would take no part in their testing or their production.
Subjects: Science and Mathematics.