Werner Heisenberg was a German theoretical physicist who made foundational contributions to quantum theory. He is best known for the development of the matrix mechanics formulation of quantum mechanics in 1925 and for asserting the uncertainty principle in 1926, although he also made important contributions to nuclear physics, quantum field theory and particle physics. He was awarded the Nobel Prize in Physics in 1932 “for the creation of quantum mechanics".
Werner Karl Heisenberg was born in Würzburg, Germany on 5 December 1901, the son of a secondary school teacher of classical languages. He studied physics and mathematics from 1920 to 1923 at Munich and at Göttingen with such illustrious teachers as Arnold Sommerfeld, Wilhelm Wien, Max Born, James Franck and David Hilbert. Sommerfeld in particular encouraged Heisenberg’s interest in atomic physics, and introduced him to Niels Bohr's work on quantum physics.
From 1924 to 1927, Heisenberg lectured at the University of Göttingen, and conducted research with Niels Bohr at the University of Copenhagen. It was during this time that the young Heisenberg developed the “matrix mechanics” formulation of quantum mechanics (in collaboration with Max Born and Pascual Jordan). Matrix mechanics was the first complete and correct definition of quantum mechanics, and it extended the Bohr model of atoms by describing how the quantum jumps occur and by interpreting the physical properties of particles as matrices that evolve over time.
It was also in Copenhagen that Heisenberg developed his famous uncertainty principle, which he first described in a letter to Wolfgang Pauli in 1927. The uncertainty principle (Heisenberg actually used the word "Ungenauigkeit" or "imprecision") states that the values of certain pairs of variables cannot both be known with complete precision, not so much due to the limitations of the researcher’s ability to measure them, but rather due to the very nature of the system itself. For example, if a particle is forced to take on a specific, precise position, then the particle's speed or momentum cannot be precisely defined (and vice versa).
In 1927, Heisenberg became professor of theoretical physics and head of the department of physics at the University of Leipzig, and among his students numbered several who went on to distinguish themselves internationally in theoretical physics. In early 1929, he and Pauli submitted the first of two papers laying the foundation for relativistic quantum field theory. He was awarded the 1932 Nobel Prize in Physics “for the creation of quantum mechanics, the application of which has, inter alia, led to the discovery of the allotropic forms of hydrogen”, although he always believed that the prize should have been shared with his collaborators on matrix mechanics, Max Born and Pascual Jordan.
The “Deutsche Physik” movement of the early 1930s was strongly anti-Semitic and biased against theoretical physics, especially quantum mechanics and the theory of relativity. When Adolf Hitler became Chancellor of Germany in 1933, some of the leading German theoretical physicists, including Arnold Sommerfeld, Max Planck and Heisenberg himself, found themselves attacked and ostracized, particularly by the movement’s two most prominent supporters, the Nobel laureates Philipp Lenard and Johannes Stark. No less a personage than the head of the SS, Heinrich Himmler, became involved in the so-called “Heisenberg Affair”, calling him a "white Jew" who should be made to "disappear". But Heisenberg fought back with an editorial and a letter to Himmler and the matter was eventually resolved.
Heisenberg met Elisabeth Schumacher at a private music recital in 1937 (he enjoyed classical music and was himself an accomplished pianist) and the two were married soon after. They were to bear twins, Maria and Wolfgang, in 1938, followed by five more children over the next 12 years: Barbara, Christine, Jochen, Martin and Verena.
In 1939, Heisenberg traveled to the United States to visit Samuel Abraham Goudsmit at the University of Michigan, but refused an invitation to emigrate to the United States. Back in Germany, in 1939, shortly after the discovery of nuclear fission, Heisenberg became one of the principal scientists leading research and development in the German nuclear energy project, known as the “Uranium Club”, and he traveled to German-occupied Copenhagen in 1941 to lecture and discuss nuclear research and theoretical physics with Niels Bohr. In 1942, he was asked by the Nazi administration to direct the Uranium Club's research more toward developing nuclear weapons and, when Heisenberg prevaricated, the authority and regulation of the project was changed.
In 1943, Heisenberg was appointed to the Chair for Theoretical Physics at Humboldt University in Berlin, and was elected to the Prussian Academy of Sciences. But, as Allied bombing increased in Berlin, he moved his family to their rural retreat in Urfeld, and later joined them there. In May 1945, at the end of the War, Heisenberg was picked up by Operation Alsos (along with nine other prominent German scientists working in the nuclear field) and was incarcerated for a time in England under Operation Epsilon.
On his release in 1946, he settled in Göttingen where he worked as director of the Max Planck Institute for Physics until 1958, and then of the expanded Max Planck Institute for Physics and Astrophysics in Berlin until 1970. Throughout this period, he continued to lecture across the world and to publish papers, including works on superconductivity, turbulence and cosmic-ray showers, as well as being appointed to various councils, commissions and associations, and receiving numerous honours and awards.
Heisenberg died of cancer of the kidneys and gall bladder at his Munich home on 1 February 1976, aged 74.
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