"Think of the time after the catastrophe, Planck had said, and I felt he was right."
—Heisenberg, recollection
Only 25 years old in October 1927, Heisenberg accepted appointment as professor of theoretical physics at the University of Leipzig, Germany. Friedrich Hund soon joined his former Göttingen colleague as Leipzig's second professor of theoretical physics. Heisenberg headed the Institute for Theoretical Physics, which was a sub-section of the university's Physics Institute, headed until 1936 by the experimentalist Peter Debye. Each of the three professors had his own students, assistants, postdocs, and laboratory technicians.
View a list of Heisenberg's students, assistants, and visitors.
Hitler came to power in January 1933. In December of that year Heisenberg was awarded the Nobel Prize for Physics (for the year 1932). Protected somewhat by the Nobel Prize, Heisenberg became a leading spokesman for modern physics in Germany. Heisenberg remained in Germany throughout the Third Reich. His reasons for remaining are still the subject of study and debate. He was not a Nazi, but he was a patriot for German culture, and apparently he felt it was his duty to remain at his post in order to help preserve what could be saved of decent German science. He never perceived that at some point this became self-defeating.
As a founder of quantum mechanics and head of the program in theoretical physics, Heisenberg attracted to Leipzig numerous first-rate students and visitors from Germany and throughout the world. During the next half decade Heisenberg and his collaborators produced major new quantum theories of solid-state crystals, the structure of molecules, the scattering of radiation by nuclei, accounts of ferromagnetism and the so-called Hall effect, and the first neutron-proton model of the nucleus (also proposed by the Russian physicist Dimitri Ivanenko).
The task now was to fit the quantum into the rest of physics theory. With Wolfgang Pauli and his collaborators in Zurich, Heisenberg and his collaborators made enormous strides toward joining together quantum mechanics and relativity theory into a relativistic quantum theory of "fields" (such as electromagnetic or material fields). Together with Dirac and others, they laid the foundations of high-energy physics research. At that time laboratory accelerators had not yet reached high energies, so this work focused on the properties of cosmic rays, highly energetic particles streaming into the Earth's atmosphere from outer space.
Heisenberg also traveled extensively during his Leipzig years. In addition to frequent visits with Bohr in Copenhagen and Pauli in Zurich, Heisenberg attended conferences in Rome and Copenhagen. He delivered a series of lectures on quantum physics at the University of Chicago in 1929, returning to Leipzig through Japan and India. He lectured on several occasions at Cambridge, England, attended the elite Solvay congresses in Brussels, and was a frequent visitor at the Ann Arbor, Michigan, summer schools on theoretical physics. During the last of these his colleagues in the United States attempted to convince Heisenberg to remain in the U.S., but he refused. Soon after Heisenberg returned to Germany, Hitler unleashed his forces into Poland, touching off World War II.
Soon after Hitler came to power, the regime began to dismiss Jews and political opponents from civil service positions, which included academic positions at all levels. During the same period, Nazi physicists, such as the Nobel-Prize-winning Johannes Stark, began an attack on modern theoretical physics, including relativity theory and quantum mechanics, calling it "Jewish physics." Heisenberg and other leaders of the physics profession attempted to oppose these developments, but without much long-term success.
"The concentration camp is obviously the most suitable place for Herr Heisenberg!"
—A Nazi functionary
Heisenberg himself was under attack by 1937, vilely insulted as a traitor in an article titled "'White Jews' in Science," appearing in an SS newspaper. He was threatened with internment in a concentration camp. The attack occurred after Arnold Sommerfeld, Heisenberg's former mentor, decided to retire, preferring his star pupil Heisenberg as his successor in Munich. Through a family acquaintanceship, Heisenberg appealed directly to the head of the SS, Heinrich Himmler, for "exoneration." After a frightening year-long investigation, the SS cleared Heisenberg of any accusations. He remained in Germany, but he never did obtain Sommerfeld's professorship.
"Heisenberg is only one example of many others...They are all representatives of Judaism in German spiritual life who must all be eliminated just as the Jews themselves."
—SS newspaper, 1937
The SS episode left Heisenberg and the German physics community shaken, and it represented a turning point in their relationship with the Nazi regime. An uneasy truce developed between the physicists and the regime. The outbreak of war in Europe and the discovery of nuclear fission in Berlin strengthened the hand of the physicists. Heisenberg and the rest of his colleagues in the "uranium project" took up work on practical applications of nuclear fission. Different scientists had different motivations for participating in the project. Heisenberg and his inner circle saw this mainly as an opportunity for self-protection, and as a demonstration of the practical value of theoretical physics. Other scientists desired, if possible, to contribute to a German victory. Heisenberg became a key figure in German war-time fission research. In 1942 he left Leipzig to accept appointment as professor of theoretical physics at the University of Berlin and interim head of the Kaiser Wilhelm Institute for Physics, Germany's main reactor research facility.
Personal events accompanied the SS assault of 1937. Several months before the assault, Heisenberg met and married a young woman who had recently received a degree in German literature, Elisabeth Schumacher, the daughter of a well-known Berlin economics professor. Nine months later she gave birth to fraternal twins. They were the first of Heisenberg's seven children.