Alternate Name

Weizsäcker, Carl Friedrich von

BornKiel, Germany, 28 June 1912

Died 2007

German theoretical physicist C. F. von Weizsäcker discovered (at about the same time as Hans Bethe ) the commonest cycle of nuclear reactions that produces energy by converting hydrogen to helium in massive stars. He also revitalized the nebular or Kant-Laplace hypothesis for the origin of the Solar System.

Born into a family of statesmen, theologians, and scientists, Weizsäcker attended schools in eight different countries before beginning the study of physics at the University of Leipzig and obtaining his D.Phil. in 1933 for work with Werner Heisenberg. His diplomat father Ernst von Weizsäcker was sentenced to jail by the Allies at Nuremberg for service under the Nazis, and his brother Richard served as President of the Federal Republic of Germany from 1984 to 1994.

Carl von Weizsäcker initially worked as assistant to Heisenberg at Leipzig, and moved to the Kaiser Wilhelm Institute für Physik in 1936 as a research physicist, becoming Privatdozent (lecturer) the next year and lecturing at the University of Berlin. He worked partly with Lise Meitner and Otto Hahn, and his attention turned to applications of nuclear physics to astrophysics. The 1932 discovery of the neutron and its relationship via the weak interaction to the proton and neutron enabled Weizsäcker to go beyond the ideas of Fritz Houtermans and Robert Atkinson and to propose how a nucleus of carbon might act as a catalyst, capturing four protons in succession, dropping off a helium, and going through the same process many times. He published a couple of papers in 1937/1938 on the transformation of elements in stellar interiors.

In 1942, Weizsäcker was appointed associate professor of theoretical physics at the University of Strasbourg. Here he devised a more sophisticated and realistic version of the nebular hypothesis of Immanuel Kant and Pierre de Laplace for the origin of the Solar System.

Von Weizsäcker argued that the original dust cloud out of which the Solar System was formed would experience turbulence and break up into a number of smaller vortices and eddies. These vortices fell into gradually larger systems with increasing distance. At the boundaries between sets of vortices, conditions were supposed to be suitable for planets to form from the continuous aggregation of progressively larger bodies. His theory was able to resolve the problem of low angular momentum of the Sun and to provide a physical explanation of the Bode-Titius law of planetary distances. While Weizsäcker’s theory was not able to resolve all the questions about planetary formation, his work directed a fresh stream of thought into this field and attracted a lot of attention from scientists in the field. Modifications and additions were later proposed by Dirk ter Haar, Hannes Alfvén , and Fred Hoyle .

In 1944, Weizsäcker returned to the Kaiser Wilhelm Institute and turned to a study of the nuclear reactions that take place in the fission of uranium and the problems of constructing a self-sustaining reactor. In April 1945, he was arrested by Allied forces along with other high-ranking German scientists. During the 8 months they were interned by the British government at Farm Hall, Godmanchester, their conversations were recorded. These form part of the historical record on how far Germany had advanced toward construction of a fission bomb.

After his return to Germany, Weizsäcker joined the staff of the Max Planck Institute for Physics at Göttingen in 1945 and remained there until 1957. During this period he also held an honorary professorship at the University of Göttingen. Then, in 1957, Weizsäcker accepted a position of professor of philosophy at the University of Hamburg. This decision was indicative of his intention to spend more time in thinking, and writing, and with matters of religion and philosophy, while holding an honorary chair at the University of Munich. During the 1960s, he was very active in the peace movement and became a strong spokesman for nuclear disarmament. He relinquished the Hamburg position in 1969 to take up the directorship of the Max Planck Institute on the Preconditions of Human Life in the Modern World in Starnberg in 1970. Weizsäcker retired from this position in 1980 having reached the age of 68. Since 1980 he has been emeritus scientific member (Mitglied) of the Max Planck Institute, Munich.

Weizsäcker married Gundalena Wille on 30 March 1937. Their children are Carl Christian, Ernest-Ulrich, Elizabeth (Mrs. Raiser), and Heinrich.

He has received many honors, including the Max Planck Medal in 1957 and 1966, the Goethe Prize (City of Frankfurt, 1958), the Order of Merit for Sciences and Arts (1961), the Arnold Raymond Prize for Physics (1965), the Erasmus Prize (1961), the Templeton Prize for Progress in Religion, and several others. He has also received honorary degrees from several universities.

Weizsäcker is a member of numerous societies. Amongst these are the Max-Planck-Gesselschaft, Deustsche Akademie der Naturforscher Leopoldina (Halle), Deutsche Akademie für Sprache und Dichtung, Göttinger Akademie der Wissenschaften, Sachsische Akademie der Wissenschaften (Leipzig), Österreichische Akademie der Wissenschaften (Wien), and Deutsche Physikalische Gessellschaft.