On June 28, 1912, German physicist at philosopher Carl Friedrich von Weizsäcker was born. Being a member of the team of physicists, who under Werner Heisenberg‘s lead performed nuclear research in Germany during World War 2, Weizsäcker later made important theoretical discoveries regarding energy production in stars from nuclear fusion processes. He also did influential theoretical work on planetary formation in the early Solar System.
“It’s useful when we learn to wonder about the right things.”
– Carl Friedrich von Weizsäcker, quoted in – The Structure of Physics, 1986
Meeting Werner Heisenberg
Carl Friedrich von Weizsäcker comes from the Palatine Württemberg family Weizsäcker. His parents were Ernst von Weizsäcker (1882-1951) and Marianne von Graevenitz (1889-1983), daughter of the Royal Adjutant General Friedrich von Graevenitz. Carl Friedrich had three younger siblings, including the later German President Richard von Weizsäcker. Carl Friedrich von Weizsäcker grew up from 1915 in Stuttgart, from 1922 in Basel and from 1925 in Copenhagen and graduated from the Goethe-Gymnasium in Berlin in 1929. Weizsäcker had met Werner Heisenberg in Copenhagen in 1927 as a teenager. Under his influence he chose physics as his subject of study. From 1929 to 1933 he studied physics, astronomy and mathematics in Berlin, Göttingen and Leipzig, among others with Werner Heisenberg, Friedrich Hund (supervisor) and Niels Bohr.
In the 1930s, von Weizsäcker worked as a scientific assistant at the Kaiser Wilhelm Institute for Physics, dealing with the binding energy of atomic nuclei (Bethe Weizsäcker formula, droplet model; 1935) and the nuclear processes that provide energy inside stars (Bethe Weizsäcker cycle; 1937/1938). In 1936 he provided the first accurate interpretation of nuclear isomers as different metastable states of the atomic nucleus. In 1937 his book Die Atomkerne (The Atomic Nuclei). He habilitated in 1936 and in the same year joined the Kaiser Wilhelm Institute for Physics in Berlin as a research assistant. In the years 1940-1942 he worked on the German uranium project. He then held the chair of theoretical physics at the Reich University of Strasbourg until 1944.
The German Uranium Project
Weizsäcker recognized the possibility of making atomic bombs even before the Second World War began. Like Heisenberg and Otto Hahn, he was a member of the German “Uranium Project” for research into nuclear fission. In the context of the uranium project, for example, he reported to the Army Weapons Office on the possibility of generating energy from uranium-238. At that time, like the other German nuclear physicists, he had no more precise knowledge of the properties of the transuranium elements. A Weizsäcker patent draft from spring 1941 is known. In addition to claims to nuclear reactors, it contains a “process for the explosive generation of energy and neutrons” which is “brought to a location in such quantities, e.g. in a bomb”. However, this patent draft was not accepted by the Patent Office and was revised and expanded within the Uranium Association working group at the Kaiser Wilhelm Institute (including Karl Wirtz). In an interview in 1957, Weizsäcker said that illusionary hopes of political influence had moved him at the time to work on research into nuclear weapons. “Only by divine grace” he was saved from the temptation to actually build the German atomic bomb. This grace consisted in the fact that “it was not possible“. The German war economy had not been able to provide the necessary resources.
After the War
“Philosophy is the science you can’t talk about without doing it yourself.”
– Carl Friedrich von Weizsäcker, The Unity of Nature, 1971
In 1945 von Weizsäcker was one of the German scientists interned by the Allies during the Alsos mission in Farm Hall (southern England) and later in Alswede. From 1946, Weizsäcker headed a department of the Max Planck Institute for Physics in Göttingen. He was an honorary professor at the Georg-August-Universität Göttingen and was admitted to the Akademie der Wissenschaften zu Göttingen in 1950. Together with Gerard Peter Kuiper he worked on the protoplanetary hypothesis of the formation of the solar system and on the theory of turbulence. In 1957 he was appointed to a chair of philosophy at the University of Hamburg. In addition to questions of scientific theory and physics in the vicinity of quantum theory, he worked on problems of the biological and social origin of man.
Physical and Philosophical Aspects of Quantum Theory
Weizsäcker worked and published on physical and philosophical aspects of quantum theory at the age of 18. The results of his early considerations were summarized and published in 1943 in Zum Weltbild der Physik (To the world view of physics). One step in the background was a work on the Second Law of Thermodynamics (1939), which clarified the special role of time for Weizsäcker’s thinking. In 1954, he put together three hypotheses, the elaboration of which determined his physical work for the next 30 years:
- The core of quantum theory is a non-classical logic (quantum logic).
- The application of this logic to its own statements defines the method of so-called second and multiple quantization.
- The application of this method to the formally simplest possible question, the binary alternative, gives a quantum theoretical explanation of the three-dimensionality of spatial space (as well as the relativistic space-time structure and the relativistic quantum field theory) (“quantum theory of the primordial alternatives”).
The Unity of Nature
A first conclusion was reached in 1958 together with Erhard Scheibe and Georg Süßmann. In particular, he succeeded in reconstructing the force-free quantum field theory axiomatically on the basis of this “original theory”. More than ten years passed before the collection of essays Die Einheit der Natur (The Unity of Nature) (1971) was published as an “interim report” of progress. Here he continues the idea of building quantum physics axiomatically from the distinction between empirically decidable “primordial alternatives”. In total, four reconstructions of abstract quantum theory were developed by v. Weizsäcker and the members of his working group, respectively, and the following are to be found in the article: “The Unity of Nature” (1971). a. by Michael Drieschner. In 1988 Thomas Görnitz succeeded in combining Weizsäcker’s estimation of the order of magnitude of the ure of a proton (one proton is 1040 ure) with established physics via Bekenstein-Hawking entropy (black hole).
Further Achievements and Political Activities
In 1943 Weizsäcker developed a theory of the formation of planets for the world view of physics and began to deal with cosmogony. He also partly developed a theory of fully developed, homogeneous turbulence with Heisenberg (from 1945), which was independently and simultaneously investigated by Andrei Kolmogorow (1941) and Lars Onsager. In 1947/48 Weizsäcker took part in meetings of the Imshausen Society, which discussed a renewal of Germany. When in 1956/57 the armament of the German Forces with tactical nuclear weapons was planned, he initiated and formulated in 1957 with Otto Hahn and other nuclear researchers the sensational manifesto of the Göttinger eighteen. In 1961, Weizsäcker initiated another manifesto with the Tübingen Memorandum, in which he spoke out with other Protestant scientists and celebrities against nuclear armament and for recognition of the Oder-Neisse border. In 1970, Weizsäcker moved to the Max Planck Institute in Starnberg, founded for him to research the living conditions of the scientific-technical world, together with several employees of the VDW Research Centre, who worked on the study of the consequences of war and war prevention. These collaborators included Horst Afheldt, Utz-Peter Reich and Philipp Sonntag. Topics such as the danger of a nuclear war, environmental degradation and the North-South conflict were the focus of the research, which attempted to stay beyond the politics of the day.
Weizsäcker was nominated four times for the Nobel Prize in Physics. In 2007, Weizsäcker died at the age of 94 in Söcking near Starnberg.
References and Further Reading:
-  Werner Heisenberg and the Uncertainty Principle, SciHi Blog
-  Otto Hahn – the Father of Nuclear Chemistry, SciHi Blog
-  Kolmogorov and the Foundations of Probability Theory, SciHi Blog
-  “Ich wollte erkennen, ob Atombomben möglich sind” (“I wanted to find out if atomic bombs were possible”)– Carl Friedrich von Weizsäcker interviewed by Michael Schaaf. uni-hamburg.de
-  Carl Friedrich von Weizsäcker, Obituary, The Telegraph, April 30, 2007
-  Dönhoff, Marion (2 March 1962). “Lobbyisten der Vernunft”[Lobbyists of reason]. Die Zeit (in German).
-  Carl Friedrich von Weizsäcker at Wikidata
-  Timeline for Carl Friedrich von Weizsäcker, via Wikidata