Carl Friedrich von Weizsäcker | |
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 Weizsäcker in 1993 | |
| Born | Carl Friedrich Weizsäcker (1912-06-28)28 June 1912 |
| Died | 28 April 2007(2007-04-28) (aged 94) Starnberg, Bavaria, Germany |
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| Scientific career | |
| Fields | Physics,philosophy |
| Institutions | Max Planck Institute |
| Doctoral advisor | Friedrich Hund |
| Doctoral students | Karl-Heinz Höcker |
Carl Friedrich Freiherr von Weizsäcker[a] (German:[kaʁlˈfʁiːdʁɪçfɔnˈvaɪtsɛkɐ]ⓘ; 28 June 1912 – 28 April 2007) was a Germanphysicist andphilosopher. He was the longest-living member of the team which performed nuclear research inNazi Germany during theSecond World War, underWerner Heisenberg's leadership. There is ongoing debate as to whether or not he and the other members of the team actively and willingly pursued the development of a nuclear bomb for Germany during this time.
A member of the prominentWeizsäcker family, he was son of the diplomatErnst von Weizsäcker, elder brother of the formerGerman PresidentRichard von Weizsäcker, father of the physicist and environmental researcherErnst Ulrich von Weizsäcker and father-in-law of the former General Secretary of theWorld Council of ChurchesKonrad Raiser.
Weizsäcker made important theoretical discoveries regarding energy production in stars fromnuclear fusion processes. He also did influential theoretical work on planetary formation in the earlySolar System.
In his late career, he focused more on philosophical, ethical and historical issues, and was awarded several international honours for his work in those areas.
Born inKiel,Schleswig-Holstein, he was the grandson ofKarl Hugo von Weizsäcker, the Prime Minister of theKingdom of Württemberg. His grandfather was ennobled in 1897 and raised to the hereditary nobility with the title of Baron (Freiherr) in 1916. As such, the four-year-old Carl Friedrich Weizsäcker became Baron Carl Friedrich von Weizsäcker. Since 1919, noble titles have legally been considered parts of the family name.
Weizsäcker was raised inStuttgart,Basel andCopenhagen. Between 1929 and 1933 Weizsäcker studiedphysics,mathematics andastronomy in Berlin,Göttingen andLeipzig, supervised by and working with Heisenberg andNiels Bohr, among others. The supervisor of hisdoctoral thesis wasFriedrich Hund.
Weizsäcker's special interests as a young researcher were the nuclear processes in stars and thebinding energy ofatomic nuclei. Together withHans Bethe he found a mechanism or pathway for the cyclic process offusion in stars (Bethe–Weizsäcker process, published 1937–1939).[1][2][3] This discovery should not be confused with his earlier (1935) development of theBethe–Weizsäcker formula, or Semi-Empirical Mass Formula (SEMF), which was a theoretical formula relating the curve ofnuclear binding energy, nuclear masses, and certain other nuclear properties.[4]
In 1938, Weizsäcker developed a theory on theformation of the Solar System, based on considerations regarding the unequal share of lighter and heavierelements in theSun and theSolar System'sterrestrial planets. His views were later generally acknowledged and refined by a large number of other physicists and astronomers. According to the theory, the Sun and itsplanets evolved from a gas cloud made up of 99%hydrogen andhelium, and 1% of heavier elements. Some 10% of the cloud remained around the Sun as an extensiveatmosphere during an initial phase, and the 1% of heavier elements within this 10% of the total mass of the cloud would tally with the fraction of roughly 1% that the planets contribute to the mass of the Solar System today.
The theory also helped to explain the empirically observed regular pattern of increase in the diameters of theorbits of the planets of the Solar System, from inward to outward. This result was a natural outcome of the increasing size of "planetary eddies" of gas and dust farther from the centre of the early solar system.
A further implication of his theory was that manystars out in the universe, with characteristics similar to the Sun, would have to be expected to possessplanetary systems similar to our own.[5]
Shortly afterthe end of the Second World War in Europe, the Russian émigré American physicistGeorge Gamow co-authored an influential paper supporting Weizsäcker's work on planetary formation in the early solar system.[6]
Afternuclear fission became known in early 1939 through the work ofOtto Hahn andLise Meitner, Weizsäcker (and by his own estimate, 200 other physicists) quickly recognised thatnuclear weapons could potentially be built. He discussed the upsetting implications in February 1939 with philosopher friend Georg Max Friedrich Valentin Picht (1913–1982).[7]
During the Second World War, Weizsäcker joined theGerman nuclear weapons program, participating in efforts to construct anatomic bomb, while based at theKaiser Wilhelm Institute in Berlin. As early as August 1939,Albert EinsteinwarnedU.S. PresidentFranklin D. Roosevelt about this research and highlighted that "the son of the German Under-Secretary of State, von Weizsäcker, is attached to the Kaiser-Wilhelm-Institut in Berlin where some of the American work on uranium is now being repeated."[8]
As a protégé ofWerner Heisenberg, Weizsäcker was present at a crucial meeting at the Army Ordnance headquarters in Berlin on 17 September 1939, at which the German atomic weapons program was launched.[9] Early in the war — possibly until 1942 — he hoped a successful nuclear weapons project would earn him political influence.[10] In July 1940 he was co-author of a report to the army on the possibility of "energy production" from refineduranium. The report also predicted the possibility of usingplutonium for the same purpose including the production of a new type of explosives.[11] During summer 1942 Weizsäcker filed a patent on a transportable "process to generate energy and neutrons by an explosion... e.g. a bomb". The patent application was found in the 1990s inMoscow.
Historians have been divided as to whether Heisenberg and his team were sincerely trying to construct a nuclear weapon, or whether their failure reflected a desire not to succeed because they did not want the Nazi regime to have such a weapon. This latter view, largely based on postwar interviews with Heisenberg and Weizsäcker, was put forward byRobert Jungk in his 1957 bookBrighter Than a Thousand Suns. In a 1957 interview with the German weeklyDer Spiegel, Weizsäcker frankly admitted to the scientific ambitions of those years "We wanted to know if chain reactions were possible. No matter what we would end up doing with our knowledge – we wanted to know."[12] Only by "divine grace", Weizsäcker said, were they spared the temptation to build the bomb as the German war economy was unable to mobilize the necessary resources.
Original sources about this question were not revealed until 1993, when transcripts of secretly recorded conversations among ten top German physicists, including Heisenberg and Weizsäcker, detained underOperation Epsilon atFarm Hall, nearCambridge in late 1945, were published. In the conversation after the group of detainees had listened to theBBC Radio news on dropping of the atomic bomb on 6 August 1945, Weizsäcker said: "I believe the reason we didn't do it was because all the physicists didn't want to do it, on principle. If we had wanted Germany to win the war we would have succeeded!"[13]
But the "Farm Hall Transcripts" also revealed that Weizsäcker had taken the lead in arguing for an agreement among the scientists that they would claim that they had never wanted to develop a German nuclear weapon. It was this version of events which was given to Jungk as the basis of his book. This story was untrue at least to the extent that the detainees also included scientists actively engaged in eager attempts to build a nuclear bomb, namelyKurt Diebner andWalther Gerlach.[14]Max von Laue later called this agreement "die Lesart" (the Version).[15] Although the memorandum which the scientists drew up was drafted by Heisenberg, von Laue wrote: "The leader in all these discussions was Weizsäcker. I did not hear any mention of any ethical point of view."[16]
Weizsäcker himself stated that Heisenberg,Karl Wirtz and he had a private agreement to study nuclear fission to the fullest possible extent in order to "decide" themselves how to proceed with its technical application. "There was no conspiracy, not even in our small three-man-circle, with certainty not to make the bomb. Just as little, there was no passion to make the bomb..."[17] In a recent report based on additional documents from Russian archives, historian Mark Walker concludes that "in comparison with Diebner [and] Gerlach ... Heisenberg and finally Weizsäcker did obviously not use all power they commanded to provide the National Socialists with nuclear weapons".[18]
However, historian of science and technologyWolf Schäfer has concluded, that Weizsäcker did want to build the bomb for Hitler. In a detailed study about Weizsäcker’s contributions to both Nazi Germany and West Germany, he distinguished between the young and the older (pacifistic) Weizsäcker, that is, the person he was from 1939 to 1945, and the person he became thereafter.[19]
The young von Weizsäcker was no clairvoyant; he expected a German victory and wanted to offer Hitler the superweapon to guarantee Germany's supremacy, not to prevent the dictator's suicide and the devastation of the country. What von Weizsäcker foresaw in 1941 was Germany's emergence as the world's first nuclear power. Thehighly talented Hitler would jump at this, he thought. The power of the atomic bomb would enable the dictator, who had already conquered Western Europe, to keep the "Anglo-Saxons" in check (USA), or rather bring them to their knees (Great Britain), and to colonize Russia. We can assume that thepolicy of peace, which the young von Weizsäcker wanted to discuss with Hitler, was the reorganization of Europe under German domination.
Ivan Supek (one of Heisenberg's students and friends) claimed[20] that Weizsäcker was the main figure behind the famous and controversialHeisenberg–Bohr meeting inCopenhagen in September 1941. Allegedly, he tried to persuade Bohr to mediate for peace between Germany and Great Britain. According to Weizsäcker's own account, he had persuaded Heisenberg to meet Bohr in order to broker an accord of the international nuclear physicist "community" not to build the bomb.[21] However, according to Bohr's (posthumously published) account of the events, Heisenberg enthusiastically promoted the prospect of German victory and wanted Bohr and his colleagues to assist in the German atomic program.[22]
Later during the war Weizsäcker worked as a professor at theReichsuniversität Straßburg. The American capture of his laboratory and papers there in December 1944 revealed to the Western Allies that the Germans had not come close to developing a nuclear weapon.[23]
Weizsäcker was allowed to return to the part of Germany administered by theWestern Allies in 1946, and became director of a department for theoretical physics in theMax Planck Institute for Physics inGöttingen. In 1952, he became the first director of the IFT (Institute of Theoretical Physics) inSão Paulo which would later become part ofUNESP.[24][25] From 1957 to 1969, Weizsäcker was professor ofphilosophy at theUniversity of Hamburg. In 1957 he won the Max Planck medal. In 1970 he formulated a "Weltinnenpolitik" (world internal policy). From 1970 to 1980, he was head of theMax Planck Institute for the Research of Living Conditions in the Modern World inStarnberg (jointly withJürgen Habermas[26]). He researched and published on the danger ofnuclear war, what he saw as the conflict between theFirst World and theThird World, and the consequences ofenvironmental degradation.
He was one of the eight signatories of theMemorandum of Tübingen which called for the recognition of theOder–Neiße line as the official border between Germany and Poland and spoke against a possible nuclear armament ofWest Germany.[27][28]
In the 1970s he founded, together with the Indian philosopherPandit Gopi Krishna, a research foundation "for western sciences and eastern wisdom". After his retirement in 1980 he became aChristian pacifist, and intensified his work on the conceptual definition of quantum physics, particularly on theCopenhagen interpretation.
His experiences in the Nazi era, and with his own behavior in that time, gave Weizsäcker an interest in questions of ethics and responsibility. In 1957, he was one of theGöttinger 18, a group of prominent German physicists who protested against the idea that theBundeswehr (West German armed forces) should be equipped withtactical nuclear weapons. He further suggested thatWest Germany should declare its definitive abdication of all kinds of nuclear weapons.[29]
In 2007, Weizsäcker died at the age of 94 inSöcking near Starnberg.[30] Opinions are split on the question of whether he accepted his share of responsibility for the German scientific community's efforts to build a nuclear weapon for Nazi Germany.[31] Schäfer documented Weizsäcker’s lifelong connection with the philosopherMartin Heidegger and has argued that he shared the philosopher’s hope for an “utopian”National Socialism.[32]
Weizsäcker developed the theory of ur-alternatives (archetypal objects), publicized in his bookEinheit der Natur (published in English asThe Unity of Nature)[33] and further developed through the 1990s.[34][35] The theoryaxiomatically constructsquantum physics from the distinction between empirically observable, binary alternatives. Weizsäcker used his theory to derive the 3-dimensionality of space[citation needed] and to estimate theentropy of aproton falling into ablack hole.
The Carl Friedrich von WeizsäckerGymnasium school was named after him, in the town ofBarmstedt,Schleswig-Holstein.
Weizsäcker was nominated four times[37] for the Nobel Prize in Physics.[38]Since 2009, the Donors' Association for German Science and the Leopoldina makes a biennial award of €50,000 "Carl Friedrich von Weizsäcker Award" for "outstanding scientific contribution to resolving socially important problems". There is a Carl-Friedrich von Weizsäcker Foundation, knowledge and responsibility – Carl Friedrich von Weizsäcker-Gesellschaft eV.
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