Deutsche Physik
Origins
This movement began as an extension of a German nationalistic movement in the physics community which went back as far as World War I. During fighting between the German army and Belgian resistance fighters after the German invasion in Belgium, the library of the Katholieke Universiteit Leuven caught fire when German troops looted and set fire to the town[citation needed]. The incident of the burning of the library led to a protest note by British scientists, which was signed also by eight distinguished British scientists, namely William Bragg, William Crookes, Alexander Fleming, Horace Lamb, Oliver Lodge, William Ramsay, Baron Rayleigh and J.J. Thomson, and in which it was assumed that the war propaganda mentioned corresponded to real behavior of German soldiers. In the year of 1915 this led to a counter-reaction in the form of an "appeal" formulated by Wilhelm Wien and addressed to German physicists and scientific publishers, which was signed by sixteen German physicists, including Arnold Sommerfeld and Johannes Stark. They claimed that German character had been misinterpreted and that attempts made over many years to reach an understanding between the two countries had obviously failed, so that conclusions had now to be drawn, in regard to the use of the English language by German scientific authors, editors of books and translators.[1] A number of German physicists, including Max Planck and the especially passionatePhilipp Lenard, a scientific rival of J.J. Thomson, had then signed further "declarations", so that gradually a "war of the minds"[2] broke out. On the German side it was suggested to avoid an unnecessary use of English language in scientific texts (concerning, e.g., the renaming of German-discovered phenomena with perceived English-derived names, such as "X-ray" instead of "Röntgen ray"). It was stressed, however, that this measure should not be misunderstood as a rejection of British scientific thought, ideas and stimulations.
After the war, the affronts of the Treaty of Versailles kept some of these nationalistic feelings running high, especially in Lenard, who in a small pamphlet[3] had already complained at the beginning of the war about England. When on January 26, 1920, an attempt had been made by the young soldier Oltwig von Hirschfelde to assassinate Matthias Erzberger, the German Chancellor, Lenard had sent a telegram of congratulation to Hirschfelde.[4] After the assassination, on June 24, 1922, of the politician Walther Rathenau, when the government had ordered the flying of flags at half mast on the day of his funeral, Lenard ignored the order at his institute in Heidelberg. Socialist students organized a demonstration against Lenard, who on the occasion was taken into protective custody by the Jewish prosecutor of state Hugo Marx.[5] This was not a sentiment unique to physics or physicists— this blend of nationalism and perceived affront from foreign and internal forces formed a key part of the popularity of the newly forming National Socialist Party (Nazis) in the late 1920s.
During the early years of the twentieth century, Albert Einstein's Theory of Relativity was met with much bitter controversy within the physics communities of the world. There were many physicists, especially the "old guard," who were suspicious of the intuitive meanings of Einstein's theories. The leading theoretician of the Deutsche Physik type of movement was Rudolf Tomaschek who had re-edited the famous physics textbook Grimsehl's Lehrbuch der Physik. In that book, which consists of several volumes, the Lorentz transformationwas accepted as well as quantum theory. However, Einstein's interpretation of the Lorentz transformation was not mentioned, and also Einstein's name was completely ignored. Many of these classical physicists resented Einstein's dismissal of the notion of a luminiferous aether, which had been a mainstay of their work for the majority of their productive lives. They were not convinced by the empirical evidence for Relativity: the measurements of the perihelion of Mercury and the null result of the Michelson-Morley experiment might be explained in other ways, they thought, and the results of the Eddington eclipse experiment were experimentally problematic enough to be dismissed as meaningless by the more devoted doubters. Many of these doubters were very distinguished experimental physicists—Lenard was himself a Nobel laureate in Physics. Although the opposition to Einstein was expressed in scientific terms, his theories were also rejected as un-German. This is because Einstein was Jewish.
Further information: History of special relativity
[edit]Under the Third Reich
When the Nazis entered the political scene, Lenard quickly attempted to ally himself with them, joining the party at an early stage. With another physics Nobel laureate, Johannes Stark, Lenard began a core campaign to label Einstein's Relativity asJewish Physics.
For a few years after the Nazi takeover in 1933, this found strong support from Nazi leadership, as it played upon a number of Nazi ideological themes, and gave yet another method to harass and delegitimize Jewish citizens and institutions. Lenard[6]and Stark enjoyed the Nazi support because it allowed them to undertake a professional coup for their preferred scientific theory, an example of using heavy-handed politics to resist an ideologically unwelcome scientific "paradigm shift". Under the rallying cry that physics should be more "German" and "Aryan," Lenard and Stark, with backing from the Nazi leadership, entered on a plan to pressure and replace physics positions at German universities with people teaching their preferred theories. By the late 1930s, there were no longer any Jewish physics professors in Germany, since under the Nuremberg Lawsof 1935 Jews were not allowed to work in universities. Stark in particular was also trying to get himself installed as the Führerof physics—not an entirely fanciful goal, given the Gleichschaltung (literally, "coordination") principle applied to other professional disciplines, such as medicine, under the Nazi regime, whereby a strict linear hierarchy was created along ideological lines.
They met with moderate success, but the support from the Nazi party was not as great as Lenard and Stark would have preferred. After a long period of harassment of the quantum physicist Werner Heisenberg, including getting him labeled a "White Jew" in the July 15, 1937, issue of SS's weekly, Das Schwarze Korps (The Black Corps), they began to fall from influence. Heisenberg was not only a pre-eminent physicist whom even the Nazis realised they were better off with than without, however "Jewish" his theory might be in the eyes of Stark and Lenard, but Heisenberg had, as a young boy, attended school with SS chief Heinrich Himmler. In a historic moment, Heisenberg's mother rang Himmler's mother and asked her if she would please tell the SS to give "Werner" a break. After beginning a full character evaluation, which Heisenberg both instigated and passed, Himmler forbade further attack on the physicist. Heisenberg would later employ his "Jewish physics," in theGerman project to develop nuclear fission for the purposes of nuclear weapons or nuclear energy use. Himmler promised Heisenberg that after Germany won the war, the SS would finance a physics institute to be directed by Heisenberg.[7]
Lenard began to play less and less of a role, and soon Stark ran into even more difficulty, as other scientists and industrialists known for being exceptionally "Aryan" came to the defense of Relativity and quantum mechanics. As historian Mark Walker puts it, "despite his best efforts, in the end his science was not accepted, supported, or used by the Third Reich. Stark spent a great deal of his time during the Third Reich fighting with bureaucrats within the National Socialist state. Most of the National Socialist leadership either never supported Lenard and Stark, or abandoned them in the course of the Third Reich."
[edit]Effect on the German nuclear program
It is occasionally put forth that there is a great irony in the Nazis' labeling modern physics as "Jewish science", since it was exactly modern physics—and the work of many European exiles—which was used to create the atomic bomb. Even if the German government had not embraced Lenard and Stark's ideas, the German antisemitic agenda was enough by itself to destroy the Jewish scientific community in Germany. Furthermore, the German nuclear energy project was never pursued with anywhere near the vigor of theManhattan Project in the United States, and for that reason would likely not have succeeded in any case.[8] The movement did not actually go as far as preventing the nuclear energy scientists from using quantum mechanics and relativity,[9] but the education of young scientists and engineers suffered, not only from the loss of the Jewish scientists but also from political appointments and other interference. In 1938, Himmler wrote to Heisenberg that he could discuss modern physics but not mention Jewish scientists such as Bohrand Einstein in connection with it.[10] The loss of so much science affected the war little in atomic energy because they lacked the necessary industrial resources to go beyond at most a few small power reactors.[citation needed] It greatly affected their aerodynamics research, but that was so far ahead before the Nazis took over that the Allies did not catch up until after the war.[citation needed] Presumably, it had more decisive effects on other areas of war related research to which physicists normally contribute, such as radar, communications and chemistry.[citation needed]
[edit]Max von Laue
Early years
Laue was born in Pfaffendorf, now part of Koblenz, to Julius Laue and Minna Zerrenner. In 1898, after passing his Abitur in Strassburg, he entered his compulsory year of military service, after which he began his studies in mathematics, physics, and chemistry, in 1899, at the University of Strassburg, the University of Göttingen, and the Ludwig Maximilians University of Munich (LMU). At Göttingen, he was greatly influenced by the physicists Woldemar Voigt and Max Abraham and the mathematician David Hilbert. After only one semester at Munich, he went to the Friedrich-Wilhelms-University of Berlin in 1902. There, he studied under Max Planck, who gave birth to the quantum theory revolution on 14 December 1900, when he delivered his famous paper before the Deutsche Physikalische Gesellschaft.[1][2] At Berlin, Laue attended lectures by Otto Lummer on heat radiation and interference spectroscopy, the influence of which can be seen in Laue’s dissertation on interference phenomena in plane-parallel plates, for which he received his doctorate in 1903.[3] Thereafter, Laue spent 1903 to 1905 at Göttingen. Laue completed his Habilitation[4] in 1906 under Arnold Sommerfeld at LMU.[5][6][7][8][9]
[edit]Career
In 1906, Laue became a Privatdozent in Berlin and an assistant to Planck. He also met Albert Einstein for the first time; they became friends and Laue went on to contribute to the acceptance and development of Einstein’s theory of relativity. Laue continued as assistant to Planck until 1909. In Berlin, he worked on the application of entropy to radiation fields and on the thermodynamic significance of the coherence of light waves.[7][9]
From 1909 to 1912, Laue was a Privatdozent at the Institute for Theoretical Physics, under Arnold Sommerfeld, at LMU. During the 1911 Christmas recess and in January 1912, Paul Peter Ewald was finishing the writing of his doctoral thesis under Sommerfeld. It was on a walk through the Englischer Garten in Munich in January, that Ewald told Laue about his thesis topic. The wavelengths of concern to Ewald were in the visible region of the spectrum and hence much larger than the spacing between the resonators in Ewald’s crystal model. Laue seemed distracted and wanted to know what would be the effect if much smaller wavelengths were considered. In June, Sommerfeld reported to the Physikalische Gesellschaft of Göttingen on the successful diffraction of x-rays by Laue, Paul Knipping and Walter Friedrich at LMU, for which Laue would be awarded the Nobel Prize in Physics, in 1914. While at Munich, he wrote the first volume of his book on relativity during the period 1910 to 1911.[8][9][10][11]
In 1912, Laue was called to the University of Zurich as an extraordinarius professor of physics. In 1913, his father was raised to the ranks of hereditary nobility; Laue then became 'Max von Laue'.[9]
From 1914 to 1919, Laue was at the University of Frankfurt as ordinarius professor of theoretical physics. From 1916, he was engaged in vacuum tube development, at the University of Würzburg, for use in military telephony and wireless communications.[6][7][8][9]
In 1919, Laue was called to the University of Berlin as ordinarius professor of theoretical physics, a position he held until 1943, when he was declared emeritus, with his consent and one year before the mandatory retirement age. At the university in 1919, other notables were Walther Nernst, Fritz Haber, and James Franck. Laue, as one of the organizers of the weekly Berlin Physics Colloquium, typically sat in the front row with Nernst and Einstein, who would come over from the Kaiser-Wilhelm-Institut für Physik in Berlin-Dahlem, where he was the director. Among Laue’s notable students at the university were Leó Szilárd, Fritz London, Max Kohler, and Erna Weber. In 1921, he published the second volume of his book on relativity.[6][8][12][13]
As a consultant to the Physikalisch-Technische Reichsanstalt (PTR), Laue met Walther Meissner who was working there on superconductivity. Meissner had discovered that a weak magnetic field decays rapidly to zero in the interior of a superconductor, which is known as the Meissner effect. Laue showed in 1932 that the threshold of the applied magnetic field which destroys superconductivity varies with the shape of the body. Laue published a total of 12 papers and a book on superconductivity. One of the papers was co-authored with Fritz London and his brother Heinz.[7][14][15][16] Meissner published a biography on Laue in 1960.[17]
The Kaiser-Wilhelm Gesellschaft zur Förderung der Wissenschaften (Today: Max-Planck Gesellschaft zur Förderung der Wissenschaften) was founded in 1911. Its purpose was to promote the sciences by founding and maintaining research institutes. One such institute was the Kaiser-Wilhelm Institut für Physik (KWIP) founded in Berlin-Dahlem in 1914, with Einstein as director. Laue was a trustee of the institute from 1917, and in 1922 he was appointed deputy director, whereupon Laue took over the administrative duties from Einstein. Einstein was traveling abroad when Adolf Hitler became Chancellor in January 1933, and Einstein did not return to Germany. Laue then became acting director of the KWIP, a position he held until 1946 or 1948, except for the period 1935 to 1939, when Peter Debye was director. In 1943, to avoid casualties to the personnel, the KWIP moved toHechingen. It was at Hechingen that Laue wrote his book on the history of physics Geschichte der Physik, which was eventually translated into seven other languages.[7][18][19]
[edit]Opposition to Nazism
Laue opposed National Socialism in general and their Deutsche Physik in particular – the former persecuted the Jews, in general, and the latter, among other things, put down Einstein’s theory of relativity as Jewish physics. Laue secretly helped scientific colleagues persecuted by National Socialist policies to emigrate from Germany, but he also openly opposed them. An address on 18 September 1933 at the opening of the physics convention in Würzburg, opposition to Johannes Stark, an obituary note on Fritz Haber in 1934, and attendance at a commemoration for Haber are examples which clearly illustrate Laue’s courageous, open opposition:
- Laue, as chairman of the Deutsche Physikalische Gesellschaft, gave the opening address at the 1933 physics convention. In it, he compared the persecution of Galileo and the oppression of his scientific views on the Solar theory of Copernicus to the then conflict and persecution over the theory of relativity by the proponents of Deutsche Physik, against the work of Einstein, labeled “Jewish physics.”
- Johannes Stark, who had received the Nobel Prize in Physics in 1919, wished to become the Führer of German physics and was a proponent of Deutsche Physik. Against the unanimous advice of those consulted, Stark was appointed President of the PTR in May 1933. However, Laue successfully blocked Stark’s regular membership in the Prussian Academy of Sciences.
- Haber received the Nobel Prize in Chemistry in 1918. In spite of this and his many other contributions to Germany, he was forced to emigrate from Germany as a result of theLaw for the Restoration of the Professional Civil Service, which removed Jews from their jobs. Laue’s obituary note[20] praising Haber and comparing his forced emigration to the expulsion of Themistocles from Athens was a direct affront to the policies of National Socialism.
- In connection with Haber, Planck and Laue organized a commemoration event held in Berlin-Dahlem on 29 January 1935, the first anniversary of Haber’s death – attendance at the event by professors in the civil service had been expressly forbidden by the government. While many scientific and technical personnel were represented at the memorial by their wives, Laue and Wolfgang Heubner were the only two professors to attend.[21][22] This was yet another blatant demonstration of Laue’s opposition to National Socialism. The date of the first anniversary of Haber’s death was also one day before the second anniversary of National Socialism seizing power in Germany, thus further increasing the affront given by holding the event.
The speech and the obituary note earned Laue government reprimands. Furthermore, in response to Laue blocking Stark’s regular membership in the Prussian Academy of Sciences, Stark, in December 1933, had Laue sacked from his position as advisor to the PTR, which Laue had held since 1925. Chapters 4 and 5, in Welker’s Nazi Science: Myth, Truth, and the Atomic Bomb, present a more detailed account of the struggle by Laue and Planck against the Nazi takeover of the Prussian Academy of Sciences.[14][23][24][25][26][27]
[edit]Hidden Nobel prize
When Nazi Germany invaded Denmark in World War II, the Hungarian chemist George de Hevesy dissolved the gold Nobel Prizes of von Laue and James Franck in aqua regia to prevent the Nazis from discovering them (it was illegal at the time to send gold out of the country, and were it discovered that Laue had done so, he could have faced prosecution in Germany.) Hevesy placed the resulting solution on a shelf in his laboratory at the Niels Bohr Institute. After the war, he returned to find the solution undisturbed and precipitated the gold out of the acid. The Nobel Society then re-cast the Nobel Prizes using the original gold.[28]
[edit]Post-war
On 23 April 1945, French troops entered Hechingen, followed the next day by a contingent of Operation Alsos – an operation to investigate the German nuclear energy effort, seize equipment, and prevent German scientists from being captured by the Soviets. The scientific advisor to the Operation was the Dutch-American physicist Samuel Goudsmit, who, adorned with a steel helmet, appeared at Laue’s home. Laue was taken into custody and taken to Huntington, England, and interned at Farm Hall, with other scientists thought to be involved in nuclear research and development.[14]
While incarcerated, Laue was a reminder to the other detainees that one could survive the Nazi reign without having “compromised”; this alienated him from others being detained.[29] During his incarceration, Laue wrote a paper on the absorption of x-rays under the interference conditions, and it was later published in Acta Crystallographica.[14] On 2 October 1945, Laue, Otto Hahn, and Werner Heisenberg, were taken to meet with Henry Hallett Dale, president of the Royal Society, and other members of the Society. There, Laue was invited to attend the 9 November 1945 Royal Society meeting in memory of the German physicist Wilhelm Conrad Röntgen, who discovered X-rays; permission was, however, not forthcoming from the military authorities detaining von Laue.[14]
Laue was returned to Germany early in 1946. He went back to being acting director of the KWIP, which had been moved to Göttingen. It was also in 1946 that the Kaiser-Wilhelm Gesellschaft was renamed the Max-Planck Gesellschaft, and, likewise, the Kaiser-Wilhelm Institut für Physik became the Max-Planck Institut für Physik. Laue also became an adjunct professor at the University of Göttingen. In addition to his administrative and teaching responsibilities, Laue wrote his book on superconductivity, Theorie der Supraleitung, and revised his books on electron diffraction, Materiewellen und ihre Interferenzen, and the first volume of his two-volume book on relativity.[8][14][30]
In July 1946, Laue went back to England, only four months after having been interned there, to attend an international conference on crystallography. This was a distinct honor, as he was the only German invited to attend. He was extended many courtesies by the British officer who escorted him there and back, and a well-known English crystallographer as his host; Laue was even allowed to wander around London on his own free will.[14]
After the war, there was much to be done in re-establishing and organizing German scientific endeavors. Laue participated in some key roles. In 1946, he initiated the founding of the Deutsche Physikalische Gesellschaft in only the British Occupation Zone, as the Allied Control Council would not initially allow organizations across occupation zone boundaries. During the war, the PTR had been dispersed; von Laue, from 1946 to 1948, worked on its re-unification across three zones and its location at new facilities in Braunschweig. Additionally, it took on a new name as the Physikalisch-Technische Bundesanstalt, but administration was not taken over by Germany until after the formation of West Germany on 23 May 1949. Circa 1948, the President of the American Physical Society asked Laue to report on the status of physics in Germany; his report was published in 1949 in theAmerican Journal of Physics.[31] In 1950, Laue participated in the creation of the Verband Deutscher Physikalischer Gesellschaften, formerly affiliated under the Nordwestdeutsche Physikalische Gesellschaft.[8][14][30]
In April 1951, Laue became director of the Max-Planck Institut für physikalische Chemie und Elektrochemie, a position he held until 1959. In 1953, at the request of Laue, the Institute was renamed the Fritz Haber Institut für physikalische Chemie und Elektrochemie der Max-Planck Gesellschaft.[14][32]
[Heisenberg's struggle with the Aryan physicists] [...] In this struggle Heisenberg was exposed to the full force of irrational Nazi passions; his enemies had little understanding of his real work, but focused on him the accumulated anger of decades. A leader of the attack was Johannes Stark, who bitterly resented the mathematical theorists who patronized his work. Sommerfeld had even mocked his name -in Germanstark means "strong"- by calling him "Giovanni Fortissimo." In December 1935, in a speech at a ceremony renaming the physics institute in Heidelberg for Philipp Renard, Stark singled out Heisenberg as "the spirit of Einstein's spirit." Heisenberg responded with an even-tempered defense of theoretical physics, including relativity, in the Nazi party newspaper Völkischer Beobachter in February 1936, but the editors appended a Stark counterattack which dismissed Heisenberg's work as "an aberration of the Jewish mind." Back and forth the paper salvos went over the next year, until Stark in July 1937 backed Heisenberg into a corner with an unrestrained assault in Das Schwarze Korps, the newspaper of the Schutzstaffeln or SS, calling him a "white Jew." By this time all traditional standards of scientific discourse had gone by the way; Stark's attack was relentlessly personal, charging that Heisenberg'scareer was based on Jewish friends and influence. Heisenberg's friend in Leipzig Baertel van der Waerden told him that being called a "white Jew" was something he could be proud of. But the honor came dear. The University of Munich promptly dropped its efforts to name Heisenberg to Sommerfeld's post, and Stark's vendetta threatened still worse: in an anonymous note the editors of Das Schwarze Korps recommended that "white Jews" like Heisenberg should be caused to "disappear". Since the SS was the private army and police of the Nazi party, and since Jews were openly beaten in the streets while Communists and other opponents of Hitler had been disappearing into concentration camps, this unambiguous threat had to be taken seriously. At this point Heisenberg's struggle with the Aryan physicists took a burlesque turn: Heisenberg's mother could claim a tenuous connection to the commander of the SS, Heinrich Himmler -their fathers had taught and been friends at the same high school in Munich, the Max Gymnasium. Hoping to reach Himmler directly with a letter protesting the attack in Das Schwarze Korps, Heisenberg asked his mother to open a private channel to the SS commander through Himmler's mother, Anna Maria Heyder, a widow in her early seventies who lived in a comfortable middle-class appartment in Munich. The mothers reached immediate understanding. [...] With Mrs. Himmler's introduction as entrée Heisenberg wrote to Himmler on July 21, vigorously protesting Stark's attack and stating he had no choice but to resign his post in Leipzig if Himmler could not put a halt to attacks in the SS newspaper. Heisenberg's new wife, Elizabeth -they had been married only a few months- was much worried when she learned of this letter; it struck her as extremely risky to invite SS scrutiny. But no lightning followed; Heisenberg's effort unfolded with glacial slowness. Not until November did Himmler finally respond to Heisenberg's letter, curtly inviting him to defend himself in detail against Stark's charges. This Heisenberg immediately did, and in the months following others came to his defense as well, including Ernst von Weizsäcker, by then the second-ranking official of the German Foreign Office, and Ulrich von Hassell, the German ambassador to Rome. An official SS inquiry under the personal direction of Reinhard Heydrich, chief of the Gestapo and Himmler's closest associate, ground on into mid-1938. More than once that spring Heisenberg was summoned to the Gestapo headquarters on Prinz Albrecht Strasse in Berlin, where he was interrogated about "the Einstein affair." These sessions were full of danger, since the SS was attempting to rule on the political implications of science it did not understand. Heisenberg was aided in his defense of the objectivity of science by a former student now in the SS, Johannes Juilfs. But despite hiw own gentle treatment, Heisenberg on these distressing trips saw clearly the fate of the friendless in the faces of others brought in for questioning. [...] At last, a year to the day after Heisenberg's letter of protest, Himmler wrote to say that he had been exonerated: "Precisely because you were recommended to me by my family, I caused your case to be examined with special care and intensity. I take pleasure in being able to inform you ... that I have ensured that there will be no further attacks on your person." In a footnote he stipulated a condition: in future Heisenberg should stick to the science under discussion, and forgo mention of the men (Einstein, Bohr) who had made it. Heisenberg was still forced to toe the line. But things might have turned out very differently. On the same day Himmler wrote to Heisenberg, July 21, 1938, he also sent a letter to Heydrich to say he had concluded that "Heisenberg is a decent person and that we cannot afford to lose or to silence decisively ["oder tot zu machen"] this man, who is still young and can still produce a rising generation in science." But Heisenberg's "rehabilitation" came too late to save his appointment as Sommerfeld's successor. The problem, he was told, was Rudolf Hess, political director of the Nazi party, who personally opposed the appointment on political grounds. Heisenberg continued to waver on the question of emigration, telling Columbia University that he was still thinking about teaching there for a semester, but declining to make a promise or set a date. In the end he went only for a few weeks in the summer of 1939, not to live and work but to say goodbye. Thomas Powers, 1993: Heisenberg's War, p. 41 (the references to notes at the end of the book have been omitted.) Little, Brown and Co., 609 pp. ======================= Heisenberg & the Bomb: An Exchange NOVEMBER 6, 2003 Jeremy Bernstein and Peter D. Lax, reply by Thomas Powers To the Editors: In his very interesting commentary on Heisenberg’s recently released letter to his wife from Copenhagen [NYR, August 14], Thomas Powers informs us that “Heisenberg apparently broke all the rules of security to tell his friend [Bohr] about the progress of German research…”—presumably on nuclear weapons. While we can never know exactly what Heisenberg told Bohr, we can know exactly what he didn’t tell him. He did not tell him that the Germans understood the role of “plutonium” as a fissionable explosive and, in particular, the role that reactors play in this. I will explain the quotation marks around “plutonium” after I explain how we know that Heisenberg did not tell Bohr about these things in Copenhagen. The reason we can be sure of this is that when Bohr left Denmark for England in the fall of 1943 he still did not know, as has been attested to by several people, including his son Aage, who were with Bohr at that time. It is confirmed in a letter that Aage Bohr sent to Powers on November 16, 1989, in which he wrote, “Heisenberg certainly drew no sketch of a reactor during his visit in 1941. The operation of a reactor was not discussed at all.”1 At the time of Heisenberg’s visit, as I will now point out, the Germans knew full well that reactors are used to manufacture plutonium. On July 17, 1940, Heisenberg’s protégé C.F. von Weizsäcker sent a five-page document to German Army Ordnance proposing what he called Eka-Rhenium as a nuclear explosive. Eka Rhenium is what we now call “neptunium.” It was soon realized that it decayed into plutonium, an element that had advantages over uranium. On February 26, 1942, a few months after his return from Copenhagen, Heisenberg delivered a lecture at the House of German Research in which he had the following to say about element 94—plutonium: As soon as such a machine [reactor] is on operation, the question of how to obtain explosive material, according to an idea of von Weizsacker, takes a new turn. In the transmutation of the uranium in the machine, a new substance comes into existence, element 94, which very probably—just like 235U_92 [uranium 235—the fissionable isotope]—is an explosive of equally unimaginable force. This substance is much easier to obtain from uranium than 235U_92, however, since it can be separated from uranium by chemical means.2 None of this did he tell Bohr. We can only conjecture what might have happened in the German program if Heisenberg had been able to make a functioning nuclear reactor capable of producing plutonium. Jeremy Bernstein Aspen, Colorado To the Editors: I read with interest in Thomas Powers’s article Heisenberg’s letter to his wife written from Copenhagen after his famous (or infamous) meeting with Niels Bohr in September 1941. If it reveals anything, it is Heisenberg’s colossal insensitivity. An important clue to the context of that famous meeting has been supplied by Arnold Kramish, physicist and later chronicler of the history of nuclear weapons. In 1941 an article appeared in the Swedish newspaper Stockholms-Tidnigendescribing an effort in the United States to build a new type of bomb, out of uranium, with unprecedented explosive power. This news was picked up by the Press Branch of the German Foreign Office, headed by Dr. P.K. Schmidt. He forwarded the report to the physicist Carl von Weizsäcker, Heisenberg’s associate on the German uranium project, and son of the German Foreign Minister Ernst von Weizsäcker. On September 4, 1941, Carl von Weizsäcker informed the Intelligence Branch of the German High Command and Bernhard Rust, minister in charge of the German uranium project. Within two weeks a scientific visit of Heisenberg and Weizsäcker to Copenhagen was arranged. The evidence is overwhelming that the real purpose of the visit was to find out what Bohr knew about the American effort. It is ironical that the report in the Swedish newspaper was premature; the American uranium project did not start until 1942, so there was nothing Heisenberg could have learned from Bohr. But Bohr found out that the Germans had an active uranium project, which he duly reported to the leaders of the Manhattan Project in 1943 after his escape to America. Powers reports that according to Elisabeth Heisenberg her husband’s strongest motivation for the trip was to prevent the use of atomic bombs on Germany. Indeed, had that happened, Heisenberg would have faced the fury of the Führer for failing to build such a weapon for the Reich. Peter D. Lax Professor Emeritus Department of Mathematics New York University New York City Thomas Powers replies: We may not know “exactly” what Heisenberg told Bohr during their meeting in Copenhagen in 1941, but we do know that it included the alarming news that work was proceeding in Germany on the development of an atomic bomb, and that Heisenberg believed the project might succeed if the war lasted long enough. “Unfortunately,” Heisenberg writes in his memoir, Physics and Beyond, “as soon as I mentioned the mere possibility of making atomic bombs, Niels became so horrified that he failed to take in the most important part of my report, namely, that an enormous technical effort was needed. Now this, to me, was so important precisely because it gave physicists the possibility of deciding whether or not the construction of atom bombs should be attempted.” Heisenberg makes it clear that the conversation ended there, and Jeremy Bernstein is probably right that Heisenberg had no chance to tell Bohr in detail how a working nuclear reactor might be used to produce the fissionable material required by bombs. Bernstein does not say why he is stressing this point, but I believe he wishes to demonstrate that Heisenberg really knew how a bomb could be built. On this point we certainly agree; indeed, Heisenberg himself stressed that it was the success of reactor experiments in the summer of 1941 which convinced his small research group that it now confronted “an open road to the atomic bomb.” But how should they deal with this possibility? If bombs were simply impossible to build, as Bohr thought he had proved before the war, then it made no difference whether Heisenberg and his friends busied themselves with atomic research. The discovery that a nuclear reaction in natural uranium would create an unstable new element, which in turn would soon decay into a still heavier fissionable material that could be used in bombs (plutonium), meant that bombs were not so difficult to build after all—still difficult, but not impossibly difficult. How scientists ought to deal with this reality was the question that brought Heisenberg to Copenhagen in September 1941, but the conversation with Bohr failed, as we have seen, and Heisenberg had to decide what to do on his own. In February 1942, as Bernstein points out, the technical aspects of plutonium production were discussed by Heisenberg at a conference in Berlin, but with officials he stressed the uncertainty and expense of trying to use the new material—as yet only a theoretical possibility—for the building of bombs. By the end of the month German military interest in atomic bombs was dead. An attempt by other scientists to revive the effort in June ended once and for all when Heisenberg convinced Albert Speer, in charge of economic mobilization for the war, that “the physicists themselves didn’t want to put much into it. By “Heisenberg’s colossal insensitivity” I presume Professor Lax is referring to Heisenberg’s hope in September 1941 that the war and the German occupation of Denmark would not have ended his friendship with Niels Bohr, nor precluded the possibility that they might still speak openly and honestly to each other. In the event Heisenberg was wrong on that point, and if he had known it in advance he probably never would have gone to Copenhagen. Arnold Kramish’s report of the Swedish press dispatch and what Carl Friedrich von Weizsäcker did with it can be found in Kramish’s book The Griffin, published in 1986. The book contains some interesting material, and some that is hard to verify; Kramish’s sourcing is erratic and often so vague as to be useless. The Swedish press dispatch, for example, is undated, and the letters of Schmidt and Weizsäcker are not sourced at all, unless they are among “the key intelligence documents…to be found in the archives of the Manhattan Project in the US National Archives.” The Manhattan Project files would fill an airplane hangar. But even taken at face value the evidence offered by Lax strikes me as underwhelming “that the real purpose of the visit was to find out what Bohr knew about the American effort.” For whom were they trying to find out? If they were on some kind of official intelligence mission there ought to be evidence of it in the files of the German bomb project, one or more of the various German intelligence agencies, the Foreign Ministry, Hitler’s personal office, and perhaps other agencies as well. Intelligence agencies record everything before, during, and after any operation in voluminous detail, and the great bulk of German files survived the war. And if Heisenberg and Weizsäcker were trying to find out what Bohr knew for themselves, so what? The best evidence for what Heisenberg had in mind in going to Copenhagen is to be found in what he did afterward, and what he did, in a meeting with Albert Speer in June 1942, was to kill official Nazi hopes of building an atomic bomb once and for all. It does not seem to me that Professor Lax has fully grasped this point: the German program to develop atomic weapons, begun with enthusiasm by the German army’s Ordnance Office in September 1939, came to an end when Heisenberg convinced Speer that the physicists thought the effort was too big, too expensive, and too uncertain for Germany to undertake in wartime. It was Heisenberg who did this, not somebody else. 1 Thomas Powers, Heisenberg's War (Da Capo, 2000), p. 536.↩ 2 Jeremy Bernstein, Hitler's Uranium Club (Copernicus, 2001), p. 340. The German original is also given.↩ |
No comments:
Post a Comment