Ladies and Gentlemen:


When "Copenhagen" opened in New York two years ago, Brian Schwartz organized a Symposium at CCNY that lasted one whole day. Likewise when the touring company came to Washington, DC in March this year. Now we are in Boston, and because this is MIT we have to say everything faster and smarter and be done in ten minutes each. So: down to the basics it is. Nevertheless, I am very grateful to both Brian Schwartz and Wiltrud Simbuerger for organizing the event for us all to confer and compare our data. My gratitude also goes to Thomas Powers and Michael Frayn, the early champions of my father’s historical records. Today I want to talk to you about how I view this record. Copenhagen has allowed for some ambiguity. Yet, it has angered some people. My remarks are particularly directed at them.


I had the privilege of growing up with a father, whose primary way of communication was through rational thought and argumentation. But also, whom I consistently experienced as a warm, caring, compassionate, and principled human being with tremendous inner strength and resources. He taught us children a love for the outdoors and for mountain climbing. He encouraged painting and played music with us. He recited poetry, made puns and jokes, played competitive as well as silly games with us, and also talked to us about the spiritual, which he termed the central order. My high school in Göttingen was just across from his institute and after school I would pick him up and on our way home for lunch we talked about physics, most of it way over my head, as, for example, the uncertainty relation was. I can remember occasions when he told me about how different the approaches to reality can be, and he compared Goethe’s approach to colors with Newton’s. They both were right, they just addressed different aspects of reality. Thus he introduced me to those things that were of great importance to him.


Music was my father’s equivalent to emotional passion, if you will. He played regularly for himself and with others, and it provided a connection to the people who were not his scientific peers. If I know him so well now, it is especially due to the many hours of music we played together.


So, when it comes to my father, I am surprisingly biased. I will today go over those areas that illustrate how some public notions have clashed with what I know from him personally.

My father had told us that the German scientists had only worked on designing and building a nuclear reactor. Other people want to believe, he tried to build an atomic bomb and failed. I am biased and trust my father, but I had to find out: last year my wife and I went to Haigerloch and looked at the reconstructed reactor. As a physicist, I clearly recognized that this was indeed a reactor, albeit without too many safety features, to put it mildly. The contrast to Los Alamos couldn’t be greater. Also, there was nothing of the industrial effort as in the V2-Rocket installations.


My father also told us that he, Otto Hahn, and other scientists advised the Nazi brass such as Speer, Milch, and others that building a nuclear weapon was possible but would take at least three years of development, knowing this would end any such program. Instead they wanted to develop a reactor. I trust my father, but I am biased and had to check it out: Thus I read from Albert Speer’s memoirs: "After the talk I asked Heisenberg how nuclear physics can be used for the production of atomic bombs. His reaction was by no means encouraging..." Further down Speer writes: "Following the recommendation by the nuclear physicists already in the fall of 1942 we gave up all claim to develop atomic bombs. After my renewed questions about deadlines I was informed that we could not count on anything before 3 or 4 years down the line. By that time the war had to be long decided. Instead, I gave permission to develop a Uranium reactor to power machines..."


My father told us that he had informed the people in the government that a bomb would require a critical mass roughly the size of a pineapple. Some people want to believe he mistakenly thought it would take several tons. I am biased but checked Diebner’s official report of the so called Uranium Club to the Army Ordnance Ministry. I read that the estimate was of 10 to 100 kg U-235 for a nuclear bomb, which translates to just about the size of a pineapple, confirming his truthfulness. This was known at the time my father went to Copenhagen.


My father spoke to us about the atrocities Germany committed during the Nazi era but he was opposed to the Nazis’ ideology, their anti-Semitism, and their leaders from the start. Others want to believe that this was not true on all three counts, and that he even worked for them. I looked for evidence in his long philosophical treatise: ‘Ordnung der Wirklichkeit’ written between 1941 and the end of ’42. Here he clearly articulates his views on the political state that the Nazis had established, a state in violation of basic law. He writes that political power is always accrued by criminal means and that revolutions hate the law, but that in the end the wrongs do right themselves throughout history. For the same reasons he was a staunch anti-Communist as well. He predicted during the 1970’s what nobody could conceive of: The fall of the Berlin wall, and re-unification of Germany before the year 2000.


My father told us that he examined the role of the scientist vis-a-vis a political system and that he was ethically opposed to building nuclear bombs for the Nazi regime. Knowing him, I believe him, but I am biased and I had to check it out. Again, in 1942 in ‘Reality and its Order’ he wrote: "Against his will, the scientist has become the people’s magician to whom the forces of nature are obedient. But his power can only turn to good when he is simultaneously a priest and acting only as mandated by the deity or by destiny."


We learned from my father that the right to free speech had been taken away, which necessitated extreme caution as a survival strategy. I accepted it as part of those dark times. Helmut Rechenberg who heads the Werner Heisenberg Archive, documents in his recent article "Copenhagen and the Nature of the German Uranium Project", which will soon appear in the "Festschrift" in honor of my father’s 100th birthday, how my father’s remark on a trip to Zürich got him in trouble with the authorities. Six months before the end of the war he dared say that Germany will lose the war, and Walter Gerlach, the project manager, had to intercede for him with Nazi officials. Earlier trips abroad, notably the Copenhagen and Holland ones, found him much more blatantly pronouncing the Nazi version of reality. He was always under watch and considered quite expendable to the regime, which was brought home to him early on when he fought for quote "Jewish Physics".


We now know that the misunderstanding between my father and Niels Bohr at their 1941 Copenhagen meeting started even before he got there: Bohr describes his reference point in the recently released documents as: "... we had to be regarded as representatives of two sides engaged in mortal combat." My father’s reference point can be found in ‘Reality and Its Order.’’"We have to continuously be mindful that it is more important to act humanely towards one another than to fulfill any professional obligations, or national obligations or political obligations."


My father told us that one of the reasons he came to Copenhagen was to ensure that the institute remained under Danish control. He achieved that. According to him, a second reason was to use his influence for Bohr’s safety. I am biased, but Bohr’s documents say: "I have always had the definite impression that you and Weizsäcker had arranged the symposium at the German Institute,[ ...], and the visit to us in order to assure yourselves that we suffered no harm and to try in every way to help us in our dangerous situation." Further, C.F. von Weizsäcker describes their actions in Copenhagen : "Anyway, we were able to talk openly and with ease to those delegates at the embassy that were close to the circle around my father. We naturally touched upon our concern about Bohr and did get assurances that they were willing to do for Bohr’s welfare whatever was within their means."


My father told us that on their walk he spoke only between the lines and as a result Bohr misunderstood him immediately. Naturally, I am biased. But, fortunately, this too is confirmed in the Bohr documents: "... where in vague terms you spoke in a manner that could only give me the firm impression that, under your leadership, everything was being done to develop weapons ...".


Do I believe that he actually tried to convey the very opposite? Of course I do, because that is what the scientists actually did when it came to that decision in Germany. Let me fast forward to April 1945: When the American Alsos mission came upon the tiny cave in the mountain where the research installation of the nuclear reactor was hidden, their expectations were dumbfounded. The deserted place showed no evidence of any bomb-building whatsoever, and on a chalkboard there was the witty ditty: "Deine Ruh, die sei Dir heilig, nur Verrückte haben’s eilig". <Keep your holy calm, only fools are madly rushing > which is hardly the motto for a feverish race towards anything. Even more telling is a diary entry, dated May 24, 1945, by Erich Bagge, one of the German scientists: "An amusing piece of news reached us this noon. The "Stars and Stripes" are featuring a 15- line piece on the failed attempts of the Germans to build an atomic bomb". The myth of failure had begun....


After the war my father did, what he always had said he needed to do. He helped rebuild and shape science in Germany. He continued to oppose arming Germany with nuclear weapons by signing the declaration of the ‘Göttingen 18’ in 1958. And to the end of his days as president of the Alexander von Humboldt Foundation he was actively expressing his belief that science is international.


Yes, I am biased, now more than ever, because whenever I was searching out the supporting evidence, I found that my biased view was verifiable by the historical records. I encourage you to use the same approach and am giving you a web- site address, if you choose to follow my advice. .....


Thank you for your attention.


[Special thanks are given to H.Rechenberg and W.Blum for their help in the research. Also to I. Heisenberg for valuable help in preparing this manuscript. Quotes were taken from H.Rechenberg’s article: "Copenhagen and the Nature of the German Uranium Project"]




Excerpt from Albert Speer’s memoirs:(p.226-228)


After the lecture I asked Heisenberg how nuclear physics could be applied to the manufacture of atom bombs. His answer was by no means encouraging. He declared, to be sure, that the scientific solution had already been found and that theoretically nothing stood in the way of building such a bomb. But the technical prerequisites for production would take years to develop, two years at the earliest, even provided that the program was given maximum support. Difficulties were compounded, Heisenberg explained, by the fact that Europe possessed only one cyclotron, and that of minimal capacity. Moreover, it was located in Paris and because of the need for secrecy could not be used to full advantage. I proposed that with the powers at my disposal as Minister of Armaments we build cyclotrons as large or larger than those in the United States. But Heisenberg said that because we lacked experience we would have to begin building only a relatively small type.

Nevertheless, General Fromm offered to release several hundred scientific assistants from the services, while I urged the scientists to inform me of the measures, the sums of money, and the materials they would need to further nuclear research. A few weeks later they presented their request: an appropriation of several hundred thousand marks and some small amounts of steel, nickel, and other priority metals. In addition, they asked for the building of a bunker, the erection of several barracks, and the pledge that their experiments would be given highest priority. Plans for building the first German cyclotron had already been approved. Rather put out by these modest requests in a matter of such crucial importance, I suggested that they take one or two million marks and correspondingly larger quantities of materials. But apparently more could not be utilized for the present, and in any case I had been given the impression that the atom bomb could no longer have any bearing on the course of the war.


On the suggestion of the nuclear physicists we scuttled the project to develop an atom bomb by the autumn of 1942, after I had again queried them about deadlines and been told that we could not count on anything for three or four years. The war would certainly have been decided long before then. Instead I authorized the development of an energy-producing uranium motor for propelling machinery. The navy was interested in that for its submarines.



Diebner’s report to the "Heereswaffenamt"; translation of the German text below.


    1. Heatengines (discussion of reactors) ...
    2. Explosives. The detrimental effect of 238U increases with increasing temperature. Thus, an explosive could only contain very small amounts of 238U. In addition to a complete isotope separation, which is principally doable but technically rather difficult, today we know in theory a second way to produce explosives. This, however, can only be tested once a heat-engine is running. By absorption of neutrons on 238U a substance ("element 94") is being formed that should be even more fissionable than 235U. Since this substance is chemically different from U it can be separated from the U of a shut-down heat engine. Presently we do not know the rate at which it is generated nor the properties of it well enough to make precise predictions.

Since in every substance there are a few free neutrons it would suffice for ignition of the explosive to spatially combine sufficient amounts (estimated at 10 – 100 kg).


Original German text (page 10-12):

    1. Wärmemaschine. ...
    2. Sprengstoff. Die störende Wirkung von 238U nimmt mit wachsender Temperatur zu. Ein Sprengstoff würde daher höchstens sehr kleine Mengen von 238U enthalten dürfen. Ausser der vollständigen Isotopentrennung, die grundsätzlich sicher durchführbar aber technisch sehr schwierig ist, kennen wir heute theoretisch einen zweiten Weg zur Herstellung eines Sprengstoffs, der aber erst erprobt werden kann, wenn eine Wärmemaschine läuft. Aus 238U bildet sich nämlich durch die Absorption von Neutronen ein Stoff ("Element 94"), der noch leichter spaltbar sein muss als 235U. Da dieser Stoff chemisch von Uran verschieden ist, muss man ihn aus dem Uran einer stillgelegten Maschine leicht abtrennen können. Doch kennen wir heute weder die Menge, in der er entsteht, noch seine Eigenschaften genau genug für eine ganz sichere Voraussage.

Da sich in jeder Substanz einige freie Neutronen befinden, würde es zur Entzündung des Sprengstoffs genügen, eine hinreichende Menge (vermutlich etwa 10-100 kg) räumlich zu vereinigen.


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