Release of documents relating to 1941 Bohr-Heisenberg meeting
DOCUMENTS RELEASED 6 FEBRUARY 2002
The family of Niels Bohr has decided to release all documents deposited at the Niels Bohr Archive, either written or dictated by Niels Bohr, pertaining specifically to the meeting between Bohr and Heisenberg in September 1941. There are in all eleven documents. The decision has been made in order to avoid possible misunderstandings regarding the contents of the documents.
The documents supplement and confirm previously published statements of Bohr's recollections of the meeting, especially those of his son, Aage Bohr.
The documents have now been organised, transcribed and translated into English at the Niels Bohr Archive. Because of the overwhelming interest in the material, it has been decided that the material should be published in full instead of being made available to scholars upon individual application, as is normal practice at the Niels Bohr Archive.
This has been done by placing facsimiles, transcriptions and translations on this website here.
An illustrated edition of the transcriptions and translations is published in the journal Naturens Verden, Vol. 84, No. 8 - 9. Reprints can be obtained from the Niels Bohr Archive for USD8/EUR8/DKK50 (prepaid).
Release of documents relating to 1941 Bohr-Heisenberg meeting.
Document 1. Draft of letter from Bohr to Heisenberg, never sent. In the handwriting of Niels Bohr's assistant, Aage Petersen. Undated, but written after the first publication, in 1957, of the Danish translation of Robert Jungk, Heller als Tausend Sonnen, the first edition of Jungk's book to contain Heisenberg's letter. Three numbered pages.
Dear Heisenberg,
I have seen a book, “Stærkere end tusind sole” [“Brighter than a thousand suns”] by Robert Jungk, recently published in Danish, and I think that I owe it to you to tell you that I am greatly amazed to see how much your memory has deceived you in your letter to the author of the book, excerpts of which are printed in the Danish edition.
Personally, I remember every word of our conversations, which took place on a background of extreme sorrow and tension for us here in Denmark. In particular, it made a strong impression both on Margrethe and me, and on everyone at the Institute that the two of you spoke to, that you and Weizsäcker expressed your definite conviction that Germany would win and that it was therefore quite foolish for us to maintain the hope of a different outcome of the war and to be reticent as regards all German offers of cooperation. I also remember quite clearly our conversation in my room at the Institute, 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 in Germany to develop atomic weapons and that you said that there was no need to talk about details since you were completely familiar with them and had spent the past two years working more or less exclusively on such preparations. I listened to this without speaking since [a] great matter for mankind was at issue in which, despite our personal friendship, we had to be regarded as representatives of two
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2
sides engaged in mortal combat. That my silence and gravity, as you write in the letter, could be taken as an expression of shock at your reports that it was possible to make an atomic bomb is a quite peculiar misunderstanding, which must be due to the great tension in your own mind. From the day three years earlier when I realized that slow neutrons could only cause fission in Uranium 235 and not 238, it was of course obvious to me that a bomb with certain effect could be produced by separating the uraniums. In June 1939 I had even given a public lecture in Birmingham about uranium fission, where I talked about the effects of such a bomb but of course added that the technical preparations would be so large that one did not know how soon they could be overcome. If anything in my behaviour could be interpreted as shock, it did not derive from such reports but rather from the news, as I had to understand it, that Germany was participating vigorously in a race to be the first with atomic weapons.
Besides, at the time I knew nothing about how far one had already come in England and America, which I learned only the following year when I was able to go to England after being informed that the German occupation force in Denmark had made preparations for my arrest.
All this is of course just a rendition of what I remember clearly from our conversations, which subsequently were naturally the subject of thorough discussions at the Institute and with other trusted friends in Denmark. It is quite another matter that, at that time and ever since, I have always had the definite impression that you and Weizsäcker
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3
had arranged the symposium at the German Institute, in which I did not take part myself as a matter of principle, 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.
This letter is essentially just between the two of us, but because of the stir the book has already caused in Danish newspapers, I have thought it appropriate to relate the contents of the letter in confidence to the head of the Danish Foreign Office and to Ambassador Duckwitz.
Document 2. First draft of congratulatory letter for Heisenberg's 60th birthday (5 December 1961), never sent. In Margrethe Bohr's handwriting. Undated. Two pages.
2. Translation.
Dear Heisenberg
Margrethe and I send you many heartfelt congratulations on the occasion of your birthday, when you can look back on such a rich life’s work in the service of the physical sciences. In particular, I think of all you achieved in the years when it was our great pleasure to have you as a colleague at the Institute in Copenhagen, and I have written a little about the memories from that time in the Festschrift that you will receive on your birthday. That does not mean that I have forgotten everything that has happened since, in which you have always played such a leading role. We have all followed your work in recent years with excitement and look forward to learning more about it when, as you told me in Brussels, you come to Copenhagen for a visit in the spring. I also hope that we shall then have the opportunity to talk to each other in greater detail about what happened during the war, about which I have been asked by so many interested parties/circles, among which such
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great historical interest in precisely those eventful times is now arising. With the wish for many more productive working years, we send you and Elisabeth and the children the warmest wishes.
Document 3. Second draft of congratulatory letter for Heisenberg's 60th birthday, never sent. Typewritten. One page.
30.11.61
Dear Heisenberg,
On the occasion of your 60th birthday, when you can look back on a life’s work which has in such rich measure contributed to the development of the physical sciences in our time, all of us here in Copenhagen send you our most heartfelt congratulations. In particular, I think of everything you achieved during the years when it was our great pleasure to have you as a colleague at the Institute, and in the Festschrift that you will receive on your birthday, I have tried to evoke some of the memories from that time, but that does not mean that I have forgotten everything that has happened since and in which you have played such a leading role. We have all followed your bold thoughts in recent years with excitement and look forward to hearing more about them when, as you told me in Brussels, you come to Copenhagen for a visit in the spring.
In recent years I have become increasingly engaged with historical questions, and as I think I told you, as a first effort I have just completed an account of my recollections of Rutherford and of the developments which his discovery of the atomic nucleus led to and which I look forward to being able to send to you soon.
I hope that, when we meet again, we shall also find the opportunity to talk a little about our experiences throughout the many years, not least during the war, when the long separation between the countries gave rise to different views of events and endeavours.
Margrethe and I send Elisabeth and you and your children our fondest greetings and warmest wishes for many happy years.
Your devoted
Document 4. Heisenberg's response to Bohr's greeting, by telegram (in BSC) on his 60th birthday. Handwritten, on Heisenberg's personal letterhead. There is also a typed version, created upon receipt. Two pages (front and back of one sheet).
WERNER HEISENBERG
München 23
Rheinlandstrasse 1
22.12.61.
Lieber Bohr!
Hab den herzlichsten Dank für Deinen Glückwunsch und den Aufsatz über die Entstehung der Quantenmechanik, der mich so lebendig an die schöne Zeit in Deinem Institut erinnert hat und an all das, was ich von Dir lernen konnte. Wie anders ist die Physik seit dieser Zeit geworden! Es kommt mir beinahe merkwürdig vor, jetzt wieder wie neulich in Brüssel an dem Kampf der Meinungen teilzunehmen und die verschiedenen widersprechenden Argumente auf die Goldwage zu legen so wie wir es vor 30 Jahren in Kopenhagen getan haben. Die jungen Physiker schauen dabei etwas verwundert zu, weil sie sich vielleicht an die Vorstellung gewöhnt haben, dass man schliesslich nur hinreichend viele Physiker an hinreichend grosse Maschinen stellen müsste, dann kommt schliesslich alles von selbst in Ordnung. Aber dies soll kein elegischer Brief sein; ich habe im Gegenteil die
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Diskussionen in Brüssel sehr genossen, und ganz besonders noch deshalb, weil Du auch wieder dabei warst. Übrigens hatte ich seitdem noch eine besondere Freude: die relative Parität von Sigma- und Lambda-Teilchen, über die ich mit Salam und anderen in Aix en Provence und Brüssel verschiedener Meinung war, ist inzwischen in Kalifornien gemessen worden und kommt ungerade heraus, so wie es aus den Rechnungen von Dürr u. mir sich ergeben hatte. Man fängt also doch an, das komplizierte Spektrum der Elementarteilchen zu verstehen.
Ich hoffe, dass es Dir gesundheitlich gut geht und dass Ihr Euch zum Jahreswechsel an den Besuchen der grossen Familie, Kindern und Enkeln, freuen könnt.
Mit vielen herzlichen Grüssen, auch von Elisabeth u. den Kindern
Dein
Werner
Document 5a. Draft of letter from Bohr to Heisenberg, never sent. Carbon copy of Document 5b, without handwritten corrections. One page.
27.12.61
Dear Heisenberg,
Thank you for your kind letter. It was a pleasure for me to attempt to evoke some memories from the old days in my small contribution to the Festschrift on your 60th birthday. At my age it is only natural that I dwell more and more on thoughts of the great adventure which we all experienced, and, as I told you in Brussels, I have in a Rutherford Lecture, of which I hope soon to be able to send you a reprint, described some of my memories both of Rutherford himself and of the developments that the discovery of the atomic nucleus led to.
At the moment I am also occupied by an account requested from many quarters of the role of nuclear physics in the dark times that we all had to live through during the last war, and thereby, as with any other historical investigation, I have felt how difficult it is to form an accurate impression of events in which many have taken part. I hope that we shall have the opportunity to talk in more detail about such questions and to clear up various misunderstandings, especially in connection with the visit by you and Weizsäcker to Copenhagen in 1942(?), the background and purpose of which I am still being asked about from many quarters.
We were all very interested to hear about the confirmation that the latest experiments have given of your conclusions about the problems of symmetry for some elementary particles, and we look forward to hearing more about this when you come to Copenhagen in the spring.
Margrethe joins me in sending the warmest wishes for a happy new year to you and all the family.
Your devoted
Document 5b. Draft of letter from Bohr to Heisenberg, never sent. Identical to Document 5a except for handwritten additions (<>) and deletions. The document includes an addition on a separate page in Niels Bohr's assistant, Jørgen Kalckar's, handwriting. Two pages.
Dear Heisenberg,
Thank you for your kind letter. It was a pleasure for me to attempt to evoke some memories from the old days in my small contribution to the Festschrift on your 60th birthday. <(1)–(2)> At my age it is only natural that I dwell more and more on thoughts of the great adventure which we all experienced, and, as I told you in Brussels, I have in a Rutherford Lecture, of which I hope soon to be able to send you a reprint, described some of my memories both of Rutherford himself and of the developments that the discovery of the atomic nucleus led to.
At the moment I am also occupied by an account requested from many quarters of the role of nuclear physics in the dark times that we all had to live through during the last war, and thereby, as with any other historical investigation, I have felt how difficult it is to form an accurate impression of events in which many have taken part. I hope that we shall
Margrethe joins me in sending the warmest wishes for a happy new year to you and all the family.
Your devoted
[HANDWRITTEN PAGE]
(1) Your remarks comparing the discussions then and such as those we experienced in the autumn at the Solvay Meeting in Brussels amused me, but I also agree that the difference is not so great, and we are all profoundly interested to hear about the confirmation that the most recent experiments have given of your conclusions as regards the relative parity of the Σ and Λ particles. We look forward to hearing more about your general views when you come to Copenhagen in the spring. (2)
Document 6. Draft document in Margrethe Bohr's handwriting. Undated. Two pages.
The conversations with German physicists in the autumn of 1942.
Through the German authorities Heisenberg and Weizsäcker had arranged a physics conference at the German Institute in Copenhagen, which had been established by the occupying power. Only a few Danes took [part] in this conference, and among them none of the leading physicists at the University’s Institute for Theoretical Physics. During those days, however, Heisenberg and Weizsäcker visited this Institute and had conversations with Chr. Møller as well as with Bohr.
During a conversation with Bohr, Heisenberg stated that he was working on the release of atomic energy and expressed his conviction that the war, if it did not end with a German victory, would be decided by such means. Heisenberg said explicitly that he did not wish to enter into technical details but that Bohr should understand that he knew what he was talking about as he had spent 2 years working exclusively on this question.
Bohr restrained himself from any comment but understood that this was important information which he was obliged to try to bring to the attention of the English.
During conversations with Møller, Heisenberg and Weizsäcker sought to explain that the attitude of the Danish people towards Germany, and that of the Danish physicists in particular, was unreasonable and indefensible since a German victory was already guaranteed and that any resistance
[NEW PAGE] against cooperation could only bring disaster to Denmark. In a conversation with Møller, Weizsäcker further stated how fortunate it was that Heisenberg’s work would mean so much for the war since it would mean that, after the expected great victory, the Nazis would adopt a more understanding attitude towards German scientific efforts.
Document 7. Incomplete draft of letter(s) from Bohr to Heisenberg, never sent. In the handwriting of Margrethe Bohr, with corrections by Niels Bohr, added in Aage Bohr's handwriting (<>). Last page may be continuation of Document 8. Undated. Three pages.
Dear Heisenberg
In recent years I have had many requests from many quarters for information regarding my experiences. Thus, like so many others, I have been invited to take part in the efforts to provide and preserve material that will shed light on the development of physics in our time and to which end the Academy in Washington has chosen a special commission. Similarly, I have [had requests] from committees that have been established in many countries to investigate all archival material that can shed light on the preparation and discussion of the application of the results of atomic physics for military purposes, and in particular I have had many enquiries about the circumstances of the visit by you and Weizsäcker to Copenhagen in 1941.
[NEW PAGE] the extent to which such an account can be published in the near future is quite another matter. In this connection I am frequently asked about the background and purpose of the visit by you and Weizsäcker to Copenhagen in 1941. It is very difficult for me to give an answer because, as you know from our conversations in Tisvilde, both shortly after the war and during you and your family’s summer stay in Liseleje, [I] got a completely different impression of the visit than the one you have described in Jungk’s book. I remember quite definitely the course of these conversations, during which I naturally took a very cautious position, when
[NEW PAGE] how all this really fits together. It is obvious that during the course of the war such a wise person as yourself must gradually lose faith in a German victory and end with the conviction of defeat, and I can therefore understand that perhaps at the end you may no longer have recalled what you had thought and what you had said during the first years of the war. But I cannot imagine that, during a meeting so boldly arranged as that in 1941, you should have forgotten what arrangements had been made in this regard with the German government authorities, and it is on that point that all the interest of other governments focuses. I therefore very much hope that, by telling me a little about this, you can contribute to the clarification of what is a most awkward matter for us all.
Document 8. Handwritten notes. First and last few words, as well as some words overwritten for clarification, in Margrethe Bohr's handwriting (<>); the remainder in Niels Bohr's handwriting. Undated. "(1)-(2)" is in Aage Bohr's handwriting; it may mean that the passage at the end of document 9 should be inserted here. Last page of Document 7 may be the continuation. One page.
Document 9. Notes dictated by Niels Bohr in the handwriting of Aage Bohr. Undated. Last sentence clearly intended to be inserted at end of first paragraph on second page ("(1)-(2)"). Three pages.
Notes to Heisenberg.
As soon as I came to England and learned about the great American English preparations, I naturally had to
When I came to England in 1943 and was acquainted with the great American– English preparations, the question of how far Germany had come was naturally of the greatest importance both for physicists and for government authorities. I had the opportunity to discuss this question thoroughly both with the English intelligence service and with members of the English government, and I naturally reported all of our experiences including in particular the impression I got both during the visit to Copenhagen by you and Weizsäcker as well as during Jensen’s.
As the war approached its conclusion and Germany’s position became ever more difficult, the fear that it should succeed in producing atomic weapons naturally decreased, nor did their use in the war against Germany become an issue. [NEW PAGE]
In that connection I have also been asked how your journey to Copenhagen was arranged and what authorization you had been given to speak to me about a question which was surrounded by such great secrecy and held such great political problems. (1)–(2)
As regards Jensen’s visit to Copenhagen in 1943, the war had already at that time taken a course quite different from what you and Weizsäcker expressed as your conviction in 1941. Jensen described the efforts to increase the production of heavy water in Norway and mentioned in this connection that, for him and other German physicists, it was only a matter of an industrial application of atomic energy. At that time, however, I had to be very cautious and sceptical, partly on the basis of rumours of new German weapons, partly because of my own difficult position due to the constant surveillance of the German police.
Of course, it is your account published in Jungk’s book which has created such keen public interest in all these wartime connections
When I, especially after the publication of Jungk’s book, about which I have been questioned not only by colleagues in many different countries, but especially as a consequence of the thorough investigations of archives, which one from
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I recall that you said in that connection that you did not know what I thought but that you had worked so closely with it yourself that
(1) (Because of the great experience that I had in subsequent years through connection with counterespionage by the secret intelligence service, I fully understand the reason for such questions.) (2)
Document 10. Incomplete draft of letter from Bohr to Heisenberg, never sent. In the handwriting of Margrethe Bohr. Undated, but written after Bohr had received reprints of his Rutherford Lecture on 15 March 1962. Five pages.
Dear Heisenberg
I hereby send a reprint of a Rutherford Lecture in which I have tried to tell a little about my memories of the developments prompted by the discovery of the atomic nucleus. As you have seen from the small article I wrote for your 60th birthday and from my lecture at the opening of the 50-year anniversary Solvay Meeting, I have been much occupied in recent years with historical studies of physics, which incidentally have now been taken up by an American committee established by the Washington Academy and the Carnegie Foundation, and the intention is that in the coming years Kuhn, who is to lead the project, will have a fixed base in Copenhagen for a secretariat and an archive.
While occupying myself with such matters I have, of course, many times felt the difficulty of giving an accurate account of developments in which many different people have taken part, and I have felt this most strongly in describing what took place during the war in connection with the atomic energy projects. In the latter case there has been very keen interest from various quarters, and the governments of several countries have even begun investigations using existing archives.
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2
Similarly, committees have been established in various countries in order to shed light on the discussions and preparations during the war that preceded the application of the results of atomic physics for military purposes, and from many quarters I have been asked in particular about the arrangement for and the purpose of the visit by you and Weizsäcker to Copenhagen in 1941.
This has been very difficult for me to answer since, as you know from our conversations after the war, I have a completely different perception of what took place during the visit than that you have expressed in your contribution to Jungk’s book.
For us in Copenhagen, who found ourselves in such a difficult and dangerous position during the German occupation, the visit was an event that had to make a quite extraordinary impression on us all, and I therefore carefully noted every word uttered in our conversation, during which, constantly threatened as we were by the surveillance of the German police, I had to assume a very cautious position. I am thinking not only of the strong conviction that you and Weizsäcker expressed concerning German victory, which did not correspond to our
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3 hopes, but more of how, during the course of the war, your conviction had to become less strong and finally end with the certainty of Germany’s defeat. Therefore it would not be incomprehensible if it were difficult for you to keep track of how, against the background of changing circumstances, statements on the part of the Germans changed from year to year. On the other hand I remember quite clearly the impression it made on me when, at the beginning of the conversation, you told me without preparation that you were certain that the war, if it lasted long enough, would be decided with atomic weapons. I did not respond to this at all, but as you perhaps regarded this as an expression of doubt, you related how in the preceding years you had devoted yourself almost exclusively to the question and were quite certain that it could be done,
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4 but you gave no hint about efforts on the part of German scientists to prevent such a development.
It is true that, during his visits to Copenhagen in 1943 on his journeys to Norway to participate in the efforts to increase the production of heavy water, Jensen did make hints in such a direction, but because of his own mission and the constantly growing rumours of new German weapons, I necessarily had to be very sceptical and extremely cautious in my ever more dangerous existence. It was only a few months later when, in order to avoid imminent arrest by the German police, I escaped to Sweden and arrived in England that I heard about the great preparations that were under way there and in the USA and how far they had come. The question of how far Germany had come occupied not only the physicists but especially the govern-
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5 ment and the secret intelligence service, and naturally I had to tell the latter and some members of the government about all the experiences we had had in Copenhagen and in particular about the visits by you and Weizsäcker and Jensen, which gave rise to thorough discussions about the conclusions which could be drawn about the information given during the conversations and their comparison with everything that the intelligence service had been able to obtain. The point which was put forward during these discussions, and with which all later enquiries have been particularly concerned, was how the visit had been arranged and what purpose lay behind it, as one has wondered in particular how and with what authorization such a dangerous matter, of such great political importance, could be taken up with someone in an occupied and hostile country.
Document 11a.
Incomplete draft of letter from Bohr to Heisenberg, never sent. First of three versions: draft in Aage Bohr's handwriting. Undated Five numbered pages.
Dear Heisenberg.
I have long been meaning to write to you on a matter about which I am constantly being asked from so many different quarters. It concerns the visit by you and Weizsäcker to Copenhagen in the autumn of 1941. As you know from our conversations in the first years after the war, we here got quite a different impression of what happened during this visit than the one you have expressed in Jungk’s book. The particular reason that I write to you is that the whole question of the atomic energy projects during the war has been made the subject of thorough studies in England based on access to government archives, including material held by the intelligence service. In this connection, I have had detailed conversations about my affiliation with the whole project, during which questions about your visit in 1941 were also brought up. I have therefore thought it most proper to try to give you as accurate an impression as possible of how we perceived the visit here.
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2.
Although we realized that behind the visit there was a wish to see how we were faring in Copenhagen in the dangerous situation during the German occupation and find out what advice you could give us, you must also have understood that it brought us, who lived only on the hope of defeat for German Nazism, in a difficult situation to meet and talk to someone who expressed as strongly as you and Weizsäcker your certain conviction of a German victory and confidence in what it would bring. Naturally, we understand that it may be difficult for you to keep track of how you thought and expressed yourselves at the various stages of the war, the course of which changed as time passed so that the conviction of German victory gradually had to weaken and finally end with the certainty of defeat.
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3.
However, what I am thinking of in particular is the conversation we had in my office at the Institute, during which, because of the subject you raised, I carefully fixed in my mind every word that was uttered. It had to make a very strong impression on me that at the very outset you stated that you felt certain that the war, if it lasted sufficiently long, would be decided with atomic weapons. I had at that time no knowledge at all of the preparations that were under way in England and America. You added, when I perhaps looked doubtful, that I had to understand that in recent years you had occupied yourself almost exclusively with this question and did not doubt that it could be done. It is therefore quite incomprehensible to me that you should think that you hinted to me that the German physicists would do all they could to prevent such an application of atomic science. During the conversation, which was only very brief, I was naturally very cautious but nevertheless thought a lot about its content, and my alarm was not lessened by hearing from the others at the Institute that Weizsäcker had stated how fortunate it would be for the position of science in Germany after the victory that you could help so significantly towards this end.
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4.
In your letter to Jungk you also mention Jensen’s visits to Copenhagen in 1943 during his journeys to Norway to participate in the efforts to increase the production of heavy water. It is true that Jensen emphasized to us that this work was only aimed at the production of energy for industrial purposes, but although we were inclined to trust his sincerity, we felt in no way certain regarding how much he himself knew about the whole effort in Germany. In those years there were often announcements from Germany of new and decisive weapons. At the meetings with Jensen, I was likewise extremely cautious as a result of the constantly growing surveillance on the part of the German police.
When I had to escape to Sweden in the autumn of 1943 in order to avoid imminent arrest and from there went to England, I learned for the first time about the already then well-advanced American–English atomic project. The question of how far Germany had come occupied not only the physicists but also the governments and the intelligence service, and I became involved in the discussions about this. I recounted all our experiences in Copenhagen, and in this connection the question was also raised about what authorization might have been given to you by the German government to touch upon such a dangerous question, with such great political consequences, with someone in an occupied and hostile country. However, the discussions had no decisive influence one way or the other, since
[NEW PAGE]
5. it was quite clear already then, on the basis of intelligence reports, that there was no possibility of carrying out such a large undertaking in Germany before the end of the war.
I have written at such length to make the case as clear as I can for you and hope that we can talk in greater detail about this when the opportunity arises.
Document 11b.
Incomplete draft of letter from Bohr to Heisenberg, never sent. Second of three versions: carbon copy of Document 11c, without the handwritten corrections. The text is practically identical to Document 11a. Underlined heading in Aage Bohr's handwriting. Three numbered pages.
Draft.
Never completed.
NB decided not to write.
26.3.1962
Dear Heisenberg.
I have long been meaning to write to you on a matter about which I am constantly being asked from so many different quarters. It concerns the visit by you and Weizsäcker to Copenhagen in the autumn of 1941. As you know from our conversations in the first years after the war, we here got quite a different impression of what happened during this visit than the one you have expressed in Jungk’s book. The particular reason that I write to you is that the whole question of the atomic energy projects during the war has been made the subject of thorough studies in England based on access to government archives, including material held by the intelligence service. In this connection, I have had detailed conversations about my affiliation with the whole project, during which questions about your visit in 1941 were also brought up. I have therefore thought it most proper to try to give you as accurate an impression as possible of how we perceived the visit here.
Although we realized that behind the visit there was a wish to see how we were faring in Copenhagen in the dangerous situation during the German occupation and find out what advice you could give us, you must also have understood that it brought us, who lived only on the hope of defeat for German Nazism, in a difficult situation to meet and talk to someone who expressed as strongly as you and Weizsäcker your certain con-
[NEW PAGE]
- 2 - viction of a German victory and confidence in what it would bring. Naturally, we understand that it may be difficult for you to keep track of how you thought and expressed yourselves at the various stages of the war, the course of which changed as time passed so that the conviction of German victory gradually had to weaken and finally end with the certainty of defeat.
However, what I am thinking of in particular is the conversation we had in my office at the Institute, during which, because of the subject you raised, I carefully fixed in my mind every word that was uttered. It had to make a very strong impression on me that at the very outset you stated that you felt certain that the war, if it lasted sufficiently long, would be decided with atomic weapons. I had at that time no knowledge at all of the preparations that were under way in England and America. You added, when I perhaps looked doubtful, that I had to understand that in recent years you had occupied yourself almost exclusively with this question and did not doubt that it could be done. It is therefore quite incomprehensible to me that you should think that you hinted to me that the German physicists would do all they could to prevent such an application of atomic science. During the conversation, which was only very brief, I was naturally very cautious but nevertheless thought a lot about its content, and my alarm was not lessened by hearing from the others at the Institute that Weizsäcker had stated how fortunate it would be for the position of science in Germany after the victory that you could help so significantly towards this end.
In your letter to Jungk you also mention Jensen’s visits to Copenhagen in 1943 during his journeys to Norway to participate in the efforts to increase the production of heavy water. It is true that Jensen emphasized to us that this work was only aimed at the production of energy for industrial purposes, but although we were inclined to trust his sincerity, we felt in no way certain regarding how much he himself knew about the whole effort in Germany.
[NEW PAGE]
- 3 -
In those years there were often announcements from Germany of new and decisive weapons. At the meetings with Jensen, I was likewise extremely cautious as a result of the constantly growing surveillance on the part of the German police.
When I had to escape to Sweden in the autumn of 1943 in order to avoid imminent arrest and from there went to England, I learned for the first time about the already then well-advanced American–English atomic project. The question of how far Germany had come occupied not only the physicists but also the governments and the intelligence service, and I became involved in the discussions about this. I recounted all our experiences in Copenhagen, and in this connection the question was also raised about what authorization might have been given to you by the German government to touch upon such a dangerous question, with such great political consequences, with someone in an occupied and hostile country. However, the discussions had no decisive influence one way or the other, since it was quite clear already then, on the basis of intelligence reports, that there was no possibility of carrying out such a large undertaking in Germany before the end of the war.
I have written at such length to make the case as clear as I can for you and hope that we can talk in greater detail about this when the opportunity arises.
Document 11c.
Incomplete draft of letter from Bohr to Heisenberg, never sent. Third of three versions: typed letter, with additions (<>) and deletions in Margrethe Bohr's handwriting. Underlined heading in Aage Bohr's handwriting. Three numbered pages.
Draft.
Never completed.
NB decided not to write.
26.3.1962
Dear Heisenberg.
I have long been meaning to write to you on a matter about which I am constantly being asked from many different quarters. It concerns the visit by you and Weizsäcker to Copenhagen in the autumn of 1941. As you know from our conversations in the first years after the war, we here got quite a different impression of what happened during this visit than the one you expressed in Jungk’s book. The particular reason that I write to you is that the whole question of the atomic energy projects during the war has been made the subject of thorough studies in England based on access to government archives, including material held by the intelligence service. In this connection, I have had detailed conversations about my affiliation with the whole project, during which questions about your visit in 1941 were also brought up. I have therefore thought it most proper to try to give you as accurate an impression as possible of how we perceived the visit here.
Although we realized that behind the visit there was a wish to see how we were faring in Copenhagen
[NEW PAGE] - 2 - viction of German victory gradually had to weaken and finally end with the certainty of defeat.
However, what I am thinking of in particular is the conversation we had in my office at the Institute, during which, because of the subject you raised, I carefully fixed in my mind every word that was uttered. It had to make a very strong impression on me that at the very outset you stated that you felt certain that the war, if it lasted sufficiently long, would be decided with atomic weapons. At that time no knowledge at all of the preparations that were under way in England and America,
In your letter to Jungk you also mention Jensen’s visits to Copenhagen in 1943 during his journeys to Norway to participate in the efforts to increase the production of heavy water. It is true that Jensen emphasized to us that this work was only aimed at the production of energy for industrial purposes, but although we were inclined to trust his sincerity, we felt in no way certain regarding how much he himself knew about the whole effort in Germany.
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In those years there were often announcements from Germany of new and decisive weapons. At the meetings with Jensen, I was likewise extremely cautious as a result of the constantly growing surveillance on the part of the German police.
When I had to escape to Sweden in the autumn of 1943 in order to avoid imminent arrest and from there went to England, I learned for the first time about the already then well-advanced American–English atomic project. The question of how far Germany had come occupied not only the physicists but also the governments and the intelligence service, and I became involved in the discussions about this. I recounted all our experiences in Copenhagen, and in this connection the question was raised about what authorization might have been given to you by the German government to touch upon such a dangerous
I have written at such length to make the case as clear as I can for you and hope that we can talk in greater detail about this when the opportunity arises.
Niels Bohr Archive, Blegdamsvej 17, DK-2100 Copenhagen Ø, Denmark http://www.nba.nbi.dk/papers/docs/cover.html