Bohr-Heisenberg Letters

Draft of the first 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.

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 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 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

Read all the Bohr – Heisenburg letters here – nba.nbi.dk

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2 Responses to Bohr-Heisenberg Letters

  1. alfy says:

    Deskarati is to be congratulated on publishing this letter. I feel now able to forgive Michael Frayn for the awful play, “Copenhagen” that he wrote about this interaction between Heisenberg and Bohr. Frayn is a nice man and he has produced some excellent writing and thought provoking plays.

    However, on wading through the translation of this tortuous letter I think I can see what he was up against. I tried to simplify Bohr’s argument by removing all the un-necessary subordinate clauses, and redundant adjectives, just to get to the meat of it. My summary follows later. Then I tried just writing the gist of it in a few sentences. My ultimate summary is this. “Heisenberg met Bohr. Bohr kept his mouth shut while Heisenberg talked. Ever after the two men had different interpretations of what that silence meant.”

    If I had waded through any more of this correspondence as poor Frayn probably did, I would have lost the will to live.

    BOHR HEISENBURG CORRESPONDENCE
    (Severe abridgement of original English translation)
    Dear Heisenberg,
    I have seen a book, [“Brighter than a thousand suns”by Robert Jungk], and I am amazed to see how much your memory has deceived you in your letter to the author.
    I remember every word of our conversations in Denmark. You and Weizsäcker expressed your conviction that Germany would win the war, and that it was foolish to maintain the hope of a different outcome, and to be reticent as regards all German offers of cooperation.
    I remember our conversation in my room at the Institute, where you gave the impression that everything was being done in Germany to develop atomic weapons. You said there was no need to talk about details since you were completely familiar with them and had spent the past two years working on such preparations.
    I listened to this without speaking. That my silence and gravity could be taken as an expression of shock at your reports that it was possible to make an atomic bomb is a misunderstanding.
    When I realized that slow neutrons could only cause fission in Uranium 235 and not 238, it was obvious to me that a bomb could be produced by separating the uraniums. In June 1939 I had given a public lecture in Birmingham about uranium fission, where I talked about the effects of such a bomb. The technical preparations would be so large that one did not know how soon they could be overcome.
    If 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.
    At the time I knew nothing about how far they had already progressed in England and America. I learned this only the following year when I fled to England on hearing that the German occupation forces in Denmark were going to arrest me.
    This is a rendition of what I remember from our conversations, which were the subject of discussions at the Institute and with other trusted friends in Denmark.
    At that time and ever since, I have always had the impression that you and Weizsäcker had arranged to visit to us, to assure yourselves that we suffered no harm and to try to help us in our dangerous situation.
    This letter is just between the two of us, but I have thought it appropriate to relate the contents of the letter in confidence to the head of the Danish Foreign Office and Ambassador Duckwitz

    [When you came to Copenhagen you told me that Germany would win the war and the Danes should try to co-operate with them. You also told me that Germany was well-advanced in preparations to make an atomic bomb, and you were closely involved with this.
    Because I was silent you took this to be shock on my part, at the news you brought. It was not surprise at the idea of an making atomic bomb, because I had lectured publicly on this, but rather the knowledge that Germany was in a race to make such a weapon. I only learned later that the British and Americans were far advanced in the process.
    I thought at the time, and ever since, that you came to Copenhagen to check that we were all right and to offer some re-assurance.]

  2. Deskarati says:

    Well that really does help to understand a little of what Bohr was thinking.
    As for the play – I can not comment as have never seen it, but I’m sure that if Alfy says its awful, then, to put it in the modern vernacular – ‘It Sucks’
    I can, on the other hand, recommend the 2002 TV adaptation of Frayn’s play Copenhagen

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