Two Letters from Werner Heisenberg to Robert Jungk,

the author of "Brighter Than a Thousand Suns".


November 17, 1956


Dear Dr. Jungk,


I want to thank you very much for having your publisher send me a copy of your fine and interesting book about the atomic scientists. Since I have been sick these last few days, I had the opportunity to read it through in its entirety and I find that, overall, you characterized the atmosphere among the atomic scientists very well. The fact that you have addressed a few delicate issues may perhaps present some difficulties also for one or the other of them. But these dangers are likely not very great. That you printed the Frank (sic!) report and Bohr's memorandum to Roosevelt at the end seems to me a special distinction of your book. For in retrospect one can hardly deny that right there the natural scientists were better at judging and analyzing the political processes than the statesmen of that time.

Nevertheless, in some details of your book I need to make a few little remarks which may serve you in a second printing by correcting minor mistakes (which tend to be unavoidable with such an undertaking).

First on page 52: This point is really quite important to me. You describe Weizsäcker's political conviction (I assume perhaps derived from conversations with Teller) and near the end you word it "He (Teller) had to assume that his old friend and fellow student would stay loyal to Hitler." Although the subsequent sentence then disputes this assertion, I do believe that the above sentence conveys a completely false impression of Weizsäcker's political conviction. I saw Weizsäcker almost daily during the years 1931 to 1935 and am probably more familiar with his political opinions back then than anyone else. First off, Weizsäcker loathed Hitler's personality and the crimes committed by his movement just as much as any other decent human being. To this revulsion undiminished later on as well, there may have, over time, been added a mix of horrified admiration, when he saw from up close (through his family) how Hitler managed to twist power out of the hands of all those highly qualified people whose efforts were directed towards positive ends in German politics, and how, in addition, he was given from abroad practically without resistance the very concessions that Brüning and Stresemann had always sought in vain. To speak of any kind of loyal feelings from Weizsäcker towards Hitler is quite certainly far off.

With the beginning of the war there arose of course for every German physicist the dreadful dilemma that each of his actions meant either a victory for Hitler or a defeat of Germany, and of course both alternatives presented themselves to us as appalling. Actually, I suppose that a similar dilemma must have existed for the physicists active on the allies' side as well, for once they were signed on during the war, they also were signed on for Stalin's victory and Russia's foray into Europe. Overall, the German physicists acted in this dilemma as conservators of sort of that which was worthy and in need of conserving, and to wait out the end of the catastrophe if one was lucky enough to still be around.

Further: page 91. I can remember the meeting with Fermi in Goudsmit's home quite well, but not at all that Fermi would have mentioned the Uranium problem. The possibility that atomic weapons might already be used in the coming war, I certainly did not consider seriously at that time; perhaps repressed it out of an inner fear. At any rate, I cannot remember, as I said, the mention of the Uranium problem, and maybe that lack of memory itself is a sign of the repression back then. The conversation with Pegram only took place somewhat later, and I told Pegram at the time with utter conviction that Hitler would lose the coming war, yet I felt I needed to stay in Germany to contribute to preserving the good in as much as it still existed. During this conversation as well, I did not seriously consider that the atomic bomb would possibly be part of a war with Hitler. On the one hand, I was hoping that the war would end sooner and on the other hand, I had a gut feeling that the difficulties with the construction of an atomic bomb (which I had not given any thought to at that time) would be extremely great.

About p.100. You are talking here near the end of the second paragraph of active resistance against Hitler, and I believe - I apologize for writing this so directly - that this passage bespeaks a complete misunderstanding of a totalitarian dictatorship. In a dictatorship active resistance can only be used by people who are perceived as participants in the system. If someone speaks publicly against the system, he most certainly is robbing himself of any possibility of active resistance. Because either he utters this criticism of the system only occasionally in a politically harmless fashion, then his political influence can be easily blocked; for instance with young people one can spread the word: Oh well, the old Professor X may be a nice old man, but of course he is incapable of understanding the enthusiasm of youth, or such thing. Or else, the dissident actually tries to motivate students for political action, then he would within a few days end up in a concentration camp, and even his martyr death would remain practically unknown because to speak of him is not allowed. I do not wish to have this remark misconstrued to imply that I myself have been in a resistance move against Hitler. On the contrary, I have always felt very ashamed before the people of July 20th, (some of whom were my friends), who at the time have put their effort into serious resistance, sacrificing their lives. But even their example shows that real resistance can only come from people who appear to be going along. Our most famous example was Canaris, who, by the way, also at times assisted us in retaining our circle of physicists.

About page 175: In the little episode during my bicycle trip to Urfeld, circumstances were as follows. Since all male civilians were drafted to the "Volkssturm", it was not an uncommon occurrence that these civilians fled from the front to the back country. To prevent this, the SS had posted SS guards at the roads to capture such fugitives, whereupon not infrequently they were hanged without a lengthy military tribunal. I had basically prepared for this peril by getting an identity document from the institute. An SS man recognized, however, that such a document could be fashioned quite easily at the institute and told me he would have to bring me in front of his commanding officer. This dangerous turn I was able to prevent by bribing him with the package of Pall-Mall cigarettes. By the way, my departure from the institute was of course neither a flight from the troops of Colonel Pash, nor from the "Volkssturm"; it was prepared carefully at the institute and only conceived out of my belief that I needed to be at the side of my family during the time of the final battles. Therefore I had remained in Hechingen until the moment when the "Volkssturm" was already dissolved and the French tanks were rolling in. I then drove off at 3 am from Hechingen on my bicycle.

Now for a few minor details: On p.177 it should read Urfeld, not Urbach. On p.224: I have read almost all the works by the English novelist Anthony Trollope, not Tobias Smollet. And finally p. 225: At the first report, I indeed did not believe in the atomic bomb, because I knew what incredible technical effort was needed to produce atomic bombs. Only at the second radio report where precisely that huge effort was reported, did I come to terms with the fact that in America actually many Billions had been spent on the atomic bomb and that hundreds of thousands of people had worked on it. The idea that the Americans had dropped a pile, I certainly did not consider seriously after the second broadcast, since that would have had only a very limited effect through radio- active contamination. And also because it would have been, in fact, quite simple since we took it for granted that the Americans could produce piles very easily should they be interested in them. But the difference between pile and bomb was completely clear to us, and, I believe, already the next day in a seminar we calculated the approximate dimensions and the workings of a bomb. Perhaps I may mention in connection to this that once in 1944, an emissary from Goering came to my institute, indicated that news had come to Germany through espionage that the Americans were close to dropping an atomic bomb over German territory, and he asked me whether I thought this was possible. I replied at the time that although I thought it still very unlikely at this time (summer 1944), since the production of the atomic bomb necessitated quite an enormous technical effort, I could, however, not completely rule it out.

p.227: The final sentence of the British officer was not addressed to Hahn; actually, Hahn was not present at this conversation at all, and I am firmly convinced that out of sheer tact even the British officer would not have answered in this fashion. This was a conversation taking place between, if I remember correctly, the British officer, Weizsäcker, and me. In this conversation which dealt with the moral right of the bombing, the officer eventually felt, in a kind of discomfiture, pressed to the statement that we ought to understand: to them the life of a British or an American soldier was more important than the lives of 70 000 Japanese civilians. One of us then replied "But there you are really very close to the moral terms of Herr Hitler". The officer, with whom we had otherwise been on very friendly terms, left us upon this with a very disturbed expression on his face. Very obviously the officer had not meant to wound us with his assertion, and probably he himself was later rather unhappy over this statement.

It would be nice if you could include a few corrections at the second printing, and I assume that you will get suggestions for such corrections from other atomic scientists as well. Once again many thanks for your interesting book.


With many regards





Los Angeles



Dear and Highly Esteemed Professor Heisenberg,

I want to thank you very much for your kind letter with the accompanying corrections. On January 15th a new edition of my book will appear in which I have already taken note of this communication.

Some of it, however, I was only able to include as a "footnote", in order to not disturb the "layout" too much. In January and February, I am now going to work on the English language edition which will appear in Great Britain with two publishers simultaneously (Gollancz and Hart-Davis) and in the USA with Harcourt, Brace and Co. The book will appear in France already in the spring and in the fall in all West-European countries.

Should you - aside from the corrections- have the desire or the inclination to help fill in one of the many gaps which my book still has of course, I would be very grateful for it. In particular, it would be of interest to me to learn more precisely about your Copenhagen conversation with Bohr during the Second World War. Also I would have liked to know more about the false alarm after the war, when two alleged agents who were later discovered to be frauds, were threatening to abduct you from Göttingen.

Only on one point was I not able to accommodate your letter. Mr von Weizsäcker himself told me a while back in Göttingen that although he had a loathing for the leaders of this "movement"(that is, not just after 1939), in its beginnings he had a certain sympathy or, let's say, understanding for National Socialism, because it appeared to him that there was the thrust of profound forces operating here. For this attitude I have had and still have quite a bit of understanding, since I have lived in and with the German Youth Movement, whose criticism of "intellectualism" was captured by the Nazis and forged into such a crudely mindless weapon.

By the way, my hope is that in the USA my book will also clear up the myth of the "Nazi" Heisenberg, which Norbert Wiener only a few months ago has warmed up again in the second volume of his autobiography.

With warm wishes for the coming year, I am respectfully


(Signed) Robert Jungk





Jan. 18th, 1957

Dear Dr. Jungk!

Many thanks for your letter, asking me to write in a little more detail about my Copenhagen conversations with Bohr during WWII. In my memory which may, of course, deceive me after such a long time, the conversation roughly unfolded the following way. My visit to Copenhagen took place in the fall of 1941; I seem to remember that it was about the end of October. At that time, as a result of our experiments with uranium and heavy water, we in our "Uranium Club" had come to the following conclusion: It will definitely be possible to build a reactor from uranium and heavy water which produces energy. In this reactor (based on a theoretical work by v. Weizsäcker) a decay product of 239-uranium will be produced which just like 235-Uranium is a suitable explosive in atomic bombs. We did not know a process for obtaining of 235-Uranium with the resources available under wartime conditions in Germany, in quantities worth mentioning. Even the production of nuclear explosives from reactors obviously could only be achieved by running huge reactors for years on end. Thus we were quite clear on the fact that the production of atomic bombs would be possible only with enormous technical resources. So we knew that in principle atomic bombs could be built, although we estimated the necessary technical effort to be even rather larger than in the end it turned out to have been. This situation seemed to us to be an especially favorable precondition as it enabled the physicists to influence further developments. For, had the production of atomic bombs been impossible, the problem would not have arisen at all; but had it been easy, then the physicists definitely could not have prevented their production. The actual givens of the situation, however, gave the physicists at that moment in time a decisive amount of influence over the subsequent events, since they had good arguments for their administrations - atomic bombs probably would not come into play in the course of the war, or else that using every conceivable effort it might yet be possible to bring them into play. That both kinds of arguments were factually fully justified was shown by the subsequent development; for, in fact, the Americans could not employ the atomic bomb against Germany any more. In this situation we believed that a talk with Bohr might be of value. This talk then took place on an evening walk in the city district near Ny-Carlsberg. Because I knew that Bohr was under surveillance by German political operatives and that statements Bohr made about me would most likely be reported back to Germany, I tried to keep the conversation at a level of allusions that would not immediately endanger my life. The conversation probably started by me asking somewhat casually whether it were justifiable that physicists were devoting themselves to the Uranium problem right now during times of war, when one had to at least consider the possibility that progress in this field might lead to very grave consequences for war technology. Bohr immediately grasped the meaning of this question as I gathered from his somewhat startled reaction. He answered, as far as I can remember, with a counter-question "Do you really believe one can utilize Uranium fission for the construction of weapons?" I may have replied "I know that this is possible in principle, but a terrific technical effort might be necessary, which one can hope, will not be realized anymore in this war." Bohr was apparently so shocked by this answer that he assumed I was trying to tell him Germany had made great progress towards manufacturing atomic weapons. In my subsequent attempt to correct this false impression I must not have wholly succeeded in winning Bohr's trust, especially because I only dared to speak in very cautious allusions ( which definitely was a mistake on my part) out of fear that later on a particular choice of words could be held against me. I then asked Bohr once more whether, in view of the obvious moral concerns, it might be possible to get all physicists to agree not to attempt work on atomic bombs, since they could only be produced with a huge technical effort anyhow. But Bohr thought it would be hopeless to exert influence on the actions in the individual countries, and that it was, so to speak, the natural course in this world that the physicists were working in their countries on the production of weapons. For an explanation of this answer one has to include the following complication which, although it was not talked about as far as I can remember, but of which I was conscious, and which may also have been on Bohr's mind, consciously or unconsciously. The prospect of producing atomic bombs while at war was at the time immeasurably greater on the American side than on the German, due to the whole prior history. Since 1933 Germany had lost a number of excellent German physicists through emigration, the laboratories at universities were ancient and poor due to neglect by the government, the gifted young people often were pushed into other professions. In the United States, however, many university institutes since 1932 had been given completely new and modern equipment, and been switched over to nuclear physics. Larger and smaller cyclotrons had been started up in various places, many capable physicists had immigrated and the interest in nuclear physics even on the part of the public was very great. Our proposition that the physicists on both sides should not advance the production of atomic bombs, was thus indirectly, if one wants to exaggerate the point, a proposition in favor of Hitler. The instinctive human position "As a decent human being one cannot make atomic weapons" thus coincided with an advantage for Germany. How far this was influencing Bohr, I cannot know of course. Everything I am writing here is in a sense an after the fact analysis of a very complicated psychological situation, where it is unlikely that every point can be accurate. - I myself was very unhappy over this conversation. The talk was then resumed a few weeks or months later by Jensen, but was equally unsuccessful. Even now, as I am writing this conversation down, I have no good feeling, since the wording of the various statements can certainly not be accurate anymore, and it would require all the fine nuances to accurately recount the actual content of the conversation in its psychological shading.

The second question in your letter concerned the alleged plans for my abduction from Göttingen in the year 1947. This event can in retrospect only be viewed in a humorous vein, of course. It caused a lot of grief for the Britons who had to care for us and guard us, and they even had to relocate us, that is Hahn and me, for a period of some time from Göttingen. Like clockwork there appeared in the middle of the night in front of my Göttingen house two masked figures who had been promised a high reward if they were delivering me to an agent. These two men turned out after their capture to have been two Hamburg harbor workers who wanted to come into some good money on the cheap. In fact, however, the man who had engaged the harbor workers was identical to the one who had informed the British of the whole caper; he was a fraud who wanted to line himself up for a good position in the Secret Service. Only a year later the whole sham blew up and it has given us much to laugh about, naturally.

What you write about Weizsäcker, I can agree on. Only, there is a great deal of difference between this "Understanding for National Socialism in its beginnings" and the terminology "Loyalty towards Hitler" that you have used in your book. Why, one could in the first years very clearly combine a certain "Understanding for National Socialism" with the loathing of the person of its leader, Hitler, by, let's say, being desolate that "A genuine, idealistic desire of the German people was abused by a figure as unsavory as Hitler". The overlap "Hitler equals National Socialism", while proven through the subsequent years, was not yet clear to many Germans in the early beginnings.

Should you revise the passage about my conversation with Bohr in your book, I would be obliged, if I could see the text before publication and make corrections, if necessary.


With many warm greetings,




Zurück zum Index