Niels Bohr and Atomic Weapons

This is a much abbreviated account of lectures given between August, 1963 and May, 1964, at the Brookhaven National Laboratory, at the University of California, at the California Institute of Technology, and at Los Alamos, New Mexico. The major deletions involve technical aspects of the bomb, and above all a summary of Bohr’s work over three decades on atomic and nuclear problems; for a review of these, vide N. Bohr; The Rutherford Memorial Lecture; Proc. Lond. Phys. Soc., 78: 1083-1115 (1961).

When in 1939 Bohr left the United States for Denmark, he did not expect that explosive application of the fission process lay close at hand. His Institute in Copenhagen, his baroque nineteenth-century home at Carlsberg, were now a very different world. For years these had been a refuge for colleagues from Germany, and then Austria. When Fermi came up to get his Nobel Prize in Stockholm, he did not go back to Italy but stopped in Copenhagen; then he came to this country. From Russia there were also refugees: Charlotte Houtermans, whose husband was in prison in Russia until the Molotov-Ribbentrop Pact, and Placzek, Weisskopf, many others. Thus Bohr had, in addition to his deep devotion to Denmark, which had kept him in Copenhagen twenty years earlier when he had been pressed to come to England, also a sense of responsibility for his wards.

The Institute was closed in 1940. The so-called Director of the dead Institute was a man who had tried to enter the living one; but Bohr had been a little too canny for that. Heisenberg and Weissacker came over from Germany, and so did others. Bohr had the impression that they came less to tell what they knew than to see if Bohr knew anything that they did not; I believe that it was a standoff.

Then in ’43 it became far too dangerous to Bohr’s freedom and life. He had been in touch with the Danish underground, and through them with the British Secret Service; he had a letter from Rutherford’s student Chadwick, then director of the Cavendish Laboratory, encouraging him to come to England. So in the last days of September, he escaped one night in a small boat to Sweden; three weeks later he was flown to England in the bomb bay of an unarmed Mosquito. They gave him an oxygen mask and a headgear with ear phones; but the Royal Air Force was not used to such great heads as Bohr’s, and he was unconscious.

But once in England and recovered, he learned from Chadwick what had been going on. To Bohr the enterprises in the United States seemed completely fantastic. Today, of course, they may seem old hat; but it made a deep impression on him that there was to be a great diffusion plant separating uranium isotopes in Oak Ridge, that uranium atoms would be made to fly through a vacuum to concentrate the lighter ones, that there were plutonium-producing reactors abuilding in Hanford, that there was even a secret place in New Mexico to make the bombs themselves. The English were much involved^* , more than is generally known in this country. There the possibility of making a bomb had been raised, as it was in this country, by refugees from tyranny in Europe; it had been well studied especially by the physicist Rudolf Peierls. The British concluded that this needed to be explored for its potential relevance to the war and, in any case, to the future. The conviction and commitment of the British Government had a great effect in converting the American effort from a series of committees, so secret from one another that they could make little progress, into a major enterprise. It soon became clear that the British had neither the resources nor the physical security that things would go better if they worked with us in the United States.

Shortly before Bohr came to England, Churchill and Roosevelt met in Quebec, and agreed on the participation of the British in the undertaking in this country and Canada. They agreed that there would be consultation between them on political and military problems; they agreed to divide the indispensable uranium, which in part did not originally belong to either of us. This agreement had been signed when Bohr came to England, and Chadwick hoped that Bohr would come to the United States and would lend his great weight to the United Kingdom’s contribution to the undertaking.

Chadwick then asked Bohr to see Sir John Anderson, later Lord Waverly. He was Chancellor of the Exchequer, in charge of the uranium project in the United Kingdom, a conservative, dour, remarkably sweet man, who was a great friend to Bohr. He asked Bohr to help in strengthening the United Kingdom mission in the enterprise, and in the enterprise itself.

By then Bohr had had his first good look. It came to him as a revelation, very much as when he learned of Rutherford’s discovery of the atomic nucleus twenty-five years before. I shall quote short passages from Bohr, and you will know what words he used at the time. Yet I think it best that I rather baldly review the points he had in mind. I run the risk of oversimplifying by so doing; but I do so because it is easy, as history has shown, for even wise men not to know what Bohr was talking about.

First of all, he was clear that if it worked, this development would bring an enormous change in the situation of the world, and of war. The word “menace,” the word “threat,” occur over and over again. When he came to Los Alamos, his first serious question was, “Is it really big enough?” I do not know whether it was; it did finally get to be.

The second point was that he knew enough of how things were in Russia—he had close friends there, Joffe and Kapitza and Landau and many others—to be quite certain that the wartime alliance would not endure the peace as things then stood. He therefore anticipated an unheard-of arms race. He came to know about the possibility of a great increase in the power of bombs by using thermonuclear reactions, and referred to this discreetly when he wrote to Anderson, to Roosevelt, to Churchill. He expected, more I think than really has happened, that these immense enterprises of 1943 would not be so hard for a nation to undertake in ’53 and ’63. He wanted to try to prevent this arms race, but to do much else besides. He was clear that one could not have an effective control of atomic energy, which would permit useful application, and a free science and a free spirit of enquiry, without a very open world. He made this quite absolute. He thought that one would have to have privacy. He needed privacy, as we all do; we have to make mistakes and correct them as we learn better. But in principle everything that might be a threat to the security of the world would have to be open to the world.

Bohr knew that the Communists took quite a disdainful attitude towards speaking or revealing the truth; he understood how very much this had gone beyond the tactical duplicity recommended by Lenin to the most dangerous kind of self-delusion. In 1948, after a visit, he wrote General Marshall, the Secretary of State, “What it would mean, if the whole picture of social conditions in every country were open for judgment and comparison, need hardly be enlarged upon.”

From all this he understood that it would not be quite in character for the Soviet Union to make an open world. He felt that it was essential to attempt to engage that government by very early consultation—consultation in a hopefully cautious spirit of friendliness with an ally that had been invaded and occupied with a desperate defensive war. He hoped we would be prepared to offer full cooperation in scientific progress and industrial exploitation, if there were any, in a world in which there were adequate safeguards and, above all, in an open world. He hoped that the situation in which the Russians would find themselves, and what we would have to offer them, and the opportunity for associating themselves with a great, forward-looking change in the world, might alter the whole character of Soviet policy, and thus set a new model of international relations. In an essential and major way force would then cease to play its decisive part, and nations would exert an influence by their example, persuasion, and the extent to which they could truly contribute to the common welfare of men. He saw an example of complementarity, of which as a youth he thought and wrote so much: the complementarity between love and justice. Of all this he spoke, while still in England, to Anderson. Just a few months before his death, Waverly said to me that he had never been reconciled to the fact that Bohr’s counsel had not been followed.

Bohr came to the United States late in 1943. His cover, which was true, was that he would try to advance the cause of international scientific collaboration after the war. Officially and secretly he came to help the technical enterprise. Most secretly of all, and with Anderson’s concurrence, he came to advance his case and his cause. When he arrived in late ’43, he saw the Ambassador of the United Kingdom, Lord Halifax, and his own Ambassador, De Kauffmann, who with great bravery and gallantry represented his nonexistent government and associated it with us in the conduct of the war. Through them he met Justice Frankfurter again. The Justice had heard in very general terms of the atomic undertaking; he listened to Bohr with growing and very deep respect. Then Bohr came with his son, Aage, his companion, his confidante, to Los Alamos.

Bohr at Los Alamos was marvelous. He took a very lively technical interest. But his real function, I think for almost all of us, was not the technical one. He made the enterprise seem hopeful, when many were not free of misgiving. Bohr spoke with contempt of Hitler, who with a few hundred tanks and planes had tried to enslave Europe for a millennium. His own high hope that the outcome would be good, that the objectivity, the cooperation of the sciences would play a helpful part, we all wanted to believe.

Early in 1944 Justice Frankfurter talked to Roosevelt about Bohr’s ideas. The President listened with great interest, and with a word of encouragement, which he asked Bohr to take back to England. At that time, Anderson had talked to the Prime Minister, seeking to extend discussion of the future of atomic energy within the British Government. This did not appeal too much to Churchill. Bohr went back in April of ’44, with the word for Anderson of Roosevelt’s interest. Bohr learned from the First Secretary of the Soviet Embassy of a letter for him from Kapitza, who had been in Cambridge, was well loved by Rutherford, well known to Bohr, and later prevented by the Russians from leaving Russia. Kapitza wrote, asking Bohr, of whose escape to Sweden he had heard, to come to Russia, saying that things had been hard, but that now they could work again, and that Bohr would be very much at home among colleagues. Bohr concluded that the Russians were interested in practical nuclear problems. His answer was friendly; he said he had other plans to promote international cooperation after the war was won.

Bohr saw Anderson again, and Sir Henry Dale, President of the Royal Society, and Cherwell, Churchill’s scientific adviser; later, at Churchill’s suggestion, they talked to Smuts, who was rightly regarded as one of the wise men of the world. But the four of them came to no more startling conclusion than that when Churchill and Roosevelt next met, they had better talk of the future. Bohr did meet with Churchill. It was not a very happy occasion. Cherwell did not do anything to prepare the Prime Minister. Churchill and Cherwell fell to bickering; Bohr could hardly talk; he did not ever like that very much, and on an occasion like this he liked it very little. He wrote earnestly to Churchill that he had come with a message from the President of the United States. I know of no answer to this letter.

Bohr came back to Los Alamos; late in August, after he had prepared a memorandum which Justice Frankfurter gave to Roosevelt, he met the Presdent, and they had a long talk. I know that Bohr was enormously encouraged. This is a part of what Bohr had written:

Indeed, it would appear that only when the question is taken up among the united nations of what concessions the various powers are prepared to make as their contribution to an adequate control arrangement, it will be possible for any one of the partners to assure themselves of the sincerity of the intentions of the others.

Of course, the responsible statesmen alone can have the insight in the actual political possibilities. It would, however, seem most fortunate that the expectations for a future harmonious international cooperation which have found unanimous expression from all sides within the united nations, so remarkably correspond to the unique opportunities which, unknown to the public, have been created by the advancement of science.

Many reasons, indeed, would seem to justify the conviction that an approach with the object of establishing common security from ominous menaces without excluding any nation from participating in the promising industrial development which the accomplishment of the project entails will be welcomed, and [will be] responded [to by] a loyal co-operation on the enforcement of the necessary far reaching control measures.

After his visit with Roosevelt, Bohr wrote a supplementary note, which may have had unhappy consequences, pointing out how close the relations between members of the scientific community had been, and saying that although statesmen must decide and act, perhaps scientists, who had known and trusted one another, could help prepare the ground.

In September, Churchill and Roosevelt met at Quebec; they seem to have saved discussion of atomic problems until they met at Hyde Park. Of this discussion there is an aide mémoire, initialled by both men. They reached three conclusions. The first—based apparently on a total misunderstanding of what Bohr was after—was that Bohr’s suggestion that the world be told about the development be rejected. That was not Bohr’s suggestion. He thought it important for Roosevelt, or someone bearing Roosevelt’s authority, to talk to Stalin, or—if there were anyone—someone bearing Stalin’s authority, about the problems of the future and about the need for a common responsibility, and about the need for an open world. Only if there could be a meeting of the minds on that, and some working out of how it could be done—and only if there were in fact such a thing as an atomic bomb—might one then publicly explain what had happened and what might come of it. But Roosevelt and Churchill harshly rejected what they misunderstood of this approach, and said that the highest secrecy should be maintained. They next said that when the bombs were ready, then, after mature deliberation, they might be used in the war against Japan. Then they said that they would like a very careful watch on Bohr; they had come not to trust him.

This was a grave development. It worked itself out before long; but this suspicion, even allayed, had stopped entirely Bohr’s communication with the President, and seriously clouded and impeded his communications with our Government. He wanted to talk to Colonel Stimson, the Secretary of War; but he never could.

In March of 1945, many months later, Bohr wrote another memorandum. The United Nations were about to have their first meeting in San Francisco, and Bohr had a great sense of urgency that the question of the atom not be let go too long:

It would seem most fortunate that the measures demanded for coping with the new situation, brought about by the advance of science and confronting mankind at a critical moment of world affairs, fit in so well with the expectations for at future intimate international co-operation which have found unanimous expression from all sides within the nations united against aggression.

Moreover, the very novelty of the situation should offer a unique opportunity of appealing to an unprejudiced attitude, and it would even appear that an understanding about this vital matter might contribute most favourably towards the settlement of other problems where history and traditions have fostered divergent viewpoints.

With regard to such wider prospects, it would in particular seem that the free access to information, necessary for common security, should have far-reaching effects in removing obstacles barring mutual knowledge about spiritual and material aspects of life in the various countries, without which respect and goodwill between nations can hardly endure.

Participation in a development, largely initiated by international scientific collaboration and involving immense potentialities as regards human welfare, would also reinforce the intimate bonds which were created in the years before the war between scientists of different nations. In the present situation these bonds may prove especially helpful in connection with the deliberations of the respective governments and the establishment of the control.

All such opportunities may, however, be forfeited if an initiative is not taken while the matter can be raised in a spirit of friendly advice. In fact, a postponement to await further developments might, especially if preparations for competitive efforts in the meantime have reached an advanced stage, give the approach the appearance of an attempt to coercion in which no great nation can be expected to acquiesce.

Indeed, it need hardly be stressed how fortunate in every respect it would be if, at the same time as the world will know of the formidable destructive power which has come into human hands, it could be told that the great scientific and technical advance has been helpful in creating a solid foundation for a future peaceful co-operation between nations.

I do not know whether Roosevelt read that memorandum. He died very shortly thereafter. When he died he was writing a speech, since published but never delivered, on the new powers of science in war, and the need for men to live in peace with one another. The hour that Roosevelt died, Lord Halifax and Justice Frankfurter were walking in Lafayette Park, talking of the bomb and of Bohr’s hopes.

With Roosevelt’s death, Bohr’s memoranda were given by Bush to Stimson. Shortly thereafter Stimson appointed a committee in which Karl Compton, Bush, and Conant were the technical members, and in which State, War, Navy, and the Office of the President were represented. It was called the Interim Committee, and its purpose was to advise the Secretary of War and the President on the future of atomic energy.

In a sense Bohr was not alone at all. Bush and Compton and Conant were clear that the only future they could envisage with hope was one in which the whole atomic development would be internationally controlled. Stimson understood this; he understood that it meant a very great change in human life; he understood that the central problem at that moment lay in our relations with Russia. The authors of the Franck Report in Chicago were clear that this was the course of hope, and so wrote. So too were the scientists who banded together after the war to form the Federation of American Scientists. So were countless others. But there were differences: Bohr was for action, for timely and responsible action. He realized that it had to be taken by those who had the power to commit and to act. He wanted to change the whole framework in which this problem would appear, early enough so that the problem would be altered by it. He believed in statesmen; he used the word over and over again; he was not very much for committees.

The Interim Committee was a committee, and proved itself by appointing another committee, the scientific panel, of which Arthur Compton, Fermi, Lawrence, and I were members. We met with the Interim Committee on the 1st of May. We talked just about the question of relations with Russia, secrecy, openness, the future of science, the future of atomic enterprises. Some remember talking about the use of the bomb; that no doubt occurred, but not in Committee session. I was very deeply impressed with General Marshall’s wisdom, and Secretary Stimson’s; I went over to the British mission and met Bohr and tried to comfort him; but he was too wise and too worldly to be comforted; he left for England soon after, quite uncertain about what, if anything, would happen.

In June the scientific panel met at Los Alamos. We recommended that, before a firm decision on the use of the bomb, our Government talk of the future to our allies. The Interim Committee met on the 21st of June; it agreed that this talk should be initiated at the meeting of the President, the Prime Minister, and Stalin, which was planned for the 16th of July at Potsdam.

We had to make a test of the bomb on technical grounds. We hoped to get it done by the 16th of July, so that the President and the Secretary of War might have some notion of whether it worked. It did. But there was not much talk with the Russians. Stimson was horrified when he saw what the Red Army was; as he wrote, he rather lost his nerve. Byrnes had been against talking to the Russians; Churchill was against saying anything. But they all agreed that if the President said something to Stalin, and used the Trinity explosion as the occasion, it would at least relieve us of the worst reproaches for double-dealing. When the news came in from New Mexico, very much more lurid then than it would seem now, the President dismissed his interpreter, Charles Bohlen, in order to keep things casual, and went over to talk to Stalin. Truman remarked that we had a new weapon which was quite powerful, and which we were thinking of using against Japan. According to Truman, Stalin said he wished us luck and hoped it would work. That was carrying casualness rather far.

With the use of the bombs, which raised separate but related questions, there came some pronouncements about international control. In late ’45, the President, the Prime Minister of England, and the Prime Minister of Canada agreed to seek some action looking toward the international control of atomic energy. The debate on legislation in this country was then in full force. Secretary Byrnes undertook to bring the matter up with the Russians when he visited Moscow. He had in mind asking them to approve the creation of a commission in the United Nations to talk about the subject. He was touchingly afraid that they would ask him how to make a bomb; but they were much less eager to talk about it than he was. Senator Vandenberg and Senator Connally asked what was meant by the often heard word “safeguards”; what did that mean? Thus Byrnes appointed a committee of five, under the chairmanship of the Under-Secretary, Mr. Acheson, to devise controls. The Under-Secretary appointed a panel, under the chairmanship of Lilienthal, to devise what was to be controlled. We worked at this longer than we should, respecting each other and the problem. As a committee document, and for the time, it was not too bad. Bohr was not happy with it; for one thing he was not satisfied because we did not center it squarely enough on the fact that there must not be secrets of any kind. We said that; but it was not all that we said. When this proposal was brought by Ambassador Baruch to the United Nations, the members of the United States Military Staff Delegation said that if this proposal were realized, there would not be any military secrets. Thus Bohr would have had his openness. But Bohr was right because nothing happened. Of this Bohr said, in true reproach: “This situation, this time calls for action. It was an action to make the bomb.”

Bohr did not quite abandon hope, although it was clear that what he had been working for, that we try to persuade the Russians ab initio to be our collaborators, allies, and guarantors of the peace, had been lost. But he still felt that it was a great cause to make an open world. In 1948 he had a long, thoughtful, grave interview with General Marshall. The Secretary of State was going to Paris to take part in the general debate of the United Nations Assembly, to explain the American position. Bohr hoped that Marshall would say that we were for doing away with secrets. With proper safeguards, in an open world, we were prepared to do it. The Secretary did not say that.

By 1950, after the first Soviet explosion, the decision to try to make the thermonuclear bombs, and in a situation in which it was clear that we had to worry about the adequacy of our armament, just before the Korean War, Bohr wrote an Open Letter to the United Nations. The letter ends; not now only for Heads of State, but for all of us:

The efforts of all supporters of international co-operation, individuals as well as nations, will be needed to create in all countries an opinion to voice, with ever increasing clarity and strength, the demand for an open world.

I cannot tell—perhaps others could tell better, but still not tell—whether early actions along the lines suggested by Bohr would have changed the course of history. There is nothing I know of Stalin and his behavior that gives one any shred of hope on that score. But Bohr advocated this action, hoping that it would create a great change in the situation. He said once in jest, thinking of the quantum theory, “another experimental arrangement.” I think myself that if we had acted wisely, clearly, and discreetly in accordance with his views, at the least we might have been freed of our rather blasphemous sense of omnipotence, of our delusions about the effectiveness of secrecy. We might have turned our society and our life toward a healthier vision of a future worth living for, an increased dedication to knowledge and to truth.

With the development of the arms race and the intensification, the bitterness of the cold war, the multimegaton warheads and rockets, Bohr concentrated more and more on what he knew he could do, on international co-operation in science, on good communication, on good will. He tended his own Institute of Theoretical Physics and the little Scandinavian institute called Nordita, both housed together in Copenhagen. He spoke at the first Atoms for Peace Conference, which marked a beginning of the erosion of formidable barriers to communication. He played a most helpful part, not only in establishing the European nuclear research center, CERN, near Geneva, but in protecting it from the provincialism of The Six, and of Euratom, and from the military preoccupation of NATO. In October, 1962 he recorded the first five interviews of what were to be a history of atomic theory. On the 18th of November he died, the retrospect incomplete.

Bohr often spoke with deep appreciation of mortality: mortality that makes it possible that what we have learned, what has proved itself, be transmitted to the next generations. On November 18th, as Bohr died, his son Aage was returning with his wife from a month in China, where he had lectured on nuclear structure.

It was much earlier, in late September 1945, that Colonel Stimson left Washington for good. He was no longer young, nor well. On that day he had a cabinet meeting where he would once again, in final and eloquent terms, advocate, now very belatedly, an open, friendly approach to Russia on the problems of the atom. Later in the day General Marshall planned to have every general officer in Washington out on the runway to salute and say goodbye to their chief. For all this, Colonel Stimson had to have his hair trimmed. He asked me to sit with him when he was in the barber’s chair. When it was time to go, he said, “Now it is in your hands.” Bohr never said that. He did not need to.