(b. New York, N.Y., 22 April 1904; d. Princeton, New Jersey, 18 February 1967) theoretical physics. Robert Oppenheimer achieved great distinction in four very different ways: through his personal research, as a teacher, as director of Los Alamos, and as the elder statesman of postwar physics. These different activities belong to different periods, except that his role as teacher overlaps in time with several of these periods. We may therefore review these different contributions separately, while following a chronological order. J. Robert Oppenheimer was the son of Julius Oppenheimer, who had immigrated as a young man from Germany. 1 The fither was a successful businessman, and the family was well-to-do. His mother, the former Ella Freedman, was a painter of near professional standard, and both parents had taste for art and music. As a boy Oppenheimer showed a wide curiosity and the ability to learn quickly. He went to the Ethical Culture School in New York, a school with high academic standards and liberal ideas. He went as a student to Harvard in 1922, and in spite of following a very broad curriculum, which included classical languages as well as chemistry and physics, he completed the four-year undergraduate course in three years and graduated summa cum laude in 1925. With all the breadth of his interests, Oppenheimer was quite clear that his own subject was physics. During his undergraduate course he profited much from the contact with Percy Bridgman, an eminent physicist who himself had wide-ranging interests and whose publications dealt with topics far beyond the field of his own experiments; they included philosophical questions. After graduating, Oppenheimer went to Europe; and during his four years of travel he established himself as a theoretical physicist. Research in Quantum Mechanics. The year 1925 marked the beginning of an exhilarating period in theoretical physics. During that year Heisenberg’s first paper on the new quantum mechanics appeared, and Dirac started to develop his own version of Heisenberg’s theory in a paper which appeared in the same year. Schrödinger’s first paper on his wave equation was published early in 1926. Up to that time the principles of the quantum theory had been grafted onto the classical equations of mechanics, with which they were not consistent. The resulting rules sometimes gave unique predictions which agreed with observation; sometimes the answers were ambiguous; and sometimes the rules could not be applied at all. The new ideas showed the way of obtaining a logically consistent and mathematically clear description, and it looked as if all the old paradoxes of atomic theory would resolve themselves. This started a period of intense activity, during which all atomic phenomena had to be reexamined in the light of the new ideas. Oppenheimer’s quickness in grasping new ideas helped him to play a part in this process. His first paper was submitted for publication in May 1926, less than four years from his entering Harvard and less than a year after Heisenherg’s first paper on quantum mechanics. 2 It shows him in full command of the new methods, with which he showed that the frequencies and intensities of molecular band spectra could be obtained unambiguously from the new mechanics. A second paper, submitted in July, is concerned with the hydrogen atom; 3 by this time he was making use of the full apparatus of matrix mechanics developed by Born. Heisenherg, and F. P. Jordan, of the alternative techniques of Dirac, and of Schrödinger’s wave mechanics. These two papers were written in Cambridge, and he acknowledged help from Ralph H. Fowler and Paul Dirac. In the second paper Oppenheimer raises the question of the continuous spectrum and discusses the question of how to formulate the normalization of the wave functions for that case. This was the beginning of his interest in a range of problems which were to occupy him for some time. In 1926 Max horn invited Oppenheimer to come to Göttingen, where he continued his work on transitions in the continuous spectrum, leading to his first calculations of the emission of X rays. He also developed, jointly with Born, the method for handling the electronic, vibrational, and rotational degrees of freedom of molecules, now one of the classical parts of quantum theory, referred to as the “Born-Oppenheimer method.” 4 He obtained his Ph.D. degree in the spring of 1927. Oppenheimer remained in Europe until 1929, spending some time with Paul Ehrenfest in Leiden and with Wolfgang Pauli in Zurich; the influence of both these men helped further to deepen his understanding of the subject. He continued with the work on radiative effects in the continuous spectrum. which he recognized as one of the important and difficult problems of the time, and found ways of improving the approximations used, which still serve as a pattern for work in this field. Among his minor papers, one deals with electron pickup by ions, a problem which requires the use of nonorthogonal wave functions. 5 In 1929 Oppenheimer accepted academic positions both at the University of California, Berkeley, and at the California Institute of Technology; and between 1929 and 1942 he divided his time between these two institutions. The list of his papers during this period might almost serve as a guide to what was important in physics at that time. He was now at the top of his form in research work, and he knew what was important, so that he did not waste his time on pedantic detail. In some of these papers Oppenheimer struggled with key problems which were not yet ripe for solution, such as the difficulties of the electromagnetic self-energy, or the paradox of the “wrong” statistics of the nitrogen nucleus (wrong because, before the discovery of the neutron, nuclei were believed to consist of protons and electrons). 6 But on others he was able to take important steps forward. He saw the importance of Dirac’s idea to avoid the difficulty of negative energy states for electrons by assuming them all filled except for a few holes, which were then positively charged particles. He showed, however, that Dirac could not be right in identifying these as protons, since they would have to have the same mass as electrons. 7 Thus he practically predicted the positron three years before its discovery by Carl Anderson. When cosmic-ray experiments showed serious contradiction with theory, Oppenheimer studied the possibility that this might indicate a breakdown of the accepted quantum theory of radiation. 8 When the discovery of the meson resolved the paradox, he took great interest in the properties of the new particle. He also developed, in a paper with J. F. Carlson, an elegant method for investigating electron-photon showers in cosmic rays. 9 In the 1930’s the cyclotron and other accelerators opened up the atomic nucleus to serious study, and Oppenheimer participated in asking important questions and in answering some of them. His paper with G. Volkoff shows a very early interest in stars with massive neutron cores. 10 During the California period Oppenheimer proved to be an outstanding teacher of theoretical physics. He attracted many pupils, both graduate students and more senior collaborators, many of whom, under his inspiration, became first-rate scholars. His important qualities as a teacher were those which characterized his research: his flair for the key question, his quick understanding, and his readiness to admit ignorance and to invite others to share his struggle for the answer. His influence on his pupils was enhanced by his perceptive interest in people and by his habit of informal and charming hospitality. After his marriage in 1940 his wife, the former Katherine Harrison, helped maintain this easy and warm hospitality. Oppenheimer still maintained a great breadth of interests, adding even Sanskrit to the languages he could, and did, read. At first his interests were exclusively academic: and he showed little interest in political questions, or in the national and world events of the day. But in the mid-1930’s he became acutely aware of the disturbing state of the world—unemployment at home, Hitler, Mussolini, and the Spanish Civil War in Europe. He became interested in politics and, like many liberal intellectuals of the day, became for a time involved with the ideas of left-wing groups. The list of publications by Oppenheimer and his group shows a break in 1941, and this marks almost the end of his personal research (the exception being three papers published after the war) but by no means of his influence on the development of physics. Atomic Energy: Los Alamos . The change was the result of Oppenheimer’s involvement with atomic energy. After the discovery of fission he, like many others, had started thinking about the possibility of the practical release of nuclear energy. With his quick perception he was aware of the importance of fast neutrons for any possible bomb. In 1940 and 1941 the idea of releasing nuclear energy was beginning to be taken seriously. A number of groups in different universities were working on the feasibility of a nuclear reactor, and others on methods for separating uranium isotopes. The latter would ultimately lead to the production of the light isotope (U 235 ) in nearly pure form, and this is capable of sustaining a chain reaction with last neutrons. The reactor work led to the production of plutonium, which can be used for the same purpose. While these efforts were well under way by the beginning of 1942, there was no coordinated work on the design of an atomic weapon, its critical size, methods of detonating it, and so on. Oppenheimer had attended some meetings at which such matters were discussed, and early in 1942 he was asked to take charge of the work on fast neutrons and on the problem of the atomic bomb. On the theoretical side Oppenheimer assembled at Berkeley a conference of first-rate theoreticians, including Edward Teller, who on that occasion first suggested the possibility of a thermonuclear explosion. The work continued in a theoretical group led by Oppenheimer at Berkeley. The experimental determination of the relevant nuclear data was divided between a large number of small nuclear physics laboratories; this hampered progress, since it was difficult for these groups to maintain adequate contact, particularly in view of the secrecy with which the whole project had to he treated. When, therefore, the United States government brought the atomic energy work under the auspices of the army and put Colonel (later General) Leslie Groves in charge of the project under the code name “Manhattan District,” Oppenheimer suggested to Groves that the weapon development be concentrated in a single laboratory. This should include the theory and the nuclear physics work as well as the chemical, metallurgical, and ordnance aspects of the project. In this way the different groups could work together effectively. Groves accepted the proposal, and on Oppenheimer’s advice chose the site of a boys’ boarding school at Los Alamos, New Mexico, a region Oppenheimer knew and loved—he had a ranch there. The remoteness of the site made access and transport problems difficult but seemed to have an advantage in reducing contacts with the outside—and therefore the risk of leakage of information. Groves not only followed Oppenheimer’s advice in the creation and location of the laboratory, but he selected Oppenheimer as its director. This was a bold decision, since Oppenheimer was a theoretician with no experience of administration or of organizing experimental work. Events proved Groves right, and the work of the laboratory was extremely effective. In the view of most of the wartime members of Los Alamos, its success owed much to Oppenheimer’s leadership. He attracted a strong team of first-rate scientists, who came because of their respect for Oppenheimer as a scientist and because of his evident sense of purpose. Inside the laboratory he was able to maintain completely free exchange of information between its scientific members; in other words, in exchange for the isolation of the laboratory and the restrictions on travel which its members had to accept, there was none of the “compartmentalization” favored in other atomic energy laboratories for the sake of security. Oppenheimer was able to delegate responsibility and to make people feel they were being trusted. At the same time his quick perception enabled him to remain in touch with all phases of the work. When there were major problems or major decisions to be taken, he guided the discussions of the people concerned in the same spirit of a joint search for the answer in which he had guided the discussions with his students. In the work he did not spare himself, and in response he obtained a sustained effort from all his staff. It seems that the laboratory was set up just in time, because when the design of the plutonium bomb was ready, enough plutonium was available for the first bomb, The plutonium bomb required a greater design and development effort than the uranium bomb, since the more intense neutron background required a much more rapid assembly from subcritical conditions to the final, highly critical configuration. Failing this, a stray neutron is likely to set off the chain reaction when the assembly is only just critical, giving an explosion of very poor efficiency. When the test of the first bomb at Alamogordo demonstrated the power of the new weapon, all spectators felt a terrified awe of the new power, mixed with pride and satisfaction at the success of their endeavors. Initially some were more conscious of the one emotion, some of the other. Oppenheimer, whose attitude to his own faults was as unmerciful as to those of others, if not more so, admitted later that he could not resist feeling satisfaction with the key part he had played in the work. Many accounts have quoted the verses from his Sanskrit studies of the Bhagavad-Gita which went through his mind at the time of the test, the first referring to the “radiance of a thousand suns” and the other saying, “I am become Death, the destroyer of worlds.” Besides the awareness of the technical achievement, Oppenheimer clearly did not lose sight of the seriousness of the implications. None of this was public knowledge until 6 August 1945, when the first uranium bomb was dropped on Hiroshima. The implications of the decision to use the bomb to destroy a city will continue to occupy historians for a long time. Oppenheimer played some part in this decision: he was one of a panel of four scientists (the others being A. H. Compton, E. Fermi, and E. O. Lawrence) who were asked in May 1945 to discuss the case for the military use of the bomb on Japan. They were told that it would he impossible to cancel or delay the planned invasion of Japan, which was sure to be very costly in lives, unless Japan surrendered beforehand. Their opinion, which Oppenheimer supported, was that a demonstration on an uninhabited island would not he effective, and that the only way in which the atom bomb could be used to end the war was by actual use on a “military” target in a populated area. Today, in retrospect, many people, including many scientists, deplore this advice and the use of the bomb. Oppenheimer commented in 1962: “I believe there was very little deliberation . The actual military plans at that time… were clearly much more terrible in every way and for everyone concerned than the use of the bomb. Nevertheless, my own feeling is that if the bombs were to he used there could have been more effective warning and much less wanton killing.…” 11 lie remained for the rest of his life acutely conscious of the responsibility he bore for his part in developing the weapon and in the decision to use it. The Aftermath of the Bomb: Princeton . At the end of 1945 Oppenheimer returned to California. This did not mean, however, returning to an ivory tower. He was by now a national figure, and his advice much in demand; he was also very seriously concerned with the issues raised by the invention of atomic weapons. He took part in the drafting of the “AchesonLilienthal Report,” which proposed the international control of atomic energy. Most of the language of this report is undoubtedly Oppenheimer’s and so, probably, are many of its ideas. The authors of this report wrote it in a generous spirit: international control of the new weapons would be used to ensure peace and to prevent any nation’s threatening another with the formidable new weapons. It probably never had much chance of becoming a political reality. A proposal embodying the outline of the report, but hardly its spirit, was presented to the United Nations by Bernard Baruch as the “Baruch Plan,” but nothing came of it. In 1946 the Atomic Energy Commission was set up under the McMahon Act, which provided for civilian control of atomic energy. The first proposal, the May-Johnson Bill, which would have led to military control, was defeated very largely because of the opposition from scientists, although Oppenheimer was prepared to accept it. The commission appointed a General Advisory Committee, with Oppenheimer as chairman; and he served in that capacity until 1952. The committee did more than give technical advice; it had great influence on the policy of the commission. Oppenheimer’s role as chairman was not to dominate opinion but to clarify the issues and to formulate people’s thoughts. In addition to the General Advisory Committee, he served on numerous other committees concerned with policy questions relating to atomic weapons and defense. In October 1947, Oppenheimer moved to Princeton, New Jersey, to become director of the Institute for Advanced Study. Until then the Institute had been a kind of retreat for great scientists and scholars who wanted to get on with their studies in peace. Under Oppenheimer’s regime the population of the Institute grew in number, and it included many young scientists, mostly as short-term members for a year or two. They included many visitors from other countries. Oppenheimer was an active member of the physics department and usually presided at seminar meetings. Under Oppenheimer’s influence the physics group became one of the centers at which the current problems of modern physics were most clearly understood. Many colleagues came to discuss their ideas with Oppenheimer, and to do so meant exposing one’s thoughts to penetrating scrutiny and sometimes to withering criticism. Oppenheimer now had less time for physics than in the prewar days, and he had to form his judgments more rapidly. He was fallible, and there were occasions when he violently and effectively attacked some unfortunate speaker whose ideas were perhaps not proved hut were worth debating: there were other instances when he hailed as very promising ideas which later proved barren. The early Princeton years were a time when there was again a buoyant optimism in physics. The theory of electrons and their electromagnetic field had been stagnant for many years because of the infinities predicted by quantum theory for the field energy of a point charge. The discovery of the “Lamb shift” in the hydrogen spectrum showed that there were some questions to which theoretical answers were needed, and the attempts to find the answers showed how one could bypass the troublesome infinities. S. Tomonaga, J. Schwinger. R. P. Feynman, and F. J. Dyson developed consistent formulations for the new form of the theory, and it was hoped that they could be extended to the proton and neutron and their interactions with the newly discovered meson field. It was a time of intense debte and discussion, and much of this took place at small ad hoc meetings of theoreticians, at which Oppenheimer was at his best in guiding discussion and in helping people to understand each other (and sometimes themselves). The phrase he used in an interview to describe the work at the Institute, “What we do not know we try to explain to each other,“ is very appropriate for these sessions. He had always had a remarkable gift for finding the right phrase, and he had now become an absolute master of the epigram. While he did not resume personal research on any substantial scale (he was coauthor of three papers on physics after the war, one of them being a criticism of somebody else’s theory), Oppenheimer’s participation in meetings at the Institute and elsewhere was still a major factor in the development of ideas in physics. As director of the institute, Oppenheimer was responsible also for the policy in other fields, including pure mathematics and history. Here the breadth of his knowledge was a unique qualification, lie did not, of course, take part in the work of the other groups as he did in physics, hut he could understand what was being done and could comment in a manner respected by the experts. Throughout the postwar period Oppenheimer wrote and lectured much. At first the subject was predominantly atomic energy and its implications, and the scheme for its international control. Later he became more concerned with the relations between the scientist and society and, from this, with the problem of conveying an adequate understanding of science to the layman. In his Reith lectures on the B.B.C., “Science and the Common Understanding,” he attempted to set out what science is about. 12 The language of such lectures was probably not easily followed in detail by the nonscientist, hut it had a poetic quality which to many listeners brought the subject closer. The “Oppenheimer Case.” In December 1953, Oppenheimer was informed that his security clearance—that is, his access to secret information—was being withdrawn, because of accusations that his loyalty was in doubt. He exerted his right to ask for hearings, and he was exposed to the grueling experience of over three weeks’ quasi-judicial hearings, in which all his past was exposed to detailed scrutiny. The charges were in part his opposition in 1949 to a crash program for developing the hydrogen bomb, and in part his contacts or associations in the late 1930’s and early 1940’s with Communists and fellow travelers, contacts which had been known to the A.E.C. many years before and had then not been considered sufficiently derogatory to impede his clearance. It is impossible to understand how these charges could he raised without remembering the atmosphere of hysterical fear of Communism of the Joseph McCarthy era and also without noting that Oppenheimer had made many enemies, who were delighted at this opportunity of curbing his influence. Some of these enemies were people he had bested in public debate, whom his devastating logic had not only shown to be wrong but also made to appear ridiculous. Others were people interested in military policy who feared his influence, which could act contrary to their interests. The hearings before the three-man Personnel Security Board were originally intended to be confidential, but eventually the transcript was published. 13 It remains an interesting historical document. The board found that Oppenheimer was “a loyal citizen” but, by a two-to-one majority, that he was to blame for opposing the hydrogen-bomb program and later was lacking in enthusiasm for it. The report of the board went to the Atomic Energy Commission. The commissioners did not uphold the board’s (majority) decision censuring Oppenheimer for his views on the hydrogen bomb—this would have caused a powerful reaction in the scientific community—but confirmed the withdrawal of his clearance, in a majority verdict, mainly on grounds of “defects of character.” This was opposed by one of the commissioners, the physicist Henry Smyth, who wrote a minority report in favor of Oppenheimer and criticizing the arguments of his colleagues. 14 Oppenheimer continued as director of the Institute and with his writing and lecturing. On many occasions audiences at his lectures gave him ovations clearly intended to express their sympathy for him and their indignation at the treatment he had received. In 1963, when the McCarthy era was an embarrassing memory, when many of the people who had conducted the Oppenheimer investigation and made decisions had been succeeded by others, and when tempers had cooled, it was decided to make a gesture of reconciliation. Oppenheimer was given the Enrico Fermi Award for 1963, a prize of high prestige awarded by the Atomic Energy Commission. The award is usually conferred by the president, and John F. Kennedy had the intention of doing so when he was assassinated. It was then conferred by Lyndon Johnson, and Oppenheimer acknowledged it with the words he had intended to say to President Kennedy: “I think it is just possible. that it has taken some charity and some courage for you to make this award today.” Oppenheimer knew for almost a year that he had throat cancer, and he could contemplate this fact and talk about it as lucidly as about a conclusion in physics.
1. There has been controversy whether in “J. Robert” the “J” stood for “’Julius,” P. M. Stern (footnote at the beginning of ch. 2 of the book cited in the bibliography) quotes evidence that this was the case. We use the style Oppenheimer used, with the explanation that the letter J “stood for nothing”. 2. Oppenheimer, “On the Quantum Theory of Vibration-Rotation Bands’ in Proceedings of the Cambridge Philosophical Society, 23 (1926), 327-335. 3. Oppenheimer, “On the Quantum Theory of the Problem of the Two Bodies,” ibid., 422-431. 4. Max Born and Oppenheimer, “Zur Quantentheorie der Molekeln” in Annalen der Physik, 4th ser., 84 (1927), 457-484. 5. Oppenheimer, “On the Quantum Theory of the Capture of I Electrons” in Physical Review,31 (1928), 349-356. 6. Oppenheimer, “Note on the Theory of the Interaction of Field and Matter,” ibid.. 35 (1930), 461-477; P. Ehrenfest and Oppenheimer, “Note on the Statistics of Nuclei” ibid., 37 (1931), 333-338. 7. Oppenheimer, “On the Theory of Electrons and Protons” ibid., 35 (1930). 562-563. 8. Oppenheimer, “Are the Formulas for the Absorption of High Energy Radiation Valid?“ ibid., 47 (1935), 44-52. 9. Oppenheimer and J. F. Carlson, “On Multiplicative Showers,” ibid, 51 (1937), 220-231. 10. Oppenheimer and G. Volkolf, “On Massive Neutron Cores” ibid., 55 (1937), 374-381. 11. Oppenheimer,The Flying Trapeze, the Whidden lectures for 1962 (London, 1964), pp. 59-60. 12. Oppenheimer, Science and the Common Understanding, Reith lectures, British Broadcasting Corporation, Nov. 1953 (New York, 1953; London, 1954). 13. United States Atomic Energy Commission, In the Matter of J. Robert Oppenheimer. Transcript of Hearings Before the Personnel Security Board(Washington, D.C., 1954). 14. United States Atomic Energy Commission, In the Matter of J. Robert Oppenheimer. Text of Principal Documents (Washington, D.C., 1954).
I Original Works. A full list of Oppenheimer’s writings can be found in the article by H. A. Bethe, in Biographical Memoirs of Fellows of the Royal Society, 14 (1968), 391-416. II. Secondary Literature. There is as yet no booklength biography of Oppenheimer. Among his obituary notices the most important are the one by Bethe, cited above, and the record of speeches at a memorial meeting by R. Serber, V. F. Weisskopf, A. Pais, and G. T. Seaborg, inPhysics Today, 20 , no. 10 (Oct. 1967), 34-53. The dual biography by Nuel Pharr Davis, Lawrence and Oppenheimer (New York, 1968), has been strongly criticized by many reviewers—for instance, F. Oppenheimer, in Physics Today, 22 , no. 2 (Feb. 1969), 77-80. Numerous books are primarily concerned with the “Oppenheimer case“ but bring in much biographical material. The most scholarly of these is P. M. Stern, The Oppenheimer Case; Security on Trial (New York, 1969). In addition there are C. P. Curtis, The Oppenheimer Case. The Trial of a Security System (New York, 1955); and J. Major, The Oppenheimer Hearing (London, 1971). H. Chevalier, Oppenheimer, The Story of a Friendship (New York, 1965), criticizes Oppenheimer for his conduct when questioned on security; it also contains many interesting facets of Oppenheimer’s life at Berkeley. There is also a considerable literature on the history of the Manhattan Project, including Oppenheimer’s part in it. The official record is A History of the United States Atomic Energy Commission, 1, R. G. Hewlett and D. E. Anderson, Jr., The New World (University Park, Pa., 1962), II, R. G. Hewlett and F. Duncan, Atomic Shield (University Park, Pa., 1969). Other examples are Leslie R. Groves, Now It Can Be To Id (New York, 1962); Lewis L. Strauss, Men and Decisions (New York, 1962); D. E. Lilienthal, Journals, II, The Atomic Energy Years 1945-1950 (New York, 1964), and III, The Venturesome Years 1950-1955 (New York, 1966); and L. Givoanetti and F. Freed, The Decision to Drop the Bomb (New York, 1965). Rudolf Peierls
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