Complementarity

Complementarity is the principle through which J. Robert Oppenheimer drew on Niels Bohr’s thought to address the relation between individuals and society, and to argue for openness about the atomic bomb. In the book’s account, its importance lies less in a technical exposition of physics than in the way Oppenheimer carried Bohr’s ideas into disputes over secrecy, political responsibility, and the future of the postwar world.

Bohr’s idea and the individual in society

In a letter to Archibald MacLeish, Oppenheimer objected to the idea that human freedom could be secured simply by emancipating the individual from society. He argued instead that human values and liberation depended on culture and on people’s relations with one another. His formulation, “Man is both an end and an instrument,” expressed the tension: a person has value in their own right, yet is also formed through obligations and relationships beyond the self.

Oppenheimer connected this argument to a midnight walk in the snow with Bohr earlier that year. He recalled Bohr’s philosophy of openness and complementarity as offering a new way to understand the individual’s relation to society—one that could answer political opponents as well as resolve their own confusions. MacLeish welcomed the letter and recognized that Oppenheimer had addressed the central issue in his essay. The book thus presents complementarity as part of Oppenheimer’s effort to think beyond a simple opposition between individual freedom and collective life; it does not, however, supply a formal scientific definition of the principle.

Openness against secrecy

The principle’s public stakes emerge in Oppenheimer’s wartime argument about disclosure. In discussions with scientists at Los Alamos, he maintained that the worst outcome would be for the new weapon to remain a military secret. If the world learned of it only in a future war, he warned, that war would almost certainly be fought with atomic weapons. The bomb should therefore be tested, and the delegates assembling for the new United Nations should begin their deliberations knowing that humanity had created a weapon of mass destruction.

This case for openness belonged to a broader dispute over how knowledge should circulate inside the Manhattan Project. Oppenheimer backed a weekly, open-ended colloquium after Hans Bethe proposed it, insisting against Leslie Groves’s resistance that scientists needed sustained discussion because earlier work had been so compartmentalized. The first meeting, held in the schoolboys’ library on April 15, 1943, brought together fewer than forty scientists to hear Robert Serber explain the project. Even there, security rules intruded: Oppenheimer had Manley ask Serber to use a neutral term such as “gadget” instead of “bomb.” As the project developed, compartmentalization increasingly obstructed discussion among scientists, and in practice the restrictions grew lax. These episodes show openness as a practical question of scientific cooperation as well as a postwar political principle, though the book does not claim that complementarity alone caused the changes in laboratory practice.

A contested boundary between science and politics

Oppenheimer’s position was not a straightforward endorsement of political debate by scientists. Robert Wilson proposed a formal meeting on the bomb’s impact late in 1944; Oppenheimer initially tried to dissuade him, warning that the security authorities might object. Victor Weisskopf later recalled Oppenheimer arguing that the bomb’s use was not the scientists’ task and that they should not involve themselves in politics. Yet Oppenheimer attended Wilson’s meeting and, in Wilson’s recollection, dominated the discussion with the case for informing the world before the war ended. The apparent contradiction is central to the principle’s political use: openness could mean public knowledge of the weapon without, in Oppenheimer’s view, making every question of its use a proper subject for scientists’ collective action.

At the meeting, Oppenheimer invoked the prospect of the United Nations and the possibility that atomic weapons would force a redefinition of national sovereignty. Wilson and other scientists found this argument persuasive, in part because they hoped international arrangements might prevent another war. Oppenheimer’s reasoning therefore joined Bohr’s emphasis on openness to a specific political hope: that disclosure could allow the postwar world to confront the weapon before secrecy made its use in a future conflict more likely.

Postwar limits and significance

After the bombings of Hiroshima and Nagasaki, Oppenheimer told Dean Acheson that many Manhattan Project scientists were disinclined to continue work on weapons, not only on a super bomb. He described such work as contrary to their hearts and spirits and rejected the role of an armaments manufacturer. When Edward Teller asked him to support continued research on the Super, Oppenheimer refused. At the same time, his participation in the 1945 Interim Committee discussion showed the limits of his influence: he did not object to the chosen target formulation, and he appeared to acquiesce when Leslie Groves proposed removing scientists considered disloyal after the bomb was used.

Complementarity, as presented here, is neither a simple program for ending secrecy nor a guarantee that scientific knowledge will produce political agreement. It gives Oppenheimer a language for describing the dependence of persons on society and a rationale for bringing knowledge of the atomic bomb into international discussion. His actions also expose the unresolved boundary between scientific responsibility and political authority: he argued that the world had to know what had been made, while sometimes discouraging scientists from debating what should be done with it.