Operation Epsilon, a 2013 play performed at Boston’s Central Square Theater, is based on conversations among Germany’s top nuclear scientists while under surveillance by the Allies at an estate in England. Credit: A. R. Sinclair Photography

Scientists and engineers who contribute to nuclear modernization programs today, or who engage in other defense-related research, may feel they have little in common with physicists working in service of the German government during World War II. The same could be said of scientists who strive to advance emerging technologies such as artificial intelligence and new genetic engineering techniques, which hold great promise but might also be used for ill. Yet researchers working on military and cutting-edge technologies are confronting the same questions that faced nuclear physicists under the Third Reich: As scientists, how can we avoid making (or stumbling into) decisions that do more harm than good? And when is it our responsibility to question, object to, or withdraw from a research project?

The pressures that lead scientists to neglect these questions are arguably most acute for those just starting their careers, who may feel they lack enough status (or job alternatives) to reject exciting research opportunities. As a young scientist who wishes to be conscious of my future impact, I take a personal interest in this issue.

Nazi Germany’s “Uranium Club.” The history of World War II-era German physicists offers a powerful example of how talented scientists can end up operating within and advancing an immoral system. Many of Germany’s leading physicists objected to policies of the Nazi regime. Werner Heisenberg, a prime architect of quantum mechanics, believed that Hitler’s victory would bring calamity, and both Carl von Weizsäcker and Karl Wirtz (among others) viewed Nazi possession of atomic weapons as a disturbing prospect—as they indicated in conversation with colleagues. According to Heisenberg, even the intensely patriotic scientist Walther Gerlach “realized the crimes of the Nazis and disapproved of them” by 1945.

Nonetheless, these atomic scientists actively worked on behalf of their government. Heisenberg and Kurt Diebner each led a team of physicists in a wartime effort to harness the energy produced by nuclear fission—a process their colleague Otto Hahn had co-discovered in 1938. Nearly all of Germany’s leading physicists worked for this secret Nazi program, known as the “Uranium Club.”

The exact aims of the nuclear program were murky. The possibility that the Uranium Club might ultimately build an atomic bomb was certainly on the table and recognized by its members early on. In 1939, physicist Paul Harteck alerted the Nazi War Ministry of the weapons applications of nuclear fission. At a conference days after Hitler invaded Poland, other Uranium Club scientists urged the physics community to pursue bomb development (according to Harteck and Erich Bagge).

Some of the program’s researchers worked specifically on uranium enrichment technologies that could have produced fuel for a weapon. In practice, however, the Uranium Club was devoted primarily to engineering a nuclear reactor, because building a bomb was deemed infeasible in the short term. The project made considerable progress toward firing up its “engine” (or reactor) but did not succeed.

Building the reactor: a political endeavor. Despite moral qualms with the Nazi regime, German physicists largely failed to decline working for the government—with Hahn and Max von Laue as notable exceptions. (Hahn was tangentially involved with the project, and historians debate his level of engagement.) But since the researchers concentrated on building a reactor, not a bomb, is it fair to excuse their actions as part of a purely scientific endeavor?

This justification has a few serious flaws. For one, working within the Nazi system was automatically political, because it signaled support for the regime. Beyond that, Uranium Club physicists were aware that Nazi war efforts might profit from energy provided by their secret reactor. Gerlach told his colleagues that he had assured Nazi officials, “In my opinion the politician who is in possession of such an engine can achieve anything he wants.”

The scientists also understood that the reactor would produce waste that could be reprocessed to yield plutonium—in Diebner’s estimation, enough to power a nuclear bomb within two years. Heisenberg and Harteck had already worked out likely bomb designs. If the Nazis had triumphed in World War II, they would likely have had time to build a nuclear weapon—using knowledge and materials produced by the Uranium Club—to be deployed against Hitler’s enemies during a subsequent conflict. The German nuclear program was therefore not only a scientific venture, but also a political one.

What drove these atomic scientists to work on nuclear power for an evil regime? It appears that the researchers were focused almost single-mindedly on furthering their scientific enterprise—German physics. Working for the Nazis gave them an opportunity to do so. This technical and innovative zeal seems to have blinded them to ethical considerations.

Indeed, when it was becoming clear that the Nazis would lose World War II, the Uranium Club researchers showed no signs of resignation, but instead worked even harder. This hints at the extent to which these scientists acted as if their sole responsibility was advancing German physics.

A revealing conversation. To understand the mentalities of 10 leading German physicists during World War II, historians can look to their reactions to the news that the United States had perfected a nuclear weapon and dropped it on Hiroshima on August 6, 1945. (By then, Allied forces had captured eight German scientists who worked on the Nazi nuclear project, as well as Hahn and von Laue, and detained them in an English house called Farm Hall, where their conversations were covertly taped.) That August evening, shocked by the atomic bombing, the physicists reflected on their own decisions.

Gerlach asked his colleagues, “What were we working for?”

Hahn replied, “To build an engine, to produce elements, to calculate the weight of atoms, to have a mass spectrograph and radioactive elements to take the place of radium.”

This exchange is striking for two reasons: First, Hahn’s emphasis on technical aims—he made no mention of the Nazi Party, the German public, or the war—displays a narrow focus on scientific progress. Second, Gerlach’s question exemplifies how, at Farm Hall, issues of right and wrong appeared to bubble to the surface for the first time—as if the physicists had neglected to discuss them during years of working together.

The words of the Uranium Club captives at Farm Hall reveal their intense wish for scientific success. When the group heard an official radio announcement describing the Hiroshima bombing, they responded with a frantic effort, all talking over one another, to determine what technical choices allowed the Allies to succeed where they had failed. Heisenberg, Diebner, Harteck, Wirtz, Weizsäcker and others debated a litany of questions: Did the Americans use uranium or plutonium fuel? If the former, could they have enriched uranium with centrifuges? Using gas diffusion? With mass spectrographs? Using photochemistry? How much material was needed to set off an explosive chain reaction? Hours later, in the middle of the night, Gerlach was still reflecting, “I would really like to know how they have done it.”

The German physicists fixated on the science behind the nuclear breakthrough because they feared that their own lack of creativity might explain how the Americans progressed so far beyond them. On producing weapons-usable uranium, Harteck mused, “If they have done it with mass spectrographs, we cannot be blamed. We couldn’t do that. But if they have done it through a trick, that would annoy me.” Heisenberg had a similar worry. He remarked, “In the case of inventions, surprises can really only occur for people who have not had anything to do with it. It’s a bit odd [that we could have missed something] after we have been working on it for five years.”

Moral confusion. At Farm Hall, the physicists’ first reaction to the Hiroshima news report was a scientific discussion, but their second response was a political one. The German atomic scientists appeared to realize, perhaps for the first time, that a great deal of moral confusion surrounded their work.

As the evening progressed, more and more questions concerning justice and ethics occurred to the physicists: Are atomic weapons inherently inhumane, and should they never be used? If the Germans had come to possess such weapons, what would be the world’s fate? What constitutes real patriotism in Nazi Germany—working for the regime’s success, or its defeat? The scientists expressed surprise and bafflement at their colleagues’ opinions, and their own views sometimes evolved from one moment to the next. The scattered, changing opinions captured in the Farm Hall transcripts highlight that, in their five years on the Nazi nuclear program, the German physicists had likely failed to wrestle meaningfully with these critical questions.

By neglecting to think beyond the project in front of them, these researchers acted as though their allegiance to a scientific discipline made their allegiance to the Nazis irrelevant. If, in 1939, they had seriously grappled with the questions that they ultimately debated at Farm Hall, the physicists might have made different decisions. Perhaps many would have abstained from the nuclear project altogether, as Hahn did, or spoken out against it, as von Laue did.

Facing the fallout of research today. Today, looking back at the Uranium Club serves to remind us scientists of how easy it is to focus on technical matters and avoid considering moral ones. This is especially true when the moral issues are perplexing, when any negative impacts seem distant, and when the science is exciting.

Scientists are traditionally expected to play a limited role: perform research and development, provide counsel on technical problems, and ignore the politics. Nearly all the German nuclear physicists opted to assume this role. But as their story reminds us, researchers cannot divorce themselves from the political implications of their work.

The case of German physicists reveals how far astray a tendency to prioritize science can lead us. It suggests that this type of complicity could happen again—and arguably does, to some degree, all the time. For instance, engineers who develop tracking or facial-recognition systems may be creating tools that can be purchased by repressive regimes intent on spying on and suppressing dissent. Accordingly, those researchers have a certain obligation to consider their role and the impact of their work.

My recent personal examination of the Farm Hall transcripts has led me to consider this issue as I survey my own career choices. Reading through job postings for young physicists, I have noticed plenty that could raise ethical questions (though there is a debate to be had over whether to reject such jobs). These positions include, for example, working as an engineer developing technology for military drones, or working to maintain and advance the US nuclear arsenal.

Some scientists, especially those with limited professional influence, might object: “If I don’t take this job, someone else will—so my decision has no real moral impact.” In my view, reflecting seriously on the societal context of a research position may prompt a scientist to accept the job—and to take it upon herself or himself to help restrain unthinking innovation at work, by raising questions about whether every feature that can be added should in fact be implemented. (The same goes for whether certain lines of research should be pursued and particular findings published.) Moreover, in cases when it might be best for a scientific community to shun a research domain or employer altogether, one’s decision to refrain from accepting a morally murky position can provoke friends and colleagues to reevaluate the nature of their own responsibilities. Individual choices have ripple effects. A query for each of us scientists to consider is, “Do I want to contribute to a culture of complacency, or of questioning?”

Looking forward, scientists should not have to wait for some human-made cataclysm (even one far less devastating than the 1945 atomic bombings) to realize and confront the moral implications of our work. The challenge for each of us, moving forward, is to ask ourselves and one another, hopefully far earlier in the research process than did Germany’s Walther Gerlach: “What are we working for?”