the splitting of the atom and its potential implications.

Then the three characters switch the time reference, slipping back to 1941 and playing out the scene of that meeting. They greet one another awkwardly. Many years have passed since they have seen each other. Many things have happened that have separated them. They begin their conversation by bringing up shared memories, those of skiing and vacationing together. Interspersed in their memories is a discussion of fission, as each scientist tries to feel the other one out, wondering where they are in their research. But the different politics, that of Nazism and the occupation of Denmark, as well as the Holocaust, keep interfering with the free flow of their conversation.

The three characters continue to discuss a mix of quantum physics—using metaphors of skiing to help explain the science—and personal tragedies, like the loss each family has felt upon the death of one son each. Then the two men go for their famous walk. While they walk, Margrethe fills in more personal details about the men’s relationship. Upon returning from their walk, Niels’s abruptness toward Heisenberg makes Margrethe suspect that whatever Heisenberg has said has deeply upset Niels. After Heisenberg leaves, Niels keeps repeating that Heisenberg cannot be right. When Margrethe asks what Niels is talking about, Niels goes into an explanation of what happens in a nuclear reaction.

Heisenberg, once again in the setting of the afterlife, returns to the discussion. The audience is provided with the beliefs that were held in the 1940s concerning why it would be so hard to create a nuclear bomb. The act ends with the men searching their memories in an attempt to figure out what was actually said at their meeting and why Heisenberg had come to visit. Their memories conflict on certain details, so no clear conclusion is reached.

Act 2

In act 2, the men exchange memories of what it was like when they first met, how they used to walk together to help them think, and how they inspired one another’s creative thought processes. They also talk about the effect their discoveries had on the world at large. They mention the names of other scientists in their field and how their theories of complementarity and uncertainty—and the “whole Copenhagen Interpretation”—came about. Margrethe suggests, as the men recount the development of their relationship, that maybe that is why Heisenberg came to Copenhagen in 1941. Maybe he wanted to get back to those earlier days when the relationship between Heisenberg and Niels was stronger and more productive. But immediately after positing this suggestion, Margrethe withdraws it. She reminds the men that they did not create their theories together. “You didn’t do any of those things together,” she tells them. Then she recalls how, even though they spent a lot of time together, they actually did their best work when they were apart.

At this point, the men turn to their metaphors for quantum physics and the difficulties in the evolving foundation of the science. There were contradictions and quarrels among the leading physicists as to how to proceed and how to calculate the data they were conceiving. Even Heisenberg and Niels fought. “You were the Pope and the Holy Office and the Inquisition all rolled into one!” Heisenberg tells Niels, referring to the fact that Niels tended to have the last word in the development of quantum physics at that time. Niels’s word was revered in the sciences. But both Niels and Heisenberg were puzzled by the way quantum physics worked. The actions of a detached electron do not always follow the path that Heisenberg’s mathematical structure suggested it should. “It was a fascinating paradox,” Niels says.

In the end, Niels points out, after their three years of collaborative research and hypotheses, the two men changed the world. “Not to exaggerate,” Niels says, “but we turned the world inside out!”

As the second act closes, the three characters return, once again, to the meeting in 1941. They discuss all the pressures they were feeling at the time. The conversation returns to the atomic bomb. Niels reminds Heisenberg that the reason Heisenberg was not able to create the bomb was that he forgot to work out a mathematical equation. Heisenberg, Niels suggests, made an assumption that turned out to be false. The solving of the mathematical equation would have showed Heisenberg his error, Niels claims. Meanwhile, Margrethe catches comments the men make that are not quite the truth. She digs deeper into what they are saying and makes them admit their personal reasons behind some of their decisions. She especially confronts Heisenberg, who tries to claim that he suffered during that time, that he was a victim. “On your hands and knees?” Margrethe says. “It’s my dear, good, kind husband who’s on his hands and knees! Literally.” She is referring to the fact that Niels ultimately had to be smuggled out of Denmark to Sweden before the Nazis came to take him away to a concentration camp. He moved from Sweden to England, and eventually to the United States. Heisenberg then confesses that he was involved in Niels’s successful escape to Sweden. He was the one who had sent word that the Nazis were coming for Niels.

The play closes on a philosophical note. The three characters remind one another that they, at the end of their lives, will turn to dust, as will their children. No more decisions will have to be made, Niels says, because at some point there may be “no more uncertainty, because there’s no more knowledge.” Then Heisenberg reminds everyone that there is still uncertainty. This is a reference not only to science but also to the fact that no one knows for sure what actually happened at that now famous 1941 meeting.