When Werner Heisenberg visited Harvard in 1973 to deliver a lecture entitled “The Development of Concepts in the History of Quantum Theory,” a group of demonstrators holding hand-written signs gathered around Science Center C. They were protesting what they saw as Heisenberg’s collaboration with the Nazi regime during the Second World War.  Heisenberg had led the German nuclear physics program during the wartime years. According to Peter Galison, Harvard Professor of the History of Science and Physics, who attended the lecture as an 18-year-old freshman, the mood was uneasy. Many of the physicists in Harvard’s department had worked on Allied wartime projects, and others had initially come to America as refugees from war torn Europe.

Heisenberg was a Nobel Prize-winning physicist, one of the inventors of quantum mechanics, and the discoverer of his eponymous uncertainty principle. Recognized as having made some of the most important contributions to physics in the twentieth century, Heisenberg’s career has nevertheless been filled with both scientific and political controversy. He battled with the physicist Erwin Schrödinger over the formulation of quantum theory during the 1920s, but during the next decade he was attacked in Germany for his adherence to “Jewish” theoretical physics, and later he was questioned for his close involvement with the German atomic research program. Heisenberg was visiting Harvard as director-emeritus of Germany’s Max Planck Institute, and as the title of his lecture suggests, history dogged him in his later years. Like many people who had held upper-level positions of authority in Germany, he had to fight against charges of complicity or collaboration with the Nazi regime. The extent of Heisenberg’s cooperation, and the progress and goals of the German atomic bomb project, have sparked recent debate with the 1998 opening of Michael Frayn’s award-winning, critically acclaimed, but controversial play Copenhagen, which deals with the historical ambiguities of Heisenberg’s visit to his mentor Niels Bohr at his home in occupied Copenhagen in 1941. David Cassidy’s well-crafted and readable biography of Heisenberg — Beyond Uncertainty: Heisenberg, Quantum Physics, and the Bomb — provides a nuanced and compelling account of Heisenberg’s life, especially the period under Nazi rule. Cassidy explores Heisenberg’s troubling response to Nazi direction as well as the difficulties he faced, presenting a complex portrait of a physicist whose first allegiance is not for family or Führer, but for physics.

Cassidy has already written a colossal and definitive biography of Heisenberg — Uncertainty: The Life and Science of Werner Heisenberg appeared in 1991 — which makes the appearance of this new book slightly unusual. This is not just an update of the previous work: it is a completely new biography, written to be accessible for a general readership unlike the scholarly Uncertainty, which was aimed at an expert audience, but it goes beyond the original work in that it explores new sources that have become available since the end of the Cold War.  Many of Heisenberg’s private letters have been published, some intriguing tidbits have come to light in Soviet archives, the Bohr estate has released drafts of letters dealing with Heisenberg’s Copenhagen visit, and finally an important collection of British transcripts of conversations between German scientists detained after the end of WWII has been declassified and published.  These materials are undoubtedly of key importance to unraveling Heisenberg’s wartime years, but they have been explored at depth in other works (the Bohr letters during the aftermath of Frayn’s Copenhagen, the British transcripts in Jeremy Bernstein’s excellent Hitler’s Uranium Club: The Secret Recordings at Farm Hall). The only thing that comes close to a revelation is Cassidy’s hints, based on some vague documents found in Soviet archives, that there was a small nuclear explosion in Germany near the end of the war.

What Cassidy does very well, however, is craft a meticulously complete and sympathetic account of Heisenberg’s professional struggles during the 1930s. Heisenberg came of age at the end of the First World War, participating in the subsequent youth movements that swept Germany during the early and chaotic Weimar years. He was the wunderkind of German physics, collaborating with Niels Bohr, Nobel laureate and founder of quantum theory. Heisenberg’s most significant contributions — the matrix formulation of quantum mechanics, discovered while recovering from hay fever on the treeless island of Helgoland in the North Sea; the famous inequality relationships of the uncertainty principle (subsequently fodder for many unfortunate metaphors) — came during the heady 1920s of German physics, a golden age of theory. But with the rise of the Nazi government, physics suddenly became a controversial subject. Many of the important theorists were Jewish, and experimental physics, which dealt with material explorations, had traditionally been more respected than the mathematical scribblings of the theorists. Theoretical physics, embodied by Einstein’s relativity theory, was attacked as “Jewish Physics,” and the once-prominent physicists Johannes Stark and Philipp Lenard led the campaign for a new Deutsche Physik, or Aryan Physics. This was both a scientifically and racially motivated program, and in hindsight fits squarely within the terrifying Nazi “scientific” project.

Heisenberg, a staunch nationalist who was committed to his country, campaigned against this bigoted and restrictive view of physics, often (and occasionally  naïvely) supporting the candidacy of Jewish physicists for research positions and opposing the application of the Nuremberg race laws.  This, along with his commitment to theoretical science, did not go unnoticed, and Stark became his nemesis, opposing Heisenberg’s nomination for important chairs of physics in Munich and Leipzig — the battles of these appointments lasted for years — and openly and vociferously questioning his loyalty. One gets the sense from Cassidy’s portrait of a frustrated and besieged physicist, one conflicted and struggling to do what he thinks is right.  But for all Heisenberg’s conviction in his defense of physics, he made compromises for political expediency. According to a 1939 Gestapo memo quoted by Cassidy, “For Heisenberg, theoretical physics is merely the working hypothesis with which the experimenter inquires of nature in suitable experiments. The evaluation occurs first and foremost through the experiment.  The theory that is confirmed by experiment is thus the clear description of the observations made in nature using the exact means of mathematics.” Never have the esoteric points of the philosophy of science had such political implications. Heisenberg was ultimately cleared to take his chair of physics, and he shortly after became director of German nuclear research.

The central points of contention in Heisenberg’s biography deal directly with his involvement in the German program of atomic research. In his later years, Heisenberg tried to hint that he had either consciously or subconsciously tried to sabotage the German bomb project, since he had only wanted to build a reactor for peaceful purposes. One interpretation of Heisenberg’s now-famous question put to Bohr during his 1941 visit to Copenhagen — “Does one as a physicist have the moral right to work on the practical exploitation of atomic energy?” — is that Heisenberg was referring to peaceful applications of nuclear power, but Cassidy dismisses this, and Bohr’s letters make clear that he believed Heisenberg to be referring directly to a bomb, not to a reactor. Other exculpatory suggestions are also rejected (for instance, that Heisenberg and the other German physicists fundamentally misunderstood atomic physics, and therefore could never have built a bomb) are rejected, but Cassidy makes clear that while Heisenberg’s project was actively to pursue an atomic weapon, his work was Quixotic and frequently irresponsible; Heisenberg had neither the manpower nor the resources to have anything close to a chance at success, and took surprising risks. By contrast to the couple thousand people involved in the underfunded German atomic research, the American Manhattan project employed hundreds of thousands of people and spent billions of dollars. This is not meant to be a defense, however, since the effort was made despite its chances of success and either a reactor or a bomb would have helped the German war machine.

The obvious parallels between Heisenberg and his American counterpart, the brilliant physicist Robert Oppenheimer (the subject of another Cassidy biography) are thankfully not dwelled upon, but Cassidy does hint at the broad moral questions faced by physicists during WWII: “The universal dilemmas created by the rise of contemporary science in concert with the contemporary global power structure: that scientists everywhere, no matter how devoted they may be to the search for truth and universal understanding, are, for many reasons, invariably drawn into work for their governments, and that many will serve their government by fashioning the weapons of war and destruction.” As the German physicist C. F. von Weizsäcker liked to point out, the atomic bomb was ultimately the product of a democratic state, produced without fear or coercion.

What disturbs Cassidy most is Heisenberg’s naïve response to the Nazi regime.  Heisenberg had multiple offers to resettle in America during the difficult years in the late 30s, but insisted that his country needed him, and that he was looking forward to rebuilding German physics after the end of Nazi rule. This devotion to physics is at the center of Heisenberg’s life. He was one of the century’s most important scientists, and yet his legacy has been tainted by complicity with the Nazi regime. As a coda to the second-to-last chapter, Cassidy offers a quote from an obituary by Samuel Goudsmit, a former student of Heisenberg, who had led the American atomic intelligence branch of the OSS: “Heisenberg was a very great physicist, a deep thinker, a fine human being, and also a courageous person … In my opinion he must be considered to have been in some respects a victim of the Nazi regime.”

Alexander Fabry ‘09 is reading and radiation.