In June 1925, while recuperating from hay fever on the pollen-free island of Helgoland in the North Sea, Werner Heisenberg conceived of the first mechanics for quantum theory -- a way to actually do it. He was 23 years old. Physicists are said to do their best work when they are barely out of their teens; this is a signal example. Until Heisenberg’s breakthrough -- which soon came to be called matrix mechanics, because it manipulated matrices, or lattices, of numbers, with weird but satisfying results -- there was no real connection between Niels Bohr’s semiclassical picture of quantum physics and the ground.
Two years later, Heisenberg came up with his now-famous (and widely co-opted by philosophers and playwrights) uncertainty principle, which in essence says you can’t simultaneously pin down the location and momentum of a subatomic particle. It is one of the pillars of the so-called Copenhagen interpretation of quantum theory, which upended classical Newtonian physics and revealed matter and energy as fundamentally discontinuous and unpredictable. End of physics lecture.
I have a photograph of Heisenberg on the wall of my office, taken shortly before his Helgoland epiphany. It’s up there because for some reason it makes me feel good. Wearing a sweater that his mom might have knitted, he’s smiling radiantly at the camera. The same photo is reproduced in “Beyond Uncertainty,” David C. Cassidy’s new biography of this controversial 20th century giant, in which he observes that in “snapshots of Heisenberg as a young man, he always appears radiant, confident, alert, and pleasant.”
References to his subject’s radiance and good nature even in the darker days of his later life occur throughout the book. It is also an excellent piece of science writing; in a chapter titled “Determining Uncertainty,” Cassidy gives the clearest explanation I have ever come across of the mind-boggling arcana of quantum physics.
Cassidy, a science historian and professor of natural science at Hofstra University, is the author of the well-received “Uncertainty” (1992), which is the parent of this new biography and is now out of print. Since its publication, the controversy over Heisenberg’s role as the scientific leader of Germany’s attempt to build an atomic bomb during World War II has been refueled by the release of letters and other documents pertaining to those efforts. As Cassidy frames the debate: “Was Heisenberg really intent on building a bomb for Hitler? If so, why did the German project make such little progress? If not, why not? Was Heisenberg actually intent on building the bomb but inept as a nuclear scientist and scientific head of the project, or were the war circumstances against rapid progress, or did he secretly sabotage the effort out of moral scruples? What does an overall view of his life and times reveal about his wartime behavior?”
Cassidy’s “overall view” of Heisenberg’s life and times brings us probably as close as we will ever come to answering those questions. It’s an even-handed treatment that illuminates Heisenberg’s all-too-human ambivalence, his nationalism, his ambition and his self-protective aptitude for denial. Cassidy points out that Heisenberg’s first love was theoretical physics and close behind was his love for his Heimat, his Germany -- particularly the south, where he was born. He was blind -- perhaps deliberately so -- to the horrors perpetrated by the Reich, but he was not a Nazi, and he was no fan of the Nazis. During the war, Cassidy makes clear, Heisenberg wanted Germany to win and German physics to regain its former glory -- and the Nazis to somehow disappear.
Another question Cassidy deals with is why Heisenberg chose not to emigrate after Hitler took over, as many other German scientists did whether or not they were Jewish. By then a Nobel laureate, he had opportunities, including an offer from Columbia University. Cassidy argues that Heisenberg, who had been vetted by the Nazis and pronounced sufficiently Aryan, was intent on remaining to combat what the Nazis called “Aryan physics” -- a retrograde physics that elevated experiment over theory and denigrated Albert Einstein’s relativity along with the dizzying heights of quantum mechanics. Heisenberg did what he could to promote theoretical physics, including relativity, at the university level. For this, he was attacked as a “white Jew,” along with his mentor Arnold Sommerfeld and the aged Max Planck, father of the quantum.
Nevertheless, when the war broke out, the Nazis found it expedient to avail themselves of Heisenberg’s services, and “he apparently convinced himself . . . that, amidst the technological and material conditions prevailing in early 1940, he could advance toward a useful energy-producing machine during the course of the war -- useful to himself, to his profession and to Germany -- while disregarding the possibility of an explosive, which, he then believed, lay in the far distant future.” That he and his colleagues failed to produce a feasible nuclear bomb -- even a feasible atomic pile -- Cassidy believes is not because they deliberately delayed the project. They did their best. Rather, the German scientists were behind the Allies in the technology of isotope separation and in their understanding of how best to moderate the fission process. Moreover, the Reich could not and did not provide them with the vast government support enjoyed by the Manhattan Project.
Cassidy does not so much exculpate Heisenberg as explain him, with a transparency that makes this biography a pleasure to read. In the harrowing last months of the war, Heisenberg wrote a letter to his mother, in which you can glimpse the insouciant 23-year-old genius who pulled the quantum theory down to Earth:
“Even when I take into account all of the misfortune that surrounds us today and that has existed in my life as in everyone’s life, I have been on the whole unbelievably lucky and I am thankful that I could be so long on this remarkable and often so wonderfully beautiful earth. . . . I have the feeling that I still have many tasks to perform here, but none of us knows how he will get through the last and strongest blast of the hurricane that still stands before us. In any event, even here I gladly give my life trustfully into the hands of that higher power that has led it until now.”