Uncertainty Summary
by David C. Cassidy

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Uncertainty Summary

(Literary Masterpieces, Critical Compilation)

It is the tragedy of Werner Heisenberg’s life, and a major theme of this well- researched biography, that the evils of National Socialism contaminated the idealistic world of science in which Heisenberg tried to find refuge and that he tried to keep pure from the poison of politics. He managed to create a body of work, including his uncertainty principle, that has had a profound influence not only on scientists but also on philosophers and other intellectuals. David Cassidy entitled his book Uncertainty not solely in reference to this famous scientific principle but to symbolize the moral uncertainties and compromises that characterized Heisenberg’s life in Germany.

Cassidy, whose education is in both physics and the history of science, has scrutinized most of what has been written by and about Heisenberg, including his private papers, to which Elisabeth Heisenberg granted him full access. His purpose in writing Uncertainty was to understand Heisenberg as a complex, multidimensional human being and as a preeminent scientist in the context of his times. Little controversy exists among historians of science that Heisenberg was one of the greatest physicists of the twentieth century, but much controversy exists concerning his conduct under National Socialism and especially about his participation in the Nazi atomic-bomb project. Cassidy does not completely solve the mysteries of Heisenberg’s actions and motives under the Nazis; in fact, he doubts that anyone will ever fully map the labyrinths of Heisenberg’s soul on these matters. Nevertheless, his is certainly the most balanced and sensitive account yet of these issues.

In 1901, Werner Heisenberg came into a world in which Max Planck was creating a new physics and German culture was widely respected. Young Heisenberg absorbed much of this culture from his father, a teacher of classical languages, and his mother, who was the daughter of a secondary-school rector. Heisenberg’s early interests were mathematics, science, and music, and by the time he was a teenager he was playing advanced compositions on the piano and studying Albert Einstein’s special theory of relativity. Werner’s secondary-school years were also the time of World War I. Germany’s defeat, economic collapse, and ensuing civil strife disillusioned him, but he found solace and meaning in the German youth movement, an exhilarating experience that helped shape his system of values. By leading groups of boys, he saw a way to create the idealistic aristocracy that would replace the materialistic state that had caused most of Germany’s troubles. Like many German intellectuals, Heisenberg hated political chaos and longed to see his nation at peace, so that music, scholarship, science, and other civilized activities could once again flourish.

In the fall of 1920, Heisenberg entered the University of Munich, where he soon switched from mathematics to physics. Under the wise and kind guidance of Arnold Sommerfeld, whose Institute for Theoretical Physics provided him with a comfortable haven, he achieved extraordinary success, publishing four research papers in spectroscopy and hydrodynamics during his first two years. He quickly mastered the quantum theory, originated by Planck and successfully applied to the hydrogen atom by Niels Bohr. Heisenberg realized that the quantum theory was in serious trouble, and he began to believe that entirely new ideas would be needed before the quantum theory could be applied successfully to elements other than hydrogen.

After receiving his doctorate in 1923, Heisenberg decided to pursue theoretical physics at Göttingen, where he wrestled with the problem of resolving the peculiar mixture of classical (continuous) and quantum (discrete) concepts in what would soon be called the old quantum theory. To help him resolve these problems, he traveled to see Bohr in Copenhagen in 1924, when he learned about a new theory of the dispersion of radiation being developed by Bohr and two of his associates. This badly flawed theory was, like a piece of dirt that causes an oyster to produce a pearl, what stimulated Heisenberg to formulate quantum mechanics. In the fall of 1924, he worked out a new mechanics of the atom. This new theory, called matrix mechanics, replaced the model developed by Bohr and Sommerfeld (which pictured electrons revolving around an atom’s nucleus like planets around the sun) with an abstract model with electrons in certain discrete energy states.

Physicists quickly recognized the great value of Heisenberg’s new mechanics regulating atomic phenomena, and they developed and applied his insights to many cases. One of these applications—Heisenberg’s prediction of allotropic forms of hydrogen—would later constitute the official grounds for awarding him the Nobel Prize in Physics in 1932. While Heisenberg and his followers were developing matrix mechanics, Erwin Schrödinger, an Austrian physicist, constructed a new quantum mechanics based on the hypothesis that electrons had wave properties. He called this wave mechanics. Heisenberg, who preferred quantum jumps between energy states, was not enthusiastic about Schrödinger’s formulation, since he did not see how one could replace states with waves. Physicists later showed that Heisenberg’s matrix mechanics and Schrödinger’s wave mechanics were equivalent.

How the new quantum mechanics was to be interpreted also generated problems. Since physicists could not specify the exact position of an atomic particle, its position was a matter of chance. This idea helped Heisenberg formulate his uncertainty principle, which concerns the accuracy with which attributes of an atomic particle can be known. In his famous 1927 paper, Heisenberg showed that the idea of a particle with a definite location and a definite speed was no longer tenable. Because of the new quantum mechanics of the atom, a scientist cannot know both where an electron is and how fast it is moving. Cassidy sees Heisenberg’s uncertainty principle as his greatest achievement in physics.

Initially, Niels Bohr disagreed with Heisenberg’s paper on the uncertainty principle because he saw this principle as a special case of his principle of complementarity, which proposed that both wave and particle pictures are needed to describe atomic phenomena. Despite Bohr’s quibbles, the uncertainty principle did much to augment Heisenberg’s already substantial reputation, and in the fall of 1927, he became professor of theoretical physics at the University of Leipzig, making him Germany’s youngest full professor. He rapidly became the leader of a group of students and collaborators that developed quantum mechanics into a powerful formalism for understanding chemical and physical phenomena. Like Sommerfeld before him, Heisenberg was now Germany’s most influential teacher of theoretical physics.

After Hitler assumed power in Germany in 1933, Heisenberg witnessed the edifice of modern physics that had been constructed largely through the work of German physicists threatened by the policies of the new National Socialist regime. Albert Einstein, whom Heisenberg knew and respected, refused to be part of Hitler’s Germany, and Nazi officials dismissed many distinguished Jewish scientists from their academic positions. Heisenberg, who regarded anti-Semitism as a political issue, refrained from public opposition to these dismissals, of which he strongly disapproved, preferring to work behind the scenes to rescind them. When he failed in these efforts, he joined with such colleagues as Planck to find worthy replacements for the vacant positions. Although Heisenberg never joined the Nazi Party, he was a patriotic German who was sympathetic with some of the ideals of National Socialism, for example, the regime’s emphasis on order, Gemeinschaft (community), strong leadership, and the excellence of German artistic and scientific culture. Despite his disapproval of the regime’s excesses, he decided not to resign in protest, and he held high positions in academia and the government throughout the Third Reich.

His outward cooperation with the regime did not prevent him from being attacked by Nazi ideologues who found his use of Einstein’s ideas in his teaching and writing reprehensible. They blocked Heisenberg from becoming Sommerfeld’s successor at Munich. In the midst of these controversies, he met and married Elisabeth Schumacher, who became his principal support when he was attacked as a “white Jew,” or secret Jewish sympathizer. These attacks led to a prolonged investigation of Heisenberg by Heinrich Himmler’s SS (Schutzstaffel, or special security force). Heisenberg ultimately was rehabilitated politically, but he paid a heavy moral price: He had to agree never to mention the names of Einstein and other Jewish scientists in his lectures and publications. This moral compromise showed how far Heisenberg was willing to go to win the regime’s endorsement, as long as he was left free to pursue his own scientific activities undisturbed.

When World War II began, Heisenberg patriotically agreed to serve the cause of Germany in whatever way he could. By this time, Germany was the only nation with a military project on nuclear energy. By October of 1939, the Kaiser Wilhelm Institute for Physics in Berlin had been requisitioned for the nuclear project, and Heisenberg, Otto Hahn, and other scientists had been recruited to investigate whether an atomic bomb could be made. Heisenberg concluded that an atomic bomb could not be made before the war’s end (which, he then believed, would come early). He and his fellow physicists believed, however, that they could build a controlled fission reactor in this time. It turned out that they were unable to build either a reactor or a bomb during the long war that followed. Cassidy does not think that Heisenberg deliberately sabotaged the project to keep the atomic bomb out of Hitler’s hands. In fact, he believes that Heisenberg and his colleagues were eager to build the bomb, to prove their worth to the regime, and the reasons they failed were incompetence and lack of support from Nazi officials.

In 1942, Heisenberg was called to Berlin to assume a professorship in theoretical physics and the directorship of the Kaiser Wilhelm Institute for Physics. This honor came with the proviso that he would continue to work for the Nazi government at home and as a cultural emissary abroad. For example, he accepted an invitation in 1943 from Hans Frank, central governor of the occupied Polish territories, to lecture in a Cracow propaganda institute, even though, two months before, Frank had overseen the slaughter of many Jews in the local ghetto. This is one example among several that Cassidy uses to show how intimately Heisenberg was tied to the Nazi regime. Despite Heisenberg’s knowledge of the horrors of the German concentration camps, he wanted Germany to win the war and rule Europe, for, as he explained to one scientist, he then saw only two possibilities: Nazi Germany or the Soviet Union. He preferred Germany as the lesser evil.

After the Allies defeated Germany in 1945, Heisenberg and other nuclear scientists were taken into custody and spent eight months at Farm Hill, an English country estate near Cambridge. Because Heisenberg and his colleagues arrogantly believed that they were far ahead of the Allies in nuclear research, news of the American atomic bomb dropped on Hiroshima came as a great shock. Heisenberg at first refused to believe it, maintaining that the bomb had to be a very large conventional explosive. With the Nagasaki bomb and further information, Heisenberg and his fellow scientists had to face their great humiliation: They had failed where the Allies had succeeded.

Cassidy condenses the final thirty-two years of Heisenberg’s life into a brief final chapter. Heisenberg returned to his country in 1946 with the goal of revivifying Ger- man science. He helped advance Germany’s nuclear power program during this time and mobilized public opinion against efforts of the North Atlantic Treaty Organization to equip the West German army with tactical nuclear weapons. In his own research, he returned to his studies of hydrodynamics, publishing an influential statistical theory of turbulence, but in general his postwar research was not as successful as what he had done before the war. His move to Munich in 1958 as director of the Max Planck Institute marked the beginning of the last period of his life, characterized by travels, lectures, and writings in which he sought to reinterpret his contributions in terms of the idealistic philosophy of his youth. He died of cancer in Munich on February 1, 1976, honored as a great physicist and forgiven by most of those he had scandalized by his wartime behavior.

Cassidy chose to emphasize in this biography Heisenberg’s involvement in theoretical physics and his participation in Germany’s revolutionary political changes. He has achieved more success in the second of these goals than in the first. His treatment of his subject’s tortuous attempts to be a good physicist in a bad time is sensitive and insightful. On the other hand, his account of Heisenberg’s scientific accomplishments is problematic because the author never seems to make up his mind for whom he is writing. He defines simple terms but leaves undefined such technical terms as phase space, which would be known only by those with advanced mathematical and scientific training. His analyses of Heisenberg’s scientific work thus are too difficult for the general reader and too plebeian for the physicist. Furthermore, chemists and physicists have found many errors in Cassidy’s explanations of key ideas. Another difficultly with this biography is the author’s cavalier treatment of chronology. His frequent jumps in time often lead to confusion and sometimes to errors. Because of his choice to emphasize science and politics, much of Heisenberg’s personal life is neglected; for example, the reader learns little about his role as father and husband. Despite these limitations and shortcomings, Cassidy’s biography is a well-researched account of a fascinating man in a turbulent time, and Uncertainty is certain to serve as the standard biography for many years to come.

Sources for Further Study

Library Journal. CXVII, March 1, 1992, p. 44.

Los Angeles Times Book Review. December 29, 1991, p. 2.

Nature. CCCLIV, December 5, 1991, p. 365.

New Scientist. CXXXV, September 26, 1992, p. 47.

The New York Review of Books. XXXIX, April 23, 1992, p. 43.

The New York Times Book Review. XCVII, March 8, 1992, p. 11.

Physics Today. XLV, June, 1992, p. 79.

Science. CCLV, February 21, 1992, p. 1001.

Science News. CXL, November 23, 1991, p. 322.

The Times Literary Supplement. March 20, 1992, p. 7.