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...
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