Niels Bohr and Albert Einstein were the two major figures in the physics revolution of the twentieth century. Einstein, the discoverer of relativity, has become almost a cult figure and the object of numerous biographies and studies; his name is known to most educated people. In comparison, Bohr, his contemporary, the conceiver of complementarity, is a more obscure figure, his contributions less well-known to scientists. Outside of his native Denmark, few nonphysicists know of him at all. Yet some of Einstein’s and Bohr’s contemporaries thought that Bohr was the more important figure in the development of physics. Almost all physicists think that Bohr was right and Einstein wrong in their attitudes toward quantum mechanics. To help restore Bohr to his proper historical status, Abraham Pais, one of Einstein’s biographers, a physicist who knew both men after World War II, has produced a detailed analysis of Bohr’s life, times, science, and influence.
Pais does not pretend that he approached his subject with detachment. Bohr was his mentor and friend. Personal recollections play an essential role in this book: Pais’s own for the years after he met Bohr, those of Bohr and others as they were related to Pais over the years, and those recorded in interviews. Pais, however, neither relies solely on human memory nor necessarily trusts it. He has read extensively in the Niels Bohr Archive of more than six thousand letters dealing with science, thousands of personal letters, and hundreds of drafts of Bohr’s scientific writings. Pais also knows the scientific literature of quantum theory. He has explored Danish political, social, and institutional history. The result is a multifaceted biography of Bohr the researcher, the institution builder, the father, the symbol of Danish science, and the seeker of international peace. Pais may be sympathetic, but he maintains his objectivity.
In writing this biography, Pais was responding to what he perceives as a declining understanding of the significance of Bohr’s role in the history of physics. Although Bohr’s contemporaries and the generation of scientists that followed recognized him as one of the giants of physics, succeeding generations have been less certain of his status. Why is this so? Bohr is remembered for three very different contributions to the development of physics. First, he developed a highly successful theory of atomic structure, one of the highlights of the so-called old quantum theory, for which he was awarded the Nobel Prize for physics in 1922. Second, he established an institute in Copenhagen that became the most important international center for theoretical physics between the world wars. There he inspired, encouraged, and supported the generation that developed quantum mechanics. Finally, he conceived of complementarity, a new type of logical relationship, in an effort to overcome the apparent logical contradiction of describing an electron sometimes as a particle, sometimes as a wave. More broadly, complementarity is “two aspects of a description that are mutually exclusive yet both necessary for a full understanding of what is to be described.” Pais concludes that the ahistorical nature of physics is a major cause of the neglect of Bohr. The Bohr atom has become a historic artifact; it was quickly superseded by quantum mechanics. The institute is now but one of many. Complementarity is ignored by physics textbooks because it is not useful in doing physics, only in understanding the philosophical underpinnings of the science. Perhaps most important, however, Bohr inspired through personal interaction, not the strength of his writings. Pais hopes that this biography will be able to transmit some sense of that inspiration that he himself felt at Bohr’s side.
This is a book that demands concentration and...
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