Monday, July 18, 2016

Keith Huxen - The Mysterious Meeting between Niels Bohr and Werner Heisenberg

In the fall of 1941, the course of history in the Second World War took a different pathway based upon a mere conversation between two men. At first glance, it would appear unlikely such an event could have such an effect, particularly since both men were intentionally vague with each other, each later maintained misunderstandings of the other’s intention, and to this day the conversation remains shrouded in mystery. The two men were civilians, not soldiers; they were scientists, not politicians; they met in Nazi-occupied territory, not in free lands where they could speak frankly. Lastly and most importantly, they were thinkers dedicated to the discovery of knowledge of the natural world, not the mass destruction of human life.

But when the participants in this uncertain conversation were Niels Bohr and Werner Heisenberg, then the import of the event becomes clearer. On the surface, the Dane of Jewish descent and the German Lutheran, separated in age by sixteen years, did not have much in common. But their lives were deeply intertwined with each other on personal, intellectual, and professional levels. They began as an internationally recognized physics professor and gifted student when they first met in 1922, the year Bohr became a Nobel laureate. But they became much more than that. Personally, Heisenberg virtually became another of Bohr’s sons and shared the intimacy of his family life. Intellectually, Bohr’s manner of thinking about physical problems in which he attempted to comprehend phenomena as a whole found balance, advancement and authenticity through collaboration with Heisenberg, whose fascination with and ability to find the music of mathematics located within physical events led to great scientific breakthroughs.

Professionally, the two men mapped and explored the quantum universe inside the atom. In 1927, Heisenberg staked his own claim to great scientific achievement when he published his “Uncertainty Principle,” which stated that the exact position of an electron within an atomic nucleus at a given time could not be known with certainty, but only statistically calculated within a probability. By that same year Bohr had developed his ideas on “complementarity” in physics, through which he incorporated Heisenberg’s physics within his own, and proposed that the seeming chaos of the quantum world and the order of the universe based upon classic physics did not refute each other, but complemented each other in a manner which we had yet to comprehend and explain. The two men were the fathers of quantum mechanics, and together they had carried out a revolution in the physics world during the 1920s. In 1932, Heisenberg joined Bohr as a Nobel laureate.

Science was traditionally seen by its practitioners as an international fraternity at the beginning of the twentieth century. Information, news of discoveries, papers and ideas flowed freely across national boundaries between scientists intent upon expanding the frontiers of knowledge. This was an idealized era in science; while not free of individual rivalries, nonetheless the atmosphere was not romanticized. Scientists viewed themselves as colleagues in the craft of pursuing higher truths, not as national rivals. This was the atmosphere of Ernest Rutherford, Max Planck, and above all, Albert Einstein. Niels Bohr also entered this idyllic prewar scientific atmosphere. In 1913, he published “On the Constitution of Atoms and Molecules,” a paper which brought him reputation and fame when he described how electrons jumped between orbits within the nucleus.

However, the instabilities of the international political system began to change this idyllic scientific atmosphere after 1914. The Great War saw scientists mobilize on behalf of their national governments to use science as a new offensive weapon, creating new and more devastating ways to kill. The Great War did not kill off this atmosphere of scientific cooperation. The German-born Einstein completed his General Theory of Relativity while employed at the University of Berlin in 1915; copies of his paper were smuggled to Allied scientists, and the British astronomer Arthur Eddington successfully arranged financing from his government during wartime to photograph a solar eclipse in 1919 to prove Einstein’s theory. Nonetheless, nationalist politics showed itself as the greatest threat to the idealized world of free inquiry and knowledge which scientists held dear.

Bohr and Heisenberg had inherited the benefits of this atmosphere in the 1920s, when together they explored the quantum revolution. However, the rise of the arch-nationalist, Adolf Hitler in Germany, ushered in a new and shocking suppression of scientific inquiry and knowledge. Even before Hitler achieved power in Germany, Heisenberg personally experienced opposition to the “new physics” by hostile German scientists who demanded a German or “Aryan Physics” which applied to natural Germans (supporters of this “Deutsch Physik” included Nobel laureates such as Johannes Stark). The revolutionary physics of relativity and uncertainty, led by Einstein, Bohr, and Heisenberg, was tied to impurity, deformity and Judaism by the Nazis in a manner similar to how they dealt with the modern art of cubism and Picasso. It should be noted that the new physics (along with Freudian psychology) had been condemned in the Soviet Union as well in the early 1920s for not conforming to the precepts of Marxist-Leninist ideology. But where Russia was seen as scientifically and technologically backward, Germany was the most advanced educational, scientific, and technological power in Europe.
After Hitler assumed the Chancellorship in January 1933, the Nazis soon banned all Jews from working for the German state or in professional capacities such as university professors. This meant that better than a hundred German physicists of Jewish descent, including Einstein, were soon displaced. An exodus of the world’s greatest scientific talent began to emigrate from Germany to receptive western nations. From his Institute of Physics attached to the University of Copenhagen in Denmark, Niels Bohr tried to assist many colleagues in finding new lives and employment.
Werner Heisenberg was not an anti-Semitic; indeed, he even tried to hire a Jewish colleague into an open position at his University of Leipzig in the 1930s. He did not join the Nazi party. However, he was a dedicated German nationalist. He participated in the military drills of his reserve unit. Most distressing to his international colleagues, he refused to follow the example of Einstein and leave Germany as a symbolic protest against the Nazi regime and its attitude towards scientific inquiry.

But advancements in the physics and political worlds were on a collision course. One of those forced to flee Germany due to Hitler’s policies was Lise Meitner, an Austrian Jewess formerly employed at the Kaiser Wilhelm Institute where she had collaborated with the chemist Otto Hahn. After her departure, Hahn continued to send to Meitner information on experiments he had conducted upon the element uranium. On a skiing holiday, while seated under Kungalv castle in Sweden on Christmas Eve 1938, Meitner and her nephew Otto Frisch successfully diagnosed and calculated that nuclear fission had taken place. Within two weeks, they had delivered to Niels Bohr their preliminary paper which he took with him to America. In January 1939, the news was made public at a physics conference at George Washington University. To leading physicists, the possibility of splitting the atom and releasing untold amounts of energy through nuclear fission was now within reach, along with the understanding that it was now theoretically possible to build an atomic bomb. 

In April 1939 the first “Uranverein,” or German “Uranium Club” was established. This was a relatively small group of forty or fifty German scientists assigned to work upon the problem of nuclear energy. This was the situation in September 1, 1939 when war came to Europe. On the day that Germany launched the invasion of Poland, the German Army Ordnance Office took over the German nuclear energy project to explore potential military applications. This second Uranverein was a military and state secret. From his posts as a professor at the University of Leipzig and Acting Director of the Kaiser Wilhelm Institute for Physics in Berlin, Heisenberg became the lead theoretician of the Uranverein, cooperating with professors spread across Germany to study and develop nuclear fission.

Initially, physicists across the globe calculated that any proposed atomic bomb project would be years in the making due to the tremendous technical difficulties, scientific problems, labor commitments, and financial resources required of the undertaking. In the meantime, however, the war moved quickly. Hitler and the Germans had invaded Norway, Denmark, Holland, Belgium, and France by the summer of 1940; from his physics institute in Copenhagen, Niels Bohr found himself living under the Nazi occupation. Only Britain fought on alone against Hitler for over a year, until in June 1941 Hitler double-crossed his ally Stalin. The German invasion of the Soviet Union was initially very successful, as Operation Barbarossa saw deep German penetration of Soviet territories. By September 1, 1941, Leningrad was completely cut off from the rest of the Soviet Union except by Lake Ladoga; the Soviet military teetered under the terrific German onslaught, and it appeared the Germans might take Moscow before Christmas. The United States officially remained a neutral nation. And the Uranverein had recently conducted experiments which hinted at the pathway to develop a self-sustaining nuclear fission reaction. The ability to create an atomic bomb appeared to be a key that might guarantee ultimate victory to whoever developed it first, with Hitlerite Germany in the lead.

It is against this historical backdrop of what appeared to be impending German victory and potential German bomb that Werner Heisenberg, Nobel Laureate, chose to arrange travel to attend a German-sponsored conference in Copenhagen in September, 1941. Bohr would not attend the conference as a protest against the Germans, but he was willing to personally see Heisenberg. Heisenberg’s purpose was to query his great mentor and friend, Niels Bohr, on a major issue troubling his mind: namely, should a physicist help build an atomic bomb for his country in wartime?

It is difficult for historians to reconstruct exactly what was said between the two men. Heisenberg was so eager he arrived four days early for the conference, but neither man could remember the exact date or place of the conversation. In later years Heisenberg recalled the conversation taking place on a long walk around the harbor in Copenhagen; Bohr recalled that it took place in his study. Heisenberg was a leader in a secret German nuclear program. To merely reveal the existence of such a program was treason, and within Hitler’s state Heisenberg would almost certainly lose his life. But for Bohr, this was countered by the fact that Heisenberg was a loyal German national, and thus working for the victory of the Nazi state… read more: