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|Werner Heisenberg (1901-1976)|
German theoretical physicist who was awarded the Nobel Prize for Physics in 1932 for his creation of the quantum mechanics. According to Heisenberg's "uncertainty principle", the position and momentum of a subatomic particle cannot be precisely determined at the same time. Although quantum mechanics did not destroy the clockwork world of Newtonian mechanics, it challenged the basic accepted concepts of the nature of reality. Heisenberg published also books about physics for the layman. During WWII, Heisenberg headed the unsuccessful German atomic effort. His role in the atom bomb program is still a matter of controversy.
"Any use of the words "position" and "velocity" with an accuracy exceeding that given by equation ... is just as meaningless as the use of words whose sense is not defined." (from Physical Principles of the Quantum Theory, 1930)
Werner Karl Heisenberg was born in Würzburg, but he grew up in Munich where his father worked at the university as a professor. A highly talented and ambitioud student, Heisenberg had no problems with languages and science at school. "He has attained his excellent achievements with playful ease; they have cost him no expenditure of effort," wrote his teacher at the end of the second grade. Heisenberg also started to take private piano lessons, and in his teens he was already an accomplished pianist. Classical music remained an important part of his life.
After WW I Heisenberg joined the Bavarian youth movement, becoming the leader of a group of Pathfinders, the German version of paramilitary Boy Scouts. Gruppe Heisenberg, as it was called, was apolitical and followed a strict moral code. Most of its members joined later the clergy, and only one – or so it has been said – became a member of the Nazi party.
Heisenberg entered the University of Munich in 1920, receiving his Ph.D. in 1923. His first research paper in physics Heisenberg published just 18 months after graduating from Munich's Maximilians-Gymnasium. In 1922-23 Heisenberg worked as an assistant to Max Born at the University of Göttingen. "His talent in unbelievable," Born praised, "but his nice, shy nature, his good temper, his eagerness and his enthusiasm are especially pleasing."
Between 1924 and 1927 Hesenberg studied in Copenhagen under the famous Danish physicist Niels Bohr. While recovering on the remote island of Helgoland from one his many attacks of hay fever, Heisenberg created in 1925 the novel ideas of "matrix mechanics", later proved to be mathematically equivalent to the simpler wave mechanics of Edwin Schrödinger. Just a few years earlier Oswald Spengler had written in The Decline of the West (1918-22): "Today the idea is openly expressed that the science of physics has reached the limit of possible knowledge." Heisenberg's breakthrough work, 'On a quantum-theoretical reinterpretation of kinematic and mechanical relations', a 15-page article, appeared in the September 1925 issue of the Zeitschrift für Physik.
In spite of complex economical and political problems, Germany became in the mid-1920s the leading country of quantum mechanics. "As is well known, quantum mechanics stands at the center of attention among physics circles of all nations," declared the Electrophysics Committee, which supported Heisenberg financially during the crisis years. From 1927 to 1941 Heisenberg served as professor of theoretical physics at the University of Leipzig. His famous "uncertainty principle" Heisenberg formulated in 1927, before his appointment to the chair.
Its key element was that in the quantum world, measuring the position or velocity an object affect the object being measured. The more accurately we know the position of an electron, the less we know about its momentum. Heisenberg also showed that the same applies to energy and time, a similarly linked pair of quantities. Observables, in effect, are produced by the measuring process. There was also another far-reaching implication of the principle, that "in a certain sense the law of causality becomes invalid," as Heisenberg noted in 'Über die Grundprinzipien der 'Quantenmechanik' (1927), his first nontechnical article for nonphysicists. Philosophically this meant that causality was an a posteriori concept, not one of the a priori categories of the understanding as Kant had argued.
"Natural science does not simply describe and explain nature," said Heisenberg in Physics and Philosophy (1958), "it is a part of the interplay between nature and ourselves; it describes nature as exposed to our method of questioning." However, there is no limit on the accuracy with which a single observable may be measured. Heisenberg's result can be summarized as
uncertainty in position x uncertainty in momentum ³ Planck's constant / 2pi.
If we were able to determine the momentum of the particle exactly – the uncertainty is reduced to zero – we would have no idea of the position – the uncertainty would be infinite. And vice versa. According to an anecdote, Bohr once said that a person who wasn't outraged on first hearing about quantum theory didn't understand what had been said.
In classical physics this interaction aspect was not a problem that needed to be considered. But in the case of electrons and other particles, the measurement cannot serve as basis for predictions of future states of the system. "In the strict formulation of the causal law – if we know the present, we can calculate the future – it is not the conclusion that is wrong but the premise," Heisenberg said, the laws and predictions of quantum mechanics "are in general only of a statistical type." Albert Einstein expressed his unhappiness with the statistical nature of the theory, stating that it "accomplishes a lot, but it does not bring us closer to the secrets of the Old One. In any case, I am convinced that He does not play dice."
Die physikalischen Prinzipien der Quantentheorie (1930), Heisenberg's first book, was based on lectures he delivered to the University of Chicago in 1929. From the United States he continued his tour to China and India. He also visited the Himalayas.
Heisenberg was not a supporter of the ideology of the Third Reich, but he remained in Germany throughout the Nazi era. After Hitler's rise to power in 1933, Jews were dismissed from public positions. Like other civil servants and soldiers, Heisenberg had to swore the oath of personal allegiance to Hitler. Due to Heisenberg's support for the physics of Einstein, he was attacked by the Nazi press. His field of science was characterized as "un-Aryan". Heisenberg himself was called a "white Jew" and a covert state enemy in the SS weekly Das Schwarze Korps. After accusations and investigations, during which Heisenberg was at least once interrogated in the SS headquarters, he was allowed to work and teach in Germany. "Heisenberg is typical of the apolitical academic," stated one of the reports, and Heinrich Himmler declared, "I believe that Heisenberg is decent, and we could not afford to lose or silence this man, who is relatively young and can educate a new generation."
In 1937 Heisenberg married the 22-year-old Elisabeth Schumacher; they had four daughters and three sons. Elisabeth's father was a professor of political economy. She had graduated from in 1936 from the University of Freiburg, where she had studied German literature, and moved then to Leipzig.
When Heisenberg traveled in the United States in the summer of 1939, he unenthusiastically predicted that the Nazis will win the war. During WW II, Heisenberg served as professor at the University of Berlin and director of the Kaiser Wilhelm Institute of Physics in Berlin, where he headed the atom bomb research as the premier nuclear physicist of the country. Most likely Heisenberg knew about the concentrations camps by 1943. "We have to keep reminding ourselves that it is more important to act humanely than to fulfill any professional, national, or political obligations," Heisenberg wrote in 1942 in a letter to his friend. After the war, he was accused of not using his influential position beyond his own circle to help people in life-and-death situations.
Heisenberg met again in 1941 in Copenhagen his former teacher and friend Niels Bohr. The real reason for the meeting is a mystery. Bohr, who had visited the United States in 1939, suspected that Heisenberg tried to find out the progress the Allied had made. Eventually Bohr escaped from the occupied Denmark back to America, where he participated in the development of the atomic bomb. German scientists failed to build a working nuclear reactor, one possible route to the ghastly weapon. While about 150,000 people was involved in helping the Allied project – the Los Alamos team consisted of about 2,000 people – only a few hundred was active in the German enterprise. However, even when Germany's collapse was looming, Heisenberg's team worked feverishly to achieve a chain reaction. Reichsmarschall Hermann Göring, the head of the Luftwaffe, was obsessed by the idea of dropping a nuclear bomb on New York.
In May 1945 Heisenberg was arrested by Colonel Pash's task force in Urfeld, where he had a cabin. The Americans met him sitting on the veranda. Along with many other leading physics, Heisenberg was interned in England. The news of Hiroshima and Nagasaki Heisenberg heard at Farm Hall, a village near Cambridge. It turned out that the German scientists did know how the bombs had been made. After the publication of David Irving's The German Atomic Bomb (1967), in which the controversial British historian saw scientific curiosity as one of the major driving forces behind the German project, Heisenberg said, that "German physicists did not insist on pursuing, by means of practical measures, a path which could not have led to success during the war."
In 1946 Heisenberg returned to Germany. The S-matrix theory of elementary particles, which Heisenberg started in the early 1940s, was widely developed during the following decades. Becoming increasingly interested in Platonism, Heisenberg argued that "one could hardly make progress in modern atomic physics without a knowledge of Greek natural philosophy. His lectures Heisenberg used to start with a reference to Greek philosophy. In 1958 Heisenberg presented his new field equation, the so-called world formula, which his old colleague Wolfgang Pauli characterized at a CERN conference in his ruthless style as "mathematically objectionable" and tore it apart. "Wolfgang's attitude to me was almost hostile," wrote Heisenberg mildly over a decade later.
Heisenberg was named in 1946 director of the Max Planck Institute (the former Kaiser Wilhelm Institute) for Physics and Astrophysics. He also helped to create the first European scientific laboratory, CERN, in Geneva, and served for more than two decades as president of the Alexander von Humboldt Foundation. In 1957 he composed the Göttingen Manifesto with 17 other scientist against the nuclear armament in Germany. Heisenberg died of cancer in Munich on February 1, 1976.
For further reading: Inner Exile: Recollections of a Life With Werner Heisenberg by Elizabeth Heisenberg (1984); Uncertainty: The Life and Science of Werner Heisenberg by David C. Cassidy (1992); Heisenberg's War: The Secret History of the German Bomb by Thomas Powers (1993); Heisenberg Probably Slept Here: The Lives, Times, and Ideas of the Great Physicists of the 20th Century by Richard P. Brennan (1996); Heisenberg and the Nazi Atomic Bomb Project, 1939-1945: A Study in German Culture by Paul Lawrence Rose (1998); 100 Years Werner Heisenberg: Works and Impact, ed. by Dietrich Papenfuß, Dieter Lüst, Wolfgang P. Schleich (2002); Uncertainty: Einstein, Heisenberg, Bohr, and the Struggle for the Soul of Science by David Lindley (2008); Heisenberg and the Interpretation of Quantum Mechanics: The Physicist as Philosopher by Kristian Camilleri (2011)