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Werner Heisenberg
Times obituary
A pioneer of quantum mechanics
Professor Werner Heisenberg died yesterday at the age of 74. He was one of the principle architects of quantum mechanics and won the Nobel Prize for Physics in 1932. He made his decisive contribution at the age of 24 but continued throughout his long and varied career to enrich physics with his insight and competence. At the age of 26, he became Professor of Theoretical Physics at the University of Leipzig, and in 1941 Professor of Physics and Director of the Kaiser Wilhelm Institute for Physics at the University of Berlin. After the Second World War, he became Director of the Max Planck Institute for Physics, first in Göttingen and then from 1958 until his retirement in 1971 in Munich, where he was also Professor of Physics. On his retirement, he was made Director Emeritus of the Planck Institute.
Werner Heisenberg was born in Würzburg on December 5, 1901. He entered the University of Munich, where his father held a chair in Greek, as a student under the brilliant teacher Sommerfeld. From the start, he was interested in the problems involved in reconciling quantum physics, which had been found necessary to describe atomic processes, with the principles of classical Newtonian mechanics and Maxwellian electrodynamics. At the turn of the century, Max Planck had first introduced the "quantum" into physics in his study of radiation. These ideas were taken further, notably by Albert Einsteiner and Niels Bohr, and a quantum theory of atoms and their interactions with radiation had been developed. This theory was an amalgam of classical mechanics and empirical rules, which had to be imposed to obtain agreement with observation. The agreement was good, but they were unsatisfactory because they contradicted some of the postulates of classical theory and were apparently without a consistent, systematic foundation By 1924 it was generally accepted that a radical break with classical physics would be needed and that a completely new quantum mechanics would have to be developed in its place. Niels Bohr had provided an anchor which attached these drifting ideas of quantum physics to the established corpus of classical physics through his correspondence principle which required still apply within a suitable limit.
Heisenberg, under Sommerfeld's tutelage, had been introduced to these theories and speculations while still a student, and his move to Göttingen in 1924, where he became a Privatdozent and assistant to Max Born, and his visit to Bohr's Institute in Copenhagen later that year, brought him into close contact with the leaders in these developments. He became convinced that the key to progress in solving the problem lay in the elimination from the theory of concepts which were not empirically capable of determination Thus, in describing the spectra of atoms, the frequencies and amplitudes associated with the line intensities were acceptable, but the orbits of the electrons in the atoms, incapable as they were of observation, were essentially meaningless and so should be excluded from the theory. By applying these rigorous concepts to the mathematically simpler problem of the pendulum, Heisenberg was able in the spring of 1925 to formulate a new system of mechanics in which the quantum rules arose naturally and to which Bohr's correspondent principle applied. Jointly with Max Born and Pascual Jordan, these new ideas were amplified, and the resulting Quantum Mechanics has supplanted classical mechanics as the theoretical basis of all of physics. For most macroscopic systems, it is well-approximated by the older Newtonian theory, but it continues to apply in the atomic domain when that one fails, and indeed even in the regime of nuclear and sub-nuclear physics.
Shortly after Heisenberg's Quantum Mechanics, or matrix mechanics as it is often called, since its mathematical formulation is in terms of matrices, Erwin Schrödinger presented his independently formulated wave mechanics, which also gave a consistent and coherent description of quantum phenomena. For a while it seemed that there were two conflicting theories, but it was soon shown that they were equivalent to alternative formulations of the same theory.
Quantum mechanics was applied with oustanding success to the physics of atomic processes, and Heisenberg was in the forefront of these heroic achievements. Perhaps his most far-reaching contribution to the further understanding of quantum mechanics was the Uncertainty Principle, which he identified as the epitome of quantum mechanics and the essential point at which it differs from classical mechanics. When a measurement is made of a dynamical variable, the observed system is necessarily disturbed; and it is a consequence of quantum mechanics that the greater the accuracy of the measurement, the greater the disturbance to the system, that disturbance being in another, complementary variable to the one measured. This renders it possible to determine with complete precision all the dynamical variables of a system; there is a minimum uncertainty in the information which can be derived by making measurements on a physical system. This notion has had a profound impact on fields other than physics through no fault of Heisenberg; this impact has often been misguided.
Heisenberg's scientific interests were not confined only to quantum mechanics and atomic physics. He proposed that the neutron and the proton could usefully be considered as two different states of the same particle and introduced the notion of isotopic spin to describe this. The further extensions of these ideas have provided one of the most fruitful methods in the field of nuclear and subnuclear physics. In the same spirit of eliminating all but observable quantities from theoretical formulations that he had used in the genesis of quantum mechanics, he introduced into the study of the interactions of elementary particles a method known as S-matrix theory, which is one of the basic techniques of that field. He also made important contributions to the theory of the solid state, and a model of the ferromagnet bears his name. He was interested in plasma physics and thermonuclear processes. From 1953 onwards, his theoretical work was mostly concerned with attempting to construct a unified field theory of elementary particles.
Heisenberg was a keen musician and throughout his life maintained a keen interest in philosophy. He was also an enthusiastic hiker and enjoyed outdoor activities. During the 1930s, when so many of his colleagues left or were expelled from Nazi Germany, he followed the advice of Max Planck and the urges of his own strong sense of patriotism to stay on through the war, the inevitability of which he recognized. He became a leader of the "Uranverein," the German wartime project working on applications of nuclear fission, and was interned in Godmanchester for a short period after his arrest by the United States After the war he played an influential part in the reestablishment of scientific research in Germany and encouraged its international outlook. In 1951 he became President of the Alexander von Humboldt Foundation. He was the recipient of many medals and prizes and was a Fellow of the Royal Society. He married Elisabeth Schumacher in 1937; they had three sons and four daughters.
A pioneer of quantum mechanics
Professor Werner Heisenberg died yesterday at the age of 74. He was one of the principle architects of quantum mechanics and won the Nobel Prize for Physics in 1932. He made his decisive contribution at the age of 24 but continued throughout his long and varied career to enrich physics with his insight and competence. At the age of 26, he became Professor of Theoretical Physics at the University of Leipzig, and in 1941 Professor of Physics and Director of the Kaiser Wilhelm Institute for Physics at the University of Berlin. After the Second World War, he became Director of the Max Planck Institute for Physics, first in Göttingen and then from 1958 until his retirement in 1971 in Munich, where he was also Professor of Physics. On his retirement, he was made Director Emeritus of the Planck Institute.
Werner Heisenberg was born in Würzburg on December 5, 1901. He entered the University of Munich, where his father held a chair in Greek, as a student under the brilliant teacher Sommerfeld. From the start, he was interested in the problems involved in reconciling quantum physics, which had been found necessary to describe atomic processes, with the principles of classical Newtonian mechanics and Maxwellian electrodynamics. At the turn of the century, Max Planck had first introduced the "quantum" into physics in his study of radiation. These ideas were taken further, notably by Albert Einsteiner and Niels Bohr, and a quantum theory of atoms and their interactions with radiation had been developed. This theory was an amalgam of classical mechanics and empirical rules, which had to be imposed to obtain agreement with observation. The agreement was good, but they were unsatisfactory because they contradicted some of the postulates of classical theory and were apparently without a consistent, systematic foundation By 1924 it was generally accepted that a radical break with classical physics would be needed and that a completely new quantum mechanics would have to be developed in its place. Niels Bohr had provided an anchor which attached these drifting ideas of quantum physics to the established corpus of classical physics through his correspondence principle which required still apply within a suitable limit.
Heisenberg, under Sommerfeld's tutelage, had been introduced to these theories and speculations while still a student, and his move to Göttingen in 1924, where he became a Privatdozent and assistant to Max Born, and his visit to Bohr's Institute in Copenhagen later that year, brought him into close contact with the leaders in these developments. He became convinced that the key to progress in solving the problem lay in the elimination from the theory of concepts which were not empirically capable of determination Thus, in describing the spectra of atoms, the frequencies and amplitudes associated with the line intensities were acceptable, but the orbits of the electrons in the atoms, incapable as they were of observation, were essentially meaningless and so should be excluded from the theory. By applying these rigorous concepts to the mathematically simpler problem of the pendulum, Heisenberg was able in the spring of 1925 to formulate a new system of mechanics in which the quantum rules arose naturally and to which Bohr's correspondent principle applied. Jointly with Max Born and Pascual Jordan, these new ideas were amplified, and the resulting Quantum Mechanics has supplanted classical mechanics as the theoretical basis of all of physics. For most macroscopic systems, it is well-approximated by the older Newtonian theory, but it continues to apply in the atomic domain when that one fails, and indeed even in the regime of nuclear and sub-nuclear physics.
Shortly after Heisenberg's Quantum Mechanics, or matrix mechanics as it is often called, since its mathematical formulation is in terms of matrices, Erwin Schrödinger presented his independently formulated wave mechanics, which also gave a consistent and coherent description of quantum phenomena. For a while it seemed that there were two conflicting theories, but it was soon shown that they were equivalent to alternative formulations of the same theory.
Quantum mechanics was applied with oustanding success to the physics of atomic processes, and Heisenberg was in the forefront of these heroic achievements. Perhaps his most far-reaching contribution to the further understanding of quantum mechanics was the Uncertainty Principle, which he identified as the epitome of quantum mechanics and the essential point at which it differs from classical mechanics. When a measurement is made of a dynamical variable, the observed system is necessarily disturbed; and it is a consequence of quantum mechanics that the greater the accuracy of the measurement, the greater the disturbance to the system, that disturbance being in another, complementary variable to the one measured. This renders it possible to determine with complete precision all the dynamical variables of a system; there is a minimum uncertainty in the information which can be derived by making measurements on a physical system. This notion has had a profound impact on fields other than physics through no fault of Heisenberg; this impact has often been misguided.
Heisenberg's scientific interests were not confined only to quantum mechanics and atomic physics. He proposed that the neutron and the proton could usefully be considered as two different states of the same particle and introduced the notion of isotopic spin to describe this. The further extensions of these ideas have provided one of the most fruitful methods in the field of nuclear and subnuclear physics. In the same spirit of eliminating all but observable quantities from theoretical formulations that he had used in the genesis of quantum mechanics, he introduced into the study of the interactions of elementary particles a method known as S-matrix theory, which is one of the basic techniques of that field. He also made important contributions to the theory of the solid state, and a model of the ferromagnet bears his name. He was interested in plasma physics and thermonuclear processes. From 1953 onwards, his theoretical work was mostly concerned with attempting to construct a unified field theory of elementary particles.
Heisenberg was a keen musician and throughout his life maintained a keen interest in philosophy. He was also an enthusiastic hiker and enjoyed outdoor activities. During the 1930s, when so many of his colleagues left or were expelled from Nazi Germany, he followed the advice of Max Planck and the urges of his own strong sense of patriotism to stay on through the war, the inevitability of which he recognized. He became a leader of the "Uranverein," the German wartime project working on applications of nuclear fission, and was interned in Godmanchester for a short period after his arrest by the United States After the war he played an influential part in the reestablishment of scientific research in Germany and encouraged its international outlook. In 1951 he became President of the Alexander von Humboldt Foundation. He was the recipient of many medals and prizes and was a Fellow of the Royal Society. He married Elisabeth Schumacher in 1937; they had three sons and four daughters.
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