BIOGRAPHIES OF PERSONS IN COPENHAGEN

Compiled by Harry Lustig

THE PROTAGONISTS

Niels Bohr
Margrethe Bohr
Werner Heisenberg
Other Scientists Mentioned in the Play

NIELS BOHR (1985 - 1962)

Niels Bohr was born in Copenhagen in 1885 to an intellectual family; his father was professor of physiology at the University, his mother came from a wealthy Jewish family that was prominent in banking, politics, philology, and education. Niels Bohr died in Copenhagen in 1962.

Bohr's early work in physics was on the classical theory of metals. After failing to interest J.J. Thomson in Cambridge in it, he moved to the Manchester laboratory of Ernest Rutherford, with whom he formed a life-long friendship. Bohr eagerly took up Rutherford's nuclear model of the atom and recognized its far-reaching implications. In particular, he explained many properties of radioactive transformations and recognized the existence of what later became known as isotopes. He became convinced that classical electrodynamics was fundamentally limited in the atomic domain and had no doubt that this limitation would be governed by Planck's quantum of action. His formula relating the range of penetration of ionizing particles in a medium to their velocity has, in its essentials, survived modern quantum mechanics.

Upon his return to Copenhagen in 1912, he married Margrethe Nørlund. Theirs was a happy and harmonious union, although Margrethe's role was not an easy one. Bohr had a sensitive nature and constantly needed the stimulus of sympathy and understanding. When children came - six sons, two of whom died young - Bohr took his duties as paterfamilias seriously. Margrethe adapted herself readily to the part of hostess and evenings at the Bohr home were distinguished by warm cordiality and exhilarating conversation.

In 1913, almost immediately upon his appointment as an assistant at the University of Copenhagen, Niels Bohr published his most important and daring contribution, the old quantum theory. This was the finding that the Rydberg formula for the frequencies of series of spectral lines could be explained only if the emission of light by an atom occurred as single quanta involving Planck's constant. Thus, while the stationary states of atomic systems could be explained by classical mechanics, the transition from one state to another was a non-classical process.

Bohr at once recognized that the quantal behavior of a system had to go over to the corresponding classical behavior for motions involving large quanta. This insight was later dubbed the Correspondence Principle. (It has only recently been challenged.) Bohr's atomic theory inaugurated what arguably were to become the two most adventurous and fruitful decades in the history of science: the invention and perfection of quantum mechanics and its successful application to the solution of numerous problems in physics, chemistry and even biology.

The Copenhagen authorities did not immediately recognize or reward Bohr's preeminence, but Rutherford did, and in the very same year, 1913, offered him a lectureship in Manchester. Bohr was glad to avail himself of the opportunity to pursue his work under the favorable conditions that prevailed there. After two years the Danes moved to offer Bohr a professorship and three years later, thanks to the intervention of friends who donated the land, they were persuaded to build Bohr a laboratory. This was the famous Institute for Theoretical Physics, of which he was the director for the rest of his life. Most of the world's great theoretical physicists and many who were good but not quite as great, spent periods of their lives at Bohr's Institute. The first to join Bohr in 1916 and to remain for ten years was H.A. Kramers; others who came during the early years included Georg von Hevesy, Oskar Klein, Wolfgang Pauli, and Werner Heisenberg.

Bohr did not rest on his laurels. In 1924, with Kramers and J.C. Slater, he published "The Quantum Theory of Radiation", a renunciation of the classical from of causality in favor of a statistical description. And even though it was Heisenberg who in1927 discovered the indeterminacy relations (inaccurately known in English as the uncertainty principle), it was Bohr who formulated their epistemological foundations in terms of the role of an observer and the complementarity, i.e. the inevitability of mutually exclusive descriptions of quantum phenomena.

By the 1930's, with atomic and solid state physics well understood through quantum mechanics, the main interest had shifted, in Copenhagen as elsewhere, to the rapidly expanding field of nuclear physics. In particular, an explanation had to be found why nuclei were so readily able to capture neutrons for a sequence of resonance energies. Bohr accomplished this in 1936 by imagining, classically, the nucleus as an assembly of nucleons (protons and neutrons) held together by short-range forces, and thus, in effect, behaving like the assembly of molecules forming a drop of liquid, a model which had been put forward earlier by George Gamow. The most important application of this theory was the interpretation of nuclear fission, which Bohr and John A. Wheeler published in 1939, immediately upon the discovery of the fission phenomenon.

This happened while Bohr held a visiting appointment at Princeton University. In 1943, in the face of the Nazi occupation of Denmark, he was able to flee to Sweden. From there he was transported to England, where he was suddenly faced, to his surprise, with the advanced stage of a project - the building of an atomic bomb - that he had deemed beyond the realm of technical accomplishment. Although as "Mr. Baker" he made some contributions to the development of the bomb at Los Alamos, his preoccupation for the rest of his life was to make statesmen and the public aware of the political and human implications of this new weapon and of the urgency of reaching a universal agreement never to use it.

Bohr applied his epistemological and philosophical ideas to many areas of science and of culture. For example he invoked complementarity in analyzing the two modes of description - the physical-chemical one and the functional one - in biology, and the influence of tradition and the environment versus that of heredity in human culture. In putting forth his epistemological ideas, Bohr was always careful to stress both the requirement of divesting oneself of all preconceived opinions and seeking guidance exclusively from the data of experience, and the equally stringent necessity of recognizing in every case the limitations inherent in the concepts used in the description of the phenomena under study.

[Portions of this account are taken from Léon Rosenfeld's article "Bohr, Niels Henrik David" in Dictionary of Scientific Biography, II, pp. 238 - 254, Charles Scribner's Sons, New York (1970)]

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MARGRETHE BOHR (1890 -1984)

Margrethe Nørlund was the daughter of Alfred Nørlund, a pharmacist from the Danish town of Slagelse, and of Emma Holm. She was a student at Frøken Banners Pigeskole in Slagelse, a type of institution in the late 19^th century, where women studies home economics, hygiene, physiology, nursing and practical things about the house, and where they could train for teaching at such schools. Margrethe Nørlund met Niels Bohr in 1909 through her brothers Niels Erik and Poul, who were friends of Bohr. They were engaged in 1910 and married in 1912 in a brief , civil ceremony.( Both Bohrs had a similar response to religion: Margrethe has written about Niels’: "There was a period of about a year...[he was] 14 or 15... where he took it all very seriously; he got taken by it. Then suddenly it was all over. It was nothing for him." About her own feelings,

Margrethe reported : "You know it was often at that age ....that one got very religious and would listen to the minister about confirmation. Then it all dissolved. And for me it was exactly the same; it disappeared completely.")

Margrethe Bohr was an indispensable companion to Niels. In the early years of their marriage she acted as his secretary-assistant, taking down drafts of his papers from dictation. (Niels reports that on one occasion, in 1912, "I went to the country with my wife and we wrote a very long paper on these things [probably an attempt to complete his work on alpha particles]." After November 1916, when their first son, Christian Alfred , was born - who, in 1934 tragically drowned while sailing with his father - Margrethe’s help in taking dictation understandably waned. Throughout their lives together Niels bounced ideas off her. She accompanied him on many of his travels and on one occasion may have saved his life. (Abraham Pais recollects in his excellent biography Niels Bohr’s Times, in Physics, Philosophy, and Policy: "We went [to Copenhagen from the Bohrs’ country home at Tisvilde, in the 1940's] by car. It was an act of faith to sit in an automobile driven by Bohr. On that occasion he complained that he felt too hot and actually let go of the wheel to take off his jacket. Mrs. Bohr’s rapid intervention saved the situation.")

All the many friends and associates who have written about their stays at the Bohrs’ home agree on Margrethe’s extraordinary contributions as a hostess and participant in the conversations.. She was very much in her element after the Bohrs moved into the sumptuous "Residence of Honor" in the Carlsberg breweries in 1932. Pais reports that at the many receptions "whether for the staff and visitors from Bohr’s institute, or for Queen Elizabeth and Prince Philip of England, or other high dignitaries, ...[she officiated] with great charm and dignity. She had the particular talent of knowing the names and some personal circumstances of all her guests. She came to be known as Dronning (Queen) Margrethe, with affectionate respect by some, with envy by others."

In March 1980 - twenty-seven years after Niels’ death - Margrethe’s 90^th birthday was celebrated with a big dinner attended by more than fifty guests - family, scientists artists, politicians. At close to midnight Margrethe began an impromptu speech and she was still going strong after several hours. She lived another four years and died just before Christmas 1984. Her remains rest close to those of her beloved Niels.

Shortly after Niels Bohr’s death, the mathematician and lomg time family friend Richard Courant, in explaining Niels’s success, wrote:"...It was not luck, rather deep insight, which led him to find in young years his wife, who, as we all know, had such a decisive role in making his whole scientific and personal activity possible and harmonious." And their son, Hans, wrote of his parents’ lives together:"...My mother was the natural and indispensable center. Father knew how much mother meant to him and never missed an opportunity to show his gratitude and love...Her opinions were his guidelines in daily affairs."

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WERNER HEISENBERG (1901 - 1976)

Heisenberg was born in1901 in Würzburg and died in 1976 in Munich, Germany. As in the case of Bohr, Heisenberg's father was a university professor, in his case of philology. Heisenberg's wife, Elisabeth, whom he married in 1937, also was the child of a professor, the noted economist Hermann Schumacher. They had seven children. Heisenberg began piano lessons early and became and remained an excellent and avid player throughout his life.

Another talent he displayed early was for mathematics and he entered the University of Munich intending to become a mathematician. However he soon came under tutelage of the renowned physics professor Arnold Sommerfeld and received his doctorate from him in 1923. Subsequently Heisenberg studied and collaborated with Max Born in Göttingen and with Niels Bohr in Copenhagen (succeeding H.A. Kramers there as Bohr's assistant in 1926). Later he also made the acquaintance of and worked with, among other physicists, Wolfgang Pauli, Enrico Fermi and P.M.A. Dirac. In 1926, at the age of twenty-five, he was called to the University of Leipzig as Germany's youngest full professor.

In 1922, in his first published paper, on the Zeeman effect, he already displayed his audacity and inventiveness. Although the model violated basic principles of both classical and the early formulation of quantum mechanics, it served as the basis of subsequent work and as an indication of the radical changes that would be needed. By 1926, with Born and Pascual Jordan, he had developed matrix mechanics, a brilliant mathematical formulation of the new quantum mechanics. However most physicists came to prefer the equivalent formulation propounded in 1926 by Erwin Schrödinger, which uses a partial differential equation - the Schrödinger equation - as its starting point. A somewhat similar fate was to be visited on Heisenberg beginning in the decades following the 1940's, when, as in 1925 for atomic interactions, he developed a theory of high energy elementary particle collisions that was based only on the observable states of the particles. While this S-matrix theory of scattering enjoyed considerable attention for several years, renormalized field theories eventually found more followers.

Heisenberg is popularly best known for his Uncertainty Principle (variously called by him Ungenauigkeit [inexactness] or Unschärfe [lack of sharpness] Relation, but later changed to Unbestimmtheit [intederminateness or even indeterminability]). Simultaneous precise measurements of canonically conjugate properties, such as the position and momentum, or energy and location in time, of a particle are in principle (and in experimental fact) not possible; the product of their lack of precision is at least as big as Planck's constant. In 1927, based largely on this insight and Bohr's recognition of complementarity, Heisenberg, Bohr, and Born presented the Copenhagen interpretation of quantum mechanics.

With Carl Friederich von Weizsäcker and others, Heisenberg also explored the philosophical interpretations of quantum mechanics, sounding the death knell of strict determinism, claiming the weakening of causality and investigating the applications of neo-Kantian notions. With Bohr he pushed the Copenhagen interpretation into chemistry and biology and even into social phenomena. With physicists such as Felix Bloch, Rudolf Peierls and Edward Teller he applied quantum mechanics to the solution of many problems, such as the helium atom and ferromagnetic materials. After 1927, drawing on the work of Dirac, Pascual Jordan, Oskar Klein, and others, Heisenberg's major scientific concern became the unification of quantum mechanics and relativity theory. Soon after the discovery of the neutron in 1932, Heisenberg developed a neutron-proton model of the nucleus by introducing the concepts of the nuclear exchange force and of isotopic spin. In 1936 Heisenberg discovered a mathematical minimum length which, he believed, marked the frontier of a new, wholly revolutionary physics.

During the entire course of his life, Heisenberg was a patriotic German. In 1919 he supported the resistance against a Bolshevik-oriented taker-over in Bavaria and in defense of the elected social-democratic government As a boy-scouts leader he strove for the renewal of German life through the direct experience of nature and the beauties of Romantic poetry, music, and thought. In the early years of the Nazi regime, he and other theoretical physicists came under attack as "white Jews", but by the outbreak of the Second World War, he and the regime had made sufficient peace with each other for Heisenberg to remain in Germany and to be put in charge of the German nuclear reactor program.

In the last, chaotic days of the War, the ALSOS mission, scientifically led by the Dutch born refugee physicist Samuel Goudsmit, captured Heisenberg and nine other German scientists. They were interned at Farm Hall, a country estate near Cambridge, England, for six months. After their repatriation Heisenberg set out to revitalize German science and to resume relations with scientists, many his former friends and colleagues, in other countries. He reestablished and headed the Kaiser Wilhelm Institute, renamed the Max Planck Institute, in Göttingen, became the President of the German Research Council and headed the German delegation at the founding of the European research center for nuclear (high energy) physics, CERN, in Geneva. In spite of the demands of his political involvements, he continued to be active in physics and to pursue his search for a consistent quantum field theory until his death.

[Much of this material is based on the article by David C. Cassidy "Heisenberg, Werner Karl" in Dictionary of Scientific Biography, Suppl. II, pp. 394 - 403, Charles Scribner's Sons, New York (1990)]

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OTHER PROMINENT SCIENTISTS MENTIONED

11 MAX BORN (1882 - 1970)

Max Born was both an important teacher of other physicists (among them Werner Heisenberg) and a major contributor to quantum mechanics. Born in Breslau, Germany (now Wroclaw, Poland) to Jewish parents, he became professor of theoretical physics at the University of Göttingen in1921 and reformulated the first law of thermodynamics. In 1926 he collaborated with Heisenberg in the mathematical formulation of quantum mechanics and a little later gave the Schrödinger equation a statistical interpretation. For this work he received the 1954 Nobel prize (sharing it with Walther Bothe for unrelated work). In 1927 he joined Bohr and Heisenberg in formulating the Copenhagen Interpretation of quantum mechanics.. He also developed a technique, known as the Born approximation, for solving scattering problems, and with J. Robert Oppenheimer, a theory of molecules. In 1933 Born, fleeing the Nazis, found refuge in England, first as a lecturer in Cambridge and in 1936 as the Tait Professor of Natural Philosophy at the University of Edinburgh.. After his retirement in 1953 Born returned to Göttingen, where he wrote books and articles on the responsibility of scientists for the use of nuclear energy in war and peace. He died in Göttingen in 1970.

61 LOUIS DE BROGLIE (1892 - 1987)

Born in Dieppe, Louis-Victor duc de Broglie was the scion of an old French noble family. Although his older brother Maurice was an experimental physicist of some achievement, Louis was destined to follow the family tradition of becoming a diplomat. He obtained a degree in history at the Sorbonne in 1909, but also studied physics and, after a period of severe conflict, chose to do a doctoral thesis in the latter field. This thesis, completed in 1924, became his one important contribution to physics. It was the notion that matter, in particular electrons, had wave as well as particle properties, the complement of Einstein’s and Planck’s findings that light acted sometimes as a particle, rather than a wave. The wavelength of the electrons was, again, connected to Planck’s constant. (The wave nature of the electron was experimentally confirmed in 1927 by Davisson and Germer in the United States and by G.P. Thomson in Scotland.) After receiving his doctorate, de Broglie remained at the Sorbonne, becoming professor of theoretical physics at the newly founded Henri Poincaré Institute in 1928 . He taught there until his retirement in 1962 and died in Paris at the age of 94. De Broglie described himself as "having much more the state of mind of a pure theoretician than that of an experimenter or engineer, loving especially the general and philosophical view". Indeed the central question in de Broglie’s life and work became the one that also informed the dialogue between Einstein and Bohr, whether the statistical nature of atomic physics reflects an ignorance of the underlying facts or whether statistics is all that can be known..

26 HENDRIK CASIMIR (1909 -

Hendrik Brugt Gerhard Casimir was born in The Hague in 1909 and educated at Leiden, Copenhagen, and Zurich. After nine years on the faculty of the University of Leiden, he joined the Philips Research Laboratory at Eindhoven in 1942 and has remained there since, achieving leading scientific and management positions. Casimir has made important fundamental contributions to applied mathematics, to theoretical physics (the Casimir operator in quantum mechanics is named after him)and to low temperature physics. The statement attributed to Heisenberg on p.79 of Copenhagen, that Casimir was dead, is fortunately in error.

19 JAMES CHADWICK (1891 -1974)

Born in the small English village of Bollington, Chadwick studied with Rutherford in Manchester. He received a first class honors degree there in 1911 and met Bohr. In 1913 he went to Berlin to work with Geiger (he of the counter) where he was caught by the outbreak of the First World War. During his interment he was allowed to continue his work and even visit German colleagues. In 1919 he went with Rutherford to Cambridge, but left for Liverpool in 1935 after Rutherford refused to acquire a cyclotron. After making many important experimental contributions to the study of radioactivity and of the nucleus he confirmed the existence of the neutron in 1932 and with Maurice Goldhaber accurately measured its mass a year later. In 1935 Chadwick received the Nobel prize for the discovery of the neutron. In World War II he was mostly occupied with. defense work and, after seeing Frisch and Peierls' paper on the small amount of uranium that would be required to produce a critical mass for a chain reaction., he headed the British atomic bomb effort. From 1948 to 1958 he served as master of Gonville and Caius College, Cambridge, but, disillusioned by academic politics, he resigned and returned to scientific research and administration. He died in Cambridge in 1974.

60 P. A. M. DIRAC (1902 - 1984)

Born in Bristol to an English mother and a (French-speaking) Swiss father, Paul Adrian Maurice Dirac began to study theoretical physics only after he had received a degree in electrical engineering form the University of Bristol and could not find work in that field. While still a student at St. John’s College, Cambridge in 1926, he made his first outstanding contribution to quantum mechanics. Applying the ideas of Einstein to those of the originators of quantum mechanics, he formulated the relativistic form of quantum theory, the Dirac equation. Among several important consequences of that theory was that there had to be negative energy states of the electron. This did not seem to be compatible with physical reality, but in a later paper, Dirac suggested that an absence of an electron in one of these states would correspond to a short-lived positive particle. The positron was discovered by Carl Anderson in 1932. In addition to introducing a quantum theory of radiation, Dirac was the co-inventor of Fermi-Dirac statistics. Although Dirac’s work was entirely mathematical - he wrote that the fundamental laws of nature "control a substratum of which we cannot form a mental picture without introducing irrelevancies" - he also believed that a theory expressing these laws could be constructed only on the basis of approximations.. Dirac was appointed Lucasian Professor of Mathematic at Cambridge University - the chair once held by Isaac Newton - in 1932 and shared the Nobel Prize with Erwin Schrödinger in 1933. Upon his retirement he became professor of physics at Florida State University in 1971.

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8 ALBERT EINSTEIN (1879 - 1955)

Every physicist - with the possible exception of those infected by Nazism - would rank Albert Einstein among the three greatest scientists of all time (together with Newton and Maxwell); to the public at large, he is the unquestioned number one. Born in Ulm in 1879 he completed his studies in physics at the Swiss Federal Institute of Technology in 1900. Unable to find an academic position he became a patent examiner in Bern. In his annus mirabilis, 1905, Einstein published five papers in the Annalen der Physik. Among them was the special theory of relativity - based on the realization that the speed of light is constant in all reference frames - which did away with the notion that time intervals were the same for everyone and led to a modification of the laws and description of motion. A mathematical consequence was that the mass and the energy of matter were related by the now famous formula E = mc². The 1905 work, for which Einstein only received the Nobel prize a full sixteen years later, was the explanation of the photoelectric effect - the process by which light knocks out electrons from metals; it was that light is composed of particles (later called photons), whose energy is determined by the same quantum of action that Planck had introduced in1900 to explain the spectrum of black body radiation and that Bohr used later to describe the emission of light by atoms. Though Einstein was thus an early and important contributor to the quantum theory, he never accepted its probabilistic nature and disputed Bohr’s Copenhagen interpretation. He and his (in some cases Marxist inspired) followers felt that behind the accepted formalism there had to be hidden variables which obeyed strict causality. Einstein would probably not have been more comfortable with modern interpretations of quantum theory, such as those involving multiple universes or decoherence. His monumental contribution of 1916, the general theory of relativity, has been eminently successful and indispensable for modern cosmology. During the second half of his life Einstein worked fruitlessly on a theory to unify gravitation and electromagnetism. After 1905 he moved around rapidly in Europe, accepting a professorial position at the Prussian Academy of Sciences in Berlin in 1914. In 1933 with the rise of the Nazis, Einstein renounced his German citizenship and came to the newly founded Institute for Advanced Studies in Princeton where he remained for the rest of his life. Since before the First World War, Einstein had been a vocal supporter of liberal causes, including anti-nationalism, pacifism and Zionism. After the discovery of fission, he allowed his name to be used as the signatory of a letter to President Franklin Roosevelt urging "watchfulness and, if necessary, quick action" on the part of the United States in atomic bomb research. This led to the Manhattan Project. The revelations after Einstein’s death that he was less than an ideal husband or father have hardly dimmed his reputation as the greatest sage and benefactor of the 20^th century.

12 ENRICO FERMI (1901 - 1954)

One of the giants of 20^th century physics, Enrico Fermi was sui generis in having made both major experimental and theoretical contributions. The importance of his contributions is evidenced by the concepts that are named after him, among them the fermions (among them the electrons, neutrons, and protons) - particles having odd half integral units of spin angular momentum and obeying Fermi - Dirac statistics; the Fermi level - a measure of the energy of the least tightly held electrons in solids, which at absolute zero temperature becomes the Fermi energy; the Fermi surface - which characterizes the electrical and thermal behavior of metals; and the universal Fermi interaction and the Fermi constant, which describe the weak interaction between fermions.

Enrico Fermi was born in Rome in 1901 and at age twenty-one earned his doctorate at the University of Pisa with a thesis on X-rays. On a fellowship he went to Göttingen to study under Max Born. After a stint of teaching mathematics at the University of Florence, his 1926 paper on the behavior of a perfect gas brought him a full professorship at the University of Rome, where he immediately developed the Fermi - Dirac statistics. In the 1930's, having learned of the discovery of the neutron by Chadwick and of the production of artificial radioactivity by the Joliot - Curies, he conceived and carried out the idea of using neutrons emitted by radioactive beryllium, but slowed down by passing through paraffin, to bombard various elements, and make them radioactive. The bombardment of uranium by these slow neutrons resulted in fission well before Hahn and his coworkers did similar experiments, but like they at first, Fermi did not realize what had happened . \In 1938 Fermi was named a Nobel laureate in physics "for his identification of new radioactive elements produced by neutron bombardment and for his discovery of nuclear reactions effected by slow neutrons". He was given permission by the Fascist government to travel to Sweden to receive the award, and he and his Jewish wife, Laura, never returned to Italy. In New York, in 1939, Fermi learned about the Meitner-Frisch identification of fission, met Bohr who suggested the possibility of a nuclear chain reaction and the importance of the isotope U 235, repeated the Hahn - Strassmann - Meitner experiments at Columbia University, and together with the Hungarian refugee physicists Leo Szilard and Eugene Wigner drafted the "Einstein letter" to President Roosevelt. In the ensuing Manhattan project, Fermi was assigned the task of producing a controlled, self-sustaining nuclear chain reaction. He succeeded on December 2, 1945, with his nuclear pile under Stagg Field at the University of Chicago, and then worked on the atomic bomb project at Los Alamos. In 1946 Fermi became Distinguished Service Professor for Nuclear Studies at the University of Chicago and received the congressional Medal of Merit. He continued to make important contributions, particularly in the new field of meson physics. Unlike many of his physicist colleagues, Fermi showed little interest in the philosophical foundations of quantum mechanics or the societal implications of science. The US Atomic Energy Commission established the Enrico Fermi Award in his honor and he was named the first recipient just before his death from cancer in 1954.

11 OTTO FRISCH (1904 - 1979)

Otto Frisch was born in Vienna to Jewish parents; Lise Meitner was his aunt. After having studied physics and mathematics, he did his early work in Germany, as an assistant to the great experimentalist Otto Stern and with the young Emilio Segrè. In 1933 the Nazi racial laws forced Frisch, Stern, and a host of other German Jewish scientists to emigrate. After a year in England, he was invited by Niels Bohr to the Institute for Theoretical Physics in Copenhagen. Although he worked mainly as an experimentalist he became famous for a joint paper with Meitner which gave the first correct interpretation of the fission phenomenon. Returning to England, he and Rudolf Peierls at Birmingham did the work that led to the British atomic bomb project. In 1943 he pursued this work at Los Alamos and in 1946 he settled permanently in England. After a year as head of the nuclear physics division in the newly established Atomic Energy Research Establishment at Harwell, he was called to the Jacksonian Professorship of Natural Philosophy in Cambridge, a post he held until his death.

26 GEORGE GAMOW (1904 - 1968)

Born in Odessa, Ukraine, George Gamow moved to Göttingen in 1928, where he explained, with the aid of quantum theory, the different lifetimes of radioactive elements. At the Institute of Theoretical Physics in Copenhagen, he was the first to propose the liquid drop model of the nucleus which Bohr later used to explain fission. Gamow became a professor of physics at George Washington University in St. Louis in1934, where, with Edward Teller, he formulated the Gamow-Teller rules of beta decay. In his studies of nuclear processes and their applications to cosmology, Gamow postulated the thermonuclear origin of the sun’s energy and also was one of the originators of the big bang theory. In 1942, with Teller, he described the internal structure of the red giant stars. Gamow practiced a well developed sense of humor: when he and his student Ralph Alpher in 1948 developed the hypothesis that the chemical elements were created by the successive capture of neutrons, he persuaded Hans Bethe to put his name on the resulting paper (almost certainly the only time that Bethe agreed to a claim of coauthorship when he did not make a major contribution). Thus was born the alliterative Alpher - Bethe - Gamow theory. In 1954 Gamow’s interests grew to include biochemistry where he proposed that the genetic code was determined by the order of recurring triplets of nucleotides, the basic components of DNA. His ideas were important for the rapid development of genetic theory that followed. Gamow held the position of professor of physics at the University of Colorado from 1956 until his death in 1968. To the public at large he is probably best known for his many popular science books, which include the "Mr. Tompkins" series (1939 - 67) and One, Two, Three...Infinity (1947).

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8 SAMUEL GOUDSMIT (1902 - 1978)

Samuel Abraham Goudsmit was born to well-to-do Dutch Jewish merchants, studied physics at the University of Leiden under Paul Ehrenfest and worked on complex spectra and the Zeeman effect. In 1925, he and his fellow Dutchman, George Uhlenbeck, following a theory of Wolfgang Pauli that there had to be fourth quantum number, established the existence of electron spin. In 1927 he moved to the University of Michigan. During World War II he worked first at the Radiation Laboratory of MIT, but later proposed the ALSOS mission and became its scientific head. In the last days of the war, ALSOS captured Heisenberg and nine other German scientists. During the mission Goudsmit learned that his parents had been exterminated in the holocaust, and, for many years, he spoke out bitterly against Heisenberg and other physicists who had worked under the Nazis. In 1947 Goudsmit accepted an offer to join the new Brookhaven National Laboratory. In 1952 he became the editor of The Physical Review, already the world's foremost physics journal, and managed it for twenty-three years, during a period of unprecedented change and expansion, spinning off the even more prestigious journal Physical Review Letters.

2 OTTO HAHN (1879 - 1968)

Except for early work in Cambridge with Sir William Ramsay and with Rutherford at McGill University in Montreal, as well as his internment at Farm Hall in 1945, Otto Hahn spent his whole life in Germany. Born in Frankfurt am Main and deceased in Göttingen, he received his doctorate at Marburg in 1901. He was a radiochemist and discovered several "radioelements", beginning with radiothorium. His collaboration with Lise Meitner in Berlin for thirty years beginning in 1907 - from 1912 on at the Kaiser Wilhelm Institute for Chemistry in Berlin-Dahlem - was exceedingly fruitful. After Chadwick's discovery of the neutron, Joliot-Curie's production of artificial radioactivity and Fermi's use of neutrons to produce additional radioactive elements, radiochemistry became nuclear chemistry. Hahn and his coworker Fritz Strassmann erroneously but understandably identified elements produced by the neutron bombardment of uranium as isotopes of radium, rather than of barium until Meitner, who by then had gone into exile in Sweden, and her nephew Otto Frisch correctly interpreted the phenomenon as the splitting of the uranium nucleus. Hahn played no role in the German reactor program during World War II and learned with horror during his internment about the Hiroshima bomb and, one would assume, with pleasure, that he was awarded the Nobel prize for Chemistry in 1944. After the War he devoted himself to the rebuilding of German science. In 1957 he was one of eighteen prominent German scientists to caution against the acquisition by Germany of nuclear weapons.

FRITZ HOUTERMANS (1903 - 1966)

Of all the scientists mentioned in Copenhagen, Fritz (Friederich Georg) Houtermans had the strangest life. Born in the then German Baltic port of Danzig, he grew up in Vienna with his half- Jewish mother. She had been the first woman in Vienna to get a doctorate in Chemistry and lectured on German literature, religion, history and philosophy. Fritz became a true Viennese in his accent, habits, repertoire of jokes, and the propensity for doing his work in cafés. In 1921 Houtermans began his study of Physics in Göttingen, but being short of money, had to interrupt it and make a living as a tour guide in Rome. He was sacked when he told a group of American ladies that the name of a fashionable street was Via Latrina. With his 1927 doctoral thesis, under James Franck, on resonance fluorescence in mercury, he moved to Berlin and with George Gamow and others did important work on alpha particle decay and absorption And he put forward the idea that nuclear reactions are the source of stellar energy. He and his wife, Charlotte Riefenstahl, who also had a physics doctorate from Göttingen, held frequent soirées at their home, which they called "Eine Kleine Nachtphysik". When the Nazis came to power in 1933, Houtermans had to flee, not (at that time) because he was one-quarter Jewish, but because he was a member of the Communist party. He secured a position in England with what is now EMI but, repelled by English cooking and attracted by his disingenuous belief in the Soviet system, went to Kharkov. There he worked with Landau and other important Russian physicists, but in 1937, like many of them, fell victim to Stalin's terror. After imprisonment and torture by the NKVD, he was extradited in 1940 to Nazi Germany, then a "friend" of the Soviet Union. He was promptly imprisoned by the Gestapo. Thanks to the intervention of Max von Laue he was released and with von Laue's and Carl von Weizsäcker's help obtained a research position in the private laboratory of Manfred von Ardenne. There Houtermans turned to the theoretical study of nuclear chain reactions. As early as 1932, long before the discovery of fission, he had pointed out the possibility of initiating chain reactions with neutrons. Now he issued a report that discussed fast neutron reactions, neutron slowing, uranium 235, the magnitude of the critical mass, and the production of element 94 (plutonium), which is fissionable by slow neutrons. Though his work could clearly have been useful to the Germans in creating a nuclear weapon and Houtermans cooperated with the Nazis by visiting occupied Kharkov on a mission for the German Army in 1941, he secretly retained his left-wing sympathies. In 1942 he managed to send a cable via Switzerland to Enrico Fermi, saying "Hurry up [with building a reactor]. We are on the track". After the War, physics research in Germany was severely circumscribed by the Allies, and in 1952 Houtermans left to become professor of physics at the University of Bern. He transformed an early 20th century laboratory into a modern Center for Physics Research. His own work concentrated on nuclear geophysics and meteorites. A life-long chain smoker, Fritz Houtermans died in Switzerland of lung cancer in 1966. (Based on the article by Iosif B. Khriplovich "The Eventful Life of Fritz Houtermans", Physics Today, July 1992, pp. 29 - 37.)

7 OSKAR KLEIN (1894 - 1977)

Swedish born Oskar Benjamin Klein was the son of that country's first rabbi, Gottlieb Klein. At the age of fifteen, Oskar was able to work with the famous physical chemist Svante Arrhenius, work which resulted in a paper. From 1918 on he frequently visited Copenhagen and was at the University of Michigan in 1923 - 25; but he spent the rest of his life in Sweden, where he received the chair of mechanics and mathematical physics at the Stockholm Högskole in 1930. Like most physicists of the era, he made contributions to many fields, as well as to philosophy, but his greatest fame resulted from his work in quantum mechanics: he is the Klein of both the Klein - Gordon and the Klein -Nishina formulas.

11 LISE MEITNER (1878 - 1968)

Lise Meitner was born and received her doctorate in physics at that city’s university in 1906. In 1907 she moved to Berlin to attend Max Planck’s lectures and to join Otto Hahn at the Kaiser Wilhelm Institute in research on radioactivity. During their three decades of collaboration, she and Hahn discovered protactinium, studied nuclear isomerism and beta decay, and, in the thirties (together with Fritz Strassmann), investigated the products of the bombardment of uranium by neutrons. Having retained her Austrian citizenship, she was able, in spite of her Jewish origins, to keep her position in Nazi Germany until 1938. This changed overnight when the Germans annexed Austria and abolished Austrian nationality. Meitner fled to Sweden in the summer of 1938. After Hahn and Strassmann had identified the element barium in neutron-bombarded uranium, it was Meitner and her nephew Otto Frisch who realized that a new process - fission - had been detected, and, in January 1939, provided the description and explanation which Bohr and Wheeler incorporated into their full theory later that year. Meitner retired to England in 1960 and died there, in Cambridge, in 1968. Many physicists are of the opinion that she should have shared in the 1944 Nobel prize that Hahn and Strassmann received for the discovery of fission; some believe that her being a woman and Jewish worked to her disadvantage. Partial amends were made in 1966 when Meitner, Hahn, and Strassmann were jointly given the Enrico Fermi Award.

7 CHRISTIAN MØLLER (1904 - 1981)

Born in Denmark in 1904, Christian Møller spent almost his entire working life as Professor of Mathematical Physics in Copenhagen, where he had been educated before continuing his studies in Rome and at Cambridge. He headed the theory group at the European Centre for Nuclear Research, CERN, from 1954 to 1957. Although he also contributed to atomic and nuclear theory, he is best known for his work in relativity, which resulted in 1952 in the publication of the much used book The Theory of Relativity.

19 J. ROBERT OPPENHEIMER (1904 -1967)

Born in New York City in 1904, J. Robert Oppenheimer as a Harvard undergraduate excelled in Latin, Greek, physics, and chemistry, published poetry and studied Oriental philosophy. After graduating in 1925 he sojourned at the Cavendish Laboratory in Cambridge. Max Born invited him to Göttingen, where he met Bohr, Dirac and other leading physicists and, in 1927, received his doctorate. After visits to Leiden and Zurich, he took up simultaneous professorial appointments at Cal Tech and the University of California at Berkeley. While he made significant contributions to theoretical physics - the Born-Oppenheimer approximation and the Oppenheimer-Phillips process are named after him, his teacher Max Born and his student Melba Phillips, respectively, his greater legacy was the training of a whole generation of first rate American physicists. In 1942 Oppenheimer was put in charge of the Manhattan Project and he chose the highlands near Santa Fe, New Mexico - where he had spent part of his boyhood - to establish the Los Alamos laboratory to build an atomic bomb. He was a brilliant leader of most of the world’s greatest physicists and of a most complex enterprise and he and his coworkers achieved the first nuclear explosion at Alamogordo on July 16, 1945. On August 6th and August 9^th, atomic bombs were dropped on Hiroshima and Nagasaki. In October of the same year, Oppenheimer resigned his post and in 1947 he became head of the Institute for Advanced Study in Princeton. As chairman of the General Advisory Committee of the Atomic Energy Commission from 1947 to 1952, he continued to play a significant role in national defense.. But in 1953, during the waning months of the McCarthy period and the height of the cold war, the Eisenhower administration revoked Oppenheimer’s security clearance. The investigation of Oppenheimer had, at least in part, been triggered by his earlier association with left wing individuals and causes, and his less than truthful accounts of some events relating to these associations did not help during the hearings. But Oppenheimer had also opposed the development of the H-bomb and there is a body of opinion which holds that Edward Teller and AEC chairman Lewis Strauss were out to rid themselves of a still powerful figure in the nuclear armaments debate. Although most of the country’s leading physicists, as well as their organization, the American Physical Society, came to Oppenheimer’s defense, his security clearance was not reinstated until1963, when.the AEC’s Fermi Award was presented to him Oppenheimer died of throat cancer at Princeton in 1967.

11 WOLFGANG PAULI (1900 - 1958)

Winner of the 1945 Nobel Prize for the exclusion principle, Wolfgang Pauli was born in Vienna in 1900. Appointed a lecturer at the University of Hamburg in 1923, he became professor of theoretical physics at the Swiss Federal Institute of Technology in1928 and moved to the Institute for Advanced Studies in Princeton in 1940. When he was twenty, Pauli wrote an authoritative 200 page encyclopedia article on the theory of relativity. In 1924 he recognized that a fourth quantum number (later identified as electron spin) was needed in the quantum theory and that it could take the value + or - _.. One year later he introduced the Pauli exclusion principle which states that in a bound system no two fermions ( such as protons, neutrons and electrons) can have the same numerical values for all of their four quantum numbers. Among other consequences, this immediately provided the reason for the structure of the periodic table of the elements. In the late 1920's it began to be noticed that in beta decay (the emission of an electron by the nucleus of an atom),some momentum and energy were generally left missing. Rather than settle for this grave violation of the conservation laws, Pauli proposed in 1931 that the missing energy and momentum were carried away by an uncharged particle with little or no mass that interacted with matter only weakly and hence very rarely. This particle, named the neutrino by Enrico Fermi, was finally observed in a difficult experiment in 1956. Following World War II, Pauli returned to Zurich, where he died in 1958. Recognized as one of the very greatest physicists of the 20^th century, Pauli was also known (and feared) for his acerbic wit. One "Pauli story" has it that after hearing a poor colloquium, he commented "this isn’t even wrong", another that he once referred to a fellow physicist as "so young, and already so unknown".

85 RUDOLPH PEIERLS (1907 - 1995)

Rudolph Ernst Peierls, born in Berlin of a Jewish father and a Catholic mother, was baptized a Protestant because his father believed in leaving options open. After studying in Berlin with Planck and in Munich with Sommerfeld, he received his doctorate in Leipzig. His postdoctoral years took him to Zurich, where he was Pauli’s assistant. Spending several years in the Soviet Union, he worked with Landau on electrodynamics His most important early work was on the physics of phonons. The disaster of 1933 took him to Manchester where he collaborated with Hans Bethe on photodisintegration and the statistical mechanics of alloys. Next, in Cambridge, Peierls did notable work in superconductivity and liquid helium and, with P.G.L. Kapur, derived the dispersion formula for nuclear reactions. In 1937 he accepted a chair at the University of Birmingham. It was there, after the discovery of fission, that Otto Frisch asked Peierls whether pure uranium 235 could make an atomic bomb, and Peierls calculated that it could. A memorandum to that effect was sent to the British Government which immediately classified it as top secret. Peierls and Frisch, as enemy aliens, were not allowed to read the document they themselves had written. Britain soon entered the atomic bomb race and in 1944 Peierls, by then a British subject, went to Los Alamos to join with the US effort. In 1963 Peierls left Birmingham for the Wykeham Chair of Theoretical Physics at Oxford.. Deeply concerned about nuclear weapons, Peierls strongly supported the Bulletin of the Atomic Scientists and the Pugwash movement until the end of his life.

MAX PLANCK (1858 - 1947)

Max Planck is not mentioned in Copenhagen, but he should have been as the discoverer of the quantum of action and thus the father of quantum mechanics. Born in 1858 in Kiel, Max Karl Ernst Ludwig Planck received his doctorate in Munich in 1879. He worked in Berlin under von Helmholtz and Kirchhoff and made contributions in thermodynamics and the theory of gases. After teaching theoretical physics in Munich and Kiel he returned to Berlin as Professor in 1889. In 1900 he solved the vexing problem of radiation from a blackbody. According to classical theory the energy of high frequency radiation came out to be infinite, a clear absurdity. Planck postulated that harmonic oscillators could emit radiation only in discrete bundles of energy involving a constant of nature, now known as Planck's constant. This is the same concept that led Bohr in 1913 to his theory of the emission of light from electron jumps in atoms with energies proportional to Planck's constant. Planck did not receive the Nobel prize until 1918. He suffered many personal misfortunes throughout his life. His wife died in 1909 and one of his sons fell in World War I. His two daughters died in childbirth and his other son was executed by the Nazis in 1944 on suspicion of conspiracy to assassinate Hitler. Although Planck remained in Germany through the Nazi period, he always acted honorably and helped Jews and other victims of the Nazis. After World War II the Kaiser Wilhelm Society and its institutes were renamed after Planck and he died, much beloved, in Göttingen in 1947.

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18 ERWIN SCHRÖDINGER (1887 -1961)

Born in Vienna, Schrödinger received his doctorate in physics at that city's university under Friedrich Hasenöhrl in 1910 and began his professional there as an assistant to the experimentalist Franz Exner. While an artillery officer in World War I, he learned about Einstein's general relativity and also used his free time to read Spinoza, Schopenhauer, Mach, and other philosophers. After demobilization he worked in Jena, Stuttgart, Vienna and Zurich and made contributions to gas and reaction kinetics, thermodynamics, mathematical statistics, color vision, and other areas. In 1924 he became familiar with Einstein's quantum papers and de Broglie's ideas. Recognizing the importance of eigenfrequencies, he developed a relativistic theory of quantum mechanics - now known as the Klein-Gordon equation, but discarded it because it did not seem to correspond to reality. (The reason is that it describes particles without spin). In 1926 he proposed the famous non-relativistic Schrödinger equation and recognized soon thereafter that it was equivalent to Heisenberg's matrix mechanics formulation. Appointed Professor in Berlin, he left there in 1933 in disgust with the Nazi takeover. At Oxford he learned that he had won the 1933 Physics Nobel Prize together with P.M.A. Dirac. He returned to his native Austria to accept a professorship at Graz only to face the Anschluss in 1938. The Irish revolutionary statesman, and former mathematics professor Eamon de Valera created the Dublin Institute of Advanced Studies which provided a haven for Schrödinger and other exiles from the Nazis. After his return to a professorship at Vienna, Schrödinger wrote an influential book What is Life on the physical foundations of biology and became interested in Indian philosophy. He died in the Tyrolean village of Alpbach in 1961.

43 EDWARD TELLER (1908 -

Born in 1908 in Budapest, Edward Teller is one of the odd dozen Hungarian scientists of Jewish origin who made major contributions in their new homelands, America and England. Like many of the others he was educated (at Karlsruhe, Munich, and Leipzig) and did his early work in Germany (at Göttingen). In 1924 he was a Rockefeller fellow in Copenhagen. He came to the US in 1935 and worked at George Washington, Columbia and Chicago universities before joining the project to produce an atomic bomb in 1943 at Los Alamos. There he directed much of his effort to making a fusion weapon. After the war he worked at the University of California, where he was director of the Lawrence Livermore (weapons) laboratory from 1958 to 1960. Although best known to the public as the "father of the H-Bomb", Teller, in his earlier years made many contributions to basic atomic and nuclear physics. His book, with Rice, The Structure of Matter was published in 1946. His non-technical books include Our Nuclear Future (1958), The Legacy of Hiroshima, and Better a Shield than a Sword (in 1988). Respected for his scientific contributions, he remains controversial among fellow physicists for his continued commitment to nuclear weapons and his denunciation of J. Robert Oppenheimer. The image of him as Dr. Strangelove is a caricature.

61 GEORGE UHLENBECK (1900 -1988)

George Eugene Uhlenbeck’s most remembered achievement is the discovery and elucidation, with Samuel Goudsmit, of electron spin. However he made many contributions to the kinetic theory of matter, statistical mechanics, atomic structure and nuclear physics. Born in Batavia, Java (now Djakarta, Indonesia) to Dutch parents, he was educated at the University of Leiden under Paul Ehrenfest, who remained his life-long model and inspiration. He joined the physics department of the University of Michigan in 1927. In 1935 he came back to the Netherlands as Kramers’ successor at the University of Utrecht and stayed until 1939 when he returned to Michigan. Except for the war years 1942 - 45, when he was at the MIT Radiation Lab, he remained at Michigan until 1960. In that year he became Professor of Physics at the Rockefeller University in New York.

38 VICTOR WEISSKOPF (1908 -

One of the 20th century's leading theoretical physicists, particularly in nuclear and in elementary particle physics, Victor Felix Weisskopf was born to high bourgeois Jewish parents in Vienna in 1908. He was educated at Göttingen and worked in Berlin, at the Eidgenössische Technische Hochschule in Zurich, and at Bohr's Institute in Copenhagen, before emigrating to the United States in 1937. After five years at the University of Rochester, he went to Los Alamos in 1943 as deputy leader of the theoretical division. Since 1945 he has been at MIT, taking time off from 1961 to 1965 to serve as Director General of the newly formed European nuclear research center CERN. His textbook Theoretical Nuclear Physics, written in 1952 with John Blatt, was a classic for many years. Weisskopf's books for general audiences include Knowledge and Wonder (1962), Physics in the 20th Century (1972), The Privilege of Being a Physicist (1989), and The Joy of Insight (1991). His numerous medals, honors, and prizes, to the regret and even vexation of some of his fellow physicists, do not include the Nobel prize.

6 CARL FRIEDRICH VON WEIZSÄCKER (1912 -

A member of a prominent German family of statesmen, theologians, and scientists, Carl Friedrich Freiherr von Weizsäcker was born in Kiel in 1912. He studied with Heisenberg and Bohr, became professor of theoretical physics in Strassburg in 1942, and worked at the Kaiser Wilhelm Institute in Berlin from 1944 and at the Max Planck Institute in Göttingen from 1946. From 1957 to 1969 he was professor of Philosophy in Hamburg and in the latter year he became Director of the Max Planck Institute for the study of science and technology in Starnberg. In 1938 von Weizsäcker published his theory of the production of energy in stars and in 1946 a theory for the creation of planetary systems. Like Bohr, Heisenberg, and many other physicists, he was interested in epistemology and the social implications of science and he advocated the use of science for peace. His father, Ernst von Weizsäcker, had been a diplomat whose career ended with service (albeit reluctant and sometimes even disloyal) to the Nazis; for this he was sentenced by the Allies to jail at Nuremberg. Carl Friedrich's brother Richard served as President of the Federal Republic of Germany from 1984 to 1994.

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