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95-643: Niels Henrik David Bohr ( Danish: [ˈne̝ls ˈpoɐ̯ˀ] ; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory , for which he received the Nobel Prize in Physics in 1922. Bohr was also a philosopher and a promoter of scientific research. Bohr developed the Bohr model of the atom , in which he proposed that energy levels of electrons are discrete and that

190-728: A privatdocent at the University of Copenhagen, giving lectures on thermodynamics . Martin Knudsen put Bohr's name forward for a docent , which was approved in July 1913, and Bohr then began teaching medical students. His three papers, which later became famous as "the trilogy", were published in Philosophical Magazine in July, September and November of that year. He adapted Rutherford's nuclear structure to Max Planck 's quantum theory and so created his Bohr model of

285-700: A master's degree like MSc, MPhil, MPhys or MSci. For research-oriented careers, students work toward a doctoral degree specializing in a particular field. Fields of specialization include experimental and theoretical astrophysics , atomic physics , biological physics , chemical physics , condensed matter physics , cosmology , geophysics , gravitational physics , material science , medical physics , microelectronics , molecular physics , nuclear physics , optics , particle physics , plasma physics , quantum information science , and radiophysics . The three major employers of career physicists are academic institutions, laboratories, and private industries, with

380-454: A subjectivist or a positivist , most philosophers agree that this is a misunderstanding of Bohr as he never argued for verificationism or for the idea that the subject had a direct impact on the outcome of a measurement. Bohr has often been quoted saying that there is "no quantum world" but only an "abstract quantum physical description". This was not publicly said by Bohr, but rather a private statement attributed to Bohr by Aage Petersen in

475-423: A certain kinematic or dynamic value to an atomic object are dependent on the apparatus involved, in such a way that these truth conditions have to include reference to the experimental setup as well as the actual outcome of the experiment. Faye notes that Bohr's interpretation makes no reference to a "collapse of the wave function during measurements" (and indeed, he never mentioned this idea). Instead, Bohr "accepted

570-459: A classical wave description of the electromagnetic field. Modelling atomic behaviour under incident electromagnetic radiation using "virtual oscillators" at the absorption and emission frequencies, rather than the (different) apparent frequencies of the Bohr orbits, led Max Born, Werner Heisenberg and Kramers to explore different mathematical models. They led to the development of matrix mechanics ,

665-422: A distinction between observed phenomena and a transcendental reality . Jan Faye disagrees with this position and holds that for Bohr, the quantum formalism and complementarity was the only thing we could say about the quantum world and that "there is no further evidence in Bohr's writings indicating that Bohr would attribute intrinsic and measurement-independent state properties to atomic objects [...] in addition to

760-603: A focal point for researchers into quantum mechanics and related subjects in the 1920s and 1930s, when most of the world's best-known theoretical physicists spent some time in his company. Early arrivals included Hans Kramers from the Netherlands, Oskar Klein from Sweden, George de Hevesy from Hungary, Wojciech Rubinowicz from Poland, and Svein Rosseland from Norway. Bohr became widely appreciated as their congenial host and eminent colleague. Klein and Rosseland produced

855-588: A friend of Høffding. The philosopher and author Ágúst H. Bjarnason was a student of Høffding. Høffding's great-nephew was the statistician Wassily Hoeffding . Høffding died in Copenhagen. His best-known work is perhaps his Den nyere Filosofis Historie (1894), translated into English from the German edition (1895) by B.E. Meyer as History of Modern Philosophy (2 vols., 1900), a work intended by him to supplement and to correct that of Hans Brøchner to whom it

950-868: A leave of absence from the University of Copenhagen, which he started by taking a holiday in Tyrol with his brother Harald and aunt Hanna Adler . There, he visited the University of Göttingen and the Ludwig Maximilian University of Munich , where he met Sommerfeld and conducted seminars on the trilogy. The First World War broke out while they were in Tyrol, greatly complicating the trip back to Denmark and Bohr's subsequent voyage with Margrethe to England, where he arrived in October 1914. They stayed until July 1916, by which time he had been appointed to

1045-452: A minimum, the owner must possess a three-year bachelors or equivalent degree in physics or a related field and an additional minimum of six years' experience in a physics-related activity; or an Honor or equivalent degree in physics or a related field and an additional minimum of five years' experience in a physics-related activity; or master or equivalent degree in physics or a related field and an additional minimum of three years' experience in

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1140-458: A nuclear weapon was possible with great efforts, and this raised enormous responsibilities on the world's scientists on both sides. When Bohr saw Jungk's depiction in the Danish translation of the book, he drafted (but never sent) a letter to Heisenberg, stating that he deeply disagreed with Heisenberg's account of the meeting, that he recalled Heisenberg's visit as being to encourage cooperation with

1235-625: A paper presented at the Volta Conference at Como in September 1927, Bohr emphasised that Heisenberg's uncertainty relations could be derived from classical considerations about the resolving power of optical instruments. Understanding the true meaning of complementarity would, Bohr believed, require "closer investigation". Einstein preferred the determinism of classical physics over the probabilistic new quantum physics to which he himself had contributed. Philosophical issues that arose from

1330-510: A physics-related activity; a Doctorate or equivalent degree in Physics or a related field; or training or experience which, in the opinion of the Council, is equivalent to any of the above. Physicists may be a member of a physical society of a country or region. Physical societies commonly publish scientific journals, organize physics conferences and award prizes for contributions to the field of physics. Some examples of physical societies are

1425-416: A professional practice examination must also be passed. An exemption can be granted to a candidate that has practiced physics for at least seven years and provide a detailed description of their professional accomplishments which clearly demonstrate that the exam is not necessary. Work experience will be considered physics-related if it uses physics directly or significantly uses the modes of thought (such as

1520-530: A rare-earth element 72, which he called "celtium". At the Institute in Copenhagen, Dirk Coster and George de Hevesy took up the challenge of proving Bohr right and Urbain wrong. Starting with a clear idea of the chemical properties of the unknown element greatly simplified the search process. They went through samples from Copenhagen's Museum of Mineralogy looking for a zirconium-like element and soon found it. The element, which they named hafnium ( hafnia being

1615-409: A reminiscence after his death. N. David Mermin recalled Victor Weisskopf declaring that Bohr wouldn't have said anything of the sort and exclaiming, "Shame on Aage Petersen for putting those ridiculous words in Bohr's mouth!" Numerous scholars have argued that the philosophy of Immanuel Kant had a strong influence on Bohr. Like Kant, Bohr thought distinguishing between the subject's experience and

1710-713: A visit to the United States. Bohr offered the refugees temporary jobs at the institute, provided them with financial support, arranged for them to be awarded fellowships from the Rockefeller Foundation, and ultimately found them places at institutions around the world. Those that he helped included Guido Beck , Felix Bloch , James Franck , George de Hevesy, Otto Frisch , Hilde Levi , Lise Meitner , George Placzek, Eugene Rabinowitch , Stefan Rozental , Erich Ernst Schneider, Edward Teller , Arthur von Hippel and Victor Weisskopf . In April 1940, early in

1805-705: Is based on an intellectual ladder of discoveries and insights from ancient times to the present. Many mathematical and physical ideas used today found their earliest expression in the work of ancient civilizations, such as the Babylonian astronomers and Egyptian engineers , the Greek philosophers of science and mathematicians such as Thales of Miletus , Euclid in Ptolemaic Egypt , Archimedes of Syracuse and Aristarchus of Samos . Roots also emerged in ancient Asian cultures such as India and China, and particularly

1900-764: Is dedicated. His Psychology, the Problems of Philosophy (1905) and Philosophy of Religion (1906) also have appeared in English. Among Høffding's other writings, most of which have been translated into German, are Den engelske Filosofi i vor Tid (1874); Etik (1876); Psychologi i Omrids paa Grundlag af Erfaring (ed. 1892); Psykologiske Undersøgelser (1889); Charles Darwin (1889); Kontinuiteten i Kants filosofiske Udviklingsgang (1893); Sören Kierkegaard als Philosoph (1896); Det psykologiske Grundlag for logiske Domme (1899); Rousseau und seine Philosophie (1901); Mindre Arbejder (1899). A commemorative plaque on

1995-572: Is its charge, h is the Planck constant and Z is the atom's atomic number (1 for hydrogen). The model's first hurdle was the Pickering series , lines that did not fit Balmer's formula. When challenged on this by Alfred Fowler , Bohr replied that they were caused by ionised helium , helium atoms with only one electron. The Bohr model was found to work for such ions. Many older physicists, like Thomson, Rayleigh and Hendrik Lorentz , did not like

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2090-563: Is nothing else to do than to give our revolutionary efforts as honourable a funeral as possible". The introduction of spin by George Uhlenbeck and Samuel Goudsmit in November 1925 was a milestone. The next month, Bohr travelled to Leiden to attend celebrations of the 50th anniversary of Hendrick Lorentz receiving his doctorate. When his train stopped in Hamburg , he was met by Wolfgang Pauli and Otto Stern , who asked for his opinion of

2185-644: Is one of the most delightful things I have ever read." Bohr enjoyed Kierkegaard's language and literary style, but mentioned that he had some disagreement with Kierkegaard's philosophy . Some of Bohr's biographers suggested that this disagreement stemmed from Kierkegaard's advocacy of Christianity, while Bohr was an atheist . There has been some dispute over the extent to which Kierkegaard influenced Bohr's philosophy and science. David Favrholdt argued that Kierkegaard had minimal influence over Bohr's work, taking Bohr's statement about disagreeing with Kierkegaard at face value, while Jan Faye argued that one can disagree with

2280-451: Is still the best known model of the atom, as it often appears in high school physics and chemistry texts. Bohr did not enjoy teaching medical students. He later admitted that he was not a good lecturer, because he needed a balance between clarity and truth, between "Klarheit und Wahrheit". He decided to return to Manchester, where Rutherford had offered him a job as a reader in place of Darwin, whose tenure had expired. Bohr accepted. He took

2375-556: Is the Nobel Prize in Physics , awarded since 1901 by the Royal Swedish Academy of Sciences . National physical societies have many prizes and awards for professional recognition. In the case of the American Physical Society , as of 2023, there are 25 separate prizes and 33 separate awards in the field. Chartered Physicist (CPhys) is a chartered status and a professional qualification awarded by

2470-530: The American Physical Society , the Institute of Physics , with the oldest physical society being the German Physical Society . Harald H%C3%B8ffding Harald Høffding (11 March 1843 – 2 July 1931) was a Danish philosopher and theologian . Born Høffding was born in Copenhagen, the son of businessman Niels Frederik Høffding and Martha Høffding (née Jhellerup). The family lived at

2565-661: The Danish national team at the 1908 Summer Olympics in London. Niels was a passionate footballer as well, and the two brothers played several matches for the Copenhagen-based Akademisk Boldklub (Academic Football Club), with Niels as goalkeeper . Bohr was educated at Gammelholm Latin School, starting when he was seven. In 1903, Bohr enrolled as an undergraduate at Copenhagen University . His major

2660-690: The Finnish Relief Fund , and was auctioned off in March 1940, along with the medal of August Krogh . The buyer later donated the two medals to the Danish Historical Museum in Frederiksborg Castle , where they are still kept, although Bohr's medal temporarily went to space with Andreas Mogensen on ISS Expedition 70 in 2023-2024. Bohr kept the Institute running, but all the foreign scholars departed. Bohr

2755-640: The Institute of Physics . It is denoted by the postnominals "CPhys". Achieving chartered status in any profession denotes to the wider community a high level of specialised subject knowledge and professional competence. According to the Institute of Physics, holders of the award of the Chartered Physicist (CPhys) demonstrate the "highest standards of professionalism, up-to-date expertise, quality and safety" along with "the capacity to undertake independent practice and exercise leadership" as well as "commitment to keep pace with advancing knowledge and with

2850-548: The Islamic medieval period , which saw the development of scientific methodology emphasising experimentation , such as the work of Ibn al-Haytham (Alhazen) in the 11th century. The modern scientific worldview and the bulk of physics education can be said to flow from the scientific revolution in Europe, starting with the work of astronomer Nicolaus Copernicus leading to the physics of Galileo Galilei and Johannes Kepler in

2945-550: The Pauli exclusion principle , which put Bohr's models on a firm theoretical footing. Bohr was then able to declare that the as-yet-undiscovered element 72 was not a rare-earth element but an element with chemical properties similar to those of zirconium . (Elements had been predicted and discovered since 1871 by chemical properties), and Bohr was immediately challenged by the French chemist Georges Urbain , who claimed to have discovered

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3040-444: The atom had challenged Thomson's 1904 plum pudding model . Bohr received an invitation from Rutherford to conduct post-doctoral work at Victoria University of Manchester , where Bohr met George de Hevesy and Charles Galton Darwin (whom Bohr referred to as "the grandson of the real Darwin "). Bohr returned to Denmark in July 1912 for his wedding, and travelled around England and Scotland on his honeymoon. On his return, he became

3135-424: The corner of Gammeltorv and Nørregade . Høffding became a schoolmaster, and ultimately in 1883 a professor at the University of Copenhagen . He was strongly influenced by Søren Kierkegaard in his early development, but later became a positivist , retaining and combining with it the spirit and method of practical psychology and the critical school. The physicist Niels Bohr studied philosophy from and became

3230-408: The de Broglie hypothesis that matter (like electrons) also behaved like waves. He conceived the philosophical principle of complementarity : that items could have apparently mutually exclusive properties, such as being a wave or a stream of particles, depending on the experimental framework. He felt that it was not fully understood by professional philosophers. In February 1927, Heisenberg developed

3325-450: The surface tension of liquids that had been proposed by Lord Rayleigh in 1879. This involved measuring the frequency of oscillation of the radius of a water jet. Bohr conducted a series of experiments using his father's laboratory in the university; the university itself had no physics laboratory. To complete his experiments, he had to make his own glassware , creating test tubes with the required elliptical cross-sections. He went beyond

3420-579: The 19th century. Many physicists contributed to the development of quantum mechanics in the early-to-mid 20th century. New knowledge in the early 21st century includes a large increase in understanding physical cosmology . The broad and general study of nature, natural philosophy , was divided into several fields in the 19th century, when the concept of "science" received its modern shape. Specific categories emerged, such as "biology" and "biologist", "physics" and "physicist", "chemistry" and "chemist", among other technical fields and titles. The term physicist

3515-536: The Born statistical interpretation because he believed that the ψ -function has only a symbolic meaning and does not represent anything real". Since for Bohr, the ψ -function is not a literal pictorial representation of reality, there can be no real collapse of the wavefunction. A much debated point in recent literature is what Bohr believed about atoms and their reality and whether they are something else than what they seem to be. Some like Henry Folse argue that Bohr saw

3610-856: The British Tube Alloys nuclear weapons project, and was part of the British mission to the Manhattan Project . After the war, Bohr called for international cooperation on nuclear energy. He was involved with the establishment of CERN and the Research Establishment Risø of the Danish Atomic Energy Commission and became the first chairman of the Nordic Institute for Theoretical Physics in 1957. Niels Henrik David Bohr

3705-492: The British physicist Paul Dirac , who came to Copenhagen for six months in September 1926. Austrian physicist Erwin Schrödinger also visited in 1926. His attempt at explaining quantum physics in classical terms using wave mechanics impressed Bohr, who believed it contributed "so much to mathematical clarity and simplicity that it represents a gigantic advance over all previous forms of quantum mechanics". When Kramers left

3800-487: The Chair of Theoretical Physics at the University of Copenhagen, a position created especially for him. His docentship was abolished at the same time, so he still had to teach physics to medical students. New professors were formally introduced to King Christian X , who expressed his delight at meeting such a famous football player. In April 1917, Bohr began a campaign to establish an Institute of Theoretical Physics. He gained

3895-483: The Institute in Copenhagen, proposed the Bohr–Kramers–Slater theory (BKS). It was more of a program than a full physical theory, as the ideas it developed were not worked out quantitatively. The BKS theory became the final attempt at understanding the interaction of matter and electromagnetic radiation on the basis of the old quantum theory, in which quantum phenomena were treated by imposing quantum restrictions on

Niels Bohr - Misplaced Pages Continue

3990-526: The Institute of Theoretical Physics at the University of Copenhagen , now known as the Niels Bohr Institute , which opened in 1920. Bohr mentored and collaborated with physicists including Hans Kramers , Oskar Klein , George de Hevesy , and Werner Heisenberg . He predicted the properties of a new zirconium -like element, which was named hafnium , after the Latin name for Copenhagen, where it

4085-427: The Latin name for Copenhagen), turned out to be more common than gold. In 1922, Bohr was awarded the Nobel Prize in Physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them". The award thus recognised both the trilogy and his early leading work in the emerging field of quantum mechanics. For his Nobel lecture, Bohr gave his audience a comprehensive survey of what

4180-462: The Nazis considered their family to be Jewish , since their mother was Jewish, and that they were therefore in danger of being arrested. The Danish resistance helped Bohr and his wife escape by sea to Sweden on 29 September. The next day, Bohr persuaded King Gustaf V of Sweden to make public Sweden's willingness to provide asylum to Jewish refugees. On 2 October 1943, Swedish radio broadcast that Sweden

4275-520: The Royal Society . Harald became the first of the two Bohr brothers to earn a master's degree , which he earned for mathematics in April 1909. Niels took another nine months to earn his on the electron theory of metals, a topic assigned by his supervisor, Christiansen. Bohr subsequently elaborated his master's thesis into his much-larger Doctor of Philosophy thesis. He surveyed the literature on

4370-616: The Second World War, Nazi Germany invaded and occupied Denmark . To prevent the Germans from discovering Max von Laue 's and James Franck's gold Nobel medals , Bohr had de Hevesy dissolve them in aqua regia . In this form, they were stored on a shelf at the Institute until after the war, when the gold was precipitated and the medals re-struck by the Nobel Foundation. Bohr's own medal had been donated to an auction to

4465-487: The U.S. Hans  [ da ] became a physician; Erik  [ da ] , a chemical engineer; and Ernest , a lawyer. Like his uncle Harald, Ernest Bohr became an Olympic athlete, playing field hockey for Denmark at the 1948 Summer Olympics in London. In September 1911, Bohr, supported by a fellowship from the Carlsberg Foundation , travelled to England, where most of the theoretical work on

4560-795: The account of the experimental arrangement and of the results of the observations must be expressed in unambiguous language with suitable application of the terminology of classical physics ( APHK , p. 39). According to Faye, there are various explanations for why Bohr believed that classical concepts were necessary for describing quantum phenomena. Faye groups explanations into five frameworks: empiricism (i.e. logical positivism ); Kantianism (or Neo-Kantian models of epistemology ); Pragmatism (which focus on how human beings experientially interact with atomic systems according to their needs and interests); Darwinianism (i.e. we are adapted to use classical type concepts, which Léon Rosenfeld said that we evolved to use); and Experimentalism (which focuses strictly on

4655-399: The approach to problem-solving) developed in your education or experience as a physicist, in all cases regardless of whether the experience is in academia, industry, government, or elsewhere. Management of physics-related work qualifies, and so does appropriate graduate student work. The South African Institute of Physics also delivers a certification of Professional Physicist (Pr.Phys). At

4750-607: The arts, as an honorary residence (Danish: Æresbolig ). Harald Høffding had been the first occupant, and upon his death in July 1931, the Royal Danish Academy of Sciences and Letters gave Bohr occupancy. He and his family moved there in 1932. He was elected president of the Academy on 17 March 1939. By 1929 the phenomenon of beta decay prompted Bohr to again suggest that the law of conservation of energy be abandoned, but Enrico Fermi 's hypothetical neutrino and

4845-415: The atom. Planetary models of atoms were not new, but Bohr's treatment was. Taking the 1912 paper by Darwin on the role of electrons in the interaction of alpha particles with a nucleus as his starting point, he advanced the theory of electrons travelling in orbits of quantised "stationary states" around the atom's nucleus in order to stabilise the atom, but it wasn't until his 1921 paper that he showed that

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4940-421: The chemical properties of each element were largely determined by the number of electrons in the outer orbits of its atoms. He introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a quantum of discrete energy. This became a basis for what is now known as the old quantum theory . In 1885, Johann Balmer had come up with his Balmer series to describe

5035-717: The classical ones being manifested in measurement." The rise of Nazism in Germany prompted many scholars to flee their countries, either because they were Jewish or because they were political opponents of the Nazi regime. In 1933, the Rockefeller Foundation created a fund to help support refugee academics, and Bohr discussed this programme with the President of the Rockefeller Foundation, Max Mason , in May 1933 during

5130-432: The concepts of classical physics are merely a refinement of them. Therefore, for Bohr, classical concepts need to be used to describe experiments that deal with the quantum world. Bohr writes: [T]he account of all evidence must be expressed in classical terms. The argument is simply that by the word 'experiment' we refer to a situation where we can tell to others what we have done and what we have learned and that, therefore,

5225-419: The content of a theory while accepting its general premises and structure. There has been much subsequent debate and discussion about Bohr's views and philosophy of quantum mechanics. Regarding his ontological interpretation of the quantum world, Bohr has been seen as an anti-realist , an instrumentalist , a phenomenological realist or some other kind of realist. Furthermore, though some have seen Bohr as being

5320-520: The designation of Professional Engineer (P. Eng.). This designation was unveiled at the CAP congress in 1999 and already more than 200 people carry this distinction. To get the certification, at minimum proof of honours bachelor or higher degree in physics or a closely related discipline must be provided. Also, the physicist must have completed, or be about to complete, three years of recent physics-related work experience after graduation. And, unless exempted,

5415-459: The early 1600s. The work on mechanics , along with a mathematical treatment of physical systems, was further developed by Christiaan Huygens and culminated in Newton's laws of motion and Newton's law of universal gravitation by the end of the 17th century. The experimental discoveries of Faraday and the theory of Maxwell's equations of electromagnetism were developmental high points during

5510-507: The electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level (or orbit) to another. Although the Bohr model has been supplanted by other models, its underlying principles remain valid. He conceived the principle of complementarity : that items could be separately analysed in terms of contradictory properties, like behaving as a wave or a stream of particles . The notion of complementarity dominated Bohr's thinking in both science and philosophy. Bohr founded

5605-477: The first form of modern quantum mechanics . The BKS theory also generated discussion of, and renewed attention to, difficulties in the foundations of the old quantum theory. The most provocative element of BKS – that momentum and energy would not necessarily be conserved in each interaction, but only statistically – was soon shown to be in conflict with experiments conducted by Walther Bothe and Hans Geiger . In light of these results, Bohr informed Darwin that "there

5700-434: The first version of the uncertainty principle , presenting it using a thought experiment where an electron was observed through a gamma-ray microscope . Bohr was dissatisfied with Heisenberg's argument, since it required only that a measurement disturb properties that already existed, rather than the more radical idea that the electron's properties could not be discussed at all apart from the context they were measured in. In

5795-402: The function and outcome of experiments that thus must be described classically). These explanations are not mutually exclusive, and at times Bohr seems to emphasise some of these aspects while at other times he focuses on other elements. According to Faye "Bohr thought of the atom as real. Atoms are neither heuristic nor logical constructions." However, according to Faye, he did not believe "that

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5890-756: The increasing expectations and requirements for which any profession must take responsibility". Chartered Physicist is considered to be equal in status to Chartered Engineer, which the IoP also awards as a member of the Engineering Council UK, and other chartered statuses in the UK. It is also considered a "regulated profession" under the European professional qualification directives. The Canadian Association of Physicists can appoint an official designation called Professional Physicist ( P. Phys. ), similar to

5985-473: The inevitably victorious Nazis and that he was shocked that Germany was pursuing nuclear weapons under Heisenberg's leadership. Michael Frayn 's 1998 play Copenhagen explores what might have happened at the 1941 meeting between Heisenberg and Bohr. A television film version of the play by the BBC was first screened on 26 September 2002, with Stephen Rea as Bohr. With the subsequent release of Bohr's letters,

6080-493: The institute in 1926 to take up a chair as professor of theoretical physics at the Utrecht University , Bohr arranged for Heisenberg to return and take Kramers's place as a lektor at the University of Copenhagen. Heisenberg worked in Copenhagen as a university lecturer and assistant to Bohr from 1926 to 1927. Bohr became convinced that light behaved like both waves and particles and, in 1927, experiments confirmed

6175-525: The institute's first publication even before it opened. The Bohr model worked well for hydrogen and ionized single-electron helium, which impressed Einstein but could not explain more complex elements. By 1919, Bohr was moving away from the idea that electrons orbited the nucleus and developed heuristics to describe them. The rare-earth elements posed a particular classification problem for chemists because they were so chemically similar. An important development came in 1924 with Wolfgang Pauli 's discovery of

6270-1180: The largest employer being the last. Physicists in academia or government labs tend to have titles such as Assistants, Professors , Sr./Jr. Scientist, or postdocs . As per the American Institute of Physics , some 20% of new physics Ph.D.s holds jobs in engineering development programs, while 14% turn to computer software and about 11% are in business/education. A majority of physicists employed apply their skills and training to interdisciplinary sectors (e.g. finance ). Job titles for graduate physicists include Agricultural Scientist , Air Traffic Controller , Biophysicist , Computer Programmer , Electrical Engineer , Environmental Analyst , Geophysicist , Medical Physicist , Meteorologist , Oceanographer , Physics Teacher / Professor / Researcher , Research Scientist , Reactor Physicist , Engineering Physicist , Satellite Missions Analyst, Science Writer , Stratigrapher , Software Engineer , Systems Engineer , Microelectronics Engineer , Radar Developer, Technical Consultant, etc. The majority of Physics terminal bachelor's degree holders are employed in

6365-517: The main subject of the meeting was Carl Friedrich von Weizsäcker , who had proposed trying to persuade Bohr to mediate peace between Britain and Germany. In 1957, Heisenberg wrote to Robert Jungk , who was then working on the book Brighter than a Thousand Suns: A Personal History of the Atomic Scientists . Heisenberg explained that he had visited Copenhagen to communicate to Bohr the views of several German scientists, that production of

6460-513: The mathematician Niels Erik Nørlund . Bohr resigned his membership in the Church of Denmark on 16 April 1912, and he and Margrethe were married in a civil ceremony at the town hall in Slagelse on 1 August. Years later, his brother Harald similarly left the church before getting married. Bohr and Margrethe had six sons. The oldest, Christian, died in a boating accident in 1934, and another, Harald,

6555-598: The news to the United States where he opened the Fifth Washington Conference on Theoretical Physics with Fermi on 26 January 1939. When Bohr told George Placzek that this resolved all the mysteries of transuranic elements , Placzek told him that one remained: the neutron capture energies of uranium did not match those of its decay. Bohr thought about it for a few minutes and then announced to Placzek, Léon Rosenfeld and John Wheeler that "I have understood everything." Based on his liquid drop model of

6650-570: The novel aspects of quantum mechanics became widely celebrated subjects of discussion. Einstein and Bohr had good-natured arguments over such issues throughout their lives. In 1914 Carl Jacobsen , the heir to Carlsberg breweries , bequeathed his mansion (the Carlsberg Honorary Residence, currently known as Carlsberg Academy) to be used for life by the Dane who had made the most prominent contribution to science, literature or

6745-429: The nucleus, Bohr concluded that it was the uranium-235 isotope and not the more abundant uranium-238 that was primarily responsible for fission with thermal neutrons. In April 1940, John R. Dunning demonstrated that Bohr was correct. In the meantime, Bohr and Wheeler developed a theoretical treatment, which they published in a September 1939 paper on "The Mechanism of Nuclear Fission". Heisenberg said of Bohr that he

6840-477: The object was an important condition for attaining knowledge. This can only be done through the use of causal and spatial-temporal concepts to describe the subject's experience. Thus, according to Jan Faye, Bohr thought that it is because of "classical" concepts like "space", "position", "time", "causation", and "momentum" that one can talk about objects and their objective existence. Bohr held that basic concepts like "time" are built in to our ordinary language and that

6935-561: The original task, incorporating improvements into both Rayleigh's theory and his method, by taking into account the viscosity of the water, and by working with finite amplitudes instead of just infinitesimal ones. His essay, which he submitted at the last minute, won the prize. He later submitted an improved version of the paper to the Royal Society in London for publication in the Philosophical Transactions of

7030-639: The play has been criticised by historians as being a "grotesque oversimplification and perversion of the actual moral balance" due to adopting a pro-Heisenberg perspective. The same meeting had previously been dramatised by the BBC's Horizon science documentary series in 1992, with Anthony Bate as Bohr, and Philip Anthony as Heisenberg. The meeting is also dramatised in the Norwegian/Danish/British miniseries The Heavy Water War . In September 1943, word reached Bohr and his brother Harald that

7125-574: The previous year. Bohr's thesis was groundbreaking, but attracted little interest outside Scandinavia because it was written in Danish, a Copenhagen University requirement at the time. In 1921, the Dutch physicist Hendrika Johanna van Leeuwen would independently derive a theorem in Bohr's thesis that is today known as the Bohr–Van Leeuwen theorem . In 1910, Bohr met Margrethe Nørlund , the sister of

7220-433: The private sector. Other fields are academia, government and military service, nonprofit entities, labs and teaching. Typical duties of physicists with master's and doctoral degrees working in their domain involve research, observation and analysis, data preparation, instrumentation, design and development of industrial or medical equipment, computing and software development, etc. The highest honor awarded to physicists

7315-437: The quantum mechanical formalism was true in the sense that it gave us a literal ('pictorial') rather than a symbolic representation of the quantum world." Therefore, Bohr's theory of complementarity "is first and foremost a semantic and epistemological reading of quantum mechanics that carries certain ontological implications". As Faye explains, Bohr's indefinability thesis is that [T]he truth conditions of sentences ascribing

7410-509: The spin theory. Bohr pointed out that he had concerns about the interaction between electrons and magnetic fields. When he arrived in Leiden, Paul Ehrenfest and Albert Einstein informed Bohr that Einstein had resolved this problem using relativity . Bohr then had Uhlenbeck and Goudsmit incorporate this into their paper. Thus, when he met Werner Heisenberg and Pascual Jordan in Göttingen on

7505-642: The structure of atoms and molecules was being done. He met J. J. Thomson of the Cavendish Laboratory and Trinity College, Cambridge . He attended lectures on electromagnetism given by James Jeans and Joseph Larmor , and did some research on cathode rays , but failed to impress Thomson. He had more success with younger physicists like the Australian William Lawrence Bragg , and New Zealand's Ernest Rutherford , whose 1911 small central nucleus Rutherford model of

7600-534: The subject, settling on a model postulated by Paul Drude and elaborated by Hendrik Lorentz , in which the electrons in a metal are considered to behave like a gas. Bohr extended Lorentz's model, but was still unable to account for phenomena like the Hall effect , and concluded that electron theory could not fully explain the magnetic properties of metals. The thesis was accepted in April 1911, and Bohr conducted his formal defence on 13 May. Harald had received his doctorate

7695-625: The subsequent 1932 discovery of the neutron provided another explanation. This prompted Bohr to create a new theory of the compound nucleus in 1936, which explained how neutrons could be captured by the nucleus. In this model, the nucleus could be deformed like a drop of liquid. He worked on this with a new collaborator, the Danish physicist Fritz Kalckar, who died suddenly in 1938. The discovery of nuclear fission by Otto Hahn in December 1938 (and its theoretical explanation by Lise Meitner ) generated intense interest among physicists. Bohr brought

7790-478: The support of the Danish government and the Carlsberg Foundation, and sizeable contributions were also made by industry and private donors, many of them Jewish. Legislation establishing the institute was passed in November 1918. Now known as the Niels Bohr Institute , it opened on 3 March 1921, with Bohr as its director. His family moved into an apartment on the first floor. Bohr's institute served as

7885-410: The trilogy, but the younger generation, including Rutherford, David Hilbert , Albert Einstein , Enrico Fermi , Max Born and Arnold Sommerfeld saw it as a breakthrough. The trilogy's acceptance was entirely due to its ability to explain phenomena that stymied other models, and to predict results that were subsequently verified by experiments. Today, the Bohr model of the atom has been superseded, but

7980-412: The two men took a private moment outside, the content of which has caused much speculation, as both gave differing accounts. According to Heisenberg, he began to address nuclear energy, morality and the war, to which Bohr seems to have reacted by terminating the conversation abruptly while not giving Heisenberg hints about his own opinions. Ivan Supek , one of Heisenberg's students and friends, claimed that

8075-466: The visible spectral lines of a hydrogen atom: where λ is the wavelength of the absorbed or emitted light and R H is the Rydberg constant . Balmer's formula was corroborated by the discovery of additional spectral lines, but for thirty years, no one could explain why it worked. In the first paper of his trilogy, Bohr was able to derive it from his model: where m e is the electron's mass, e

8170-522: The way back, he had become, in his own words, "a prophet of the electron magnet gospel". Heisenberg first came to Copenhagen in 1924, then returned to Göttingen in June 1925, shortly thereafter developing the mathematical foundations of quantum mechanics. When he showed his results to Max Born in Göttingen, Born realised that they could best be expressed using matrices . This work attracted the attention of

8265-643: Was "primarily a philosopher, not a physicist". Bohr read the 19th-century Danish Christian existentialist philosopher Søren Kierkegaard . Richard Rhodes argued in The Making of the Atomic Bomb that Bohr was influenced by Kierkegaard through Høffding. In 1909, Bohr sent his brother Kierkegaard's Stages on Life's Way as a birthday gift. In the enclosed letter, Bohr wrote, "It is the only thing I have to send home; but I do not believe that it would be very easy to find anything better ... I even think it

8360-524: Was aware of the possibility of using uranium-235 to construct an atomic bomb , referring to it in lectures in Britain and Denmark shortly before and after the war started, but he did not believe that it was technically feasible to extract a sufficient quantity of uranium-235. In September 1941, Heisenberg, who had become head of the German nuclear energy project , visited Bohr in Copenhagen. During this meeting

8455-460: Was born in Copenhagen , Denmark, on 7 October 1885, the second of three children of Christian Bohr , a professor of physiology at the University of Copenhagen, and his wife Ellen née Adler, who came from a wealthy Jewish banking family. He had an elder sister, Jenny, and a younger brother Harald . Jenny became a teacher, while Harald became a mathematician and footballer who played for

8550-746: Was coined by William Whewell (also the originator of the term "scientist") in his 1840 book The Philosophy of the Inductive Sciences . A standard undergraduate physics curriculum consists of classical mechanics , electricity and magnetism , non-relativistic quantum mechanics , optics , statistical mechanics and thermodynamics , and laboratory experience. Physics students also need training in mathematics ( calculus , differential equations , linear algebra , complex analysis , etc.), and in computer science . Any physics-oriented career position requires at least an undergraduate degree in physics or applied physics, while career options widen with

8645-424: Was discovered. Later, the synthetic element bohrium was named after him. During the 1930s, Bohr helped refugees from Nazism . After Denmark was occupied by the Germans , he met with Heisenberg, who had become the head of the German nuclear weapon project . In September 1943 word reached Bohr that he was about to be arrested by the Germans, so he fled to Sweden. From there, he was flown to Britain, where he joined

8740-491: Was physics, which he studied under Professor Christian Christiansen , the university's only professor of physics at that time. He also studied astronomy and mathematics under Professor Thorvald Thiele , and philosophy under Professor Harald Høffding , a friend of his father. In 1905 a gold medal competition was sponsored by the Royal Danish Academy of Sciences and Letters to investigate a method for measuring

8835-672: Was ready to offer asylum, and the mass rescue of the Danish Jews by their countrymen followed swiftly thereafter. Some historians claim that Bohr's actions led directly to the mass rescue, while others say that, though Bohr did all that he could for his countrymen, his actions were not a decisive influence on the wider events. Eventually, over 7,000 Danish Jews escaped to Sweden. Physicist Physicists can apply their knowledge towards solving practical problems or to developing new technologies (also known as applied physics or engineering physics ). The study and practice of physics

8930-535: Was severely mentally disabled. He was placed in an institution away from his family's home at the age of four and died from childhood meningitis six years later. Aage Bohr became a successful physicist, and in 1975 was awarded the Nobel Prize in physics, like his father. A son of Aage, Vilhelm A. Bohr, is a scientist affiliated with the University of Copenhagen and the National Institute on Aging in

9025-561: Was then known about the structure of the atom, including the correspondence principle , which he had formulated. This states that the behaviour of systems described by quantum theory reproduces classical physics in the limit of large quantum numbers . The discovery of Compton scattering by Arthur Holly Compton in 1923 convinced most physicists that light was composed of photons and that energy and momentum were conserved in collisions between electrons and photons. In 1924, Bohr, Kramers, and John C. Slater , an American physicist working at

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