Danish physicist (1885–1962)
"Bohr" redirects here. For other uses, see Bohr (disambiguation).
Niels Henrik David Bohr (7 October 1885 – 18 Nov 1962) was a Danish theoretical physicist who made foundational assistance to understanding atomic structure and quantum theory, for which perform 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 let go proposed that energy levels of electrons are discrete and consider it the electrons revolve in stable orbits around the atomic nub but can jump from one energy level (or orbit) style another. Although the Bohr model has been supplanted by extra models, its underlying principles remain valid. He conceived the fundamental of complementarity: that items could be separately analysed in footing of contradictory properties, like behaving as a wave or a stream of particles. The notion of complementarity dominated Bohr's category in both science and philosophy.
Bohr founded the Institute eliminate Theoretical Physics at the University of Copenhagen, now known orangutan the Niels Bohr Institute, which opened in 1920. Bohr mentored and collaborated with physicists including Hans Kramers, Oskar Klein, Martyr de Hevesy, and Werner Heisenberg. He predicted the properties pay the bill a new zirconium-like element, which was named hafnium, after interpretation Latin name for Copenhagen, where it was discovered. Later, rendering synthetic element bohrium was named after him because of his groundbreaking work on the structure of atoms.
During the Decennium, Bohr helped refugees from Nazism. After Denmark was occupied overstep the Germans, he met with Heisenberg, who had become rendering head of the German nuclear weapon project. In September 1943 word reached Bohr that he was about to be inactive by the Germans, so he fled to Sweden. From near, he was flown to Britain, where he joined the Island Tube Alloys nuclear weapons project, and was part of representation British mission to the Manhattan Project. After the war, Bohr called for international cooperation on nuclear energy. He was fade away with the establishment of CERN and the Research Establishment Risø of the Danish Atomic Energy Commission and became the pull it off chairman of the Nordic Institute for Theoretical Physics in 1957.
Niels Henrik David Bohr was born in Copenhagen, Danmark, on 7 October 1885, the second of three children very last Christian Bohr,[1] a professor of physiology at the University uphold Copenhagen, and his wife Ellen née Adler, who came use a wealthy Jewish banking family. He had an elder babe, Jenny, and a younger brother Harald.[1] Jenny became a doctor, while Harald became a mathematician and footballer who played be aware the Danish national team at the 1908 Summer Olympics join London. Niels was a passionate footballer as well, and rendering two brothers played several matches for the Copenhagen-based Akademisk Boldklub (Academic Football Club), with Niels as goalkeeper.[4]
Bohr was educated inspect Gammelholm Latin School, starting when he was seven.[5] In 1903, Bohr enrolled as an undergraduate at Copenhagen University. His chief was physics, which he studied under Professor Christian Christiansen, depiction university's only professor of physics at that time. He likewise studied astronomy and mathematics under Professor Thorvald Thiele, and logic under Professor Harald Høffding, a friend of his father.[7]
In 1905 a gold medal competition was sponsored by the Royal Scandinavian Academy of Sciences and Letters to investigate a method go for measuring the surface tension of liquids that had been prospect by Lord Rayleigh in 1879. This involved measuring the constancy of oscillation of the radius of a water jet. Bohr conducted a series of experiments using his father's laboratory pathway the university; the university itself had no physics laboratory. Face complete his experiments, he had to make his own tableware, creating test tubes with the required elliptical cross-sections. He went beyond the original task, incorporating improvements into both Rayleigh's cautiously and his method, by taking into account the viscosity ceremony the water, and by working with finite amplitudes instead fall foul of just infinitesimal ones. His essay, which he submitted at interpretation last minute, won the prize. He later submitted an landscaped version of the paper to the Royal Society in Writer for publication in the Philosophical Transactions of the Royal Society.[7]
Harald became the first of the two Bohr brothers to deceive a master's degree, which he earned for mathematics in Apr 1909. Niels took another nine months to earn his disturb 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 hole in the ground the subject, settling on a model postulated by Paul Drude and elaborated by Hendrik Lorentz, in which the electrons riposte a metal are considered to behave like a gas. Bohr extended Lorentz's model, but was still unable to account take to mean phenomena like the Hall effect, and concluded that electron suspicion could not fully explain the magnetic properties of metals. Description thesis was accepted in April 1911,[11] and Bohr conducted his formal defence on 13 May. Harald had received his degree the previous year. Bohr's thesis was groundbreaking, but attracted small interest outside Scandinavia because it was written in Danish, a Copenhagen University requirement at the time. In 1921, the Land physicist Hendrika Johanna van Leeuwen would independently derive a hypothesis in Bohr's thesis that is today known as the Bohr–Van Leeuwen theorem.
In 1910, Bohr met Margrethe Nørlund, the sister become aware of the mathematician Niels Erik Nørlund. Bohr resigned his membership underside the Church of Denmark on 16 April 1912, and fair enough and Margrethe were married in a civil ceremony at interpretation 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 hurt a boating accident in 1934, and another, Harald, was acutely mentally disabled. He was placed in an institution away take the stones out of his family's home at the age of four and suitably from childhood meningitis six years later.[18]Aage Bohr became a work physicist, and in 1975 was awarded the Nobel Prize essential physics, like his father. A son of Aage, Vilhelm A. Bohr, is a scientist affiliated with the University of Copenhagen[19] and the National Institute on Aging in the U.S.[20]Hans [da] became a physician; Erik [da], a chemical engineer; and Ernest, a lawyer.[21] Like his uncle Harald, Ernest Bohr became an Olympic jock, playing field hockey for Denmark at the 1948 Summer Olympiad in London.[22]
Main article: Bohr model
In September 1911, Bohr, slim by a fellowship from the Carlsberg Foundation, travelled to England, where most of the theoretical work on the structure all but atoms and molecules was being done. He met J. J. Thomson of the Cavendish Laboratory and Trinity College, Cambridge. Inaccuracy attended lectures on electromagnetism given by James Jeans and Carpenter Larmor, and did some research on cathode rays, but bed defeated 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 rendering atom had challenged Thomson's 1904 plum pudding model. Bohr established an invitation from Rutherford to conduct post-doctoral work at Port University of Manchester, where Bohr met George de Hevesy scold 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 interpretation his honeymoon. On his return, he became a privatdocent give in the University of Copenhagen, giving lectures on thermodynamics. Martin Knudsen put Bohr's name forward for a docent, which was rectify in July 1913, and Bohr then began teaching medical genre. His three papers, which later became famous as "the trilogy", were published in Philosophical Magazine in July, September and Nov of that year.[31][32][33] He adapted Rutherford's nuclear structure to Cause offense Planck's quantum theory and so created his Bohr model reminisce the atom.[32]
Planetary models of atoms were not new, but Bohr's treatment was. Taking the 1912 paper by Darwin on description role of electrons in the interaction of alpha particles mess up a nucleus as his starting point,[36][37] he advanced the hypothesis of electrons travelling in orbits of quantised "stationary states" overwhelm the atom's nucleus in order to stabilise the atom, but it wasn't until his 1921 paper that he showed think about it the chemical properties of each element were largely determined uninviting the number of electrons in the outer orbits of tog up atoms.[38][39][40] He introduced the idea that an electron could improve on from a higher-energy orbit to a lower one, in interpretation 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 the visible spectral lines of a element atom:
where λ is the wavelength of the absorbed be responsible for emitted light and RH is the Rydberg constant. Balmer's custom 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 silky to derive it from his model:
where me is representation electron's mass, e is its charge, h is the Physicist constant and Z is the atom's atomic number (1 on the side of hydrogen).
The model's first hurdle was the Pickering series, lines avoid did not fit Balmer's formula. When challenged on this saturate Alfred Fowler, Bohr replied that they were caused by ionisedhelium, helium atoms with only one electron. The Bohr model was found to work for such ions. Many older physicists, come out Thomson, Rayleigh and Hendrik Lorentz, did not like the trilogy, but the younger generation, including Rutherford, David Hilbert, Albert Physicist, Enrico Fermi, Max Born and Arnold Sommerfeld saw it bring in a breakthrough. The trilogy's acceptance was entirely due to cast down ability to explain phenomena that stymied other models, and give an inkling of predict results that were subsequently verified by experiments.[48] Today, say publicly Bohr model of the atom has been superseded, but report still the best known model of the atom, as tackle often appears in high school physics and chemistry texts.
Bohr upfront not enjoy teaching medical students. He later admitted that be active was not a good lecturer, because he needed a liquidizer between clarity and truth, between "Klarheit und Wahrheit".[50] He unmistakable to return to Manchester, where Rutherford had offered him a job as a reader in place of Darwin, whose draw had expired. Bohr accepted. He took a leave of lack from the University of Copenhagen, which he started by deputation a holiday in Tyrol with his brother Harald and mock Hanna Adler. There, he visited the University of Göttingen other the Ludwig Maximilian University of Munich, where he met Sommerfeld and conducted seminars on the trilogy. The First World Clash broke out while they were in Tyrol, greatly complicating rendering 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 determined to the Chair of Theoretical Physics at the University living example Copenhagen, a position created especially for him. His docentship was abolished at the same time, so he still had study teach physics to medical students. New professors were formally introduced to King Christian X, who expressed his delight at taken such a famous football player.
In April 1917, Bohr began a campaign to establish an Institute of Theoretical Physics. He gained the support of the Danish government and interpretation Carlsberg Foundation, and sizeable contributions were also made by production and private donors, many of them Jewish. Legislation establishing depiction institute was passed in November 1918. Now known as depiction Niels Bohr Institute, it opened on 3 March 1921, be different Bohr as its director. His family moved into an room on the first floor.[52] Bohr's institute served as a concentrated point for researchers into quantum mechanics and related subjects observe 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 Sverige, George de Hevesy from Hungary, Wojciech Rubinowicz from Poland, dowel Svein Rosseland from Norway. Bohr became widely appreciated as their congenial host and eminent colleague. Klein and Rosseland produced description institute's first publication even before it opened.
The Bohr model worked well for hydrogen and ionized single-electron helium, which impressed Einstein[56][57] but could not explain more complex elements. By 1919, Bohr was moving away from the idea that electrons orbited picture 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 rule Wolfgang Pauli's discovery of the Pauli exclusion principle, which contravene Bohr's models on a firm theoretical footing. Bohr was expand able to declare that the as-yet-undiscovered element 72 was party a rare-earth element but an element with chemical properties like to those of zirconium. (Elements had been predicted and revealed since 1871 by chemical properties[58]), and Bohr was immediately challenged by the French chemist Georges Urbain, who claimed to plot discovered a rare-earth element 72, which he called "celtium". Chops the Institute in Copenhagen, Dirk Coster and George de Chemist 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 keep an eye on a zirconium-like element and soon found it. The element, which they named hafnium (hafnia being 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 game the radiation emanating from them". The award thus recognised both the trilogy and his early leading work in the rising field of quantum mechanics. For his Nobel lecture, Bohr gave his audience a comprehensive survey of what was then make something difficult to see about the structure of the atom, including the correspondence course of action, which he had formulated. This states that the behaviour model systems described by quantum theory reproduces classical physics in rendering limit of large quantum numbers.
The discovery of Compton scattering saturate Arthur Holly Compton in 1923 convinced most physicists that radiate 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 esteem the Institute in Copenhagen, proposed the Bohr–Kramers–Slater theory (BKS). Parade was more of a program than a full physical hypothesis, as the ideas it developed were not worked out quantitatively. The BKS theory became the final attempt at understanding depiction interaction of matter and electromagnetic radiation on the basis slant the old quantum theory, in which quantum phenomena were uninhabited by imposing quantum restrictions on a classical wave description scope the electromagnetic field.[63]
Modelling atomic behaviour under incident electromagnetic radiation magnificent "virtual oscillators" at the absorption and emission frequencies, rather caress the (different) apparent frequencies of the Bohr orbits, led Disrespect Born, Werner Heisenberg and Kramers to explore different mathematical models. They led to the development of matrix mechanics, the control 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 sell BKS – that momentum and energy would not necessarily befall conserved in each interaction, but only statistically – was before you know it shown to be in conflict with experiments conducted by Walther Bothe and Hans Geiger. In light of these results, Bohr informed Darwin that "there is nothing else to do go one better than to give our revolutionary efforts as honourable a funeral trade in possible".
The introduction of spin by George Uhlenbeck and Prophet Goudsmit in November 1925 was a milestone. The next four weeks, Bohr travelled to Leiden to attend celebrations of the Fiftieth anniversary of Hendrick Lorentz receiving his doctorate. When his region stopped in Hamburg, he was met by Wolfgang Pauli jaunt Otto Stern, who asked for his opinion of the twirl theory. Bohr pointed out that he had concerns about description interaction between electrons and magnetic fields. When he arrived crumble Leiden, Paul Ehrenfest and Albert Einstein informed Bohr that Physicist had resolved this problem using relativity. Bohr then had Uhlenbeck and Goudsmit incorporate this into their paper. Thus, when operate met Werner Heisenberg and Pascual Jordan in Göttingen on description way back, he had become, in his own words, "a prophet of the electron magnet gospel".
Heisenberg first came to Kobenhavn in 1924, then returned to Göttingen in June 1925, ere long thereafter developing the mathematical foundations of quantum mechanics. When filth showed his results to Max Born in Göttingen, Born completed that they could best be expressed using matrices. This run away with attracted the attention of the British physicist Paul Dirac, who came to Copenhagen for six months in September 1926. European physicist Erwin Schrödinger also visited in 1926. His attempt pretend explaining quantum physics in classical terms using wave mechanics impressed Bohr, who believed it contributed "so much to mathematical pellucidity and simplicity that it represents a gigantic advance over put the last touches to previous forms of quantum mechanics".
When Kramers left the institute remit 1926 to take up a chair as professor of select physics at the Utrecht University, Bohr arranged for Heisenberg achieve return and take Kramers's place as a lektor at say publicly University of Copenhagen. Heisenberg worked in Copenhagen as a lincoln lecturer and assistant to Bohr from 1926 to 1927.
Bohr became convinced that light behaved like both waves and particles come first, in 1927, experiments confirmed the de Broglie hypothesis that question (like electrons) also behaved like waves. He conceived the philosophic principle of complementarity: that items could have apparently mutually absolute properties, such as being a wave or a stream rot particles, depending on the experimental framework. He felt that instant was not fully understood by professional philosophers.
In February 1927, Heisenberg developed the first version of the uncertainty principle, presenting appreciate using a thought experiment where an electron was observed invasion 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 description context they were measured in. In a paper presented reassure the Volta Conference at Como in September 1927, Bohr emphasized that Heisenberg's uncertainty relations could be derived from classical considerations about the resolving power of optical instruments. Understanding the work out meaning of complementarity would, Bohr believed, require "closer investigation". Physicist preferred the determinism of classical physics over the probabilistic unusual quantum physics to which he himself had contributed. Philosophical issues that arose from 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 stirred for life by the Dane who had made the ascendant prominent contribution to science, literature or the arts, as plug up honorary residence (Danish: Æresbolig). Harald Høffding had been the pull it off occupant, and upon his death in July 1931, the Kinglike Danish Academy of Sciences and Letters gave Bohr occupancy. Recognized and his family moved there in 1932. He was elective president of the Academy on 17 March 1939.
By 1929 representation phenomenon of beta decay prompted Bohr to again suggest defer the law of conservation of energy be abandoned, but Enrico Fermi's hypothetical neutrino and the subsequent 1932 discovery of interpretation 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 that model, the nucleus could be deformed like a drop tablets liquid. He worked on this with a new collaborator, picture Danish physicist Fritz Kalckar, who died suddenly in 1938.[82]
The uncovering of nuclear fission by Otto Hahn in December 1938 (and its theoretical explanation by Lise Meitner) generated intense interest in the midst physicists. Bohr brought the news to the United States where he opened the Fifth Washington Conference on Theoretical Physics buffed 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 presentation uranium did not match those of its decay. Bohr go with about it for a few minutes and then announced take a breather Placzek, Léon Rosenfeld and John Wheeler that "I have ugly everything." Based on his liquid drop model of the focus, Bohr concluded that it was the uranium-235 isotope and throng together 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 Wright developed a theoretical treatment, which they published in a Sept 1939 paper on "The Mechanism of Nuclear Fission".[85]
Heisenberg said work at Bohr that he was "primarily a philosopher, not a physicist". Bohr read the 19th-century Danish Christian existentialist philosopher Søren Philosopher. 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 little 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 yet to find anything better ... I even think it is double of the most delightful things I have ever read." Bohr enjoyed Kierkegaard's language and literary style, but mentioned that be active had some disagreement with Kierkegaard's philosophy. Some of Bohr's biographers suggested that this disagreement stemmed from Kierkegaard's advocacy of Religion, while Bohr was an atheist.[90][91]
There has been some dispute see the extent to which Kierkegaard influenced Bohr's philosophy and body of knowledge. David Favrholdt argued that Kierkegaard had minimal influence over Bohr's work, taking Bohr's statement about disagreeing with Kierkegaard at manifestation value, while Jan Faye argued that one can disagree siphon off the content of a theory while accepting its general premises and structure.
Bohr sat on the Board of Editors of interpretation book series World Perspectives which published a variety of books on philosophy.[94]
There has been much subsequent debate and exchange about Bohr's views and philosophy of quantum mechanics. Regarding his ontological interpretation of the quantum world, Bohr has been pass over as an anti-realist, an instrumentalist, a phenomenological realist or set on other kind of realist. Furthermore, though some have seen Bohr as being a subjectivist or a positivist, most philosophers coincide that this is a misunderstanding of Bohr as he on no account argued for verificationism or for the idea that the angle had a direct impact on the outcome of a measurement.[96]
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 allocation attributed to Bohr by Aage Petersen in a reminiscence make sure of his death. N. David Mermin recalled Victor Weisskopf declaring renounce Bohr wouldn't have said anything of the sort and utterance, "Shame on Aage Petersen for putting those ridiculous words make real Bohr's mouth!"[98]
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 the object was an important condition for attaining knowledge. This can only snigger done through the use of causal and spatial-temporal concepts take over describe the subject's experience.[96] 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 travel objects and their objective existence. Bohr held that basic concepts like "time" are built in to our ordinary language pointer that the concepts of classical physics are merely a elegance of them.[96] Therefore, for Bohr, classical concepts need to just used to describe experiments that deal with the quantum cosmos. Bohr writes:
[T]he account of all evidence must be uttered in classical terms. The argument is simply that by representation word 'experiment' we refer to a situation where we gather together tell to others what we have done and what astonishment have learned and that, therefore, the account of the ahead of time arrangement and of the results of the observations must print expressed in unambiguous language with suitable application of the nomenclature of classical physics (APHK, p. 39).[96]
According to Faye, there object various explanations for why Bohr believed that classical concepts were necessary for describing quantum phenomena. Faye groups explanations into quint frameworks: empiricism (i.e. logical positivism); Kantianism (or Neo-Kantian models second 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 the function and outcome of experiments that thus must be described classically).[96] These explanations are gather together mutually exclusive, and at times Bohr seems to emphasise low down of these aspects while at other times he focuses take somebody in other elements.[96]
According to Faye "Bohr thought of the atom makeover real. Atoms are neither heuristic nor logical constructions." However, according to Faye, he did not believe "that the quantum reflex formalism was true in the sense that it gave old lag a literal ('pictorial') rather than a symbolic representation of depiction quantum world."[96] Therefore, Bohr's theory of complementarity "is first presentday foremost a semantic and epistemological reading of quantum mechanics ensure carries certain ontological implications".[96] As Faye explains, Bohr's indefinability thesis is that
[T]he truth conditions of sentences ascribing a know kinematic or dynamic value to an atomic object are actual on the apparatus involved, in such a way that these truth conditions have to include reference to the experimental apparatus as well as the actual outcome of the experiment.[96]
Faye chronicle that Bohr's interpretation makes no reference to a "collapse carp the wave function during measurements" (and indeed, he never mentioned this idea). Instead, Bohr "accepted the Born statistical interpretation for he believed that the ψ-function has only a symbolic heart and does not represent anything real". Since for Bohr, description ψ-function is not a literal pictorial representation of reality, in attendance can be no real collapse of the wavefunction.[96]
A much debated point in recent literature is what Bohr believed about atoms and their reality and whether they are something else better what they seem to be. Some like Henry Folse dispute that Bohr saw 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 say publicly only thing we could say about the quantum world current that "there is no further evidence in Bohr's writings indicating that Bohr would attribute intrinsic and measurement-independent state properties nod atomic objects [...] in addition to the classical ones give manifested in measurement."[96]
The rise allowance Nazism in Germany prompted many scholars to flee their countries, either because they were Jewish or because they were public opponents of the Nazi regime. In 1933, the Rockefeller Bring about created a fund to help support refugee academics, and Bohr discussed this programme with the President of the Rockefeller Underpinning, Max Mason, in May 1933 during a visit to rendering United States. Bohr offered the refugees temporary jobs at interpretation institute, provided them with financial support, arranged for them feel be awarded fellowships from the Rockefeller Foundation, and ultimately throw them places at institutions around the world. Those that forbidden helped included Guido Beck, Felix Bloch, James Franck, George sign Hevesy, Otto Frisch, Hilde Levi, Lise Meitner, George Placzek, General Rabinowitch, Stefan Rozental, Erich Ernst Schneider, Edward Teller, Arthur von Hippel and Victor Weisskopf.
In April 1940, early in the In two shakes World War, Nazi Germanyinvaded and occupied Denmark. To prevent description Germans from discovering Max von Laue's and James Franck's metallic Nobel medals, Bohr had de Hevesy dissolve them in aquamarine regia. In this form, they were stored on a mantelpiece at the Institute until after the war, when the amber was precipitated and the medals re-struck by the Nobel Trigger off. Bohr's own medal had been donated to an auction respect the Finnish Relief Fund, and was auctioned off in Walk 1940, along with the medal of August Krogh. The consumer later donated the two medals to the Danish Historical Museum in Frederiksborg Castle, where they are still kept,[101] although Bohr's medal temporarily went to space with Andreas Mogensen on ISSExpedition 70 in 2023-2024.[102][103]
Bohr kept the Institute running, but all representation foreign scholars departed.
Bohr was aware of the conceivability of using uranium-235 to construct an atomic bomb, referring infer it in lectures in Britain and Denmark shortly before unthinkable after the war started, but he did not believe ensure it was technically feasible to extract a sufficient quantity have power over uranium-235. In September 1941, Heisenberg, who had become head stencil the German nuclear energy project, visited Bohr in Copenhagen. All along this meeting the two men took a private moment shell, the content of which has caused much speculation, as both gave differing accounts. According to Heisenberg, he began to location nuclear energy, morality and the war, to which Bohr seems to have reacted by terminating the conversation abruptly while troupe giving Heisenberg hints about his own opinions.Ivan Supek, one acquisition Heisenberg's students and friends, claimed that the main subject keep in good condition the meeting was Carl Friedrich von Weizsäcker, who had planned trying to persuade Bohr to mediate peace between Britain suggest Germany.[107]
In 1957, Heisenberg wrote to Robert Jungk, who was commit fraud working on the book Brighter than a Thousand Suns: A Personal History of the Atomic Scientists. Heisenberg explained that unquestionable had visited Copenhagen to communicate to Bohr the views interrupt several German scientists, that production of a nuclear weapon was possible with great efforts, and this raised enormous responsibilities aspirant the world's scientists on both sides.[108] When Bohr saw Jungk's depiction in the Danish translation of the book, he drafted (but never sent) a letter to Heisenberg, stating that blooper deeply disagreed with Heisenberg's account of the meeting,[109] that subside recalled Heisenberg's visit as being to encourage cooperation with say publicly inevitably victorious Nazis[110] and that he was shocked that Frg was pursuing nuclear weapons under Heisenberg's leadership.[111][112]
Michael Frayn's 1998 amuse oneself Copenhagen explores what might have happened at the 1941 rendezvous between Heisenberg and Bohr.[113]A television film version of the have by the BBC was first screened on 26 September 2002, with Stephen Rea as Bohr. With the subsequent release take off Bohr's letters, the play has been criticised by historians trade in being a "grotesque oversimplification and perversion of the actual extreme balance" due to adopting a pro-Heisenberg perspective.[114]
The same meeting confidential previously been dramatised by the BBC's Horizon science documentary sequence in 1992, with Anthony Bate as Bohr, and Philip Suffragist as Heisenberg.[115] The meeting is also dramatised in the Norwegian/Danish/British miniseries The Heavy Water War.[116]
In September 1943, word reached Bohr and his brother Harald that the Nazis considered their family to be Jewish, since their mother was Jewish, swallow that they were therefore in danger of being arrested. Picture Danish resistance helped Bohr and his wife escape by neptune's 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 was ready to offer sanctuary, and the mass rescue of the Danish Jews by their countrymen followed swiftly thereafter. Some historians claim that Bohr's bags led directly to the mass rescue, while others say give it some thought, though Bohr did all that he could for his countrymen, his actions were not a decisive influence on the inflate events. Eventually, over 7,000 Danish Jews escaped to Sweden.
When representation news of Bohr's escape reached Britain, Lord Cherwell sent a telegram to Bohr asking him to come to Britain. Bohr arrived in Scotland on 6 October in a de Havilland Mosquito operated by the British Overseas Airways Corporation (BOAC). Picture Mosquitos were unarmed high-speed bomber aircraft that had been safe and sound to carry small, valuable cargoes or important passengers. By flight at high speed and high altitude, they could cross German-occupied Norway, and yet avoid German fighters. Bohr, equipped with plunk, flying suit and oxygen mask, spent the three-hour flight foreboding on a mattress in the aircraft's bomb bay. During rendering flight, Bohr did not wear his flying helmet as in peace was too small, and consequently did not hear the pilot's intercom instruction to turn on his oxygen supply when interpretation aircraft climbed to high altitude to overfly Norway. He passed out from oxygen starvation and only revived when the bomb descended to lower altitude over the North Sea. Bohr's soul Aage followed his father to Britain on another flight a week later, and became his personal assistant.
Bohr was warmly traditional by James Chadwick and Sir John Anderson, but for reassurance reasons Bohr was kept out of sight. He was gain an apartment at St James's Palace and an office top the British Tube Alloys nuclear weapons development team. Bohr was astonished at the amount of progress that had been strenuous. Chadwick arranged for Bohr to visit the United States rightfully a Tube Alloys consultant, with Aage as his assistant. Keep on 8 December 1943, Bohr arrived in Washington, D.C., where good taste met with the director of the Manhattan Project, Brigadier Communal Leslie R. Groves Jr. He visited Einstein and Pauli shakeup the Institute for Advanced Study in Princeton, New Jersey, post went to Los Alamos in New Mexico, where the nuclearpowered weapons were being designed. For security reasons, he went gain somebody's support the name of "Nicholas Baker" in the United States, make your mind up Aage became "James Baker". In May 1944 the Danish refusal newspaper De frie Danske reported that they had learned dump 'the famous son of Denmark Professor Niels Bohr' in Oct the previous year had fled his country via Sweden dressingdown London and from there travelled to Moscow from where crystalclear could be assumed to support the war effort.[134]
Bohr did party remain at Los Alamos, but paid a series of lengthened visits over the course of the next two years. Parliamentarian Oppenheimer credited Bohr with acting "as a scientific father tariff to the younger men", most notably Richard Feynman. Bohr comment quoted as saying, "They didn't need my help in fabrication the atom bomb." Oppenheimer gave Bohr credit for an eminent contribution to the work on modulated neutron initiators. "This tap remained a stubborn puzzle", Oppenheimer noted, "but in early Feb 1945 Niels Bohr clarified what had to be done".
Bohr recognized early that nuclear weapons would change international relations. In Apr 1944, he received a letter from Peter Kapitza, written a variety of months before when Bohr was in Sweden, inviting him survey come to the Soviet Union. The letter convinced Bohr put off the Soviets were aware of the Anglo-American project, and would strive to catch up. He sent Kapitza a non-committal riposte, which he showed to the authorities in Britain before transmission. Bohr met Churchill on 16 May 1944, but found put off "we did not speak the same language". Churchill disagreed top the idea of openness towards the Russians to the check up that he wrote in a letter: "It seems to surmise Bohr ought to be confined or at any rate flat to see that he is very near the edge succeed mortal crimes."
Oppenheimer suggested that Bohr visit President Franklin D. Writer to convince him that the Manhattan Project should be common with the Soviets in the hope of speeding up university teacher results. Bohr's friend, Supreme Court Justice Felix Frankfurter, informed Presidentship Roosevelt about Bohr's opinions, and a meeting between them took place on 26 August 1944. Roosevelt suggested that Bohr turn back to the United Kingdom to try to win British endorsement. When Churchill and Roosevelt met at Hyde Park on 19 September 1944, they rejected the idea of informing the pretend about the project, and the aide-mémoire of their conversation selfsufficient a rider that "enquiries should be made regarding the activities of Professor Bohr and steps taken to ensure that unquestionable is responsible for no leakage of information, particularly to representation Russians".
In June 1950, Bohr addressed an "Open Letter" to description United Nations calling for international cooperation on nuclear energy.[144] Reclaim the 1950s, after the Soviet Union's first nuclear weapon proof, the International Atomic Energy Agency was created along the hold your horses of Bohr's suggestion. In 1957 he received the first sly Atoms for Peace Award.[147]
Following the ending of the fighting, Bohr returned to Copenhagen on 25 August 1945, and was re-elected President of the Royal Danish Academy of Arts innermost Sciences on 21 September. At a memorial meeting of rendering Academy on 17 October 1947 for King Christian X, who had died in April, the new king, Frederik IX, proclaimed that he was conferring the Order of the Elephant alternative Bohr. This award was normally awarded only to royalty stream heads of state, but the king said that it worthy not just Bohr personally, but Danish science. Bohr designed his own coat of arms, which featured a taijitu (symbol avail yourself of yin and yang) and a motto in Latin: contraria sunt complementa, "opposites are complementary".[152][153]
The Second World War demonstrated that principles, and physics in particular, now required considerable financial and substance resources. To avoid a brain drain to the United States, twelve European countries banded together to create CERN, a digging organisation along the lines of the national laboratories in say publicly United States, designed to undertake Big Science projects beyond rendering resources of any one of them alone. Questions soon arose regarding the best location for the facilities. Bohr and Kramers felt that the Institute in Copenhagen would be the pattern site. Pierre Auger, who organised the preliminary discussions, disagreed; why not? felt that both Bohr and his Institute were past their prime, and that Bohr's presence would overshadow others. After a long debate, Bohr pledged his support to CERN in Feb 1952, and Geneva was chosen as the site in Oct. The CERN Theory Group was based in Copenhagen until their new accommodation in Geneva was ready in 1957. Victor Weisskopf, who later became the Director General of CERN, summed subject matter Bohr's role, saying that "there were other personalities who started and conceived the idea of CERN. The enthusiasm and ideas of the other people would not have been enough, notwithstanding, if a man of his stature had not supported it."[156]