Bruger:Metalindustrien/Kasse3

• Niels Bohr
• en:Niels Bohr
• translate

Tidlige år

Bohr blev født i København 7. oktober 1885 ind i Bohr-familien af videnskabsfolk og forskere, som det andet barn af Christian Bohr, der var professor i fysiologi ved Københavns Universitet, og Ellen Bohr (født Adler), der var datter af David B. Adler fra Adler-familien, en velhavende jødisk familie af bankfolk. Han havde en storesøster, Jenny, og en lillebror, Harald. Jenny blev lærerinde, mens Harald blev matematiker og fodboldspiller, der spillede på Danmarks fodboldlandshold ved Sommer-OL 1908 i London. Niels var ligeledes en passioneret fodboldspiller og de to brødre spillede flere kampe for det københavnske fodboldhold Akademisk Boldklub, med Niels som målmand.

Bohr som ung mand

Bohr begyndte på Gammelholm Forberedelsesskole da han var syv år gammel. I 1903 blev Bohr påbegyndte han sin bacheloruddannelse på Københavns Universitet. Hans hovedfag var fysik, som han studerede under professor Christian Christiansen, der på daværende tidspunkt var universitetets eneste fysikprofessor. Han studerede også astronomy og matematik under professor Thorvald Thiele og filosofi under professor Harald Høffding, der havde et venskab med Bohrs far.

I 1905 sponsorerede Videnskabernes Selskab en guldmedaljekonkurrence, der skulle undersøge en metode til måling af væskers overfladespænding, som var blevet fremført af Lord Rayleigh i 1879. Dette involverede måling af oscillationsfrekvensen af radius på en vandstråle. Bohr udførte en række eksperimenter i sin fars laboratorium på universitetet, da universitetet på daværende tidspunkt ikke selv havde et fysiklaboratorium. Han blev nødt til at fremstille sine egne glasartikler for at kunne færdiggøre sine eksperimenter, og skabte på denne måde reagensglas med de nødvendige elliptiske tværsnit. I sidste ende gik han længere end den oprindelige opgave og indarbejdede forbedringer i både Rayleigh's teori og metode ved at tage hensyn til vandets viskositet og arbejde med begrænsede amplituder i stedet for uendelige små. Hans svar, som han indsendte i sidste øjeblik, vandt konkurrencen. Han indsendte senere en forbedret version af svaret til Royal Society i London til udgivelse i Philosophical Transactions of the Royal Society.

Harald fik, som den første af de to Bohr-brødre, en magistergrad, hvilket han opnåede i matematik i april 1909. Ni måneder senere opnåede Niels sin magistergrad i metallernes elektronteori, et emne som han blev tildelt af sin vejleder, Christiansen. Bohr videreudviklede efterfølgende sin artikel til sin langt større dr. phil. Han undersøgte den eksisterende faglitteratur på området og valgte en model fremsat af Paul Drude og uddybet af Hendrik Lorentz, hvori elektronerne i et metal menes at opføre sig som en gas. Bohr udvidede Lorentz's model, men var stadig ikke i stand til at forklare fænomener såsom Hall-effekten og konkluderede at elektronteorien ikke kunne forklare metallers magnetiske egenskaber fuldt ud. Afhandlingen blev accepteret i april 1911 og Bohr forsvarede den 13. maj. Harald havde modtaget sin doktorgrad året før. Bohrs afhandling var banebrydende på områder, men fik ikke den store opmærksomhed udenfor Skandinavien da den var skrevet på dansk, hvilket på daværende tidspunkt var et krav på Københavns Universitet. Ti år senere, i 1921, ville den hollandske fysiker Hendrika Johanna van Leeuwen uafhængigt udlede en sætning af Bohrs afhandling, der i dag er kendt som Bohr-Van leeuwen-sætningen.

Bohr og Margrethe Nørlund ved deres forlovelse i 1910.

I 1910 mødte Bohr Margrethe Nørlund, matematikeren Niels Erik Nørlunds søster. Bohr meldte sig ud af Folkekirken 16. april 1912 og han og Margrethe blev efterfølgende gift ved en borgerlig vielse på Slagelse Rådhus 1. august. Flere år senere fulgte hans bror Harald i Bohrs fodspor ved at forlade Folkekirken før sin vielse. Bohr og Margrethe fik seks sønner. Den ældste, Christian, døde i en sejlulykke i 1934. En anden, Harald, var alvorligt mentalt handicappet, blev anbragt på en institution som 4-årig og døde af meningitis seks år senere. En tredje søn, Aage Bohr, blev en kendt fysiker, og vandt i 1975 Nobelprisen i fysik ligesom sin far. Af de tre resterende sønner blev Hans Bohr læge, Erik Bohr blev kemiingeniør og Ernest Bohr blev advokat. Ligesom sin onkel Harald blev Ernest Bohr også olympisk atlet og spillede på det danske landshold i hockey i Sommer-OL 1948 i London.

Fysik

Bohrs atommodel

Hovedartikel: Bohrs atommodel.

I september 1911 rejste Bohr til England på et stipendium fra Carlsbergfondet, og England kom dermed til at danne rammen om det meste af Bohrs teoretiske arbejde på atomer og molekylers struktur. Her mødte han J. J. Thomson fra Cavendish Laboratory og Trinity College (Cambridge), og skønt Bohr deltog i forelæsninger om elektromagnetisme givet af James Jeans og Joseph Larmor og selv forskede kortvarigt i katodestråler gjorde hans forskning ikke indtryk på Thomson. Bohr havde mere held med yngre fysikere såsom australske William Lawrence Bragg og New Zealandske Ernest Rutherford, der i 1911 havde fremsat en atommodel med en lille central kerne, og dermed havde udfordret Thomsons rosinbollemodel fra 1904. Rutherford inviterede Bohr til at udføre postdoc-arbejde ved Victoria University of Manchester, hvor Bohr mødte George de Hevesy og Charles Galton Darwin (som Bohr omtalte som "den rigtige Darwins barnebarn").

Bohr vendte hjem til Danmark i juli 1912 til sit bryllup og rejste rundt i England og Skotland på bryllupsrejse. Herefter blev han privatdocent ved Københavns Universitet og begyndte at afholde forelæsninger om termodynamik. Martin Knudsen anbefalede Bohr til en docentstilling, hvilket blev godkendt i juli 1913, hvorefter Bohr begyndte at undervise medicinstuderende. Hans tre artikler, der senere blev kendt som "trilogien", blev udgivet i Philosophical Magazine i juli, september og november samme år. Han tilpassede Rutherfords atomstruktur Max Plancks kvanteteori og skabte herved det, der blev kendt som Bohrs atommodel.

Planetariske atommodeller var ikke nye, men Bohrs anvendelse af dem var. Bohr tog udgangspunkt i Darwins artikel fra 1912 om elektronernes rolle i interaktionen mellem alfapartikler og en kerne, og fremsatte den teori at elektronerne rejser i omløbsbaner (kaldet "skaller") af kvantiserede "stationære tilstande" rundt om atomets kerne for at stabilisere atomet. Det var dog først i hans artikel fra 1921 at han påviste at hvert grundstofs kemiske egenskaber i høj grad blev bestemt af antallet af elektroner i dets atoms ydre skaller. Han introducerede ideen om at et elektron kunne falde fra en skal med højere energi til en lavere, og i den proces udskille et kvantum af diskret energi. Dette kom til at danne grundlaget for den tidlige kvanteteori.

Bohrs atommodel af brintatomet. Et negativt-ladet elektron, begrænset til en atomorbital, kredser om en lille, positivt-ladet kerne; et kvantespring mellem kredsløbene medfører udskilning eller absorbering af en mængde elektromagnetisk stråling.

Udviklingen af atommodeller i det 20. århundrede: Thomson, Rutherford, Bohr, Heisenberg/Schrödinger

I 1885 fandt Johann Balmer på Balmer-serien til at beskrive brintatomets synlige spektrallinjer:

${\frac {1}{\lambda }}=R_{\mathrm {H} }\left({\frac {1}{2^{2}}}-{\frac {1}{n^{2}}}\right)\quad {\text{for}}\ n=3,4,5,...$

hvor λ er det absorberede eller udsendte lys' bølgelængde og R_H er Rydbergkonstanten. Balmers formel blev senere underbygget af opdagelsen af yderligere spektrallinjer, men i de mellemliggende 30 år kunne ingen forklare hvorfor den virkede. I den første artikel i hans trilogi var Bohr i stand til at aflede den fra sin model:

$R_{Z}={2\pi ^{2}m_{e}Z^{2}e^{4} \over h^{3}}$

hvor m_e er elektronens masse, e er dets ladning, h er Plancks konstant og Z er atomets atomnummer (hvilket for brint er 1).

Modellens første forhindring var Pickering-serien, linjer der ikke passede i Balmers formel. Da Bohr blev udfordret på dette punkt af Alfred Fowler svarede han at de skyldtes ioniseret helium, dvs. heliumatomer med kun en enkelt elektron. Bohrs atommodel fungerede med sådanne ioner. Mange ældre fysikere, såsom Thomson, Rayleigh og Hendrik Lorentz, brød sig ikke om trilogien, men den yngre generation, heriblandt Rutherford, David Hilbert, Albert Einstein, Enrico Fermi, Max Born og Arnold Sommerfeld så den som et gennembrud. Den generelle accept af trilogiens udsagn afhang helt og holdents af dens evne til at forklare fænomener, der hindrede andre modeller, og forudsige resultater, der efterfølgende kunne bekræftes af eksperimenter. I dag er Bohrs atommodel blevet afløst af nyere modeller, men den er stadig den bedst-kendte atommodel i verden og figurerer ofte i fysik- og kemibøger i diverse uddannelsesinstitutioner.

Bohr brød sig ikke om at undervise medicinstuderende. Han besluttede sig for at vende tilbage til Manchester, hvor Rutherford havde tilbudt ham et job som reader som erstatning for Darwin, hvis ansættelsestid var udløbet. Bohr accepterede. Han tog orlov fra Københavns Universitet, og påbegyndte sin orlov med en ferie i Sydtyrol med sin bror Harald og tante Hanna Adler. Dér besøgte han Göttingen Universitet og Ludwig-Maximilians-Universität München, hvor han mødte Sommerfeld og afholdt seminarer på baggrund af trilogien. 1. verdenskrig brød ud mens de opholdt sig i Tyrol, hvilket komplicerede rejsen tilbage til Danmark og Bohrs efterfølgende rejse med Margrethe til England, hvor han ankom i oktober 1914. De forblev i England frem til juli 1916, hvor Bohr i mellemtiden var blevet udpeget til at lede forskningen i teoretisk fysik på Københavns Universitet - en stilling der blev oprettet specielt til ham. Hans docentat blev samtidig afskaffet, så han var stadig nødt til at undervise medicinstuderende. De nye professorer blev formelt introduceret for kong Christian 10., som var henrykt over at møde en så berømt fodboldspiller.

Institut for Teoretisk Fysik

I april 1917 begyndte Bohr at arbejde for at få oprettet et Institut for Teoretisk Fysik på Københavns Universitet. Han blev støttet af den danske regering og Carlsbergfondet, og modtog anseelige donationer fra både private og industridonorer - heraf mange jødiske. Lovgivning til at etablere instituttet blev vedtaget i 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 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 the institute's first publication even before it opened.

The Niels Bohr Institute, part of the University of Copenhagen

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 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 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 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 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 the Institute in Copenhagen, proposed the Bohr–Kramers–Slater theory (BKS). It was more a programme than a full physical theory, as the ideas it developed were not worked out quantitatively. 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 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, 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 is nothing else to do than to give our revolutionary efforts as honourable a funeral as possible".

Quantum mechanics

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 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 the way back, he had become, in his own words, "a prophet of the electron magnet gospel".

1927 Solvay Conference in Brussels, October 1927. Bohr is on the right in the middle row, next to Max Born.

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 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 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 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 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 a paper presented at 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 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 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 to be used for life by the Dane who had made the most prominent contribution to science, literature or the arts, as an honorary residence (dansk: 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 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 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 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".

Philosophy

Heisenberg said of Bohr that he 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 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 the content of a theory while accepting its general premises and structure.

Quantum physics

Bohr and Albert Einstein (image from 1925) had a long-running debate about the metaphysical implication of quantum physics.

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 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 as saying that there is "no quantum world" but only an "abstract quantum physical description". This was not said by Bohr, but rather by Aage Petersen attempting to summarize Bohr's philosophy in a reminiscence after Bohr's 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 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 the concepts of classical physics are merely a refinement of them. Therefore, for Bohr, we need to use classical concepts to describe experiments that deal with the quantum world. Bohr writes:

It is decisive to recognize that, however far the phenomena transcend the scope of classical physical explanation, the 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, 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 in which classical ideas are a priori concepts that the mind imposes on sense impressions); 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 which thus must be described classically). These explanations are not mutually exclusive, and at times Bohr seems to emphasize 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 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

the truth conditions of sentences ascribing 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 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 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 (though quite unintelligible and inaccessible to us) in addition to the classical ones being manifested in measurement."

Nazism and Second World War

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 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 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 the Fund for Finnish Relief, 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.

Bohr kept the Institute running, but all the foreign scholars departed.

Meeting with Heisenberg

Werner Heisenberg (left) with Bohr at the Copenhagen Conference in 1934

Bohr 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 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 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 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 never understood the purpose of Heisenberg's visit, was shocked by Heisenberg's opinion that Germany would win the war, and that atomic weapons could be decisive.

Michael Frayn's 1998 play Copenhagen explores what might have happened at the 1941 meeting between Heisenberg and Bohr. A BBC television film version of the play was first screened on 26 September 2002, with Stephen Rea as Bohr, Daniel Craig as Heisenberg, and Francesca Annis as Margrethe Bohr. 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 dramatized in the Norwegian/Danish/British miniseries The Heavy Water War.

Manhattan Project

In September 1943, word reached Bohr and his brother Harald that 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 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.

Bohr with James Franck, Albert Einstein and Isidor Isaac Rabi (LR)

When the 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). The Mosquitos were unarmed high-speed bomber aircraft that had been converted to carry small, valuable cargoes or important passengers. By flying at high speed and high altitude, they could cross German-occupied Norway, and yet avoid German fighters. Bohr, equipped with parachute, flying suit and oxygen mask, spent the three-hour flight lying on a mattress in the aircraft's bomb bay. During the flight, Bohr did not wear his flying helmet as it was too small, and consequently did not hear the pilot's intercom instruction to turn on his oxygen supply when the aircraft climbed to high altitude to overfly Norway. He passed out from oxygen starvation and only revived when the aircraft descended to lower altitude over the North Sea. Bohr's son Aage followed his father to Britain on another flight a week later, and became his personal assistant.

Bohr was warmly received by James Chadwick and Sir John Anderson, but for security reasons Bohr was kept out of sight. He was given an apartment at St James's Palace and an office with the British Tube Alloys nuclear weapons development team. Bohr was astonished at the amount of progress that had been made. Chadwick arranged for Bohr to visit the United States as a Tube Alloys consultant, with Aage as his assistant. On 8 December 1943, Bohr arrived in Washington, D.C., where he met with the director of the Manhattan Project, Brigadier General Leslie R. Groves Jr. He visited Einstein and Pauli at the Institute for Advanced Study in Princeton, New Jersey, and went to Los Alamos in New Mexico, where the nuclear weapons were being designed. For security reasons, he went under the name of "Nicholas Baker" in the United States, while Aage became "James Baker". In May 1944 the Danish resistance newspaper De frie Danske reported that they had learned that 'the famous son of Denmark Professor Niels Bohr' in October the previous year had fled his country via Sweden to London and from there travelled to Moscow from where he could be assumed to support the war effort.

Bohr did not remain at Los Alamos, but paid a series of extended visits over the course of the next two years. Robert Oppenheimer credited Bohr with acting "as a scientific father figure to the younger men", most notably Richard Feynman. Bohr is quoted as saying, "They didn't need my help in making the atom bomb." Oppenheimer gave Bohr credit for an important contribution to the work on modulated neutron initiators. "This device remained a stubborn puzzle," Oppenheimer noted, "but in early February 1945 Niels Bohr clarified what had to be done."

Bohr recognised early that nuclear weapons would change international relations. In April 1944, he received a letter from Peter Kapitza, written some months before when Bohr was in Sweden, inviting him to come to the Soviet Union. The letter convinced Bohr that the Soviets were aware of the Anglo-American project, and would strive to catch up. He sent Kapitza a non-committal response, which he showed to the authorities in Britain before posting. Bohr met Churchill on 16 May 1944, but found that "we did not speak the same language". Churchill disagreed with the idea of openness towards the Russians to the point that he wrote in a letter: "It seems to me Bohr ought to be confined or at any rate made to see that he is very near the edge of mortal crimes."

Oppenheimer suggested that Bohr visit President Franklin D. Roosevelt to convince him that the Manhattan Project should be shared with the Soviets in the hope of speeding up its results. Bohr's friend, Supreme Court Justice Felix Frankfurter, informed President Roosevelt about Bohr's opinions, and a meeting between them took place on 26 August 1944. Roosevelt suggested that Bohr return to the United Kingdom to try to win British approval. When Churchill and Roosevelt met at Hyde Park on 19 September 1944, they rejected the idea of informing the world about the project, and the aide-mémoire of their conversation contained a rider that "enquiries should be made regarding the activities of Professor Bohr and steps taken to ensure that he is responsible for no leakage of information, particularly to the Russians".

In June 1950, Bohr addressed an "Open Letter" to the United Nations calling for international cooperation on nuclear energy. In the 1950s, after the Soviet Union's first nuclear weapon test, the International Atomic Energy Agency was created along the lines of Bohr's suggestion. In 1957 he received the first ever Atoms for Peace Award.

Later years

Bohr's coat of arms, 1947. Argent, a taijitu (yin-yang symbol) Gules and Sable. Motto: Contraria sunt complementa ("opposites are complementary").

With the war now ended, Bohr returned to Copenhagen on 25 August 1945, and was re-elected President of the Royal Danish Academy of Arts and Sciences on 21 September. At a memorial meeting of the Academy on 17 October 1947 for King Christian X, who had died in April, the new king, Frederick IX, announced that he was conferring the Order of the Elephant on Bohr. This award was normally awarded only to royalty and heads of state, but the king said that it honoured not just Bohr personally, but Danish science. Bohr designed his own coat of arms which featured a taijitu (symbol of yin and yang) and a motto in latin: contraria sunt complementa, "opposites are complementary".

The Second World War demonstrated that science, and physics in particular, now required considerable financial and material resources. To avoid a brain drain to the United States, twelve European countries banded together to create CERN, a research organisation along the lines of the national laboratories in the United States, designed to undertake Big Science projects beyond the 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 ideal site. Pierre Auger, who organised the preliminary discussions, disagreed; he 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 February 1952, and Geneva was chosen as the site in October. 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 up 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, however, if a man of his stature had not supported it."

Meanwhile, Scandinavian countries formed the Nordic Institute for Theoretical Physics in 1957, with Bohr as its chairman. He was also involved with the founding of the Research Establishment Risø of the Danish Atomic Energy Commission, and served as its first chairman from February 1956.

Bohr died of heart failure at his home in Carlsberg on 18 November 1962. He was cremated, and his ashes were buried in the family plot in the Assistens Cemetery in the Nørrebro section of Copenhagen, along with those of his parents, his brother Harald, and his son Christian. Years later, his wife's ashes were also interred there. On 7 October 1965, on what would have been his 80th birthday, the Institute for Theoretical Physics at the University of Copenhagen was officially renamed to what it had been called unofficially for many years: the Niels Bohr Institute.

Accolades

Se også: List of things named after Niels Bohr.

Bohr received numerous honours and accolades. In addition to the Nobel Prize, he received the Hughes Medal in 1921, the Matteucci Medal in 1923, the Franklin Medal in 1926, the Copley Medal in 1938, the Order of the Elephant in 1947, the Atoms for Peace Award in 1957 and the Sonning Prize in 1961. He became foreign member of the Royal Netherlands Academy of Arts and Sciences in 1923, and of the Royal Society in 1926. The Bohr model's semicentennial was commemorated in Denmark on 21 November 1963 with a postage stamp depicting Bohr, the hydrogen atom and the formula for the difference of any two hydrogen energy levels: $h\nu =\epsilon _{2}-\epsilon _{1}$. Several other countries have also issued postage stamps depicting Bohr. In 1997, the Danish National Bank began circulating the 500-krone banknote with the portrait of Bohr smoking a pipe. On 7 October 2012, in celebration of Niels Bohr's 127th birthday, a Google Doodle depicting the Bohr model of the hydrogen atom appeared on Google's home page. An asteroid, 3948 Bohr, was named after him, as was the Bohr lunar crater and bohrium, the chemical element with atomic number 107.

Bibliography

The Theory of Spectra and Atomic Constitution (Drei Aufsätze über Spektren und Atombau), 1922

• Bohr, Niels (1922). The Theory of Spectra and Atomic Constitution; three essays. Cambridge: Cambridge University Press.
• —— (2008). Nielsen, J. Rud (red.). Volume 1: Early Work (1905–1911). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Hoyer, Ulrich (red.). Volume 2: Work on Atomic Physics (1912–1917). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Nielsen, J. Rud (red.). Volume 3: The Correspondence Principle (1918–1923). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Nielsen, J. Rud (red.). Volume 4: The Periodic System (1920–1923). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Stolzenburg, Klaus (red.). Volume 5: The Emergence of Quantum Mechanics (mainly 1924–1926). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Kalckar, Jørgen (red.). Volume 6: Foundations of Quantum Physics I (1926–1932). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Kalckar, Jørgen (red.). Volume 7: Foundations of Quantum Physics I (1933–1958). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Thorsen, Jens (red.). Volume 8: The Penetration of Charged Particles Through Matter (1912–1954). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Peierls, Rudolf (red.). Volume 9: Nuclear Physics (1929–1952). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Favrholdt, David (red.). Volume 10: Complementarity Beyond Physics (1928–1962). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Aaserud, Finn (red.). Volume 11: The Political Arena (1934–1961). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Aaserud, Finn (red.). Volume 12: Popularization and People (1911–1962). Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.
• —— (2008). Aaserud, Finn (red.). Volume 13: Cumulative Subject Index. Niels Bohr Collected Works. Amsterdam: Elsevier. ISBN 978-0-444-53286-2. OCLC 272382249.

See also

• EPR paradox

References

• Aaserud, Finn (2006). Kokowski, M. (red.). Niels Bohr's Mission for an 'Open World' (PDF). Proceedings of the 2nd ICESHS. Cracow. s. 706-709. Hentet 26 juni 2011.{{cite conference}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• Aaserud, Finn; Heilbron, J. L. (2013). Love, Literature and the Quantum Atom: Niels Bohr's 1913 Trilogy Revisited. Oxford: Oxford University Press. ISBN 978-0-19-968028-3.
• Bohr, Niels (1928). "The Quantum Postulate and the Recent Development of Atomic Theory". Nature. 121 (3050): 580-590. Bibcode:1928Natur.121..580B. doi:10.1038/121580a0. S2CID 4097746.
• Bohr, Niels (1985) [1922]. "Nobel Prize Lecture: The Structure of the Atom (excerpts)". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 91–97. ISBN 978-0-674-62415-3.
• Bohr, Niels (1985) [1949]. "The Bohr-Einstein Dialogue". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 121–140. ISBN 978-0-674-62415-3.
  • Excerpted from: Bohr, Niels (1949). "Discussions with Einstein on Epistemological Problems in Atomic Physics". I Schilpp, Paul Arthur (red.). Albert Einstein: Philosopher-Scientist. Evanston, Illinois: Library of Living Philosophers. s. 208-241.
• Camilleri, K.; Schlosshauer, M. (2015). "Niels Bohr as Philosopher of Experiment: Does Decoherence Theory Challenge Bohr's Doctrine of Classical Concepts?". Studies in History and Philosophy of Modern Physics. 49: 73-83. arXiv:1502.06547. Bibcode:2015SHPMP..49...73C. doi:10.1016/j.shpsb.2015.01.005. S2CID 27697360.
• Cockroft, John D. (1 november 1963). "Niels Henrik David Bohr. 1885–1962". Biographical Memoirs of Fellows of the Royal Society. 9 (10): 36-53. doi:10.1098/rsbm.1963.0002.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• Favrholdt, David (1992). Niels Bohr's Philosophical Background. Copenhagen: Munksgaard. ISBN 978-87-7304-228-1.
• Faye, Jan (1991). Niels Bohr: His Heritage and Legacy. Dordrecht: Kluwer Academic Publishers. ISBN 978-0-7923-1294-9.
• Gowing, Margaret (1985). "Niels Bohr and Nuclear Weapons". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 266–277. ISBN 978-0-674-62415-3.
• Heilbron, John L. (1985). "Bohr's First Theories of the Atom". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 33–49. ISBN 978-0-674-62415-3.
• Heisenberg, Elisabeth (1984). Inner Exile: Recollections of a Life With Werner Heisenberg. Boston: Birkhäuser. ISBN 978-0-8176-3146-8.
• Hilberg, Raul (1961). The Destruction of the European Jews. Vol. 2. New Haven, Connecticut: Yale University Press. ISBN 978-0-300-09557-9.
• Honner, John (marts 1982). "The Transcendental Philosophy of Niels Bohr". Studies in History and Philosophy of Science Part A. 13 (1): 1-29. Bibcode:1982SHPSA..13....1H. doi:10.1016/0039-3681(82)90002-4. ISSN 0039-3681.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• Hund, Friedrich (1985). "Bohr, Göttingen, and Quantum Mechanics". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 71–75. ISBN 978-0-674-62415-3.
• Jammer, Max (1989). The Conceptual Development of Quantum Mechanics. Los Angeles: Tomash Publishers. ISBN 978-0-88318-617-6. OCLC 19517065.
• Jones, R . V. (1978). Most Secret War. London: Hamilton. ISBN 978-0-241-89746-1. OCLC 3717534.
• Jones, R. V. (1985). "Meetings in Wartime and After". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 278–287. ISBN 978-0-674-62415-3.
• Kennedy, P. J. (1985). "A Short Biography". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 3–15. ISBN 978-0-674-62415-3.
• Kieler, Jørgen (2007). Resistance Fighter: A Personal History of the Danish Resistance. Translated from the Danish by Eric Dickens. Jerusalem: Gefen Publishing House. ISBN 978-965-229-397-8.
• Kragh, Helge (1985). "The Theory of the Periodic System". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 50–67. ISBN 978-0-674-62415-3.
• Kragh, Helge (2012). Niels Bohr and the quantum atom: the Bohr model of atomic structure, 1913–1925. Oxford: Oxford University Press. ISBN 978-0-19-965498-7. OCLC 769989390.
• MacKinnon, Edward (1985). "Bohr on the Foundations of Quantum Theory". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 101–120. ISBN 978-0-674-62415-3.
• Medawar, Jean; Pyke, David (2001). Hitler's Gift: The True Story of the Scientists Expelled by the Nazi Regime. New York: Arcade Publishing. ISBN 978-1-55970-564-6.
• Mermin, N. David (2004). "What's Wrong With This Quantum World?". Physics Today. 52 (2): 10. Bibcode:2004PhT....57b..10M. doi:10.1063/1.1688051.
• Pais, Abraham (1991). Niels Bohr's Times, In Physics, Philosophy and Polity. Oxford: Clarendon Press. ISBN 978-0-19-852049-8.
• Perović, Slobodan (2021). From data to quanta : Niels Bohr's vision of physics. Chicago London: The University of Chicago Press. ISBN 978-0-226-79833-2. OCLC 1237650827.
• Powers, Thomas (1993). Heisenberg's War: The Secret History of the German Bomb. New York: Knopf. ISBN 978-0-316-71623-9.
• Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon and Schuster. ISBN 978-0-671-44133-3.
• Richardson, W. Mark; Wildman, Wesley J., red. (1996). Religion and Science: History, Method, Dialogue. London, New York: Routledge. ISBN 978-0-415-91667-7.
• Rife, Patricia (1999). Lise Meitner and the Dawn of the Nuclear Age. Boston: Birkhäuser. ISBN 978-0-8176-3732-3.
• Rozental, Stefan (1967). Niels Bohr: His Life and Work as Seen by his Friends and Colleagues. Amsterdam: North-Holland. ISBN 978-0-444-86977-7. Previously published by John Wiley & Sons in 1964.{{cite book}}: CS1-vedligeholdelse: postscript (link)
• Stadtler, Bea; Morrison, David Beal; Martin, David Stone (1995). The Holocaust: A History of Courage and Resistance. West Orange, New Jersey: Behrman House. ISBN 978-0-87441-578-0.
• Stewart, Melville Y. (2010). Science and Religion in Dialogue, Two Volume Set. Maiden, Massachusetts: John Wiley & Sons. ISBN 978-1-4051-8921-7.
• Stuewer, Roger H. (1985). "Niels Bohr and Nuclear Physics". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 197–220. ISBN 978-0-674-62415-3.
• Thirsk, Ian (2006). De Havilland Mosquito: An Illustrated History, Volume 2. Manchester: MBI Publishing Company. ISBN 978-0-85979-115-1.
• The Conferences at Quebec 1944. Foreign Relations of the United States. Washington, D.C.: U.S. Government Printing Office. 1972. OCLC 631921397.
• Wheeler, John A. (1985). "Physics in Copenhagen in 1934 and 1935". I French, A. P.; Kennedy, P. J. (red.). Niels Bohr: A Centenary Volume. Cambridge, Massachusetts: Harvard University Press. s. 221–226. ISBN 978-0-674-62415-3.
• The Coins and Banknotes of Denmark (PDF). Danmarks Nationalbank. 2005. ISBN 978-87-87251-55-6. Arkiveret fra originalen (PDF) 23 maj 2011. Hentet 7 september 2010.{{cite book}}: CS1-vedligeholdelse: Dato automatisk oversat (link)

Further reading

• Aaserud, Finn (februar 2002). "Release of documents relating to 1941 Bohr-Heisenberg meeting". Niels Bohr Archive. Arkiveret fra originalen 21 oktober 2012. Hentet 2 marts 2013.{{cite web}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• Blaedel, Niels (1988). Harmony and Unity: The Life of Niels Bohr. Madison, Wisconsin: Science Tech. ISBN 978-0-910239-14-1. OCLC 17411890.
• Feilden, Tom (3 februar 2010). "The Gunfighter's Dilemma". news.bbc.co.uk. Hentet 2 marts 2013.{{cite news}}: CS1-vedligeholdelse: Dato automatisk oversat (link) Bohr's researches on reaction times.
• Moore, Ruth (1966). Niels Bohr: The Man, His Science, and the World They Changed. New York: Knopf. ISBN 978-0-262-63101-3. OCLC 712016.
• Ottaviani, Jim; Purvis, Leland (2004). Suspended in Language: Niels Bohr's Life, Discoveries, and the Century He Shaped. Ann Arbor, Michigan: G.T. Labs. ISBN 978-0-9660106-5-7. OCLC 55739245.
• Frayn, Michael (2000). Copenhagen. New York: Anchor Books. ISBN 978-0-413-72490-8. OCLC 44467534.
• Segrè, Gino (2007). Faust in Copenhagen: A Struggle for the Soul of Physics. New York: Viking. ISBN 978-0-670-03858-9. OCLC 76416691.
• Vilhjálmsson, Vilhjálmur Örn; Blüdnikow, Bent (2006). "Rescue, Expulsion, and Collaboration: Denmark's Difficulties with its World War II Past". Jewish Political Studies Review. 18: 3-4. ISSN 0792-335X. Hentet 29 juni 2011.{{cite journal}}: CS1-vedligeholdelse: Dato automatisk oversat (link)

External links

Søsterprojekter med yderligere information: Billeder og medier fra Wikimedia Commons Opslag i Wikiordbogen

• Niels Bohr Archive
• "The Bohr-Heisenberg meeting in September 1941". American Institute of Physics. Hentet 2 marts 2013.{{cite web}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• "Resources for Frayn's Copenhagen: Niels Bohr". Massachusetts Institute of Technology. Hentet 9 oktober 2013.{{cite web}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• "Video – Niels Bohr (1962) : Atomic Physics and Human Knowledge". Lindau Nobel Laureate Meetings. Hentet 9 juli 2014.{{cite web}}: CS1-vedligeholdelse: Dato automatisk oversat (link)
• Author profile in the database zbMATH
• Værker af {{{navn}}} på Project Gutenberg
• Metalindustrien/Kasse3 på Internet Movie Database (engelsk)
• Newspaper clippings about Metalindustrien/Kasse3 i Pressearchiv 20. Jahrhundert fra ZBW
• Skabelon:Nobelprize including the Nobel Lecture, 11 December 1922 The Structure of the Atom
• Oral history interview transcript for Niels Bohr on 31 October 1962, American Institute of Physics, Niels Bohr Library & Archives - interviews conducted by Thomas S. Kuhn, Leon Rosenfeld, Erik Rudinger, and Aage Petersen
• Oral history interview transcript for Niels Bohr on 1 November 1962, American Institute of Physics, Niels Bohr Library & Archives
• Oral history interview transcript for Niels Bohr on 7 November 1962, American Institute of Physics, Niels Bohr Library & Archives
• Oral history interview transcript for Niels Bohr on 14 November 1962, American Institute of Physics, Niels Bohr Library & Archives
• Oral history interview transcript for Niels Bohr on 17 November 1962, American Institute of Physics, Niels Bohr Library & Archives