Editing Niels Bohr (section)

== Second World War ==

=== Assistance to refugee scholars===
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 R. von Hippel|Arthur von Hippel]] and [[Victor Weisskopf]].{{sfn|Pais|1991|pp=382–386}}

In April 1940, early in the Second World War, [[Nazi Germany]] [[Occupation of Denmark|invaded and occupied Denmark]].{{sfn|Pais|1991|p=476}} To prevent the Germans from discovering [[Max von Laue]]'s and James Franck's [[Nobel Prize medal|gold Nobel medal]]s, 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 [[Finnish Relief Fund]], and was auctioned off in March 1940, along with the medal of [[August Krogh]]. The buyer later donated the two medals to the Danish Historical Museum in [[Frederiksborg Castle]], where they are still kept,<ref>{{cite web |title=A unique gold medal |website=www.nobelprize.org |url=https://www.nobelprize.org/prizes/about/the-nobel-medals-and-the-medal-for-the-prize-in-economic-sciences/ |access-date=6 October 2019 |archive-date=11 April 2017 |archive-url= https://web.archive.org/web/20170411152140/https://historical.ha.com/itm/miscellaneous/georg-wittig-nobel-prize-medal-in-chemistry-received-in-1979-together-with-four-additional-medals/a/6165-49227.s |url-status=live }}</ref> although Bohr's medal temporarily went to space with [[Andreas Mogensen]] on [[International Space Station|ISS]] [[Expedition 70]] in 2023-2024.<ref>{{cite web |last1=Howell |first1=Elizabeth |title=Astronaut shows off vintage Nobel Prize in space — and talks 'quantum dots' ISS experiment (video) |url=https://www.space.com/international-space-station-nobel-prize-experiment |website=[[Space.com]] |date=12 December 2023}}</ref><ref>{{cite web |title=Andreas Mogensen leverer Nobelprismedalje retur til Frederiksborg |url=https://dnm.dk/pressepakke/andreas-mogensen-leverer-nobelpris-medalje-retur-til-frederiksborg/ |website=Frederiksborg |language=da-DK |date=14 June 2024}}</ref>

Bohr kept the Institute running, but all the foreign scholars departed.{{sfn|Pais|1991|pp=480–481}}

=== Meeting with Heisenberg ===
[[File:Heisenbergbohr.jpg|thumb|right|Werner Heisenberg (left) with Bohr at the Copenhagen Conference in 1934|alt=A young man in a white shirt and tie and an older man in suit and tie sit at a table, on which there is a tea pot, plates, cups and saucers and beer bottles.]]
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.{{sfn|Gowing|1985|pp=267–268}} 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.{{sfn|Heisenberg|1984|p=77}} [[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.<ref>{{cite web |author=Portal Jutarnji.hr |date=19 March 2006 |url=http://jutarnji.hr/clanak/art-2006,3,19,supek_intervju,17440.jl?artpg=1 |title=Moj život s nobelovcima 20. stoljeća |trans-title=My Life with the 20th century Nobel Prizewinners |work=[[Jutarnji list]] |language=hr |access-date=13 August 2007 |quote={{lang|hr |Istinu sam saznao od Margrethe, Bohrove supruge.&nbsp;... Ni Heisenberg ni Bohr nisu bili glavni junaci toga susreta nego Carl Friedrich von Weizsaecker.&nbsp;... Von Weizsaeckerova ideja, za koju mislim da je bila zamisao njegova oca koji je bio Ribbentropov zamjenik, bila je nagovoriti Nielsa Bohra da posreduje za mir između Velike Britanije i Njemačke.}} [I learned the truth from Margrethe, Bohr's wife.&nbsp;... Neither Bohr nor Heisenberg were the main characters of this encounter, but Carl Friedrich von Weizsaecker. Von Weizsaecker's idea, which I think was the brainchild of [[Ernst von Weizsäcker|his father]] who was [[Ribbentrop]]'s deputy, was to persuade Niels Bohr to mediate for peace between Great Britain and Germany.] |archive-date=28 June 2009 |archive-url=https://web.archive.org/web/20090628102407/http://jutarnji.hr/clanak/art-2006,3,19,supek_intervju,17440.jl?artpg=1  }} An interview with Ivan Supek relating to the 1941 Bohr&nbsp;– Heisenberg meeting.</ref>

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.<ref>{{cite web |url=http://www.childrenofthemanhattanproject.org/MP_Misc/Bohr_Heisenberg/bohr_2.htm |title=Letter From Werner Heisenberg to Author Robert Jungk |access-date=21 December 2006 |last=Heisenberg |first=Werner |author-link=Werner Heisenberg |publisher=The Manhattan Project Heritage Preservation Association, Inc. |url-status=usurped |archive-url = https://web.archive.org/web/20061017232033/http://childrenofthemanhattanproject.org/MP_Misc/Bohr_Heisenberg/bohr_2.htm <!-- Bot retrieved archive --> |archive-date = 17 October 2006}}</ref> When Bohr saw Jungk's depiction in the Danish translation of the book, he drafted (but never sent) a letter to Heisenberg, stating that he deeply disagreed with Heisenberg's account of the meeting,<ref>"I am greatly amazed to see how much your memory has deceived you in your letter to the author of the book"</ref> that he recalled Heisenberg's visit as being to encourage cooperation with the inevitably victorious Nazis<ref>"...you and Weizsäcker expressed your definite conviction that Germany would win and that it was therefore quite foolish for us to maintain the hope of a different outcome of the war and to be reticent as regards all German offers of cooperation'</ref> and that he was shocked that Germany was pursuing nuclear weapons under Heisenberg's leadership.<ref>"...you spoke in a manner that could only give me the firm impression that, under your leadership, everything was being done in Germany to develop atomic weapons... [...] If anything in my behaviour could be interpreted as shock, it did not derive from such reports but rather from the news, as I had to understand it, that Germany was participating vigorously in a race to be the first with atomic weapons."</ref><ref>{{cite web |url=http://www.nbarchive.dk/collections/bohr-heisenberg/ |title=Release of documents relating to 1941 Bohr-Heisenberg meeting |access-date=4 June 2007 |archive-url = https://web.archive.org/web/20170217070953/http://www.nbarchive.dk/collections/bohr-heisenberg/ |archive-date =17 February 2017|last=Aaserud |first=Finn |date=6 February 2002 |publisher=Niels Bohr Archive}}</ref>

[[Michael Frayn]]'s 1998 play ''[[Copenhagen (play)|Copenhagen]]'' explores what might have happened at the 1941 meeting between Heisenberg and Bohr.<ref>{{cite web |url=http://www.complete-review.com/reviews/fraynm/cophagen.htm |title=Copenhagen – Michael Frayn |publisher=The Complete Review |access-date=27 February 2013 |archive-date=29 April 2013 |archive-url=https://web.archive.org/web/20130429014906/http://www.complete-review.com/reviews/fraynm/cophagen.htm |url-status=live }}</ref> [[Copenhagen (2002 film)|A television film version]] of the play by the [[BBC]] was first screened on 26 September 2002, with [[Stephen Rea]] as Bohr. With the subsequent release of Bohr's letters, the play has been criticised by historians as being a "grotesque oversimplification and perversion of the actual moral balance" due to adopting a pro-Heisenberg perspective.<ref>{{cite journal|title='Copenhagen': An Exchange|first1=Gerald |last1=Holton |author-link1=Gerald Holton |first2=Jonothan |last2=Logan |first3=Thomas |last3=Powers |author-link3=Thomas Powers |first4=Michael |last4=Frayn |journal=The New York Review of Books |author-link4=Michael Frayn |publisher=The New York Review|date=11 April 2002|volume=49 |issue=6 |url=https://www.nybooks.com/articles/2002/04/11/copenhagen-an-exchange/ |access-date=18 May 2024}}</ref>

The same meeting had previously been dramatised by the BBC's ''[[Horizon (BBC TV series)|Horizon]]'' science documentary series in 1992, with [[Anthony Bate]] as Bohr, and Philip Anthony as Heisenberg.<ref>''Horizon: Hitler's Bomb'', [[BBC Two]], 24 February 1992</ref> The meeting is also dramatised in the Norwegian/Danish/British miniseries ''[[The Heavy Water War]]''.<ref>{{cite web |url=http://www.channel4.com/programmes/the-saboteurs/episode-guide/ |title=The Saboteurs – Episode Guide |publisher=Channel 4 |access-date=3 March 2017 |archive-date=3 March 2017 |archive-url=https://web.archive.org/web/20170303123755/http://www.channel4.com/programmes/the-saboteurs/episode-guide/ |url-status=live }}</ref>

=== Manhattan Project ===
In September 1943, word reached Bohr and his brother Harald that the Nazis [[Nuremberg Laws|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.{{sfn|Rozental|1967|p=168}}{{sfn|Rhodes|1986|pp=483–484}} 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.{{sfn|Rhodes|1986|pp=483–484}}{{sfn|Hilberg|1961|p=596}}{{sfn|Kieler|2007|pp=91–93}}{{sfn|Stadtler|Morrison|Martin|1995|p=136}} Eventually, over 7,000 Danish Jews escaped to Sweden.{{sfn|Pais|1991|p=479}}

[[File:Portrait of Albert Einstein, Niels Bohr, James Franck and Rabi.jpg|thumb|Bohr with (LR) [[James Franck]], [[Albert Einstein]] and [[Isidor Isaac Rabi]]]]
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).{{sfn|Jones|1985|pp=280–281}}{{sfn|Powers|1993|p=237}} 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]].{{sfn|Thirsk|2006|p=374}} 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.{{sfn|Rife|1999|p=242}}{{sfn|Medawar|Pyke|2001|p=65}}{{sfn|Jones|1978|pp=474–475}} Bohr's son Aage followed his father to Britain on another flight a week later, and became his personal assistant.{{sfn|Jones|1985|pp=280–282}}

Bohr was warmly received by [[James Chadwick]] and Sir [[John Anderson, 1st Viscount Waverley|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.{{sfn|Jones|1985|pp=280–282}}{{sfn|Pais|1991|pp=491}} Chadwick arranged for Bohr to visit the United States as a Tube Alloys consultant, with Aage as his assistant.{{sfn|Cockcroft|1963|p=46}} 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 National Laboratory|Los Alamos]] in [[New Mexico]], where the nuclear weapons were being designed.{{sfn|Pais|1991|pp=498–499}} For security reasons, he went under the name of "Nicholas Baker" in the United States, while Aage became "James Baker".{{sfn|Gowing|1985|p=269}} 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.<ref>{{cite news |title= Professor Bohr ankommet til Moskva |trans-title= Professor Bohr arrived in Moscow |url= http://www.illegalpresse.dk/papers#/paper?paper=72&page=826 |newspaper= [[De frie Danske]] |date= May 1944 |page= 7 |access-date= 18 November 2014 |language= da |archive-date= 16 November 2018 |archive-url= https://web.archive.org/web/20181116000610/http://www.illegalpresse.dk/papers#/paper?paper=72&page=826 |url-status= live }}</ref>

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]].{{sfn|Pais|1991|p=497}} Bohr is quoted as saying, "They didn't need my help in making the atom bomb."{{sfn|Pais|1991|p=496}} Oppenheimer gave Bohr credit for an important contribution to the work on [[modulated neutron initiator]]s. "This device remained a stubborn puzzle", Oppenheimer noted, "but in early February 1945 Niels Bohr clarified what had to be done".{{sfn|Pais|1991|p=497}}

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.{{sfn|Gowing|1985|p=270}} Bohr met Churchill on 16 May 1944, but found that "we did not speak the same language".{{sfn|Gowing|1985|p=271}} 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."{{sfn|Aaserud|2006|p=708}}

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.{{sfn|Rhodes|1986|pp=528–538}}{{sfn|Aaserud|2006|pp=707–708}} 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 [[Quebec Agreement#Hyde Park Aide-Mémoire|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".{{sfn|U.S. Government|1972|pp=492–493}}

In June 1950, Bohr addressed an "Open Letter" to the [[United Nations]] calling for international cooperation on nuclear energy.{{sfn|Aaserud|2006|pp=708–709}}<ref>{{cite journal |last=Bohr |first=Niels |date=9 June 1950 |url=http://www.fredsakademiet.dk/library/dkpeace/dkpeace15.htm |title=To the United Nations (open letter) |journal=Impact of Science on Society |volume=I |issue=2 |page=68 |access-date=12 June 2012 |archive-date=8 March 2013 |archive-url=https://web.archive.org/web/20130308122903/http://www.fredsakademiet.dk/library/dkpeace/dkpeace15.htm |url-status=live }}<br />• {{cite journal |last=Bohr |first=Niels |date=July 1950 |pages=213–219 |url=https://books.google.com/books?id=4g0AAAAAMBAJ&q=%22atomic+energy+project%22+1944&pg=PA214 |title=For An Open World |journal=Bulletin of the Atomic Scientists |volume=6 |issue=7 |access-date=26 June 2011 |doi=10.1080/00963402.1950.11461268 |bibcode=1950BuAtS...6g.213B |archive-date=30 October 2023 |archive-url=https://web.archive.org/web/20231030202300/https://books.google.com/books?id=4g0AAAAAMBAJ&q=%22atomic+energy+project%22+1944&pg=PA214#v=snippet&q=%22atomic%20energy%20project%22%201944&f=false |url-status=live }}</ref>{{sfn|Pais|1991|pp=513–518}} In the 1950s, after the [[RDS-1|Soviet Union's first nuclear weapon test]] in 1949, the [[International Atomic Energy Agency]] was created along the lines of Bohr's suggestion.{{sfn|Gowing|1985|p=276}} In 1957 he received the first ever [[Atoms for Peace Award]].<ref>{{cite web |url=http://libraries.mit.edu/archives/research/collections/collections-mc/pdf/mc10.pdf |title=Guide to Atoms for Peace Awards Records |first=Elizabeth |last=Craig-McCormack |publisher=[[Massachusetts Institute of Technology]] |access-date=28 February 2013 |archive-url=https://web.archive.org/web/20100311073706/http://libraries.mit.edu/archives/research/collections/collections-mc/pdf/mc10.pdf |archive-date=11 March 2010 }}</ref>