59 Fun Facts About Niels Bohr

Bohr's 1922 Nobel citation praised his work on the structure of atoms and on what emanating from them?

Radiation completed the citation, and Einstein's prize for 1921 was handed out in 1922 as well, since the committee had found no 1921 nomination good enough and held it back a year.

Niels Bohr first steered the physicist Max Delbrück toward which science?

Biology became Delbrück's life's work after Bohr sparked his interest in it, and in 1969 he shared a Nobel Prize for discoveries about how viruses replicate.

Bohr's father Christian was a university professor of which subject?

Physiology was Christian Bohr's subject, and since the university had no physics laboratory, young Niels did the experiments for his first paper in his father's lab instead.

Which actor plays Niels Bohr in Christopher Nolan's 2023 film Oppenheimer?

Kenneth Branagh plays him, and the film has Oppenheimer snatch a poisoned apple just before Bohr can bite it, though there is no evidence Bohr was ever part of the real incident.

In which position did Niels Bohr play for the football club Akademisk Boldklub?

Goalkeeper was his spot in the 1905 season, but despite an oft-repeated claim he never played for Denmark, unlike his brother Harald, who won Olympic silver in 1908.

In a story often told about Bohr, a lucky horseshoe is said to work even without what?

Belief in it isn't needed, the quip goes, yet some tellings have Bohr merely passing on the joke about a neighbour's or a fellow physicist's horseshoe, not his own.

A quip often credited to Bohr says prediction is very difficult, especially about what?

The future is the punchline, yet the earliest known version was spoken, unattributed, in Denmark's parliament in 1937-38, and the line has also been credited to the cartoonist Storm P.

Bohr's doctoral thesis was on the electron theory of what?

Metals: Bohr showed that classical electron theory could not explain their magnetic properties, which convinced him that atomic physics needed a radical break.

Why did Bohr's 1911 doctoral thesis attract little attention?

It was written in Danish, and the Dutch physicist Hendrika van Leeuwen later rediscovered one of its theorems independently in her own doctoral thesis.

In 1911 Bohr went to Cambridge to work under which Nobel laureate, who showed little interest in his thesis?

J. J. Thomson had lost interest in electron theory and paid little attention to Bohr's thesis, so in 1912 Bohr moved on to Rutherford's laboratory in Manchester.

Bohr's long debate with Einstein over quantum theory began at which 1927 gathering in Brussels?

The Solvay Conference of 1927 was where Einstein raised his objection to the probability view of quantum theory, opening a debate with Bohr that the two carried on for years.

Bohr's 1913 model of the atom married Rutherford's nucleus to whose quantum theory?

Max Planck's quanta rescued Rutherford's atom: by classical physics its electrons should spiral into the nucleus, but Bohr's quantised orbits kept it stable.

Bohr's three 1913 atomic papers, 'the trilogy', appeared in which British journal?

Philosophical Magazine carried all three, and the atom they described, electrons in fixed orbits around a nucleus, is still the best-known picture of an atom.

Whose decades-old formula for hydrogen's spectral lines did Bohr's 1913 model finally explain?

Balmer's formula had fitted hydrogen's lines since the 1880s though nobody knew why, until the first paper of Bohr's trilogy derived it from his model.

Challenged over the Pickering series of spectral lines, Bohr correctly said they came from what?

Ionised helium: Pickering and Fowler had blamed an unusual form of hydrogen, but Bohr's analysis, confirmed by tests in Rutherford's laboratory, won Fowler over.

Einstein called Bohr's atomic model 'the highest form of' what 'in the sphere of thought'?

Musicality: in his Autobiographical Notes, Einstein marvelled that Bohr had found the laws of spectral lines on a foundation Einstein saw as insecure and contradictory.

In the early 1920s, Bohr's picture of how electrons are arranged in atoms explained what?

The periodic table: Bohr showed that the electrons in an atom's outer orbits largely decide its chemical properties, giving the table's repeating pattern a physical reason.

Which brewery's foundation gave Bohr the grant for his 1911 study trip to England?

Carlsberg: its founder J. C. Jacobsen willed the brewery itself to the foundation, so profits from beer have paid for science in Denmark ever since.

Which element, predicted by Bohr to resemble zirconium, was discovered at his institute?

Hafnium: a French chemist had claimed element 72 was a rare earth, but it turned up in Norwegian zircon, just as Bohr's theory had said.

At Los Alamos, which future Nobel laureate did Bohr seek out for one-on-one talks to test his ideas?

Richard Feynman: most others were too in awe of Bohr to argue with him, but Feynman would say plainly when an idea was crazy.

The 'Bohr Festival', a series of seven lectures, took place in which German university town?

Göttingen: there Bohr first met the student Werner Heisenberg, who by 1924 had come to work with him.

Bohr's correspondence principle says the new physics reproduces classical physics in the limit of what?

Large quantum numbers: Bohr boldly assumed the match held roughly even for small ones, and used it to predict how bright spectral lines should be.

The 1924 Bohr-Kramers-Slater theory proposed energy and momentum were conserved only how?

Statistically, not event by event, but experiments by Bothe and Geiger soon disproved it, and Bohr asked for 'as honourable a funeral as possible'.

Bohrium's discoverers feared its name would be confused with which element?

Boron: they wanted 'nielsbohrium', but IUPAC said no element had used a scientist's full name, and bohrium became official in 1997.

Which philosophical principle did Bohr conceive to reconcile wave and particle descriptions?

Complementarity: Bohr thought it through on a skiing holiday in Norway in early 1927 and first presented it that September at a congress in Como.

Which film genre did Bohr enjoy watching at the cinema with his students?

Westerns: he would accept each unlikely rescue in the plot, but not that someone just happened to be there with a film camera.

Bohr's 1936 theory of the compound nucleus pictured the nucleus as behaving like what?

A drop of liquid: the model let Lise Meitner and Otto Frisch explain in 1939 how an atomic nucleus could split in two.

In 1939 Bohr worked out that fission with slow neutrons was mainly due to which isotope?

Uranium-235: Bohr argued that this rare isotope, not the far more common uranium-238, was responsible, and in April 1940 Dunning's team at Columbia University proved him right.

With whom did Bohr publish 'The Mechanism of Nuclear Fission' in September 1939?

John Wheeler: they took up the problem after Bohr brought news of fission to America, and their paper appeared on 1 September 1939, the day Germany invaded Poland.

To hide two Nobel medals from the Nazis at Bohr's institute, George de Hevesy dissolved them in what?

Aqua regia: the solution sat undisturbed on a shelf through the occupation, and after the war the Nobel Foundation recast the medals from the recovered gold.

Bohr's own Nobel medal was auctioned in 1940 to raise money for what?

Finnish relief: August Krogh gave his Nobel medal to the same auction, and an anonymous buyer later presented both medals to the museum at Frederiksborg Castle.

Which astronaut took Bohr's Nobel medal to the International Space Station in 2023?

Andreas Mogensen borrowed it from the museum at Frederiksborg Castle and showed it on camera from orbit in December 2023, while he was commanding the station.

Michael Frayn's 1998 play about the mysterious 1941 meeting between Bohr and Heisenberg is called what?

Copenhagen: the debate it stirred led to the 2002 release of Bohr's unsent letters, in which he rejected Heisenberg's own account of the meeting.

After fleeing to Sweden in 1943, Bohr urged King Gustaf V to make a public offer of what?

Asylum for Jewish refugees: Swedish radio broadcast the offer on 2 October 1943, and nearly all of Denmark's Jews were soon carried to safety by sea.

Why did Bohr pass out at high altitude while flying to Britain in the bomb bay of a Mosquito?

His helmet was too small, so he never heard the pilot's order over the intercom to switch on his oxygen, and came round only when the plane flew lower.

Under what alias did Bohr travel in the United States during the Manhattan Project?

Nicholas Baker: the false name hid a famous identity, and his son, travelling with him, went by 'James Baker'.

Which of Bohr's sons won the Nobel Prize in Physics in 1975?

Aage: one of six sons, he spent the last two years of the war as his father's assistant and secretary in London, Washington and Los Alamos.

Which wartime leader wrote that Bohr 'ought to be confined', near 'the edge of mortal crimes'?

Winston Churchill: when Bohr met him in May 1944 to argue for openness about the bomb, the talk failed, and Bohr said 'we did not speak the same language'.

Which Supreme Court justice, a friend of Bohr, passed his ideas on the bomb to President Roosevelt?

Felix Frankfurter: Roosevelt went on to meet Bohr in private on 26 August 1944 and heard his case for overtures to the Soviets.

To which body did Bohr address his 1950 'Open Letter' on control of nuclear energy?

The United Nations: in the letter Bohr repeated his plea for an 'open world', in which nations would freely share scientific information with each other.

In 1957 Bohr became the first ever recipient of which honour?

Atoms for Peace Award: President Eisenhower, whose call to put nuclear science to peaceful use had inspired the prize, spoke at the ceremony where Bohr received it.

Bohr's Order of the Elephant, conferred in 1947, was normally reserved for whom?

Royalty and heads of state: as a knight of the order, Bohr had his coat of arms hung beside royal ones in the chapel of Frederiksborg Castle.

Which symbol did Bohr put on the coat of arms he designed for himself?

Yin and yang: Bohr needed a coat of arms after he was made a knight of the Order of the Elephant in 1947, and chose the ancient Chinese symbol.

Bohr helped set up CERN, whose laboratory was built near which city?

Geneva, although CERN's theory group started out at Bohr's institute and grew strong there before moving to the new laboratory.

Which play did physicists at Bohr's institute parody in 1932, a century after its author died?

Faust: in the spoof the Lord stood for Bohr himself, and the three archangels were played as Eddington, Jeans and Milne.

The 1997 500-krone banknote showed Bohr doing what?

Smoking a pipe: it kept going out because Bohr kept talking, and he got through so many matches that colleagues gave him giant boxes of them for his birthday.

Before marrying Margrethe in 1912, Bohr resigned his membership of what?

The Church of Denmark, and that August he and Margrethe married in a civil ceremony at the town hall in Slagelse.

How did Bohr's eldest son Christian die in 1934?

A boating accident: Christian, the eldest son, drowned at sea while out on a sailing trip with his father.

Bohr's son Ernest represented Denmark at the 1948 Olympics in which sport?

Field hockey, but in his first game Denmark lost 9–0 to Pakistan, and the team went out in the group stage.

Which philosopher's book did Bohr send to his brother as a birthday gift?

Soren Kierkegaard, whose ideas some historians think reached Bohr through his philosophy teacher Høffding and helped shape his outlook.

In a 1999 Physics World poll, Bohr came fourth behind Einstein, Newton and whom?

Maxwell: at celebrations held for him in Cambridge in 1931, Bohr said the language of Newton and Maxwell would remain the language of physicists for all time.

Bohr's 1913 model of the atom is often pictured as a tiny what?

Solar system, though Bohr broke with the picture at once: his electrons were allowed only certain orbits and could jump between them but never sit in between.

Early in his university career, Bohr disliked being obliged to teach physics to which future professionals?

Medical students, and he was unhappy enough in the job to accept an offer to go back to Manchester instead.

Which British physicist told Bohr he was taught never to start a sentence without knowing its end?

Paul Dirac said it when Bohr was struggling to finish a sentence in an article he was writing.

Which American family's money paid to expand Bohr's institute in the 1920s?

The Rockefellers: Bohr told their International Education Board in 1923 that Denmark could not raise the money, and the board granted $40,000 to enlarge the institute.

Which two physicists met Bohr's train at Hamburg in 1925 to ask about electron spin?

Wolfgang Pauli and Otto Stern: Bohr told them he had doubts, but talks with Einstein and Ehrenfest in Leiden soon changed his mind.

Which physicist led the discussion with Bohr at the January 1939 Washington Conference on Theoretical Physics?

Enrico Fermi: once the meeting closed, researchers at the Carnegie Institution showed the two of them the atom-splitting experiment in their laboratory.

Bohr chaired the atomic energy commission that built its research station at which site?

Risø: the laboratory later moved into sustainable energy research and was merged into the Technical University of Denmark in 2007.

Which cemetery holds both Bohr's ashes and Hans Christian Andersen's grave?

Assistens Cemetery began in 1760 as a burial ground for the poor, laid out because the graveyards inside the city walls had run out of room.