91 Facts About Niels Bohr

Niels Henrik David Bohr was a Danish physicist who made foundational contributions to understanding atomic structure and quantum theory, for which he received the Nobel Prize in Physics in 1922.

Niels Bohr developed the Niels Bohr model of the atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level to another.

Niels Bohr conceived the principle of complementarity: that items could be separately analysed in terms of contradictory properties, like behaving as a wave or a stream of particles.

The notion of complementarity dominated Niels Bohr's thinking in both science and philosophy.

Niels Bohr mentored and collaborated with physicists including Hans Kramers, Oskar Klein, George de Hevesy, and Werner Heisenberg.

Niels Bohr predicted the existence of a new zirconium-like element, which was named hafnium, after the Latin name for Copenhagen, where it was discovered.

Niels Henrik David Bohr was born in Copenhagen, Denmark, on 7 October 1885, the second of three children of Christian Bohr, a professor of physiology at the University of Copenhagen, and his wife Ellen Adler, who came from a wealthy Jewish banking family.

Niels Bohr had an elder sister, Jenny, and a younger brother Harald.

Niels Bohr was a passionate footballer as well, and the two brothers played several matches for the Copenhagen-based Akademisk Boldklub, with Niels Bohr as goalkeeper.

Niels Bohr was educated at Gammelholm Latin School, starting when he was seven.

In 1903, Niels Bohr enrolled as an undergraduate at Copenhagen University.

Niels Bohr's major was physics, which he studied under Professor Christian Christiansen, the university's only professor of physics at that time.

Niels Bohr conducted a series of experiments using his father's laboratory in the university; the university itself had no physics laboratory.

Niels Bohr went beyond the original task, incorporating improvements into both Rayleigh's theory and his method, by taking into account the viscosity of the water, and by working with finite amplitudes instead of just infinitesimal ones.

Niels Bohr later submitted an improved version of the paper to the Royal Society in London for publication in the Philosophical Transactions of the Royal Society.

Niels Bohr took another nine months to earn his on the electron theory of metals, a topic assigned by his supervisor, Christiansen.

Niels Bohr surveyed the literature on the subject, settling on a model postulated by Paul Drude and elaborated by Hendrik Lorentz, in which the electrons in a metal are considered to behave like a gas.

Niels Bohr extended Lorentz's model, but was still unable to account for phenomena like the Hall effect, and concluded that electron theory could not fully explain the magnetic properties of metals.

The thesis was accepted in April 1911, and Niels Bohr conducted his formal defence on 13 May Harald had received his doctorate the previous year.

Niels Bohr's thesis was groundbreaking, but attracted little interest outside Scandinavia because it was written in Danish, a Copenhagen University requirement at the time.

Niels Bohr was placed in an institution away from his family's home at the age of four and died from childhood meningitis six years later.

Aage Niels Bohr became a successful physicist, and in 1975 was awarded the Nobel Prize in physics, like his father.

In September 1911, Niels Bohr, supported by a fellowship from the Carlsberg Foundation, travelled to England, where most of the theoretical work on the structure of atoms and molecules was being done.

Niels Bohr met JJ Thomson of the Cavendish Laboratory and Trinity College, Cambridge.

Niels Bohr attended lectures on electromagnetism given by James Jeans and Joseph Larmor, and did some research on cathode rays, but failed to impress Thomson.

Niels Bohr 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 the atom had challenged Thomson's 1904 plum pudding model.

Niels Bohr received an invitation from Rutherford to conduct post-doctoral work at Victoria University of Manchester, where Niels Bohr met George de Hevesy and Charles Galton Darwin.

Niels Bohr returned to Denmark in July 1912 for his wedding, and travelled around England and Scotland on his honeymoon.

Niels Bohr adapted Rutherford's nuclear structure to Max Planck's quantum theory and so created his Bohr model of the atom.

Niels Bohr introduced the idea that an electron could drop from a higher-energy orbit to a lower one, in the process emitting a quantum of discrete energy.

When challenged on this by Alfred Fowler, Niels Bohr replied that they were caused by ionised helium, helium atoms with only one electron.

Niels Bohr decided to return to Manchester, where Rutherford had offered him a job as a reader in place of Darwin, whose tenure had expired.

Niels Bohr took a leave of absence from the University of Copenhagen, which he started by taking a holiday in Tyrol with his brother Harald and aunt Hanna Adler.

Niels Bohr's docentship was abolished at the same time, so he still had to teach physics to medical students.

Niels Bohr gained the support of the Danish government and the Carlsberg Foundation, and sizeable contributions were made by industry and private donors, many of them Jewish.

Niels Bohr's family moved into an apartment on the first floor.

Niels 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.

Niels Bohr became widely appreciated as their congenial host and eminent colleague.

The Niels Bohr model worked well for hydrogen and ionized single electron Helium which impressed Einstein, but could not explain more complex elements.

Niels 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.

In 1922 Niels 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".

Modelling atomic behaviour under incident electromagnetic radiation using "virtual oscillators" at the absorption and emission frequencies, rather than the apparent frequencies of the Niels Bohr orbits, led Max Born, Werner Heisenberg and Kramers to explore different mathematical models.

In light of these results, Niels Bohr informed Darwin that "there is nothing else to do than to give our revolutionary efforts as honourable a funeral as possible".

The next month, Niels Bohr travelled to Leiden to attend celebrations of the 50th anniversary of Hendrick Lorentz receiving his doctorate.

Niels Bohr pointed out that he had concerns about the interaction between electrons and magnetic fields.

Niels Bohr then had Uhlenbeck and Goudsmit incorporate this into their paper.

When Kramers left the institute in 1926 to take up a chair as professor of theoretical physics at the Utrecht University, Niels Bohr arranged for Heisenberg to return and take Kramers's place as a lektor at the University of Copenhagen.

Niels Bohr became convinced that light behaved like both waves and particles and, in 1927, experiments confirmed the de Broglie hypothesis that matter behaved like waves.

Niels Bohr 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.

Niels Bohr felt that it was not fully understood by professional philosophers.

Niels 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.

Understanding the true meaning of complementarity would, Niels Bohr believed, require "closer investigation".

Einstein and Niels Bohr had good-natured arguments over such issues throughout their lives.

Niels Bohr was elected president of the Academy on 17 March 1939.

Niels Bohr worked on this with a new collaborator, the Danish physicist Fritz Kalckar, who died suddenly in 1938.

Niels 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 Niels 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.

In 1909, Niels Bohr sent his brother Kierkegaard's Stages on Life's Way as a birthday gift.

Some of Niels Bohr's biographers suggested that this disagreement stemmed from Kierkegaard's advocacy of Christianity, while Niels Bohr was an atheist.

Furthermore, though some have seen Niels Bohr as being a subjectivist or a positivist, most philosophers agree that this is a misunderstanding of Niels Bohr as he never argued for verificationism or for the idea that the subject had a direct impact on the outcome of a measurement.

Niels Bohr has often been quoted as saying that there is "no quantum world" but only an "abstract quantum physical description".

Niels 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.

Faye notes that Niels Bohr's interpretation makes no reference to a "collapse of the wave function during measurements".

Some like Henry Folse argue that Niels Bohr saw a distinction between observed phenomena and a transcendental reality.

In 1933, the Rockefeller Foundation created a fund to help support refugee academics, and Niels Bohr discussed this programme with the President of the Rockefeller Foundation, Max Mason, in May 1933 during a visit to the United States.

Niels 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.

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

Niels 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.

Ivan Supek, one of Heisenberg's students and friends, claimed that the main subject of the meeting was Carl Friedrich von Weizsacker, who had proposed trying to persuade Niels Bohr to mediate peace between Britain and Germany.

When Niels Bohr saw Jungk's depiction in the Danish translation of the book, he drafted 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.

The next day, Niels Bohr persuaded King Gustaf V of Sweden to make public Sweden's willingness to provide asylum to Jewish refugees.

Some historians claim that Niels Bohr's actions led directly to the mass rescue, while others say that, though Niels Bohr did all that he could for his countrymen, his actions were not a decisive influence on the wider events.

Niels Bohr, equipped with parachute, flying suit and oxygen mask, spent the three-hour flight lying on a mattress in the aircraft's bomb bay.

Niels Bohr passed out from oxygen starvation and only revived when the aircraft descended to lower altitude over the North Sea.

Niels Bohr was warmly received by James Chadwick and Sir John Anderson, but for security reasons Niels Bohr was kept out of sight.

Niels Bohr was given an apartment at St James's Palace and an office with the British Tube Alloys nuclear weapons development team.

Niels Bohr was astonished at the amount of progress that had been made.

Chadwick arranged for Niels Bohr to visit the United States as a Tube Alloys consultant, with Aage as his assistant.

On 8 December 1943, Bohr arrived in Washington, DC, where he met with the director of the Manhattan Project, Brigadier General Leslie R Groves Jr.

Niels Bohr 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.

Niels 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 Niels Bohr with acting "as a scientific father figure to the younger men", most notably Richard Feynman.

Niels Bohr recognised early that nuclear weapons would change international relations.

Niels Bohr sent Kapitza a non-committal response, which he showed to the authorities in Britain before posting.

Niels Bohr met Churchill on 16 May 1944, but found that "we did not speak the same language".

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.

In June 1950, Niels Bohr addressed an "Open Letter" to the United Nations calling for international cooperation on nuclear energy.

Niels Bohr designed his own coat of arms which featured a taijitu and a motto in Latin: contraria sunt complementa, "opposites are complementary".

Niels Bohr died of heart failure at his home in Carlsberg on 18 November 1962.

Niels Bohr became foreign member of the Royal Netherlands Academy of Arts and Sciences in 1923, an international member of the United States National Academy of Sciences in 1925, a member of the Royal Society in 1926, an international member of the American Philosophical Society in 1940, and an international honorary member of the American Academy of Arts and Sciences in 1945.

An asteroid, 3948 Niels Bohr, was named after him, as was the Niels Bohr lunar crater and bohrium, the chemical element with atomic number 107.