Niels Bohr
On the 7th of October 1885, Niels Henrik David Bohr was born in Copenhagen, Denmark. He grew up as the second of three children to Christian Bohr and Ellen Adler. His father served as a professor of physiology at the University of Copenhagen. His mother came from a prominent Jewish banking family. Bohr had an elder sister named Jenny and a younger brother named Harald. The two brothers played football together for the Akademisk Boldklub club. Niels played as a goalkeeper while Harald became a mathematician who competed in the 1908 Summer Olympics.
In 1905, the Royal Danish Academy of Sciences and Letters sponsored a gold medal competition. Lord Rayleigh had proposed a method for measuring surface tension that required precise experiments. Bohr conducted his work using glassware he made himself inside his father's laboratory. The university lacked its own physics lab at the time. He measured the frequency of oscillation of a water jet radius with great care. His essay won the prize despite being submitted at the last minute. He later published an improved version of this paper in London.
Bohr traveled to England in September 1911 on a fellowship from the Carlsberg Foundation. He met J.J. Thomson at the Cavendish Laboratory and Trinity College Cambridge. James Jeans and Joseph Larmor gave lectures on electromagnetism during his stay. Ernest Rutherford invited him to Manchester for post-doctoral work. There he met George de Hevesy and Charles Galton Darwin. Bohr returned to Denmark in July 1912 after his wedding honeymoon.
He began teaching medical students as a Privatdocent at Copenhagen University in July 1913. Three papers published in Philosophical Magazine became known as the trilogy. He adapted Rutherford's nuclear structure to Max Planck's quantum theory. This created the Bohr model of the atom where electrons revolve in stable orbits. Electrons could jump between energy levels by emitting discrete quanta of energy. The model explained the Balmer series of hydrogen spectral lines. It also accounted for ionized helium lines that Alfred Fowler had challenged. Older physicists like Lord Rayleigh disliked the work while younger scientists saw it as a breakthrough. Albert Einstein called the model the highest form of musicality in thought.
In April 1917, Bohr launched a campaign to establish an Institute of Theoretical Physics. The Danish government and Carlsberg Foundation provided support along with private donors. Legislation passed in November 1918 allowed the institute to open on the 3rd of March 1921. Bohr served as its director from the start. His family moved into an apartment on the first floor of the new building. Hans Kramers and Oskar Klein were among the early arrivals who worked there.
Wolfgang Pauli discovered the exclusion principle in 1924 which put Bohr's models on firm theoretical footing. Dirk Coster and George de Hevesy found hafnium at Copenhagen's Museum of Mineralogy. They proved Bohr right against French chemist Georges Urbain's claim. The element turned out more common than gold. Werner Heisenberg came to Copenhagen in 1924 and returned in June 1925. He developed matrix mechanics with Max Born's help. Erwin Schrödinger visited in 1926 with wave mechanics that impressed Bohr. Heisenberg took Kramers' place as lektor when Kramers left for Utrecht University.
Bohr conceived the philosophical principle of complementarity in 1927. Items could have apparently mutually exclusive properties like being a wave or stream of particles depending on experimental framework. He felt professional philosophers did not fully understand this idea yet. Albert Einstein preferred classical physics determinism over probabilistic quantum physics. They engaged in good-natured arguments about these issues throughout their lives. Einstein resolved problems regarding electron spin using relativity before meeting Bohr in Leiden.
Heisenberg presented his uncertainty principle in February 1927 using a gamma-ray microscope thought experiment. Bohr disagreed since it required only measurement disturbance rather than radical context dependence. At the Como Conference in September 1927, Bohr emphasized deriving relations from classical optical instrument resolving power. He believed true understanding required closer investigation into complementarity meaning. Philosophical issues arising from novel quantum aspects became widely celebrated discussion subjects. Einstein and Bohr maintained their debates until death despite their mutual respect.
In September 1943 word reached Bohr that Nazis considered his family Jewish due to his mother's background. The Danish resistance helped him and his wife escape by sea to Sweden on the 29th of September. King Gustaf V of Sweden made public asylum availability the next day. Swedish radio broadcast readiness for refugees on the 2nd of October 1943. Over 7,000 Danish Jews escaped to Sweden following these events. Bohr arrived in Scotland on the 6th of October aboard a de Havilland Mosquito operated by BOAC.
The aircraft flew high over German-occupied Norway to avoid fighters. Bohr spent three hours lying on a mattress in the bomb bay without an oxygen mask. His flying helmet was too small so he could not hear pilot instructions. He passed out from oxygen starvation before reviving when descending over the North Sea. Aage followed his father to Britain a week later as personal assistant. Lord Cherwell sent a telegram asking him to come to Britain immediately after hearing news.
Bohr arrived in Washington D.C. on the 8th of December 1943 meeting Manhattan Project director Leslie Groves. He visited Einstein and Pauli at Princeton Institute for Advanced Study then went to Los Alamos. Security required using names Nicholas Baker and James Baker for himself and son. Robert Oppenheimer credited Bohr with acting as scientific father figure to younger men like Richard Feynman. Bohr clarified modulated neutron initiators in early February 1945 though stating bombs did not need his help.
He recognized nuclear weapons would change international relations immediately. Peter Kapitza invited him to Soviet Union in April 1944 suggesting awareness of Anglo-American project. Churchill wrote that Bohr ought be confined near edge of mortal crimes regarding openness to Russians. Roosevelt met Bohr on the 26th of August 1944 but Hyde Park conference rejected sharing information. In June 1950 Bohr addressed United Nations calling for international cooperation on nuclear energy. The International Atomic Energy Agency formed along lines of his suggestion during the 1950s.
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Common questions
When and where was Niels Bohr born?
Niels Henrik David Bohr was born on the 7th of October 1885 in Copenhagen, Denmark. He grew up as the second of three children to Christian Bohr and Ellen Adler.
What did Niels Bohr achieve in his 1905 gold medal competition essay?
Niels Bohr won a gold medal from the Royal Danish Academy of Sciences and Letters for an essay measuring surface tension using self-made glassware. The university lacked its own physics lab at the time so he conducted experiments inside his father's laboratory.
How did Niels Bohr explain electron behavior in his atomic model?
Niels Bohr created the Bohr model of the atom where electrons revolve in stable orbits and jump between energy levels by emitting discrete quanta of energy. This model explained the Balmer series of hydrogen spectral lines and accounted for ionized helium lines that Alfred Fowler had challenged.
When did the Institute of Theoretical Physics open under Niels Bohr leadership?
Legislation passed in November 1918 allowed the institute to open on the 3rd of March 1921 with Niels Bohr serving as director from the start. His family moved into an apartment on the first floor of the new building while Hans Kramers and Oskar Klein worked there early on.
Why did Niels Bohr escape Denmark during World War II?
Word reached Niels Bohr in September 1943 that Nazis considered his family Jewish due to his mother's background. The Danish resistance helped him and his wife escape by sea to Sweden on the 29th of September before he traveled to Scotland.
What role did Niels Bohr play in the Manhattan Project after arriving in Washington D.C?
Niels Bohr arrived in Washington D.C. on the 8th of December 1943 meeting Manhattan Project director Leslie Groves and visited Los Alamos. Robert Oppenheimer credited Niels Bohr with acting as a scientific father figure to younger men like Richard Feynman.