Because of the Nazi occupation, Niels Bohr escapes from Denmark. He first goes to Sweden, then in Britain and, on December 8 1943, he arrives in the USA. There, Bohr pays extended visits to Los Alamos giving his suggestions to the theoretical groups working on the design of the nuclear weapons. He tries without success to convince Churchill and Roosevelt of the necessity to share the information concerning the atomic bomb with the Soviet Union. On 25 August 1945, he comes back to Copenhagen.

After W. Heisenberg proposes the indeterminacy principle, N. Bohr develops the principle of complementarity. These two principles constitute the Copenhagen Interpretation of quantum mechanics that has been one of the most widely diffused interpretations of quantum mechanics. Bohr first communicates the principle to the community of physicists in a lecture he delivers on 16 September 1927 at the International Physics Congress held in Como, Italy, attended by many leading physicists of the era.

Niels Bohr is invited by E. Rutherford to conduct post-doctoral work at Victoria University in Manchester where Rutherford is establishing his own laboratory. The work in Manchester is very fruitful. Here, Bohr begins working on the theoretical improvement of the Rutherford model of the atom based on electrons orbiting around a nucleus - model that is unstable both dynamically and radiatively.

Niels Bohr is born in Copenhagen, Denmark, as the son of Christian Bohr, Professor of Physiology at Copenhagen University, and his wife Ellen, née Adler. During his boyhood, Bohr enjoys the lively cultural environment surrounding his father’s professional life.

Niels Bohr is Appointed Professor of Theoretical Physics at Copenhagen University, a chair that has been created specifically for him.

Niels Bohr is Privatdozent at Copenhagen University, giving lectures on thermodynamics. There, he develops the model of the atom based on the Max Planck's quantum theory adapted to Rutherford's planetary model. The Bohr atom is a momentous advancement in quantum physics and it is the central reason underlying the Nobel Prize given to Bohr in 1922. The Bohr model of the atom is published between September and November 1913 as a trilogy called "On the Constitution of Atoms and Molecules."

Niels Bohr works on the nuclear theory. He develops the compound model of the nucleus. Employing this model, L. Meitner and O. Frisch are able to describe theoretically the discovery of nuclear fission in 1938. Developments of the model lead to the liquid drop model. Bohr, in collaboration with Wheeler, predict that uranium-235 isotope is primarily responsible for fission. This discovery is central for the developments of nuclear reactors and nuclear weapons in the following years.

Niels Bohr enrols at the University of Copenhagen, where he studies under the guidance of Professor Christian Christiansen, the university's only professor of physics at that time. In 1905, Bohr win a gold medal in a scentific competition sponsored by the Royal Danish Academy of Sciences and Letters. In his master's thesis, Bohr begins working on the structure of matter by elaborating on the electronic theory of metals.

On March 3, 1921 the Institute for Theoretical Physics at the University of Copenhagen is inaugurated and Bohr becomes its Director. In the 1920s and 1930s, Bohr's Institute becomes a crucial point for the training and the meeting of researchers working on quantum physics and plays a crucial role in the development of quantum mechanics and related subjects.

Niels Bohr continues his studies at Cambridge, UK, where he follows the experimental work going on in the Cavendish Laboratory under Sir J.J. Thomson's guidance. There, he pursues his own theoretical studies, but fails to impress Thomson.

Niels Bohr is educated at the Gammelholm Latin School in Copenhagen, starting when he is seven.

Niels Bohr decides to return at the Victoria University in Manchester, where Rutherford has offered him a job as a Lecturer.

Niels Bohr dies of heart failure at his home in Carlsberg, Copenhagen, on 18 November 1962.

Niels Bohr receives the Nobel Prize in Physics "for his services in the investigation of the structure of atoms and of the radiation emanating from them."

Niels Bohr completes his dissertation in physics by extending his thesis. By generalizing the assumptions of the Lorentz-Drude theory, Bohr deduces that it is not possible to derive the diamagnetic and paramagnetic properties of metals from the accepted laws of electromagnetism. Bohr reaches the conclusion that it is necessary a revision of classic electromagnetism in order to deal with atomic phenomena.

Niels Bohr marries Margrethe Nørlund, the sister of the mathematician Niels Erik Nørlund in a civil ceremony at the town hall in Slagelse. They go for the honeymoon in England and Scotland. They have six children. One of them, Aage Bohr will win the 1975 Nobel Prize in Physics.

Martin Knudsen obtains for Bohr a position as Lecturer for medical students at the University of Copenhagen.

Niels Bohr attends the fifth Solvay International conference held in Brussels. In this conference, Bohr makes a clearer exposition of the principle of complementarity. While this conference is important for spreading the Copenhagen interpretation, it is also famous because Einstein and Bohr begin debating on the interpretation of quantum mechanics. The Bohr-Einstein debate will continue for several years and it is considered one of the most interesting foundational debates of modern physics.

Niels Bohr formulates and develops the principle of correspondence, which becomes one of the central tools in the development of quantum physics.