Chronological Overview

1855

• November 11, 1855: Death of Søren Kierkegaard

1864

• James Clerk Maxwell, “A dynamical theory of the electromagnetic field”

1884

• September 30, 1884: Death of Rasmus Nielsen

1885

• October 7, 1885: Birth of Niels Henrik David Bohr in the residence of his mother’s family – Strandgade, Copenhagen

1886

• Christian Bohr is appointed “lektor” (assistant professor) of physiology at the University of Copenhagen. He and his family move to the residence at the Surgical Academy on Bredgade.

1887

• April 22: Harald Bohr, Niels’s younger brother, is born. Harald became a notable mathematician and also an accomplished soccer player, representing Denmark at the 1908 Olympics (where they won the silver medal).
• Birth of Erwin Schrödinger

1891

• NB begins elementary school at Gammelholms Latin- and Real School

1897

• JJ Thomson discovers the electron.

1900

• Max Planck introduces the concept of the quantum of action, laying the groundwork for quantum theory. (Bohr will repeatedly say that it is this discovery — that there is a smallest quantum of action — that requires a reconsideration of the foundations of scientific description. )
• Read more about Planck’s quantum theory in the Stanford Encyclopedia of Philosophy.
• Birth of Wolfgang Pauli

1901

• Birth of Werner Heisenberg

1902

• Birth of Paul Dirac

1903

• NB matriculates at the University of Copenhagen. He takes the year-long Filosofikum course taught by Harald Høffding.

1904

• J.J. Thomson’s “plum pudding” model of the atom.

1905

• B wins the gold medal from the Danish Royal Society for an essay on the surface tension of water.
• Light Quantum Hypothesis: Albert Einstein proposes the idea of light quanta (photons), a fundamental concept in quantum mechanics.
• Special Theory of Relativity: Einstein formulates the special theory of relativity, revolutionizing our understanding of space and time.
• Both of these developments influenced Bohr’s thinking on atomic structure.

1911

• Rutherford model of the atom
• B’s father, Christian Bohr, dies on February 3, 1911.
• Bohr defends his doctoral dissertation (May 13, 1911) titled “Studies on the Electron Theory of Metals” (Metallernes Elektrontheori), at the University of Copenhagen.
• September: NB travels to Cambridge to take up post-doctoral fellowship in J.J. Thomson’s lab.

1912

• March: NB moves to Rutherford’s lab in Manchester.
• April 16: NB rejects his membership in the Lutheran Church of Denmark
• July 24: NB returns to Denmark.
• August 1. Bohr marries Margrethe Nørlund, who becomes his lifelong partner and intellectual collaborator. They would have six children together.

1913

• B publishes three landmark papers on the structure of atoms, introducing the Bohr model, which describes electrons orbiting the nucleus in quantized energy levels. “On the constitution of atoms and molecules, parts I, II, and III”
• These papers were crucial in the development of quantum mechanics and earned him international recognition.
• Explore Bohr’s model in more detail in the Stanford Encyclopedia of Philosophy.

1914

• Franck-Hertz experiment
• October: Bohr becomes lecturer in physics at Manchester.

1916

• March 5: Christian Bohr, named after Niels’ father, is born. Tragically, he would die in a sailing accident at age 18.
• B is appointed to a professorship at the University of Copenhagen. This marks the beginning of his leadership in Danish physics and his growing international influence.

1920

• NB visits Berlin and meets Planck and Einstein for the first time.

1921

• Establishment of the Institute for Theoretical Physics in Copenhagen (now named the Niels Bohr Institute)
• Paul Ehrenfest visits Copenhagen for the first time.

1922

• June: NB lectures in Göttingen and meets Heisenberg and Pauli for the first time.
• December 10: NB is awarded the Nobel Prize in Physics “for his services in the investigation of the structure of atoms and of the radiation emanating from them.” Nobel Prize details can be found on the official Nobel Prize website.
• June 19: Birth of Aage (son), who would also win a Nobel Prize in physics

1923

• Bohr, along with Hendrik Kramers and John Slater, proposes the Bohr-Kramers-Slater (BKS) theory, suggesting that energy conservation might be violated in individual atomic processes (Bohr, Kramers, and Slater 1924). Bohr’s willingness to abandon energy conservation is striking, since he will later argue that conservation laws are a crucial part of quantum-mechanical description.
• The BKS theory was eventually refuted, but it played an important role in the development of quantum mechanics.

1924

• Bohr elaborates on his correspondence principle, which states that the behavior of systems described by quantum mechanics replicates classical physics in the limit of large quantum numbers. This principle was key in developing the quantum theory and connecting it with classical mechanics.
• Easter: Heisenberg makes a first, short visit to Copenhagen.
• De Broglie: Matter waves. Einstein had shaken the boat by proposing that light might be a particle instead of a wave. Now de Broglie turns the tables by suggesting that material objects (e.g. electrons) are wave-like. Niels Bohr will become gripped by the idea that these two pictures provide different kinds of insight about the physical world. On the theory of quanta

1925

• Bothe-Geiger Experiment: Demonstrates that energy is conserved in individual processes, contradicting the BKS theory.
• Compton-Simon Experiment: Provides further evidence against the BKS theory.
• July 25: Heisenberg publishes his paper on matrix mechanics, a formulation of quantum mechanics.
• Heisenberg and the development of quantum mechanics are discussed in the Stanford Encyclopedia of Philosophy.
• November 16: Three man paper (Born, Heisenberg, and Jordan)

1926

• January 26: Schrödinger publishes his series of papers on wave mechanics, another formulation of quantum mechanics.
• June 25: Born’s statistical interpretation of the wavefunction. This interpretation was initially resisted by Schrödinger, and is still resisted by many philosophers today.
  
• October: Schrödinger visits Copenhagen and delivers lectures. During this visit, tensions between Schrödinger and Heisenberg arose, leading to debates about the interpretation of quantum mechanics.
• There are conflicting accounts about how this visit went, and about how Niels Bohr handled himself. The historian of science Mara Beller argues that Bohr was an intellectual bully who wouldn’t allow Schrödinger to get a word in edgewise (Beller 1999). And yet, in letters after the event, Schrödinger described Bohr as self-effacing.
• More on the Schrödinger-Bohr relationship

1927

• Winter: Differences of opinion begin to arise between Bohr and Heisenberg. Tensions rise. Bohr leaves Copenhagen for a personal retreat to Tretten, Norway, and while here, Bohr lands upon the idea of “complementarity”. (TO DO: It’s not clear that he starts using this word until he begins drafting the Como lecture. At some point he also uses the word “reciprocity”.)
• March 23: Heisenberg’s article about the uncertainty relations
• September 16: B delivers the famous Como lecture, where he formally introduces the principle of complementarity. Explore the principle of complementarity in the Stanford Encyclopedia of Philosophy.
• October 24-29: The fifth Solvay Conference takes place, where Bohr and Heisenberg further develop the Copenhagen interpretation of quantum mechanics. It is at this conference that Heisenberg presents his uncertainty principle, which states that certain pairs of physical properties, like position and momentum, cannot both be known to arbitrary precision. More on the Solvay Conference and the uncertainty principle.

1929

• B discusses analogies between physics and psychology.

1930

• Solvay conference: Einstein presents the photon box thought experiment.
• Pauli proposes the idea of the neutrino to resolve the apparent violation of energy conservation in beta decay.

1932

• Heisenberg spends significant time in Copenhagen, where he works closely with Bohr on the interpretation of quantum mechanics. This period is crucial in solidifying the Copenhagen interpretation as a leading view in the physics community.
• Read about Heisenberg’s work in Copenhagen in the Stanford Encyclopedia of Philosophy.
• August 15: Bohr’s lecture “Light and Life”

1933

• Bohr and Rosenfeld, “Zur Frage der Messbarkeit der elektromagnetischen Feldgrössen”

1935

• The Einstein-Podolsky-Rosen (EPR) paper is published, challenging the completeness of quantum mechanics. - Details on the EPR argument can be found in the Stanford Encyclopedia of Philosophy.
• B responds with a defense of quantum mechanics, arguing that the EPR paper misunderstands the nature of measurement and quantum states.
• Grete Hermann visits Copenhagen.

1936

• B hosts an important conference in Copenhagen on the Unity of Science. This meeting was part of the broader international movement known as the Unity of Science movement, which sought to integrate different branches of knowledge into a coherent whole. The conference brought together prominent scientists and philosophers, including Otto Neurath and Karl Popper.
• The meeting highlighted Bohr’s interest in the philosophical implications of science and his belief in the need for interdisciplinary dialogue.
• More on the Unity of Science movement can be found in the Stanford Encyclopedia of Philosophy.

1943

• Bohr, of partial Jewish descent, flees Denmark to escape capture by the Nazis. Bohr escapes to Sweden by boat and eventually makes his way to the United States, where he contributes to the Manhattan Project. (There’s also an exciting story about Bohr’s being flown from Sweden to England by a British fighter pilot.) Learn more about Bohr’s escape and his role in the Manhattan Project.

1945

• John Bell begins studying physics at Queen’s University Belfast

1949

• Bohr writes an open letter to the United Nations, advocating for international cooperation on nuclear energy and arms control. He emphasizes the importance of transparency and communication among nations to prevent nuclear conflict.
• Bohr’s open letter can be explored further on the Nobel Prize website.

1952

• David Bohm, “A suggested interpretation of the quantum theory in terms of ‘hidden’ variables I and II”

1954

• B plays a key role in the founding of CERN, the European Organization for Nuclear Research, as part of his commitment to international scientific collaboration. Learn more about Bohr’s involvement in CERN
• Niels Bohr visits Princeton, bringing his assistant Aage Petersen with him. Aage befriends Hugh Everett.

1955

• CERN meeting in Geneva
• Bohr-Pauli correspondence about the subject-object distinction (letters of Feb 15, Mar 3, Mar 11, and Mar 25)

1956

• Everett travels to Copenhagen, hoping to dicuss his ideas with Bohr.

1957

• Establishment of the International Centre for Theoretical Physics (ICTP). While not directly founding ICTP, Bohr’s legacy and advocacy for international scientific cooperation influenced the establishment of institutions like ICTP. His work inspired many physicists involved in its creation, emphasizing the importance of fostering scientific research in developing countries.
• Learn more about ICTP.
• Hugh Everett, “Relative state formulation of quantum mechanics”

1958

• The Niels Bohr Institute at the University of Copenhagen celebrates significant anniversaries, reflecting Bohr’s enduring legacy in the field of physics. The institute continues to be a leading center for research in quantum mechanics and other areas of physics.
• Bohr remains actively involved in mentoring young physicists and contributing to theoretical physics discussions.

1960

• Bohr continues to advocate for the responsible use of scientific knowledge, particularly in the context of nuclear energy and weapons. He emphasizes the ethical obligations of scientists to consider the broader implications of their work on humanity.
• Bohr participates in various international forums and discussions aimed at promoting peace and ethical considerations in scientific advancements.

1962

• Bohr is interviewed by a team of historians of science, including Thomas Kuhn and John Heilbron. Transcripts
• November 18: Niels Bohr dies, aged 77, at the Carlsberg residence.

1963

• Bell’s theorem

References

(Stolzenburg 1977)