Niels Bohr

Niels Henrik David Bohr was born on 7 October 1885 in Copenhagen, Denmark, into an academically prominent family. His father, Christian Bohr, was a professor of physiology at the University of Copenhagen, and his mother, Ellen Adler Bohr, came from a distinguished Danish-Jewish family. His brother Harald Bohr became a notable mathematician.

Bohr studied physics at the University of Copenhagen, earning his doctorate in 1911 with a dissertation on the electron theory of metals. He subsequently travelled to England, working first with J.J. Thomson at the Cavendish Laboratory in Cambridge and then with Ernest Rutherford in Manchester. It was in Manchester that Bohr began developing his model of the atom.

In 1913, Bohr published a series of papers that became foundational in atomic physics. His model proposed that electrons orbit the nucleus in discrete energy levels and that atoms emit or absorb radiation when electrons transition between these levels. This model successfully explained the hydrogen spectrum and introduced the concept of quantized atomic states, building on earlier work by Max Planck and Albert Einstein.

Bohr returned to Copenhagen as a professor and in 1920 founded the Institute for Theoretical Physics at the University of Copenhagen, later renamed the Niels Bohr Institute. The institute became one of the most important centers of theoretical physics in the world during the 1920s and 1930s, attracting leading physicists including Werner Heisenberg, Wolfgang Pauli, and Paul Dirac.

Bohr was awarded the Nobel Prize in Physics in 1922 for his investigation of the structure of atoms and the radiation emanating from them. He made further contributions to quantum mechanics, including formulating the principle of complementarity, which holds that quantum objects can exhibit wave-like or particle-like properties depending on the experimental context, but not both simultaneously. This became central to what is often called the Copenhagen interpretation of quantum mechanics.

During the German occupation of Denmark in World War II, Bohr was warned of his impending arrest and escaped to Sweden in 1943, later travelling to the United States to participate in the Manhattan Project at Los Alamos. After the war, he advocated for international cooperation in the peaceful uses of atomic energy.

Bohr died on 18 November 1962 in Copenhagen. He is widely regarded as one of the most influential physicists of the twentieth century.