Great European: Niels Bohr

Niels Henrik David Bohr, born on 18th November 1885 was one of the most influential physicists of the 20th century.  One of the early pioneers of quantum physics, his work not only helped revolutionize the field he was working in, he also helped change the way we look at the world.

Bohr’s most important contribution to physics is the Bohr model, that depicts the atom as a small, positively charged nucleus surrounded by electrons that travel in circular orbits around the nucleus. It represents an important step in the development of modern quantum mechanics. Other notable concepts developed by Bohr include the correspondence principle, a bridge between classical mechanics and quantum mechanics, and the  concept of complementarity, which postulates that the knowledge of certain measurements necessarily leads to a lack of knowledge regarding other measurable variables. In his scientific works Bohr was among the first to make the claim that the modus of observation determines what is the essence of any given apparatus. His work thus raised completely new questions regarding our understanding of the nature of knowledge in general.
In 1921 he received the Hughes medal and in 1922 the Nobel Price for physics.


The young Niels Bohr.

Bohr was brought up in an environment where regular scientific debate was part of everyday life. His father, Christian Bohr was a Professor of physiology, his brother would later become a professor of mathematics.

Aged 22 Bohr was already way ahead of his fellow students at the University of Kopenhagen. In 1907 he received the gold medal of the Royal Danish Academy for his work on the surface tension of liquids. After graduation with his doctoral thesis in 1911 he continued his work at Cambridge and later Manchester, where he would meet his wife Margarethe Nørlund with whom he’d have six children. Their son Aage Niels Bohr would also receive the physics nobel in 1975.

In 1926/7 Werner Heisenberg joined Bohr at his institute in Copenhagen, where he developed his famous uncertainty principle while Bohr formulated the concept of complementarity. Both where published in 1927 and together formed the Copenhagen interpretation of quantum theory.

During German occupation Bohr, who’s mother was Jewish, was engaged in the resistance. With the fight becoming increasingly dangerous, he and his brother Harald were warned that they were soon to be arrested and successfully fled to Sweden in 1943. He was soon exfiltrated by the British in a spectacular escape during which he nearly suffocated on an airplane after not hearing the pilot’s instruction to put on his oxygen mask. From Britain he continued his journey to the US. There he was engaged in the Rockefeller Institute’s effort to help European scientists flee the German occupied territories and consulted on the Manhattan Project.

After the war Bohr returned to Copenhagen and was re-elected President of the Royal Danish Academy of Arts and Sciences and was soon thereafter awarded the Order of the Elephant, an honor that had up until then only been given to royalty and heads of state. For the occasion Bohr designed his own coat of arms, featuring a symbol of yin and yang and his life’s and work’s motto in Latin: contraria sunt complementa.

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