Niels Henrik David Bohr

Born: October 7, 1885 Died: November 18, 1962

Niels Bohr was born in , to Christian Bohr and Ellen Adler. His father, Christian Bohr, was a physiology teacher at the and his mother, Ellen Adler, was the daughter of a prominent Jewish politician and banker. The Bohr family was well to do and enjoyed and a comfortable lifestyle. Bohr’s parents were both intellects who enjoyed the pursuit of knowledge and lively discussion of such. The Bohr home was often a meeting place for discussion groups and as such the Bohr children were exposed to a stimulating environment from an early age. Niels was the middle child, having an older sister (Jenny) and a younger brother (Harald). Niels and his brother were best friends throughout their entire lives. They attended university together, and played on the university soccer team together. Harald went on to become a successful mathematician and even finished his doctorate before his older brother Niels did. In later years, Niels frequently wrote letters to Harald, confiding his new theories and research in him. In 1903 Niels began his undergraduate degree at the University of Copenhagen where he majored in physics. He obtained his masters and doctorate from the University of Copenhagen, earning his doctorate in 1911. Both his masters and doctorate thesis were concerned with the electron theory of metals, the latter being entitled “ Studies on the elcectron theory of metals”. He dedicated this thesis to his father who had passed away earlier in the year. Niels met Margethe Norlund in 1909 and they were married on August 1, 1912. Margethe was a great supporter of her husband and they were happily married for over 50 years. The two had 6 children together, although only 4 lived to adulthood. In 1934, their oldest son, Christian, (who was 17) drowned while sailing with Niels. The surviving 4 children were successful in life, becoming doctors, lawyers and engineers. Their son, Aage, was also a physicist and won the Nobel Prize for physics in 1975 for his work “on the discovery of the connection between collective motion and particle motion in atomic nuclei and the development of the theory of the structure of the atomic nucleus based on this connection.” 1n 1911 Niels traveled to Cambridge to work with JJ Thomson. The two did not hit it off so after completing his work, Niels moved on to Manchester to work with Ernest Rutherford. At this time Rutherford had just put forth his theory that the atom was composed of a positively charged nucleus being orbited by clouds of negatively charged electrons. Incorporating Rutherford’s theory with quantum ideas of Planck and Einstein, Bohr came up with his own “quantum postulates” to describe the structure of the atom. In 1913 he published his papers on the quantum theory of atomic structure. He was awarded the Nobel Prize for this work in 1922. From 1913-1916 Niels worked as a docent in both Manchester and Copenhagen, and although he enjoyed his time at this, he was extremely pleased to be given the chair of theoretical physics at the University of Copenhagen in 1916 (this was a position which he lobbied to have created several years back). In 1921 the Institute for Theoretical Physics was opened at the University of Copenhagen. The institute was specifically established for him by the university and was funded by the Carlsberg brewery. Here, many well known scientists (Pauli, Heisenbeg, Dirac) came to study, research, discover and discuss quantum physics with . During World War II Niels and his family were forced to escape Denmark because of their Jewish ancestry. During this time he worked in Britain and in Los Alamos on the “Manhattan Project” to build an atomic bomb. His work on nuclear fission was not without concern though and he lobbied Roosevelt, Churchill and the UN for the control of nuclear weapons. After the war Niels returned to Denmark where he remained director of his institute until his death in 1962.

Niel’s Bohr Contributions:

1. The Bohr Atom

2. Clarification of problems associated with quantum physics. -while many others made significant discoveries and contributions to quantum theory, Niels Bohr devoted more than 50 years to interpreting, understanding and defending the theory -concept of complentarity: an object may have dual nature (i.e. wave/particle) that mutually exclude each other but we must understand both to fully understand the object’s properties; the way an object behaves depends on the apparatus we use to observe it

3. Nuclear Physics -Liquid drop theory: permitted the understanding of the mechanism of nuclear fission - recognized the different roles of uranium isotopes in the fission, this fact played a key role in technical development leading to the release of atomic energy

References

Course Textbooks: Uncle Tungsten: Memories of a Chemical Boyhood Introducing Quantum Theory

Other Books: Niels Bohr: Gentle Genius of Denmark by Ray Spangenburg & Diane K. Moser Niels Bohr’s Times: In physics, philosophy and polity by Abraham Pais Copenhagen by Michael Frayn

Websites: www-groups.dcs.st-and.ac.uk/~history www.nobelprize.org/physics/laureates/1922/bohr-bio.html www.pbs.org/wbgh/aso/databank/entries/bpbohr.html www-groups.dcs.st-and.uk/~history/HistTopics/The_Quantum_age_begins/html www.nbi.dk/nbi-history.html