Niels Henrik David Bohr (1885 – 1962)

17th Jan 2020 @ 9 min read

“Anyone who is not shocked by quantum theory has not understood it.”
―Niels Bohr

Niels Bohr was a Danish Nobel laureate and widely known for his atomic theory. He is considered one of the influential physicists of the 20th century. His contributions to understanding of atoms have greatly shaped the modern atomic theory. He was the first to apply the quantum theory to atoms; his atomic theory is now called the Bohr model or Rutherford-Bohr model.

Early Life

On 7th October 1885, Bohr was born in Copenhagen to Christian Bohr, a Danish Physician and Ellen Adler Bohr, who was a Danish Jewish. He was the second child; he had an elder sister, Jenny, who became a teacher and a younger brother, Harald, a mathematician and member Denmark national football team. His father was a prominent scientist in Denmark and was nominated twice for a Nobel Prize.

Although raised in scientific background, Bohr and his brother enjoyed playing football. Besides football, he loved to repair everything he could get his hands on; he repaired family watches and bicycles, and other mechanical devices.

School

When in school, he stood the first. His worst subject was Danish writing. At the end of schooling years, his interest grew in science and was able to note mistakes in textbooks. He completed his matriculation from Gammelholm Latin School and enrolled at Copenhagen University in 1903.

Higher education

In the first year of his graduate, he studied astronomy and mathematics under Prof. Thorvald Thiele and philosophy under Prof. Harald Høffding. Under the guidance of Prof. Christian Christiansen, he studied physics. In 1909, Bohr obtained his Master degree and his Doctorate in 1911.

While pursuing his master, he won a competition and was awarded a gold medal by the Royal Danish Academy of Sciences and Letters. The aim of the competition is to devise a method for measuring the surface tension of liquids. His work was published in the Transactions of the Royal Society in 1908.

Bohr was intrigued with electrons. He did his doctorate thesis on the electron theory of metals. It was accepted in April 1911 and was ground-breaking. A year later, Hendrika Johanna van Leeuwe, a Dutch physicist, developed a theorem from the Bohr thesis, which is now called the Bohr-van Leeuwen theorem.

Family

He met Margrethe Nørlund, his future wife, roughly after the completion of his master. Margrethe Nørlund was the sister of the mathematician Niels Erik Nørlund, a friend of Harald. The couple fell in love and got engaged in 1910 and married in Slagelse on 1 August 1912.

They had six sons: Christian (died by an accident), Harald (died by meningitis), Aage (became a physicist like his father and was honoured the Nobel Prize in 1975), Hans (became a physician), Erik Bohr (pursued chemical engineering), and Ernest (the youngest of all became a lawyer).

Career

After finishing his doctorate, he travelled abroad to England for further studies, which was supported by the Carlsberg Foundation. He met numerous scientists of his time, notably J. J. Thomson, the discoverer of the electron; James Jeans, an English physicist, astronomer, and mathematician; Joseph Larmor, an Irish physicist and mathematician; and William Lawrence Bragg, an Australian-British physicist.

In April 2012, he received an invitation from Ernest Rutherford to continue his postdoctoral research at Victoria University of Manchester, which he accepted. While working Rutherford, he realised that Rutherford's atom is incontinent and unstable. He took Max Planck's idea quanta of energy and combined with Rutherford's model. This developed into the Bohr's model. The model was pretty successful in explaining many of the shortcomings its predecessor had, particularly the spectral lines of hydrogen. His theory got published in 1913 in three papers, aka the trilogy. It acquired the attention of many scientists and kept developing over the course of time. Even though the model has supplanted, it is still famous and found in chemistry textbooks.

In 1916, Bohr was appointed to the chair of theoretical physics at the University of Copenhagen. He began a campaign to raise funds for construction and development of a modern institute with better laboratories and classrooms. His plea was approved in November 1918 by the Danish parliament and the Niels Bohr Institute, formerly University of Copenhagen’s Institute for Theoretical Physics, was established in March 1921. Bohr was made the director of the institute.

Bohr was awarded the Nobel Prize in Physics in 1922 for his trilogy. In the same year, Einstein also received his delayed Nobel Prize in Physics, not for his relativity but for his photoelectric effect.

In 1924, Bohr along with Kramers and Slater formulated the Bohr–Kramers–Slater theory (BKS theory). 1925 was a very important year in the history of science. The modern quantum mechanics arose. Bohr came in contact with prominent scientist including Paul Ehrenfest, Albert Einstein, Werner Heisenberg, Pascual Jordan, and Erwin Schrödinger. He enjoyed the company of Einstein; their contentious discussions about quantum mechanics is called as the Bohr–Einstein debates.

Between 1922 and 1928, many scientists visited Copenhagen and held meetings with Bohr. They shared various opinions about the nature of matter. Towards the end of 1927, Bohr convinced the light could behave as both particle and wave.

Rise of Nazis

Around 1933, Nazism dominance increased in Germany. Consequently, many people absconded their country, especially Jews. Bohr provided assistance to the refugees. In April 1940, the Nazi invaded Denmark. To prevent the Nobel medals of Max von Laue and James Franck falling into the hands of the Nazi, Bohr dissolved the gold medals in aqua regia. Max von Laue was a German physicist and oppose the Nazi regime, and James Franck was also a German physicist but a Jewish. Later, the metal was precipitated and the medals were reconstructed.

In September 1941, Werner Heisenberg, who a German physicist and the head of the German nuclear energy project, made a visit to Bohr in Copenhagen. The purpose of the exchange is still unclear. There are widespread speculations about it.

On 29 September 1943, Bohr along with his wife escaped to Sweden in the fear of execution by the Nazi because his mother was from a Jewish family. Sweden also provided shelter to many Danish Jews by the persuasive efforts of Bohr.

Shortly, he migrated to Scotland and was warmly welcomed by James Chadwick and John Anderson. His son Aage followed his father to Britain and became his assistance later on.

International Atomic Energy Agency Formation

On 8 December 1943, Bohr visited Washington DC as a member of the British group of scientists. The purpose of the visit was to produce a nuclear weapon. In a series of extended visits to the US, he also met Einstein, Pauli, Feynman, and Oppenheimer. He condemned the secrecy of the development of the nuclear weapon and tried to convince President Roosevelt and Churchill. He recognised the rise of nuclear race between the US and the Soviets. After failing attempts to convince Americans and the British, he addressed an open letter to the UN for the collaboration of nuclear energy. In 1957, the International Atomic Energy Agency Formation was established with the aim to promote peaceful use of nuclear energy. In the same year, he was awarded the first-ever Atoms for Peace Award.

The final years

After the end of the war, he returned to his home town, Copenhagen and went about reviving his institute. He had played an important role in the formation of CERN, the European Organization for Nuclear Research. He had many grandsons and appreciated spending time with them. Bohr died on 18 November 1962 at 77 and was buried at Assistens Cemetery in Copenhagen. His reason for his death was heart failure.