Niels Henrik David Bohr – Complementarity

12 Mar 2024

He was a Danish physicist who lived between 7 October 1885 and 18 November 1962, and won the Nobel Prize in Physics in 1922 for her work helping to understand atomic structures and quantum theory.
Niels Henrik David Bohr was born on October 7, 1885 in Copenhagen, Denmark. His father was a famous medical professor at the University of Copenhagen and his mother was the daughter of a wealthy banker. Niels and his brother Harald, who was two years younger than him and later became a famous mathematician, graduated from the University of Copenhagen with excellent grades. At the same time, they were both playing for the Denmark national football team.
Niels Bohr went to Cambridge University with a scholarship from Carlsberg breweries to study J.J. He went to Thompson's laboratory. After staying there for a few months, he joined Ernest Rutherford at Manchester University. After returning to Denmark in 1912, he took an important step in quantum physics by building the atomic model known under his name. He thought about the relationship between quantum physics and classical physics. In 1916 he returned to the University of Copenhagen as a professor of physics.
He developed the "liquid droplet model" of the atomic nucleus. Bohr, who was appointed head of the Copenhagen Institute for Theoretical Physics, received the Nobel Prize in 1922 for his studies on the structure of atoms and the radiation emitted from them. Bohr's interpretation of quantum mechanics (Copenhagen interpretation) was found around this time.
After Denmark was occupied by the Germans in World War II, she fled to Sweden and from there passed to the USA.
He participated in the Atomic bomb project at Alamos (Manhattan Project) in Los Alamos, New Mexico, and contributed to the development of the atomic bomb. However, as soon as the war ended, he returned to Denmark and worked to prevent the use and spread of the atomic bomb.
He was chosen as the 4th best physicist of all time by the evaluations of 100 leading physicists. He is surpassed by Einstein, Newton and Maxwell respectively.
Bohr developed the Bohr Atomic Model, in which he stated that the energy levels of electrons are discrete and that they rotate in discontinuous areas of orbits around the nucleus, 'like the movement of the planets around the Sun, except that they can pass from one energy level (orbit) to another.
Bohr explains the principle of complementarity as follows: elements can be separated and evaluated in terms of their contradictory properties, such as particles behaving like waves or a stream. The concept of complementarity became a dominant concept in Bohr's thoughts in both science and philosophy.
Bohr read Soren Kierkegaard, a 19th-century Danish Christian existentialist philosopher. Richard Rhodes stated in “The Making of the Atomic Bomb” that Bohr was influenced by Kierkegaard through Hoffding. The debates between Bohr and Kiekegaard stemmed mostly from Bohr's atheism.
In 1909, he sent Kierkegaard's "Steps on the Path of Life" as a gift to Bohr's brother. Bohr wrote in a sealed envelope: “This is the only thing I have to be at home, but to think that it is easy to find something better than this. In fact, he is one of the nicest people.” He used his expressions.
According to physicist and historian Arthur I. Miller, cubism directly helped Bohr to explain the principle of complementarity in quantum theory. Just as something can be both a particle and a wave and only one of them can be detected, when cubist artists projected a scene on the canvas from all possible perspectives, we, the observers, could only choose one of these different perspectives. So it is the way you look at the picture. The development that inspired Bohr occurred after he read a book on cubist theory by Jean Metzinger and Albert Gleizes. In the book, the integrated existence of an electron had both wave and particle properties, and the idea was put forward that only one of its properties was selected during observation.
According to Werner Heisenberg's uncertainty principle, in quantum physics, the position (coordinates) and momentum (mass x velocity) of a particle cannot be measured simultaneously with absolute accuracy. With this principle, the "probabilistic" character of quantum mechanics is revealed. In the wave/particle duality, if we emphasize one aspect of the event (for example, the particle), it makes the other aspect uncertain, and the exact relationship between these two is determined by the uncertainty principle.

 Niels Bohr put forward the idea of ​​complementarity to better understand the wave/particle connection and considered both the particle description and the wave description as two complementary descriptions of the same reality. Bohr argued that this could be a useful concept outside the field of physics. Because the opposites yin and yang relate to each other in a polar or complementary manner, the modern concept of complementarity is the result of ancient Chinese thought that had a profound influence on Niels Bohr
Perhaps Bohr's greatest contribution to modern physics was his development of the atomic model. The Bohr model of the atom shows the atom with a positively charged nucleus and electrons circulating around it. Bohr was the first scientist to discover that electrons revolve in different orbits around the nucleus and that the number of electrons in these orbits determines the properties of the atom.

Bohrium atom, whose atomic number is 107 in the periodic table, is named after Niels Bohr.

liquid droplet model
Niels Bohr's theoretical work made significant contributions to the understanding of nuclear fusion. The droplet in his liquid droplet model represented the atom. If a sufficient amount of energy was supplied to this atom, the atom would split into two almost equal parts and a huge amount of energy would be released. This theory was used in the 1930s in attempts to split the uranium atom, which would later be used to make an atomic bomb.
His Debate with Einstein and Quantum Theory
The concept of complementarity, about which Bohr published several papers between 1933 and 1962, predicts that an electron moves either as a wave or as a particle. But he cannot act as both at the same time.

Anyone who is not shocked by quantum theory has not yet understood it. –Niels Bohr

Einstein always criticized quantum theory and therefore Bohr's work. This discussion between Bohr and Einstein contributed to the understanding of the hundred-year-old quantum theory. Regarding quantum theory, Einstein said: 'God does not play dice.' he said. In response to this, Niels Bohr said, 'Einstein, stop telling God what to do.' He is said to have said.

This debate has also brought new gains to the scientific world. Einstein presented the EPR Paradox to refute the uncertainty principle of quantum theory. The epr paradox actually led to the further development of quantum theory.
EPR Paradox: Imagine you have two particles. You measure their weight, combine the particles, and gently push them. A problem arises here. Their speeds and positions must be related. If you measure the position of the particle, even if you cannot measure its speed, this does not mean that it does not have a certain speed. As a solution to this, Einstein suggested that the speed of the second particle could be measured and the speed could be known since everything was mathematically related.

Death of Niels Bohr

Niels Bohr died of heart failure on November 18, 1962. His body was cremated and placed in an area in the family cemetery. Later, his wife's ashes were also placed here. On October 7, 1965, on the 80th anniversary of Niels Bohr's birth, the Institute for Theoretical Physics at the University of Copenhagen changed its name to the Niels Bohr Institute.

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