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Niels Bohr

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   CAPTION: Niels Bohr

   Niels Henrik David Bohr
   Niels Henrik David Bohr
         Born       October 7, 1885
                    Copenhagen, Denmark
         Died       November 18, 1962
                    Copenhagen, Denmark
     Nationality    Danish
        Field       Physicist
     Institution    University of Copenhagen
   Doctoral Advisor Christian Christiansen
      Known for     Copenhagen interpretation
                    Complementarity
    Notable Prizes  Nobel Prize (1922)

   Niels (Henrik David) Bohr [nels ˈb̥oɐ̯ˀ] ( October 7, 1885 – November
   18, 1962) was a Danish physicist who made fundamental contributions to
   understanding atomic structure and quantum mechanics. Bohr is widely
   considered one of the greatest physicists of the twentieth century.

Contributions to physics

     * Bohr's model
     * The electron's orbital angular momentum is quantized; L=nħ.
     * The theory that electrons travel in discrete orbits around the
       atom's nucleus, with the chemical properties of the element being
       largely determined by the number of electrons in each of the outer
       orbits.
     * The idea that an electron could drop from a higher-energy orbit to
       a lower one, emitting a photon (light quantum) of discrete energy
       (this became the basis for quantum theory).
     * Much work on the Copenhagen interpretation of quantum mechanics.
     * The principle of complementarity: that items could be separately
       analyzed as having several contradictory properties.

   He received the Nobel Prize for Physics for this work in 1922.

Biography

Early years

   Enlarge

   Niels Bohr was born in Copenhagen, Denmark in 1885. His father,
   Christian Bohr, was professor of physiology at the University of
   Copenhagen, while his mother, Ellen Adler Bohr, came from a wealthy
   Sephardic Jewish family prominent in Danish banking and parliamentary
   circles. His brother was Harald Bohr, a mathematician and Olympic
   soccer player who played in the Danish national team; Niels Bohr was a
   passionate soccer player as well, and the two brothers played a number
   of matches for Akademisk Boldklub.

   Bohr received his doctorate from Copenhagen University in 1911 under
   Christian Christiansen. He then studied under Ernest Rutherford in the
   Victoria University of Manchester in England. On the basis of
   Rutherford's theories, Bohr published his model of atomic structure in
   1913, introducing the theory of electrons traveling in orbits around
   the atom's nucleus, the chemical properties of the element being
   largely determined by the number of electrons in the outer orbits. Bohr
   also introduced the idea that an electron could drop from a
   higher-energy orbit to a lower one, emitting a photon (light quantum)
   of discrete energy. This became a basis for quantum theory.

Middle years

   Niels Bohr and Albert Einstein debating quantum theory at Paul
   Ehrenfest's home in Leiden (December 1925).
   Enlarge
   Niels Bohr and Albert Einstein debating quantum theory at Paul
   Ehrenfest's home in Leiden (December 1925).

   In 1916, Niels Bohr became a professor at the University of Copenhagen,
   and director of the newly constructed "Institute of Theoretical
   Physics" in 1920. In 1922, Bohr was awarded the Nobel Prize in physics
   "for his services in the investigation of the structure of atoms and of
   the radiation emanating from them". Bohr's institute served as a focal
   point for theoretical physicists in the 1920s and '30s, and most of the
   world's best known theoretical physicists of that period spent some
   time there.

   Bohr also conceived the principle of complementarity: that items could
   be separately analyzed as having several contradictory properties. For
   example, physicists currently conclude that light is both a wave and a
   stream of particles — two apparently mutually exclusive properties — on
   the basis of this principle. Bohr also found philosophical applications
   for this daringly original principle. Albert Einstein much preferred
   the determinism of classical physics over the probabilistic new physics
   of Bohr (to which Max Planck and Einstein himself had contributed). He
   and Bohr had good-natured arguments over the truth of this principle
   throughout their lives (see Bohr Einstein debate). One of Bohr's most
   famous students was Werner Heisenberg, a crucial figure in the
   development of quantum mechanics, who was also head of the German
   atomic bomb project.

   Niels Bohr and his wife Margrethe Nørlund had six children. Two died
   young, and most of the others went on to lead successful lives. One,
   Aage Niels Bohr, also became a very successful physicist; like his
   father, he won a Nobel Prize.

Later years, death, and legacy

   In 1941, during the German occupation of Denmark in World War II, Bohr
   was visited by Heisenberg in Copenhagen (see next section). In 1943,
   shortly before he was to be arrested by the German police, Bohr escaped
   to Sweden, and then traveled to London.

   He worked at the secret Los Alamos laboratory in New Mexico, USA, on
   the Manhattan Project, where, according to Richard Feynman, he was
   known by the assumed name of Nicholas Baker for security reasons. His
   role in the project was important. He was seen as a knowledgeable
   consultant or "father confessor" on the project. He was concerned about
   a nuclear arms race, and is quoted as saying "That is why I went to
   America. They didn't need my help in making the atom bomb." .

   Bohr believed that atomic secrets should be shared by the international
   scientific community. After meeting with Bohr, J. Robert Oppenheimer
   suggested Bohr visit President Franklin Roosevelt to convince him that
   the Manhattan Project should be shared with the Russians in the hope of
   speeding up its results. Roosevelt suggested Bohr return to England to
   try to win British approval. Churchill opposed the idea.^

   After the war he returned to Copenhagen, advocating the peaceful use of
   nuclear energy. He died in Copenhagen in 1962. He is buried in the
   Assistens Kirkegård in the Nørrebro section of Copenhagen.

   The element bohrium is named in his honour. He is pictured on the 500
   kr. Danish bank note. In 1965, three years after Bohr's death, the
   institute of physics at the university of Copenhagen changed its name
   to the Niels Bohr Institute.

Kierkegaard's influence on Bohr

   It is generally accepted that Bohr read the 19th century Danish
   philosopher Søren Kierkegaard. In 1909, Bohr sent his brother
   Kierkegaard's Stages on Life's Way as a birthday gift. In the enclosed
   letter, Bohr wrote, "It is the only thing I have to send; but I do not
   believe that it would be very easy to find anything better.... I even
   think it is one of the most delightful things I have ever read." Bohr
   enjoyed Kierkegaard's language and literary style, but mentioned that
   he had some "disagreement with [Kierkegaard's ideas]".

   Given this, there has been some dispute over whether Kierkegaard
   influenced Bohr's philosophy and science. David Favrholdt argues that
   Kierkegaard had minimal influence over Bohr's work; taking Bohr's
   statement about disagreeing with Kierkegaard at face value, while Jan
   Faye argues the opposing point of view; by arguing that one can
   disagree with the content of a theory while accepting its general
   premise and structure. ^

Relationship with Heisenberg

   Bohr and Heisenberg enjoyed a strong mentor/mentee relationship up to
   the onset of World War II. At that point, the relationship became
   somewhat strained because Bohr, with his Jewish heritage, remained in
   occupied Denmark, while Heisenberg remained in Germany. Heisenberg made
   a now-famous visit to Bohr in September 1941, and during a private
   moment, began to discuss nuclear weapons and the war efforts. Michael
   Frayn's play Copenhagen, which ran on Broadway for a time, explores
   what might have happened at the 1941 meeting between Heisenberg and
   Bohr. The truth of the historical event is still a matter of scholarly
   debate, as neither Bohr nor Heisenberg spoke about it in any detail,
   and they were alone in the woods. While some suggest that the
   relationship became somewhat strained at this meeting, other evidence
   suggests that the fracture occurred much later. In correspondence to
   his wife, Heisenberg described the final visit of the trip: "Today I
   was once more, with Weizsaecker, at Bohr's. In many ways this was
   especially nice, the conversation revolved for a large part of the
   evening around purely human concerns, Bohr was reading aloud, I played
   a Mozart Sonata (A-Major)."

   In 1957, while the author Robert Jungk was working on the book Brighter
   Than a Thousand Suns, Heisenberg wrote to Jungk explaining that he had
   visited Copenhagen to communicate to Bohr his view that scientists on
   neither side should help develop the atomic bomb, that the German
   attempts were entirely focused on energy production, and that
   Heisenberg's circle of colleagues tried to keep it that way. However,
   Heisenberg acknowledged that his cryptic approach of the subject had
   so-alarmed Bohr that the discussion failed. Heisenberg nuanced his
   claims, though, and avoided implication that he and his colleagues had
   purposely sabotaged the bomb effort. However, this nuance was lost in
   Jungk's original publication of the book, which strongly implied that
   the German atomic bomb project was rendered purposely stillborn by
   Heisenberg.

   When Bohr saw this erroneous depiction in the Danish translation of
   Jungk's book, he disagreed wholeheartedly. He said that while
   Heisenberg had indeed discussed the subject of nuclear weapons in
   Copenhagen that Heisenberg never alluded to the fact that Heisenberg
   might be resisting efforts to build such weapons. He dismissed the idea
   of any pact as an after-the-fact construction. He drafted several
   letters to inform Heisenberg about this but never sent any of them.

Quotations

     * "And anyone who thinks they can talk about quantum theory without
       feeling dizzy hasn't yet understood the first thing about it."
     * "If quantum mechanics hasn't profoundly shocked you, you haven't
       understood it yet."
     * "Nothing exists until it is measured."
     * "A triviality is a statement whose opposite is false. However, a
       great truth is a statement whose opposite may well be another great
       truth."
     * "Your theory is crazy, but it's not crazy enough to be true."
     * "How wonderful that we have met with a paradox. Now we have some
       hope of making progress!"
     * "Einstein, stop telling God what to do." Sometimes quoted
       including: "...with his dice."
     * Alternate version: "Don't you think caution is needed when using
       ordinary language to ascribe attributes to God?"
     * "The complement of truth is clearness."
     * "It is very difficult to make an accurate prediction, especially
       about the future."
     * "An expert is a person who has made all the mistakes that can be
       made in a very narrow field."
     * "Never talk faster than you think."
     * "There are some things so serious you have to laugh at them."

Trivia

     * On The Simpsons episode " I Am Furious Yellow," when When Dinosaurs
       Get Drunk gets cancelled, it is replaced by The Boring World of
       Niels Bohr much to Homer's discontent.

     * Around 1999, Niels Bohr and the University of Copenhagen began
       appearing as parts of "The Barometer Problem" , an unverified urban
       legend illustrating lateral thinking.

     * Niels Bohr was featured in the video game Secret Weapons Over
       Normandy by Lucasarts.

     * Bohr has an Erdos number of 5.

     * Fellow of American Philosophical Society (1940)

     * Nobel Prize (1922), Hughes Medal (1921), Matteucci Medal (1923),
       Copley Medal (1938)

     * Wife: Margrethe Nørlund (m. 1912)

     * Son: Aage Niels Bohr

     * Bohr was Left handed

     * On a Space Ghost Coast to Coast episode entitled "Captain &
       Tennille" Space Ghost babbles: "What in the name of the coefficient
       of the speed of light, multiplied by the red shift to the
       hypotenuse of the nth root, hypotenuse, hypotenuse..." Niels Bohr
       is mentioned as being the only person who "gets" him.

Books about Bohr

     * Niels Bohr: The Man, His Science, and the World They Changed, by
       Ruth Moore; ISBN 0-262-63101-6
     * Niels Bohr's Times, In Physics, Philosophy and Polity, by Abraham
       Pais; ISBN 0-19-852049-2
     * Suspended In Language: Niels Bohr's Life, Discoveries, And The
       Century He Shaped by Jim Ottaviani (graphic novel); ISBN
       0-9660106-5-5
     * Harmony and Unity : The Life of Niel's Bohr, by Niels Blaedel; ISBN
       0-910239-14-2

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