# Neils Bohr: Wikis

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Niels Bohr

Born Niels Henrik David Bohr
7 October 1885
Copenhagen, Denmark
Died 18 November 1962 (aged 77)
Copenhagen, Denmark
Nationality Denmark
Fields Physics
Institutions University of Copenhagen
University of Manchester
Alma mater University of Cambridge
University of Copenhagen
Ernest Rutherford
Doctoral students Hendrik Anthony Kramers
Known for Copenhagen interpretation
Complementarity
Bohr model
Sommerfeld–Bohr theory
BKS theory
Bohr-Einstein debates
Influences Ernest Rutherford
Influenced Werner Heisenberg
Wolfgang Pauli
Paul Dirac
Lise Meitner
Max Delbrück
and many others
Notable awards Nobel Prize in Physics (1922)
Signature
Notes
Harald Bohr is his younger brother, and Aage Bohr is his son.

Niels Henrik David Bohr (Danish pronunciation: [nels ˈb̥oɐ̯ˀ]; 7 October 1885 – 18 November 1962) was a Danish physicist who made foundational contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. Bohr mentored and collaborated with many of the top physicists of the century at his institute in Copenhagen. He was part of a team of physicists working on the Manhattan Project. Bohr married Margrethe Nørlund in 1912, and one of their sons, Aage Bohr, grew up to be an important physicist who in 1975 also received the Nobel prize. Bohr has been described as one of the most influential physicists of the 20th century.[1]

## Biography

### Early years

Bohr was born in Copenhagen, Denmark, in 1885. His father, Christian Bohr, a devout Lutheran, was professor of physiology at the University of Copenhagen (it is his name which is given to the Bohr shift or Bohr effect), while his mother, Ellen Adler Bohr, came from a wealthy Jewish family prominent in Danish banking and parliamentary circles. His brother was Harald Bohr, a mathematician and Olympic footballer who played on the Danish national team. Niels Bohr was a passionate footballer as well, and the two brothers played a number of matches for the Copenhagen-based Akademisk Boldklub, with Niels in goal. There is, however, no truth in the oft-repeated claim that Niels Bohr emulated his brother Harald by playing for the Danish national team.[2]

In 1903 Bohr enrolled as an undergraduate at Copenhagen University, initially studying philosophy and mathematics. In 1905, prompted by a gold medal competition sponsored by the Royal Danish Academy of Sciences and Letters, he conducted a series of experiments to examine the properties of surface tension, using his father's laboratory in the university, familiar to him from assisting there since childhood. His essay won the prize, and it was this success that decided Bohr to abandon philosophy and adopt physics.[3] As a student under Christian Christiansen he received his doctorate in 1911. As a post-doctoral student, Bohr first conducted experiments under J. J. Thomson at Trinity College, Cambridge. He then went on to study under Ernest Rutherford at the 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 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.

Niels Bohr and his wife Margrethe Nørlund Bohr had six sons. Their oldest died in a tragic boating accident and another died from childhood meningitis. The others went on to lead successful lives, including Aage Bohr, who became a very successful physicist and, like his father, won a Nobel Prize in physics, in 1975.

### Physics

In 1916, Niels Bohr became a professor at the University of Copenhagen. With the assistance of the Danish government and the Carlsberg Foundation, he succeeded in founding the Institute of Theoretical Physics in 1921, of which he became its director.[4] 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.

Niels Bohr as a young man. Exact date of photo unknown.
Niels Bohr and Albert Einstein debating quantum theory at Paul Ehrenfest's home in Leiden (December 1925).

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 behaves either as a wave or a stream of particles depending on the experimental framework — two apparently mutually exclusive properties — on the basis of this principle. Bohr found philosophical applications for this daringly original principle. Albert Einstein much preferred the determinism of classical physics over the probabilistic new quantum physics (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 debates).

Werner Heisenberg worked as an assistant to Bohr and university lecturer in Copenhagen from 1926 to 1927. It was in Copenhagen, in 1927, that Heisenberg developed his uncertainty principle, while working on the mathematical foundations of quantum mechanics. Heisenberg was later to be head of the German atomic bomb project. In 1941, during the German occupation of Denmark in World War II, Bohr was visited by Heisenberg in Copenhagen (see section below). In 1943, shortly before he was to be arrested by the German police, Bohr escaped to Sweden, and then traveled to London.

### Atomic research

Niels Bohr worked at the top-secret Los Alamos laboratory in New Mexico, U.S., on the Manhattan Project, where he was known by the assumed name of Nicholas Baker for security reasons.[5] His role in the project was important and was 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."[6]

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 D. 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 the United Kingdom to try to win British approval. Winston Churchill disagreed with the idea of openness towards the Russians to the point that he wrote in a letter: "It seems to me Bohr ought to be confined or at any rate made to see that he is very near the edge of mortal crimes."[7]

After the war Bohr returned to Copenhagen, advocating the peaceful use of nuclear energy. When awarded the Order of the Elephant by the Danish government, he designed his own coat of arms which featured a taijitu (symbol of yin and yang) and the Latin motto contraria sunt complementa: opposites are complementary.[8] He died in Copenhagen in 1962 of heart failure.[9] He is buried in the Assistens Kirkegård in the Nørrebro section of Copenhagen.

## Kierkegaard's influence on Bohr

It is generally accepted that Bohr read the 19th century Danish philosopher Søren Kierkegaard. Richard Rhodes argues in The Making of the Atomic Bomb that Bohr was influenced by Kierkegaard via the philosopher Harald Høffding, who was strongly influenced by Kierkegaard and who was an old friend of Bohr's father. 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 home; 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]."[11]

Given this, there has been some dispute over whether Kierkegaard influenced Bohr's philosophy and science. David Favrholdt[12] argues that Kierkegaard had minimal influence over Bohr's work; taking Bohr's statement about disagreeing with Kierkegaard at face value, while Jan Faye[13] endorses the opposing point of view by arguing that one can disagree with the content of a theory while accepting its general premises and structure.[14]

## Relationship with Heisenberg

Bohr and Werner Heisenberg enjoyed a strong mentor/protégé relationship up to the onset of World War II. Heisenberg had made Bohr aware of his talent during a lecture in 1922 in Göttingen. During the mid-1920s, Heisenberg worked with Bohr at the institute in Copenhagen. Heisenberg, like most of Bohr's assistants, learned Danish. Heisenberg's uncertainty principle was developed during this period, as was Bohr's complementarity principle.

By the time of World War II, the relationship became strained; this was in part because Bohr, with his partially-Jewish heritage, remained in occupied Denmark, while Heisenberg remained in Germany and became head of the German nuclear effort. Heisenberg made a famous visit to Bohr in September 1941 and during a private moment it seems that he began to address nuclear energy and morality as well as the war. Neither Bohr nor Heisenberg spoke about it in any detail or left written records of this part of the meeting and they were alone and outside.[15] Bohr seems to have reacted by terminating that conversation abruptly while not giving Heisenberg hints in any direction.

While some suggest that the relationship became strained at this meeting, other evidence shows that the level of contact had been reduced considerably for some time already. Heisenberg suggested that the fracture occurred 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)."[16] Ivan Supek, one of Heisenberg's students and friends, claimed that the main figure of the meeting was actually Weizsäcker who tried to persuade Bohr to mediate peace between Great Britain and Germany.[17]

### Tube Alloys

"Tube Alloys" was the code-name for the British nuclear weapon program. British intelligence inquired about Bohr's availability for work or insights of particular value. Bohr's reply made it clear that he could not help. This reply, like his reaction to Heisenberg, made sure that if Gestapo intercepted anything attributed to Bohr it would point to no knowledge regarding nuclear energy as it stood in 1941. This does not exclude the possibility that Bohr privately made calculations going further than his work in 1939 with Wheeler.

After leaving Denmark in the dramatic day and night (October 1943) when most Jews were able to escape to Sweden due to exceptional circumstances (see Rescue of the Danish Jews), Bohr was quickly asked again to join the British effort and he was flown to the UK. He was evacuated from Stockholm in 1943 in an unarmed De Havilland Mosquito operated by British Overseas Airways Corporation (BOAC). Passengers on BOAC's Mosquitos were carried in an improvised cabin in the bomb bay. The flight almost ended in tragedy as Bohr did not don his oxygen equipment as instructed and passed out at high altitude. He would have died had not the pilot surmising from Bohr's lack of response to intercom communication that he had lost consciousness, descended to a lower altitude for the remainder of the flight. Bohr's comment was that he had slept like a baby for the entire flight.

As part of the UK team on "Tube Alloys" Bohr went to Los Alamos. Oppenheimer credited Bohr warmly for his guiding help during certain discussions among scientists there. Discreetly, he met President Franklin D. Roosevelt and later Winston Churchill to warn against the perilous perspectives that would follow from separate development of nuclear weapons by several powers rather than some form of controlled sharing of the knowledge, which would spread quickly in any case. Only in the 1950s after the immense surprise that the Soviets developed the weapons independently, was it possible to create the International Atomic Energy Agency along the lines of Bohr's suggestion.

### Speculation

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 either side should help prevent development of 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.[18] Heisenberg acknowledged that his cryptic approach of the subject had so alarmed Bohr that the discussion failed. Heisenberg nuanced his claims and avoided the implication that he and his colleagues had sabotaged the bomb effort; this nuance was lost in Jungk's original publication of the book, which implied that the German atomic bomb project was obstructed by Heisenberg.

When Bohr saw Jungk's erroneous depiction in the Danish translation of the book, he disagreed. He drafted (but never sent) a letter to Heisenberg, stating that while Heisenberg had indeed discussed the subject of nuclear weapons in Copenhagen, Heisenberg had never alluded to the fact that he might be resisting efforts to build such weapons. Bohr dismissed the idea of any pact as hindsight.[19]

Michael Frayn's play Copenhagen, which was performed in London (for five years), Copenhagen, Gothenburg, Rome, Athens, Geneva and on Broadway in New York, explores what might have happened at the 1941 meeting between Heisenberg and Bohr. Frayn points in particular to the onus of being one of the few to understand what it would mean to create a nuclear weapon.

## Open World

Bohr advocated informing the Soviet authorities that the atomic bomb would soon be in use. In 1944 he obtained an audience with Winston Churchill, who became worried about whether Bohr was a security risk.[20] In 1950 he addressed an 'Open Letter' to the United Nations.[21]

## Legacy

### Secondary

• Niels Bohr Collected Works 13-Volume Limited Edition Set, General Editor, Finn Aaserud; ISBN 978-0-444-53286-2.
• 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.
• Niels Bohr: His Life and Work As Seen by His Friends and Colleagues, edited by Stefan Rozental, John Wiley & Sons, 1964.
• 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.
• Niels Bohr: A Centenary Volume, edited by A. P French and P.J. Kennedy. ISBN 0-674-62415-7.
• Copenhagen Michael Frayn ISBN 0413724905
• Faust in Copenhagen: A Struggle for the Soul of Physics by Gino Segre; ISBN 0-670-03858-X.

## References

1. ^ Murdoch, Dugald (2000) "Bohr" in Newton-Smith, N. H. (ed.) A Companion to the Philosophy of Science. Great Britain: Blackwell Publishers, p. 26. ISBN 0-631-23020-3.
2. ^ James Dart. "Bohr's footballing career". Guardian. Retrieved 2010-03-10.
3. ^ Rhodes, Richard (1986). The Making of the Atomic Bomb. New York: Simon and Schuster. pp. 62–63. ISBN 0-671-44133-7.
4. ^ Finn Aaserud. "History of the institute: The establishment of an institute". Niels Bohr Institute. Retrieved 2008-05-11.
5. ^ Pais, Abraham. Niels Bohr's Times, In Physics, Philosophy and Polity p.496
6. ^ Long, Doug. "Niels Bohr - The Atomic Bomb and beyond". Hiroshima - was it necessary?. Retrieved 2006-12-21.
7. ^ Rhodes (1986:528-538)
8. ^ "Bohr crest". University of Copenhagen. 1947-10-17. Retrieved 2007-03-16.
9. ^ Pais, Abraham. Niels Bohr's Times, In Physics, Philosophy and Polity p.529
10. ^ Rhodes (1986:282-88)
11. ^ Register, Bryan (1997-12-01). "Complementarity: Content, Context and Critique". Retrieved 2006-12-21.
12. ^ Favrholdt, David. Niels Bohr’s Philosophical Background. Copenhagen: Munksgaard (1992): pp. 42-63.
13. ^ Faye, Jan. "Niels Bohr: His Heritage and Legacy." Dordrecht: Kluwer Academic Publishers (1991).
14. ^ Mark Richardson, et al. Religion & Science: History, Method, Dialogue. Routledge 1996, pg.289
15. ^ Heisenberg, Elisabeth (1984). Inner Exile: Recollections of a Life With Werner Heisenberg. Boston MA: Birkhauser. p. 77 et seq. ISBN 0817631461.
16. ^ Heisenberg, Werner. "Letter from Werner Heisenberg to his wife Elisabeth written during his 1941 visit in Copenhagen". Heisenberg, Jochen. Retrieved 2006-12-21.
17. ^
18. ^ Heisenberg, Werner. "Letter From Werner Heisenberg to Author Robert Jungk". The Manhattan Project Heritage Preservation Association, Inc.. Retrieved 2006-12-21.
19. ^ Aaserud, Finn (2002-02-06). "Release of documents relating to 1941 Bohr-Heisenberg meeting". Niels Bohr Archive. Retrieved 2007-06-04.
20. ^ Niels Bohr’s mission for an ‘open world’. Retrieved 15 November 2008.
21. ^ To the United Nations by Niels Bohr accessed 15 November 2008
22. ^ "The coins and banknotes of Denmark". National Bank of Denmark. 2005. p. 20. Retrieved 2008-05-03.

# Quotes

Up to date as of January 14, 2010
(Redirected to Niels Bohr article)

### From Wikiquote

Anyone who is not shocked by quantum theory has not understood it.

Niels Henrik David Bohr () was a Danish physicist. He received the Nobel Prize for Physics in 1922 for his contributions which were essential to modern understandings of atomic structure and quantum mechanics.

## Sourced

We must be clear that when it comes to atoms, language can be used only as in poetry.
• We must be clear that when it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images and establishing mental connections.
• In his first meeting with Werner Heisenberg in early summer 1920, in response to questions on the nature of language, as reported in Discussions about Language (1933); quoted in Defense Implications of International Indeterminacy (1972) by Robert J. Pranger, p. 11, and Theorizing Modernism : Essays in Critical Theory (1993) by Steve Giles, p. 28
• The great extension of our experience in recent years has brought light to the insufficiency of our simple mechanical conceptions and, as a consequence, has shaken the foundation on which the customary interpretation of observation was based.
• "Atomic Physics and the Description of Nature" (1934)
• Isolated material particles are abstractions, their properties being definable and observable only through their interaction with other systems.
• "Atomic Physics and the Description of Nature" (1934)
The word "reality" is also a word, a word which we must learn to use correctly.
• What is it that we humans depend on? We depend on our words... Our task is to communicate experience and ideas to others. We must strive continually to extend the scope of our description, but in such a way that our messages do not thereby lose their objective or unambiguous character ... We are suspended in language in such a way that we cannot say what is up and what is down. The word "reality" is also a word, a word which we must learn to use correctly.
• Quoted in Philosophy of Science Vol. 37 (1934), p. 157, and in The Truth of Science : Physical Theories and Reality (1997) by Roger Gerhard Newton, p. 176
• For a parallel to the lesson of atomic theory regarding the limited applicability of such customary idealisations, we must in fact turn to quite other branches of science, such as psychology, or even to that kind of epistemological problems with which already thinkers like Buddha and Lao Tzu have been confronted, when trying to harmonize our position as spectators and actors in the great drama of existence.
• Speech on quantum theory at Celebrazione del Secondo Centenario della Nascita di Luigi Galvani, Bologna, Italy (October 1937)
Physics is to be regarded not so much as the study of something a priori given, but rather as the development of methods of ordering and surveying human experience.
• We are all agreed that your theory is crazy. The question that divides us is whether it is crazy enough to have a chance of being correct.
• Said to Wolfgang Pauli after his presentation of Heisenberg's and Pauli's nonlinear field theory of elementary particles, at Columbia University (1958), as quoted in Symposium on Basic Research (1959) by Dael Lee Wolfle, p. 66
• Your theory is crazy, but it's not crazy enough to be true.
• As quoted in First Philosophy: The Theory of Everything (2007) by Spencer Scoular, p. 89
• There are many slight variants on this remark:
• We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough.
• We are all agreed that your theory is crazy. The question is whether it is crazy enough enough to be have a chance of being correct.
• We in the back are convinced your theory is crazy. But what divides us is whether it is crazy enough.
• Your theory is crazy, the question is whether it's crazy enough to be true.
• Yes, I think that your theory is crazy. Sadly, it's not crazy enough to be believed.
It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature...
• Physics is to be regarded not so much as the study of something a priori given, but rather as the development of methods of ordering and surveying human experience. In this respect our task must be to account for such experience in a manner independent of individual subjective judgement and therefor objective in the sense that it can be unambiguously communicated in ordinary human language.
• "The Unity of Human Knowledge" (October 1960)
• There is no quantum world. There is only an abstract physical description. It is wrong to think that the task of physics is to find out how nature is. Physics concerns what we can say about nature...
• As quoted in "The philosophy of Niels Bohr" by Aage Petersen, in the Bulletin of the Atomic Scientists Vol. 19, No. 7 (September 1963); The Genius of Science: A Portrait Gallery (2000) by Abraham Pais, p. 24, and Niels Bohr: Reflections on Subject and Object (2001) by Paul. McEvoy, p. 291
• Every valuable human being must be a radical and a rebel, for what he must aim at is to make things better than they are.
• As quoted in The World of the Atom;; (1966) by Henry Abraham Boorse and Lloyd Motz, p. 741
• How wonderful that we have met with a paradox. Now we have some hope of making progress.
• As quoted in Niels Bohr : The Man, His Science, & the World They Changed (1966) by Ruth Moore, p. 196
• Two sorts of truth: trivialities, where opposites are obviously absurd, and profound truths, recognised by the fact that the opposite is also a profound truth.
• As quoted by his son Hans Bohr in "My Father", published in Neils Bohr : His Life and Work (1967), p. 328
• Unsourced variant : The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
• As quoted in Max Delbrück, Mind from Matter: An Essay on Evolutionary Epistemology, (1986) p. 167. It is the hallmark of any deep truth that its negation is also a deep truth
• An expert is a man who has made all the mistakes which can be made in a very narrow field.
• As quoted by Edward Teller (10 October 1972), and A Dictionary of Scientific Quotations (1991) by Alan L. Mackay, p. 35
Some subjects are so serious that one can only joke about them.
• Every sentence I utter must be understood not as an affirmation, but as a question.
• As quoted in A Dictionary of Scientific Quotations (1991) by Alan L. Mackay, p. 35
• Anyone who is not shocked by quantum theory has not understood it.
• As quoted in Meeting the Universe Halfway (2007) by Karen Michelle Barad, p. 254, with a footnote citing The Philosophical Writings of Niels Bohr (1998).
• Variants: Those who are not shocked when they first come across quantum mechanics cannot possibly have understood it.
Those who are not shocked when they first come across quantum theory cannot possibly have understood it.
Anyone who is not shocked by quantum theory has not understood a single word.
If you think you can talk about quantum theory without feeling dizzy, you haven't understood the first thing about it.
Truth and clarity are complementary.
• Some subjects are so serious that one can only joke about them.
• As quoted in The Genius of Science: A Portrait Gallery (2000) by Abraham Pais, p. 24
• Some things are so serious that one can only joke about them.
• Variant without any citation as to author in Denial is not a river in Egypt (1998) by Sandi Bachom, p. 85.
• Truth and clarity are complementary.
• As quoted in Quantum Theory and the Flight from Realism : Philosophical Responses to Quantum Mechanics (2000) by Christopher Norris, p. 234
• It is not enough to be wrong, one must also be polite.
• As quoted in The Genius of Science: A Portrait Gallery (2000) by Abraham Pais, p. 24
• Never express yourself more clearly than you are able to think.
• As quoted in Values of the Wise : Humanity's Highest Aspirations (2004) by Jason Merchey, p. 63

## Disputed

• It is better to not understand something true, than to understand something false.
Stop telling God what to do with his dice.
• Prediction is very difficult, especially about the future.
• As quoted in Teaching and Learning Elementary Social Studies (1970) by Arthur K. Ellis, p. 431
• The above quote is also attributed to various humourists and the Danish poet Piet Hein: "det er svært at spå - især om fremtiden"
• It is also attributed to danish cartoonist Storm P (Robert Storm Petersen).
• Stop telling God what to do with his dice.
• A response to Einstein's assertion that "God doesn't play dice"; a similar statement is attributed to Enrico Fermi
• Variant: Einstein, don't tell God what to do.
• Of course not ... but I am told it works even if you don't believe in it.
• Reply to a visitor to his home in Tisvilde who asked him if he really believed a horseshoe above his door brought him luck, as quoted in Inward Bound : Of Matter and Forces in the Physical World (1986) by Abraham Pais, p. 210
• In most published accounts of this anecdote such was Bohr's reply to his friend, but in the earliest account thus far located, in The Interaction Between Science and Philosophy (1974) by Samuel Sambursky, p. 357, Bohr was at a friend's house and asked "Do you really believe in this?" to which his friend replied "Oh, I don't believe in it. But I am told it works even if you don't believe in it."
• Variant: No, but I'm told it works even if you don't believe in it.

## Unsourced

Not often in life has a human being caused me such joy by his mere presence as you did. ~ Albert Einstein
• It is a great pity that human beings cannot find all of their satisfaction in scientific contemplativeness.

• Not often in life has a human being caused me such joy by his mere presence as you did.
• I remember discussions with Bohr which went through many hours till very late at night an ended almost in despair; and when at the end of the discussion I went alone for a walk in the neighbouring park I repeated to myself again and again the question: Can nature possibly be so absurd as it seemed to us in these atomic experiments?
• One of the favorite maxims of my father was the distinction between the two sorts of truths, profound truths recognized by the fact that the opposite is also a profound truth, in contrast to trivialities where opposites are obviously absurd.
• Hans Henrik Bohr, writing about his father in "My father" in Niels Bohr - His Life and Work As Seen By His Friends and Colleagues (1967), S. Rozental, ed.