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Home > Dictionary of Science Quotations > Scientist Names Index B > Niels Bohr Quotes

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Niels Bohr
(7 Oct 1885 - 18 Nov 1962)

Danish physicist.


Science Quotes by Niels Bohr (20 quotes)

Contraria sunt complementa.
Opposites are complementary.
— Niels Bohr
Motif on Niels Bohr's coat of arms.
Science quotes on:  |  Aphorism (13)

[About describing atomic models in the language of classical physics:] 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.
— Niels Bohr
As quoted by Werner Heisenberg, as translated by Arnold J. Pomerans, in Physics and Beyond: Encounters and Conversations (1971), 41. The words are not verbatim, but as later recollected by Werner Heisenberg describing his early encounter with Bohr in 1920.
Science quotes on:  |  Atom (164)  |  Classical Physics (4)  |  Concern (30)  |  Connection (39)  |  Creation (129)  |  Description (40)  |  Establishing (4)  |  Fact (325)  |  Image (15)  |  Language (71)  |  Mental (16)  |  Poet (26)  |  Poetry (63)

A visitor to Niels Bohr's country cottage, noticing a horseshoe hanging on the wall, teasing the eminent scientist about this ancient superstition. “Can it be true that you, of all people, believe it will bring you luck?'
'Of course not,' replied Bohr, 'but I understand it brings you luck whether you believe it or not.'”
— Niels Bohr
As described in Clifton Fadiman (ed.), Andrι Bernard (ed.), Bartlett's Book of Anecdotes (2000), 68.
Science quotes on:  |  Believe (14)  |  Luck (22)  |  Superstition (33)  |  Understanding (231)

Anyone who is not shocked by the quantum theory has not understood it.
— Niels Bohr
Atomic Physics and Human Knowledge (1958). Quoted in Eric Middleton, The New Flatlanders (2007), 19.
Science quotes on:  |  Quantum Theory (36)  |  Understanding (231)

But, but, but ... if anybody says he can think about quantum theory without getting giddy it merely shows that he hasn't understood the first thing about it!
— Niels Bohr
Quoted in Otto R. Frisch, What Little I Remember (1979), 95.
Science quotes on:  |  Quantum Theory (36)  |  Understanding (231)

Every sentence I utter must be understood not as an affirmation but as a question.
[A caution he gives his students, to be wary of dogmatism.]
— Niels Bohr
In Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
Science quotes on:  |  Affirmation (4)  |  Dogmatism (5)  |  Question (159)  |  French Saying (51)  |  Sentence (10)  |  Understanding (231)  |  Utterance (3)

How wonderful that we have met this paradox. Now we have some hope of making progress.
[Comment to observers when an experiment took an unexpected turn.]
— Niels Bohr
In Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
Science quotes on:  |  Paradox (22)  |  Progress (200)

If we couldn't laugh at ourselves, that would be the end of everything.
— Niels Bohr
Comment made to Professor Erik Riidinger, 1962. Quotation supplied and translated by Professor Erik Rüdinger, Niels Bohr Archive.
Science quotes on:  |  Aphorism (13)

In physics we deal with states of affairs much simpler than those of psychology and yet we again and again learn that our task is not to investigate the essence of things—we do not at all know what this would mean&mash;but to develop those concepts that allow us to speak with each other about the events of nature in a fruitful manner.
— Niels Bohr
Letter to H.P.E. Hansen (20 Jul 1935), Niels Bohr Archive. In Jan Faye, Henry J. Folse, Niels Bohr and Contemporary Philosophy (1994), 83.
Science quotes on:  |  Affair (10)  |  Again (3)  |  Allow (5)  |  Concept (38)  |  Dealing (4)  |  Development (122)  |  Essence (19)  |  Event (49)  |  Fruitful (9)  |  Investigation (83)  |  Knowledge (679)  |  Learning (130)  |  Manner (11)  |  Meaning (52)  |  Nature (534)  |  Physics (156)  |  Psychology (69)  |  Simplicity (92)  |  Speaking (30)  |  State (43)  |  Task (32)  |  Thing (27)

One thought [spectra are] marvellous, but it is not possible to make progress there. Just as if you have the wing of a butterfly then certainly it is very regular with the colors and so on, but nobody thought one could get the basis of biology from the coloring of the wing of a butterfly.
— Niels Bohr
Quoted from Interviews (I, 7) in 'The Genesis of the Bohr Atom', J.L. Heilbron and T.S. Kuhn, Historical Studies in the Physical Sciences (1969), 257, reprinted in J. L. Heilbron, Historical Studies in the Theory of Atomic Structure (1981), 195.
Science quotes on:  |  Atom (164)  |  Butterfly (9)  |  Colour (32)

Predictions can be very difficult—especially about the future.
— Niels Bohr
Quoted in H. Rosovsky, The University: An Owners Manual (1991), 147. It is said that Bohr used to quote this saying to illustrate the differences between Danish and Swedish humour. Bohr always attributed the saying to Robert Storm Petersen (1882-1949), a well-known Danish artist and writer. However, the saying did NOT originate from Petersen. It may have been said in the Danish Parliament between 1935 and 1939 [Information supplied courtesy of Professor Erik Rüdinger, Niels Bohr Archive, Copenhagen].
Science quotes on:  |  Future (110)  |  Prediction (48)

The existence of life must be considered as an elementary fact that can not be explained, but must be taken as a starting point in biology, in a similar way as the quantum of action, which appears as an irrational element from the point of view of classical mechanical physics, taken together with the existence of elementary particles, forms the foundation of atomic physics. The asserted impossibility of a physical or chemical explanation of the function peculiar to life would in this sense be analogous to the insufficiency of the mechanical analysis for the understanding of the stability of atoms.
— Niels Bohr
'Light and Life', Nature, 1933, 131, 458.
Science quotes on:  |  Atom (164)  |  Atomic Physics (4)  |  Biology (83)  |  Classical Physics (4)  |  Life (460)  |  Quantum (8)

The old saying of the two kinds of truth. To the one kind belongs statements so simple and clear that the opposite assertion obviously could not be defended. The other kind, the so-called 'deep truths', are statements in which the opposite also contains deep truth.
— Niels Bohr
Niels Bohr, 'Discussion with Einstein on Epistemological Problems in Atomic Physics', in P. A. Schilpp (ed.), Albert Einstein: Philosopher-Scientist (1949), 240.
Science quotes on:  |  Truth (450)

The present state of atomic theory is characterized by the fact that we not only believe the existence of atoms to be proved beyond a doubt, but also we even believe that we have an intimate knowledge of the constituents of the individual atoms.
— Niels Bohr
'The structure of the atom', Nobel Lecture, 11 December 1922. In Nobel Lectures: Physics 1922-1941 (1998), 5.
Science quotes on:  |  Atom (164)  |  Atomic Theory (11)

Truth is something that we can attempt to doubt, and then perhaps, after much exertion, discover that part of the doubt is not justified.
— Niels Bohr
Quoted in Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
Science quotes on:  |  Attempt (41)  |  Discovery (360)  |  Doubt (67)  |  Exertion (6)  |  Justification (20)  |  Part (55)  |  Truth (450)

What is that we human beings ultimately depend on? We depend on our words. We are suspended in language. Our task is to communicate experience and ideas to others.
— Niels Bohr
Quoted in Aage Petersen, 'The Philosophy of Niels Bohr', Bulletin of the Atomic Scientists, 1963, 19, 10.
Science quotes on:  |  Communication (37)  |  Human Nature (34)  |  Language (71)  |  Word (97)

When asked ... [about] an underlying quantum world, Bohr would answer, 'There is no quantum world. There is only an abstract quantum 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.'
— Niels Bohr
As quoted in Aage Petersen, 'The Philosophy of Niels Bohr', Bulletin of the Atomic Scientists, 1963, 19, 12. Note: Bohr's remark, although in quotation marks, should not be regarded as a direct quote in these exact words. It is a generalised statement in the article author's words to represent Bohr's viewpoint. This is explained in a footnote in Michael Frayn, The Human Touch (2007), 431 based on an article by N. David Mermin in Physics Today (Feb 2004).
Science quotes on:  |  Nature (534)  |  Physics (156)

When it comes to atoms, language can be used only as in poetry.
— Niels Bohr
Quoted in K. C. Cole, 'On Imagining the Unseeable', Discover, 1982, 3, 70.
Science quotes on:  |  Atom (164)  |  Language (71)  |  Poetry (63)

When searching for harmony in life one must never forget that in the drama of existence we are ourselves both actors and spectators.
— Niels Bohr
Niels Bohr, 'Discussion with Einstein on Epistemological Problems in Atomic Physics', in P. A. Schilpp (ed.), Albert Einstein: Philosopher-Scientist (1949), 236.
Science quotes on:  |  Life (460)

You must come to Copenhagen to work with us. We like people who can actually perform thought experiments!
— Niels Bohr
Said to Otto Frisch. Quoted in Otto R. Frisch, What Little I Remember (1979), 76.
Science quotes on:  |  Experiment (369)  |  Otto Robert Frisch (5)



Quotes by others about Niels Bohr (15)

When Bohr is about everything is somehow different. Even the dullest gets a fit of brilliancy.
Isidor I. Rabi in Daniel J. Kevles, The Physicists (1978), 201.

But it is necessary to insist more strongly than usual that what I am putting before you is a model—the Bohr model atom—because later I shall take you to a profounder level of representation in which the electron instead of being confined to a particular locality is distributed in a sort of probability haze all over the atom.
Messenger Lectures (1934), New Pathways in Science (1935), 34.
Science quotes on:  |  Atom (164)  |  Electron (43)  |  Probability (56)

At the beginning of this debate Stephen [Hawking] said that he thinks that he is a positivist, whereas I am a Platonist. I am happy with him being a positivist, but I think that the crucial point here is, rather, that I am a realist. Also, if one compares this debate with the famous debate of Bohr and Einstein, some seventy years ago, I should think that Stephen plays the role of Bohr, whereas I play Einstein's role! For Einstein argued that there should exist something like a real world, not necessarily represented by a wave function, whereas Bohr stressed that the wave function doesn't describe a 'real' microworld but only 'knowledge' that is useful for making predictions.
Debate at the Isaac Newton Institute of the Mathematical Sciences, Cambridge University (1994), transcribed in Stephen Hawking and Roger Penrose, The Nature of Space and Time (1996), 134-135.
Science quotes on:  |  Albert Einstein (174)  |  Quantum Physics (15)

We [Frisch and Lise Meitner] walked up and down in the snow, I on skis and she on foot (she said and proved that she could get along just as fast that way), and gradually the idea took shape that this was no chipping or cracking of the nucleus but rather a process to be explained by Bohr's idea that the nucleus was like a liquid drop; such a drop might elongate and divide itself.
Otto Frisch and John A. Wheeler, 'The Discovery of Fission', Physics Today, Nov 1967, 20, 47.
Science quotes on:  |  Lise Meitner (8)  |  Nucleus (21)

You can talk about people like Buddha, Jesus, Moses, Confucius, but the thing that convinced me that such people existed were the conversations with Bohr.
About his time working with Niels Bohr in Copenhagen.
Quoted in Dennis Overbye, 'John A. Wheeler, Physicist Who Coined the Term Black Hole, Is Dead at 96', New York Times (14 Apr 2008).

People were pretty well spellbound by what Bohr said… While I was very much impressed by [him], his arguments were mainly of a qualitative nature, and I was not able to really pinpoint the facts behind them. What I wanted was statements which could be expressed in terms of equations, and Bohr's work very seldom provided such statements. I am really not sure how much later my work was influenced by these lectures of Bohr's... He certainly did not have a direct influence because he did not stimulate one to think of new equations.
Recalling the occasion in May 1925 (a year before receiving his Ph.D.) when he met Niels Bohr who was in Cambridge to give a talk on the fundamental difficulties of the quantum theory.
In History of Twentieth Century Physics (1977), 109. In A. Pais, 'Playing With Equations, the Dirac Way'. Behram N. Kursunoglu (Ed.) and Eugene Paul Wigner (Ed.), Paul Adrien Maurice Dirac: Reminiscences about a Great Physicist (1990), 94.
Science quotes on:  |  Equation (46)  |  Quantum Theory (36)

I admired Bohr very much. We had long talks together, long talks in which Bohr did practically all the talking.
Recalling his Sep 1926-Feb 1927 stay in Copenhagen.
In History of Twentieth Century Physics (1977), 109. In A. Pais, 'Playing With Equations, the Dirac Way'. Behram N. Kursunoglu (Ed.) and Eugene Paul Wigner (Ed.), Paul Adrien Maurice Dirac: Reminiscences about a Great Physicist (1990), 94.
Science quotes on:  |  Biography (199)

Our scientific work in physics consists in asking questions about nature in the language that we possess and trying to get an answer from experiment by the means at our disposal. In this way quantum theory reminds us, as Bohr has put it, of the old wisdom that when searching for harmony in life one must never forget that in the drama of existence we are ourselves both players and spectators. It is understandable that in our scientific relation to nature our own activity becomes very important when we have to deal with parts of nature into which we can penetrate only by using the most elaborate tools.
The Copenhagen Interpretation of Quantum Theory (1958). In Steve Adams, Frontiers (2000), 13.
Science quotes on:  |  Experiment (369)  |  Quantum Theory (36)  |  Question (159)  |  Research (360)

Physicists speak of the particle representation or the wave representation. Bohr's principle of complementarity asserts that there exist complementary properties of the same object of knowledge, one of which if known will exclude knowledge of the other. We may therefore describe an object like an electron in ways which are mutually exclusive—e.g., as wave or particle—without logical contradiction provided we also realize that the experimental arrangements that determine these descriptions are similarly mutually exclusive. Which experiment—and hence which description one chooses—is purely a matter of human choice.
The Cosmic Code: Quantum Physics as the Language of Nature (1982), 94.
Science quotes on:  |  Arrangement (25)  |  Assertion (16)  |  Choice (40)  |  Contradiction (22)  |  Description (40)  |  Determination (37)  |  Electron (43)  |  Exclusion (7)  |  Existence (150)  |  Experiment (369)  |  Knowledge (679)  |  Mutual (12)  |  Object (47)  |  Particle (45)  |  Physicist (74)  |  Property (46)  |  Realization (22)  |  Representation (17)  |  Speaking (30)  |  Wave (32)

Bohr’s standpoint, that a space-time description is impossible, I reject a limine. Physics does not consist only of atomic research, science does not consist only of physics, and life does not consist only of science. The aim of atomic research is to fit our empirical knowledge concerning it into our other thinking. All of this other thinking, so far as it concerns the outer world, is active in space and time. If it cannot be fitted into space and time, then it fails in its whole aim and one does not know what purpose it really serves.
Letter to Willy Wien (25 Aug 1926). Quoted in Walter Moore, Schrφdinger: Life and Thought (1989), 226.
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After the discovery of spectral analysis no one trained in physics could doubt the problem of the atom would be solved when physicists had learned to understand the language of spectra. So manifold was the enormous amount of material that has been accumulated in sixty years of spectroscopic research that it seemed at first beyond the possibility of disentanglement. An almost greater enlightenment has resulted from the seven years of Röntgen spectroscopy, inasmuch as it has attacked the problem of the atom at its very root, and illuminates the interior. What we are nowadays hearing of the language of spectra is a true 'music of the spheres' in order and harmony that becomes ever more perfect in spite of the manifold variety. The theory of spectral lines will bear the name of Bohr for all time. But yet another name will be permanently associated with it, that of Planck. All integral laws of spectral lines and of atomic theory spring originally from the quantum theory. It is the mysterious organon on which Nature plays her music of the spectra, and according to the rhythm of which she regulates the structure of the atoms and nuclei.
Atombau und Spektrallinien (1919), viii, Atomic Structure and Spectral Lines, trans. Henry L. Brose (1923), viii.
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Nobody knows how the stand of our knowledge about the atom would be without him. Personally, [Niels] Bohr is one of the amiable colleagues I have met. He utters his opinions like one perpetually groping and never like one who believes himself to be in possession of the truth.
Quoted in Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
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[Niels Bohr] is a national pride to his fellow Danes. In Denmark, Bohr's standing is only slightly less than that of the royal family and Hans Christian Anderson. When the wife of an American physicist casually told a gentleman seated next to her on a Copenhagen streetcar that her husband was studying under Professor Bohr, the old man jumped to his feet, swept off his hat with a flourish and bowed deeply.
Quoted in Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
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[Student describing Niels Bohr's main gift, the ability to synthesize:] Like Socrates, he wages a fight to bring harmony out of chaos and diversity.
Anonymous
Quoted in Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 52.
Science quotes on:  |  Chaos (33)  |  Diversity (32)  |  Fight (8)  |  Gift (26)  |  Harmony (27)  |  Socrates (9)  |  Synthesis (23)

[About the great synthesis of atomic physics in the 1920s:] It was a heroic time. It was not the doing of any one man; it involved the collaboration of scores of scientists from many different lands. But from the first to last the deeply creative, subtle and critical spirit of Niels Bohr guided, restrained, deepened and finally transmuted the enterprise.
Quoted in Bill Becker, 'Pioneer of the Atom', New York Times Sunday Magazine (20 Oct 1957), 54.
Science quotes on:  |  Atomic Physics (4)  |  Collaboration (9)  |  Creativity (45)  |  Deep (17)  |  Difference (135)  |  Enterprise (6)  |  Guide (17)  |  Land (27)  |  Scientist (237)  |  Spirit (52)  |  Subtlety (6)  |  Transmutation (10)


See also:
  • todayinsci icon 7 Oct - short biography, births, deaths and events on date of Bohr's birth.
  • book icon Suspended In Language: Niels Bohr's Life, Discoveries, And The Century He Shaped, by Jim Ottaviani. - book suggestion.
  • booklist icon Booklist for Niels Bohr.

Carl Sagan Thumbnail In science it often happens that scientists say, 'You know that's a really good argument; my position is mistaken,' and then they would actually change their minds and you never hear that old view from them again. They really do it. It doesn't happen as often as it should, because scientists are human and change is sometimes painful. But it happens every day. I cannot recall the last time something like that happened in politics or religion. (1987) -- Carl Sagan
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