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John von Neumann

Date de naissance: 28. décembre 1903
Date de décès: 8. février 1957

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John von Neumann, né Neumann János Lajos en 1903 à Budapest et mort en 1957 à Washington, est un mathématicien et physicien américano-hongrois. Il a apporté d'importantes contributions tant en mécanique quantique qu'en analyse fonctionnelle, en théorie des ensembles, en informatique, en sciences économiques ainsi que dans beaucoup d'autres domaines des mathématiques et de la physique. Il a de plus participé aux programmes militaires américains.

Citations John von Neumann

„I think that it is a relatively good approximation to truth — which is much too complicated to allow anything but approximations — that mathematical ideas originate in empirics.“

— John Von Neumann
Context: I think that it is a relatively good approximation to truth — which is much too complicated to allow anything but approximations — that mathematical ideas originate in empirics. But, once they are conceived, the subject begins to live a peculiar life of its own and is … governed by almost entirely aesthetical motivations. In other words, at a great distance from its empirical source, or after much "abstract" inbreeding, a mathematical subject is in danger of degeneration. Whenever this stage is reached the only remedy seems to me to be the rejuvenating return to the source: the reinjection of more or less directly empirical ideas. "The Mathematician", in The Works of the Mind (1947) edited by R. B. Heywood, University of Chicago Press, Chicago

„In the second place, and more important, no one really knows what entropy really is, so in a debate you will always have the advantage.“

— John Von Neumann
Context: You should call it entropy, for two reasons. In the first place your uncertainty function has been used in statistical mechanics under that name, so it already has a name. In the second place, and more important, no one really knows what entropy really is, so in a debate you will always have the advantage. Suggesting to Claude Shannon a name for his new uncertainty function, as quoted in Scientific American Vol. 225 No. 3, (1971), p. 180.

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„Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin.“

— John Von Neumann
Context: Any one who considers arithmetical methods of producing random digits is, of course, in a state of sin. For, as has been pointed out several times, there is no such thing as a random number — there are only methods to produce random numbers, and a strict arithmetic procedure of course is not such a method. On mistaking pseudorandom number generators for being truly "random" — this quote is often erroneously interpreted to mean that von Neumann was against the use of pseudorandom numbers, when in reality he was cautioning about misunderstanding their true nature while advocating their use. From "Various techniques used in connection with random digits" by John von Neumann in Monte Carlo Method (1951) edited by A.S. Householder, G.E. Forsythe, and H.H. Germond <!-- National Bureau of Standards Applied Mathematics Series, 12 (Washington, D.C.: U.S. Government Printing Office, 1951): 36-38. -->

„A large part of mathematics which becomes useful developed with absolutely no desire to be useful, and in a situation where nobody could possibly know in what area it would become useful; and there were no general indications that it ever would be so.“

— John Von Neumann
Context: A large part of mathematics which becomes useful developed with absolutely no desire to be useful, and in a situation where nobody could possibly know in what area it would become useful; and there were no general indications that it ever would be so. By and large it is uniformly true in mathematics that there is a time lapse between a mathematical discovery and the moment when it is useful; and that this lapse of time can be anything from 30 to 100 years, in some cases even more; and that the whole system seems to function without any direction, without any reference to usefulness, and without any desire to do things which are useful. "The Role of Mathematics in the Sciences and in Society" (1954) an address to Princeton alumni, published in John von Neumann : Collected Works (1963) edited by A. H. Taub <!-- Macmillan, New York -->; also quoted in Out of the Mouths of Mathematicians : A Quotation Book for Philomaths (1993) by R. Schmalz

„If people do not believe that mathematics is simple, it is only because they do not realize how complicated life is.“

— John Von Neumann
Remark made by von Neumann as keynote speaker at the first national meeting of the Association for Computing Machinery in 1947, as mentioned by Franz L. Alt at the end of "Archaeology of computers: Reminiscences, 1945--1947", Communications of the ACM, volume 15, issue 7, July 1972, special issue: Twenty-fifth anniversary of the Association for Computing Machinery, p. 694.

„Young man, in mathematics you don't understand things. You just get used to them.“

— John Von Neumann
Reply, according to Dr. Felix T. Smith of Stanford Research Institute, to a physicist friend who had said "I'm afraid I don't understand the method of characteristics," as quoted in The Dancing Wu Li Masters: An Overview of the New Physics (1979) by Gary Zukav, Bantam Books, p. 208, footnote.

„There probably is a God. Many things are easier to explain if there is than if there isn't.“

— John Von Neumann
As quoted in John Von Neumann : The Scientific Genius Who Pioneered the Modern Computer, Game Theory, Nuclear Deterrence and Much More (1992) by Norman Macrae, p. 379

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„With four parameters I can fit an elephant, and with five I can make him wiggle his trunk.“

— John Von Neumann
Attributed to von Neumann by Enrico Fermi, as quoted by Freeman Dyson in [http://dx.doi.org/10.1038/427297a "A meeting with Enrico Fermi" in Nature 427 (22 January 2004) p. 297]

„If you say why not bomb them tomorrow, I say why not today? If you say today at five o' clock, I say why not one o' clock?“

— John Von Neumann
As quoted in "The Passing of a Great Mind" by Clay Blair, Jr., in LIFE Magazine (25 February 1957), p. 96

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„It is just as foolish to complain that people are selfish and treacherous as it is to complain that the magnetic field does not increase unless the electric field has a curl. Both are laws of nature.“

— John Von Neumann
As quoted "John von Neumann (1903 - 1957)" by Eugene Wigner, in Year book of the American Philosophical Society (1958); later in Symmetries and Reflections : Scientific Essays of Eugene P. Wigner (1967), p. 261

„When we talk mathematics, we may be discussing a secondary language built on the primary language of the nervous system.“

— John Von Neumann
As quoted in John von Neumann, 1903-1957 (1958) by John C. Oxtoby and B. J. Pettis, p. 128

„You don't have to be responsible for the world that you're in.“

— John Von Neumann
Advice given by von Neumann to Richard Feynman as quoted in "Los Alamos from Below" in Surely You're Joking, Mr. Feynman! (1985).

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