# Frasi di John Von Neumann

## John Von Neumann

**Data di nascita:** 28. Dicembre 1903**Data di morte:** 8. Febbraio 1957

John von Neumann, nato János Lajos Neumann: IPA: [ˈjaːnoʃ ˈlɒjoʃ ˈnojmɒn [in effetti: Margittai Neumann János Lajos] , è stato un matematico, fisico e informatico ungherese naturalizzato statunitense.

Generalmente considerato come uno dei più grandi matematici della storia moderna oltre ad essere una delle personalità scientifiche preminenti del XX secolo, a lui si devono contributi fondamentali in numerosi campi come la teoria degli insiemi, analisi funzionale, topologia, fisica quantistica, economia, informatica, teoria dei giochi, fluidodinamica e in molti altri settori della matematica.

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### Frasi John Von Neumann

### „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

### „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. -->

### „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.

### „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

### „The calculus was the first achievement of modern mathematics and it is difficult to overestimate its importance. I think it defines more unequivocally than anything else the inception of modern mathematics; and the system of mathematical analysis, which is its logical development, still constitutes the greatest technical advance in exact thinking.“

— John Von Neumann

As quoted in Bigeometric Calculus: A System with a Scale-Free Derivative (1983) by Michael Grossman, and in Single Variable Calculus (1994) by James Stewart.

### „You wake me up early in the morning to tell me that I'm right? Please wait until I'm wrong.“

— John Von Neumann

As quoted by Jacob Bronowski in The Ascent of Man TV series

### „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

### „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 "A meeting with Enrico Fermi" in Nature 427 (22 January 2004) p. 297 http://dx.doi.org/10.1038/427297a

### „If one has really technically penetrated a subject, things that previously seemed in complete contrast, might be purely mathematical transformations of each other.“

— John Von Neumann

As quoted in Proportions, Prices, and Planning (1970) by András Bródy

### „The sciences do not try to explain, they hardly even try to interpret, they mainly make models. By a model is meant a mathematical construct which, with the addition of certain verbal interpretations, describes observed phenomena. The justification of such a mathematical construct is solely and precisely that it is expected to work.“

— John Von Neumann

"Method in the Physical Sciences", in The Unity of Knowledge (1955), ed. L. G. Leary (Doubleday & Co., New York), p. 157

### „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

### „The goys have proven the following theorem…“

— John Von Neumann

Statement at the start of a classroom lecture, as quoted in 1,911 Best Things Anyone Ever Said (1988) by Robert Byrne.

### „It is exceptional that one should be able to acquire the understanding of a process without having previously acquired a deep familiarity with running it, with using it, before one has assimilated it in an instinctive and empirical way… Thus any discussion of the nature of intellectual effort in any field is difficult, unless it presupposes an easy, routine familiarity with that field. In mathematics this limitation becomes very severe.“

— John Von Neumann

As quoted in "The Mathematician" in The World of Mathematics (1956), by James Roy Newman

### „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).