Richard Feynman citations
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Richard Phillips Feynman est un physicien américain, l'un des plus influents de la seconde moitié du XXe siècle, en raison notamment de ses travaux sur l'électrodynamique quantique, les quarks et l'hélium superfluide.

Il reformula entièrement la mécanique quantique à l'aide de son intégrale de chemin qui généralise le principe de moindre action de la mécanique classique et inventa les diagrammes qui portent son nom et qui sont désormais largement utilisés en théorie quantique des champs .

Pendant la Seconde Guerre mondiale, il fut impliqué dans le développement de la bombe atomique américaine. Après la Seconde Guerre mondiale, il enseigna à l'université Cornell puis au Caltech où il effectua des travaux fondamentaux notamment dans la théorie de la superfluidité et des quarks. Sin-Itiro Tomonaga, Julian Schwinger et lui sont colauréats du prix Nobel de physique de 1965 pour leurs travaux en électrodynamique quantique. Vers la fin de sa vie, son action au sein de la commission d'enquête sur l'accident de la navette spatiale Challenger l'a fait connaître du grand public américain.

Pédagogue remarquable, il est le rédacteur de nombreux ouvrages de vulgarisation reconnus. Parmi ces livres, les Feynman lectures on physics, un cours de physique de niveau universitaire qui, depuis sa parution, est devenu un classique pour tous les étudiants de premier cycle en physique et leurs professeurs. Il raconte aussi ses nombreuses aventures dans plusieurs ouvrages : Surely You're Joking, Mr. Feynman! et What Do You Care What Other People Think?. Ce tome est lié au soutien moral que sa première épouse Arline lui donnait, l'encourageant par ce biais dans sa poursuite intellectuelle en tant que libre-penseur. Wikipedia  

✵ 11. mai 1918 – 15. février 1988   •   Autres noms Richard Feynman Philips, Richard Phillips Feynman, Ричард Филлипс Фейнман
Richard Feynman photo
Richard Feynman: 186   citations 4   J'aime

Richard Feynman citations célèbres

“Je pense pouvoir dire sans trop me tromper que personne ne comprend la mécanique quantique.”

I think I can safely say that nobody understands quantum mechanics
en

“Si, dans un cataclysme, toute notre connaissance scientifique devait être détruite et qu'une seule phrase passe aux générations futures, quelle affirmation contiendrait le maximum d'informations dans le minimum de mots? Je pense que c'est l'hypothèse atomique (ou le fait atomique, ou tout autre nom que vous voudrez lui donner) que toutes les choses sont faites d'atomes - petites particules qui se déplacent en mouvement perpétuel, s'attirant mutuellement à petite distance les unes les autres et se repoussant lorsque l'on veut les faire se pénétrer. Dans cette seule phrase, vous verrez qu'il y a une énorme quantité d'information sur le monde, si on lui applique un peu d'imagination et de réflexion.”

If, in some cataclysm, all of scientific knowledge were to be destroyed, and only one sentence passed on to the next generations of creatures, what statement would contain the most information in the fewest words? I believe it is the atomic hypothesis (or the atomic fact, or whatever you wish to call it) that all things are made of atoms little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another. In that one sentence, you will see, there is an enormous amount of information about the world, if just a little imagination and thinking are applied.
en

“[…] nous avons toujours eu (chut, chut, fermez les portes!), nous avons toujours eu beaucoup de mal à comprendre l'image du monde que nous offre la mécanique quantique. Du moins, en ce qui me concerne, parce que je suis assez âgé, je ne suis pas encore parvenu à me convaincre que tous ces trucs-là étaient évidents. OK, ça m'énerve toujours. Ainsi quelques étudiants plus jeunes… Vous savez ce que c'est : à chaque nouvelle idée, il faut une ou deux générations pour constater qu'elle ne pose pas de vraie difficulté. Il n'est toujours pas évident pour moi qu'il n'y a pas de vrai problème. Je ne peux pas définir le vrai problème donc je soupçonne qu'il n'y a pas de vrai problème mais je ne suis pas sûr qu'il n'y ait pas de vrai problème.”

[...] we have always had (secret, secret, close the doors!) we have always have had a great deal of difficulty in understanding the world view that quantum mechanics represents. At least I do, because I'm an old enough man that I haven't got to the point that this stuff is obvious to me. Okay, I still get nervous with it. And therefore, some of the youngest students...you know how it always is, every new idea, it takes a generation or two until it becomes obvious that there's no real problem. It has not yet become obvious to me that there is no real problem. I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem.
en

“il s’agit en quelque sorte d’une caractéristique de la simplicité de la nature.”

sur le fait qu'il existe de nombreuses manières de formuler une même théorie, Discours de réception du prix Nobel.
Citation rapportée

Cette traduction est en attente de révision. Est-ce correct?

Richard Feynman: Citations en anglais

“The same equations have the same solutions”

volume II; lecture 12, "Electrostatic Analogs"; p. 12-1
The Feynman Lectures on Physics (1964)

“Suppose two politicians are running for president, and one goes through the farm section and is asked, "What are you going to do about the farm question?" And he knows right away - bang, bang, bang. Now he goes to the next campaigner who comes through. "What are you going to do on the farm problem?" "Well, I don't know. I used to be a general, and I don't know anything about farming. But it seems to me it must be a very difficult problem, because for twelve, fifteen, twenty years people have been struggling with it, and people say that they know how to solve the farm problem. And it must be a hard problem. So the way I intend to solve the farm problem is to gather around me a lot of people who know something about it, to look at all the experience that we have had with this problem before, to take a certain amount of time at it, and then to come to some conclusion in a reasonable way about it. Now, I can't tell you ahead of time what solution, but I can give you some of the principles I'll try to use - not to make things difficult for individual farmers, if there are any special problems we will have to have some way to take care of them," etc., etc., etc.
Now such a man would never get anywhere in this country, I think. It's never been tried, anyway. This is in the attitude of mind of the populace, that they have to have an answer and that a man who gives an answer is better than a man who gives no answer, when the real fact of the matter is, in most cases, it is the other way around. And the result of this of course is that the politician must give an answer. And the result of this is that political promises can never be kept. It is a mechanical fact; it is impossible. The result of that is that nobody believes campaign promises. And the result of that is a general disparaging of politics, a general lack of respect for the people who are trying to solve problems, and so forth. It's all generated from the very beginning (maybe - this is a simple analysis). It's all generated, maybe, by the fact that the attitude of the populace is to try to find the answer instead of trying to find a man who has a way of getting at the answer.”

Richard Feynman livre The Meaning of It All

lecture III: "This Unscientific Age"
The Meaning of It All (1999)

“I had too much stuff. My machines came from too far away.”

Reflecting on the failure of his presentation at the "Pocono Conference" of 30 March - 1 April 1948.
interview with Sylvan S. Schweber, 13 November 1984, published in QED and the Men Who Made It: Dyson, Feynman, Schwinger, and Tomonaga (1994) by Silvan S. Schweber, p. 436

“A very great deal more truth can become known than can be proven.”

"The Development of the Space-Time View of Quantum Electrodynamics," Nobel Lecture http://nobelprize.org/physics/laureates/1965/feynman-lecture.html (11 December 1965)

“And this is medicine?”

Comment to psychiatrist who examines Feynman and states he (the psychiatrist) has studied medicine.
Part 3: "Feynman, The Bomb, and the Military", "Uncle Sam Doesn't Need <u>You</u>", p. 159
Surely You're Joking, Mr. Feynman! (1985)

“This dying is boring.”

last words (15 February 1988), recalled by sister Joan Feynman, in Christopher Sykes, editor, No Ordinary Genius: The Illustrated Richard Feynman (1994), p. 254

“What I cannot create, I do not understand.Know how to solve every problem that has been solved.”

on his blackboard at the time of death in February 1988; from a photo in the Caltech archives http://archives.caltech.edu/pictures/1.10-29.jpg

“We absolutely must leave room for doubt or there is no progress and no learning. There is no learning without having to pose a question. And a question requires doubt. People search for certainty. But there is no certainty. People are terrified — how can you live and not know?”

Richard Feynman livre The Pleasure of Finding Things Out

It is not odd at all. You only think you know, as a matter of fact. And most of your actions are based on incomplete knowledge and you really don't know what it is all about, or what the purpose of the world is, or know a great deal of other things. It is possible to live and not know.
from lecture "What is and What Should be the Role of Scientific Culture in Modern Society", given at the Galileo Symposium in Italy (1964)
The Pleasure of Finding Things Out (1999)

“The philosophy of science is as useful to scientists as ornithology is to birds.”

Attributed to Feynman, many times, by the British historian of science Brian Cox.
Disputed and/or attributed

“Do not keep saying to yourself, if you can possibly avoid it, "But how can it be like that?"”

Richard Feynman livre The Character of Physical Law

because you will get "down the drain", into a blind alley from which nobody has yet escaped. Nobody knows how it can be like that.
Concerning the apparent absurdities of quantum behavior.
Source: The Character of Physical Law (1965), chapter 6, “Probability and Uncertainty — the Quantum Mechanical View of Nature,” p. 129

“What do we mean by “understanding” something? We can imagine that this complicated array of moving things which constitutes “the world” is something like a great chess game being played by the gods, and we are observers of the game. We do not know what the rules of the game are; all we are allowed to do is to watch the playing. Of course, if we watch long enough, we may eventually catch on to a few of the rules. The rules of the game are what we mean by fundamental physics.”

Even if we knew every rule, however, we might not be able to understand why a particular move is made in the game, merely because it is too complicated and our minds are limited. If you play chess you must know that it is easy to learn all the rules, and yet it is often very hard to select the best move or to understand why a player moves as he does. So it is in nature, only much more so.
volume I; lecture 2, "Basic Physics"; section 2-1, "Introduction"; p. 2-1
The Feynman Lectures on Physics (1964)

“Western civilization, it seems to me, stands by two great heritages. One is the scientific spirit of adventure — the adventure into the unknown, an unknown which must be recognized as being unknown in order to be explored; the demand that the unanswerable mysteries of the universe remain unanswered; the attitude that all is uncertain; to summarize it — the humility of the intellect. The other great heritage is Christian ethics — the basis of action on love, the brotherhood of all men, the value of the individual — the humility of the spirit.
These two heritages are logically, thoroughly consistent. But logic is not all; one needs one's heart to follow an idea. If people are going back to religion, what are they going back to? Is the modern church a place to give comfort to a man who doubts God — more, one who disbelieves in God? Is the modern church a place to give comfort and encouragement to the value of such doubts? So far, have we not drawn strength and comfort to maintain the one or the other of these consistent heritages in a way which attacks the values of the other? Is this unavoidable? How can we draw inspiration to support these two pillars of western civilization so that they may stand together in full vigor, mutually unafraid? Is this not the central problem of our time?”

remarks (2 May 1956) at a Caltech YMCA lunch forum http://calteches.library.caltech.edu/49/2/Religion.htm

“I can live with doubt, and uncertainty, and not knowing. I think it's much more interesting to live not knowing than to have answers which might be wrong. I have approximate answers, and possible beliefs, and different degrees of certainty about different things, but I'm not absolutely sure of anything. There are many things I don't know anything about, such as whether it means anything to ask "Why are we here?"”

Richard Feynman livre The Pleasure of Finding Things Out

I might think about it a little bit, and if I can't figure it out then I go on to something else. But I don't have to know an answer. I don't feel frightened by not knowing things, by being lost in the mysterious universe without having any purpose — which is the way it really is, as far as I can tell. Possibly. It doesn't frighten me.
Source: No Ordinary Genius (1994), p. 239, from interview in "The Pleasure of Finding Things Out" (1981): video http://www.youtube.com/watch?v=NEwUwWh5Xs4&t=48m10s

“Poets say science takes away from the beauty of the stars — mere globs of gas atoms. Nothing is "mere."”

I too can see the stars on a desert night, and feel them. But do I see less or more? The vastness of the heavens stretches my imagination — stuck on this carousel my little eye can catch one-million-year-old light. A vast pattern — of which I am a part... What is the pattern, or the meaning, or the why? It does not do harm to the mystery to know a little about it. For far more marvelous is the truth than any artists of the past imagined! Why do the poets of the present not speak of it? What men are poets who can speak of Jupiter if he were a man, but if he is an immense spinning sphere of methane and ammonia must be silent?
volume I; lecture 3, "The Relation of Physics to Other Sciences"; section 3-4, "Astronomy"; p. 3-6
The Feynman Lectures on Physics (1964)

“…study hard what interests you the most in the most undisciplined, irreverent and original manner possible.”

excerpt from letter to J. M. Szabados (30 November 1965), quoted in "Perfectly Reasonable Deviations from the Beaten Track The Letters of Richard P. Feynman" (2005) by Michelle Feynman and Carl Feynman, p. 206

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