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Richard Feynman

Date de naissance: 11. mai 1918
Date de décès: 15. février 1988
Autres noms: Richard Feynman Philips, Richard Phillips Feynman, Ричард Филлипс Фейнман

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.

Citations Richard Feynman

„[…] 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.“

—  Richard Feynman

[...] 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

„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.“

—  Richard Feynman

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

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

—  Richard Feynman

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

„It is really quite impossible to say anything with absolute precision, unless that thing is so abstracted from the real world as to not represent any real thing.“

—  Richard Feynman

" New Textbooks for the "New" Mathematics http://calteches.library.caltech.edu/2362/1/feynman.pdf", Engineering and Science volume 28, number 6 (March 1965) p. 9-15 at p. 14
Paraphrased as "Precise language is not the problem. Clear language is the problem."
Contexte: The real problem in speech is not precise language. The problem is clear language. The desire is to have the idea clearly communicated to the other person. It is only necessary to be precise when there is some doubt as to the meaning of a phrase, and then the precision should be put in the place where the doubt exists. It is really quite impossible to say anything with absolute precision, unless that thing is so abstracted from the real world as to not represent any real thing.Pure mathematics is just such an abstraction from the real world, and pure mathematics does have a special precise language for dealing with its own special and technical subjects. But this precise language is not precise in any sense if you deal with real objects of the world, and it is only pedantic and quite confusing to use it unless there are some special subtleties which have to be carefully distinguished.

„We are not to tell nature what she’s gotta be.“

—  Richard Feynman

Sir Douglas Robb Lectures, University of Auckland (1979); lecture 1, "Photons: Corpuscles of Light" http://www.youtube.com/watch?v=eLQ2atfqk2c&t=48m01s
Contexte: We are not to tell nature what she’s gotta be. … She's always got better imagination than we have.

„I learned very early the difference between knowing the name of something and knowing something.“

—  Richard Feynman, livre What Do You Care What Other People Think?

"The Making of a Scientist," p. 14 <!-- Feynman used variants of this bird story repeatedly: (1) "What is Science?", presented at the fifteenth annual meeting of the National Science Teachers Association, in New York City (1966) published in The Physics Teacher, volume 7, issue 6 (1969), p. 313-320. (2) Interview for the BBC TV Horizon program "The Pleasure of Finding Things Out" (1981), published in Christopher Sykes, No Ordinary Genius: The Illustrated Richard Feynman (1994), p. 27. -->
What Do You Care What Other People Think? (1988)
Contexte: You can know the name of that bird in all the languages of the world, but when you're finished, you'll know absolutely nothing whatever about the bird. You'll only know about humans in different places, and what they call the bird. … I learned very early the difference between knowing the name of something and knowing something.

„Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.“

—  Richard Feynman

The Value of Science (1955)
Contexte: The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain. Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

„The real problem in speech is not precise language. The problem is clear language.“

—  Richard Feynman

" New Textbooks for the "New" Mathematics http://calteches.library.caltech.edu/2362/1/feynman.pdf", Engineering and Science volume 28, number 6 (March 1965) p. 9-15 at p. 14
Paraphrased as "Precise language is not the problem. Clear language is the problem."
Contexte: The real problem in speech is not precise language. The problem is clear language. The desire is to have the idea clearly communicated to the other person. It is only necessary to be precise when there is some doubt as to the meaning of a phrase, and then the precision should be put in the place where the doubt exists. It is really quite impossible to say anything with absolute precision, unless that thing is so abstracted from the real world as to not represent any real thing.Pure mathematics is just such an abstraction from the real world, and pure mathematics does have a special precise language for dealing with its own special and technical subjects. But this precise language is not precise in any sense if you deal with real objects of the world, and it is only pedantic and quite confusing to use it unless there are some special subtleties which have to be carefully distinguished.

„We can deduce, often, from one part of physics like the law of gravitation, a principle which turns out to be much more valid than the derivation.“

—  Richard Feynman, livre The Character of Physical Law

Source: The Character of Physical Law (1965), chapter 2, “ The Relation of Mathematics to Physics http://www.youtube.com/watch?v=M9ZYEb0Vf8U” referring to the law of conservation of angular momentum
Contexte: Now we have a problem. We can deduce, often, from one part of physics like the law of gravitation, a principle which turns out to be much more valid than the derivation. This doesn't happen in mathematics, that the theorems come out in places where they're not supposed to be!

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„I hope you accept Nature as She is — absurd.“

—  Richard Feynman, livre QED: The Strange Theory of Light and Matter

Source: QED: The Strange Theory of Light and Matter (1985), p. 10
Contexte: The theory of quantum electrodynamics describes Nature as absurd from the point of view of common sense. And it agrees fully with experiment. So I hope you accept Nature as She is — absurd.

„Have no respect whatsoever for authority; forget who said it and instead look what he starts with, where he ends up, and ask yourself, "Is it reasonable?"“

—  Richard Feynman, livre What Do You Care What Other People Think?

"What Do You Care What Other People Think?", p. 28-29
What Do You Care What Other People Think? (1988)
Contexte: Doubting the great Descartes … was a reaction I learned from my father: Have no respect whatsoever for authority; forget who said it and instead look what he starts with, where he ends up, and ask yourself, "Is it reasonable?"

„We are at the very beginning of time for the human race. It is not unreasonable that we grapple with problems. But there are tens of thousands of years in the future. Our responsibility is to do what we can, learn what we can, improve the solutions, and pass them on.“

—  Richard Feynman

The Value of Science (1955)
Contexte: We are at the very beginning of time for the human race. It is not unreasonable that we grapple with problems. But there are tens of thousands of years in the future. Our responsibility is to do what we can, learn what we can, improve the solutions, and pass them on.
... It is our responsibility to leave the people of the future a free hand. In the impetuous youth of humanity, we can make grave errors that can stunt our growth for a long time. This we will do if we say we have the answers now, so young and ignorant as we are. If we suppress all discussion, all criticism, proclaiming "This is the answer, my friends; man is saved!" we will doom humanity for a long time to the chains of authority, confined to the limits of our present imagination. It has been done so many times before.
... It is our responsibility as scientists, knowing the great progress which comes from a satisfactory philosophy of ignorance, the great progress which is the fruit of freedom of thought, to proclaim the value of this freedom; to teach how doubt is not to be feared but welcomed and discussed; and to demand this freedom as our duty to all coming generations.

„If our small minds, for some convenience, divide this glass of wine, this universe, into parts — physics, biology, geology, astronomy, psychology, and so on — remember that nature does not know it!“

—  Richard Feynman

volume I; lecture 3, "The Relation of Physics to Other Sciences"; section 3-7, "How did it get that way?"; p. 3-10
Contexte: A poet once said, "The whole universe is in a glass of wine." We will probably never know in what sense he meant that, for poets do not write to be understood. But it is true that if we look at a glass of wine closely enough we see the entire universe. There are the things of physics: the twisting liquid which evaporates depending on the wind and weather, the reflections in the glass, and our imagination adds the atoms. The glass is a distillation of the Earth's rocks, and in its composition we see the secrets of the universe's age, and the evolution of stars. What strange arrays of chemicals are in the wine? How did they come to be? There are the ferments, the enzymes, the substrates, and the products. There in wine is found the great generalization: all life is fermentation. Nobody can discover the chemistry of wine without discovering, as did Louis Pasteur, the cause of much disease. How vivid is the claret, pressing its existence into the consciousness that watches it! If our small minds, for some convenience, divide this glass of wine, this universe, into parts — physics, biology, geology, astronomy, psychology, and so on — remember that nature does not know it! So let us put it all back together, not forgetting ultimately what it is for. Let it give us one more final pleasure: drink it and forget it all!

„I cannot define the real problem, therefore I suspect there's no real problem, but I'm not sure there's no real problem.“

—  Richard Feynman

" Simulating Physics with Computers http://www.cs.berkeley.edu/~christos/classics/Feynman.pdf", International Journal of Theoretical Physics, volume 21, 1982, p. 467-488, at p. 471
Contexte: We 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 younger 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's 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.

„The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think.“

—  Richard Feynman

The Value of Science (1955)
Contexte: The scientist has a lot of experience with ignorance and doubt and uncertainty, and this experience is of very great importance, I think. When a scientist doesn’t know the answer to a problem, he is ignorant. When he has a hunch as to what the result is, he is uncertain. And when he is pretty darn sure of what the result is going to be, he is still in some doubt. We have found it of paramount importance that in order to progress we must recognize our ignorance and leave room for doubt. Scientific knowledge is a body of statements of varying degrees of certainty — some most unsure, some nearly sure, but none absolutely certain. Now, we scientists are used to this, and we take it for granted that it is perfectly consistent to be unsure, that it is possible to live and not know. But I don’t know whether everyone realizes this is true. Our freedom to doubt was born out of a struggle against authority in the early days of science. It was a very deep and strong struggle: permit us to question — to doubt — to not be sure. I think that it is important that we do not forget this struggle and thus perhaps lose what we have gained.

„It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life.“

—  Richard Feynman

Rogers Commission Report (1986)
Contexte: It appears that there are enormous differences of opinion as to the probability of a failure with loss of vehicle and of human life. The estimates range from roughly 1 in 100 to 1 in 100,000. The higher figures come from the working engineers, and the very low figures from management. What are the causes and consequences of this lack of agreement? Since 1 part in 100,000 would imply that one could put a Shuttle up each day for 300 years expecting to lose only one, we could properly ask "What is the cause of management's fantastic faith in the machinery?"
We have also found that certification criteria used in Flight Readiness Reviews often develop a gradually decreasing strictness. The argument that the same risk was flown before without failure is often accepted as an argument for the safety of accepting it again. Because of this, obvious weaknesses are accepted again and again, sometimes without a sufficiently serious attempt to remedy them, or to delay a flight because of their continued presence.

„There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower. It only adds. I don't understand how it subtracts.“

—  Richard Feynman, livre What Do You Care What Other People Think?

"The Making of a Scientist," p. 11: video http://www.youtube.com/watch?v=NEwUwWh5Xs4&t=26s
What Do You Care What Other People Think? (1988)
Contexte: I have a friend who's an artist, and he sometimes takes a view which I don't agree with. He'll hold up a flower and say, "Look how beautiful it is," and I'll agree. But then he'll say, "I, as an artist, can see how beautiful a flower is. But you, as a scientist, take it all apart and it becomes dull." I think he's kind of nutty. … There are all kinds of interesting questions that come from a knowledge of science, which only adds to the excitement and mystery and awe of a flower. It only adds. I don't understand how it subtracts.

„I have a limited intelligence and I've used it in a particular direction.“

—  Richard Feynman, livre The Pleasure of Finding Things Out

" The Pleasure of Finding Things Out http://www.worldcat.org/wcpa/servlet/DCARead?standardNo=0738201081&standardNoType=1&excerpt=true", p. 2-3, transcript of BBC TV Horizon interview (1981): video http://www.youtube.com/watch?v=NEwUwWh5Xs4&t=2m53s
The Pleasure of Finding Things Out (1999)
Contexte: I've always been rather very one-sided about the science, and when I was younger, I concentrated almost all my effort on it. I didn't have time to learn, and I didn't have much patience for what's called the humanities; even though in the university there were humanities that you had to take, I tried my best to avoid somehow to learn anything and to work on it. It's only afterwards, when I've gotten older and more relaxed that I've spread out a little bit — I've learned to draw, and I read a little bit, but I'm really still a very one-sided person and don't know a great deal. I have a limited intelligence and I've used it in a particular direction.

„The fact that this danger did not lead to a catastrophe before is no guarantee that it will not the next time, unless it is completely understood. When playing Russian roulette the fact that the first shot got off safely is little comfort for the next.“

—  Richard Feynman

Rogers Commission Report (1986)
Contexte: The acceptance and success of these flights is taken as evidence of safety. But erosion and blow-by are not what the design expected. They are warnings that something is wrong. The equipment is not operating as expected, and therefore there is a danger that it can operate with even wider deviations in this unexpected and not thoroughly understood way. The fact that this danger did not lead to a catastrophe before is no guarantee that it will not the next time, unless it is completely understood. When playing Russian roulette the fact that the first shot got off safely is little comfort for the next. The origin and consequences of the erosion and blow-by were not understood. They did not occur equally on all flights and all joints; sometimes more, and sometimes less. Why not sometime, when whatever conditions determined it were right, still more leading to catastrophe?
In spite of these variations from case to case, officials behaved as if they understood it, giving apparently logical arguments to each other often depending on the "success" of previous flights.

„Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Etiam egestas wisi a erat. Morbi imperdiet, mauris ac auctor dictum.“

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