# Paul Dirac idézet

## Paul Dirac

**Születési dátum:** 8. augusztus 1902**Halál dátuma:** 20. október 1984

Paul Adrien Maurice Dirac brit Nobel-díjas fizikus, a kvantummechanika egyik megalapozója, Wigner Jenő sógora.

A relativisztikus kvantummechanika alapegyenletének, a Dirac-egyenletnek a megalkotója. Az egyenletből arra következtetett, hogy léteznie kell az elektron pozitív töltésű antirészecskéjének. Ezt pozitronnak nevezte el. Wikipedia

### Idézetek Paul Dirac

### „I was taught at school never to start a sentence without knowing the end of it.“

http://www-history.mcs.st-and.ac.uk/Printonly/Dirac.html

### „If we are honest — and scientists have to be — we must admit that religion is a jumble of false assertions, with no basis in reality. The very idea of God is a product of the human imagination.“

Remarks made during the Fifth Solvay International Conference (October 1927), as quoted in Physics and Beyond: Encounters and Conversations (1971) by Werner Heisenberg, pp. 85-86; these comments prompted the famous remark later in the day by Wolfgang Pauli: "Well, our friend Dirac, too, has a religion, and its guiding principle is "God does not exist and Dirac is His prophet." Variant translations and paraphrases of that comment are listed in the "Quotes about Dirac" section below.

Kontextus: If we are honest — and scientists have to be — we must admit that religion is a jumble of false assertions, with no basis in reality. The very idea of God is a product of the human imagination. It is quite understandable why primitive people, who were so much more exposed to the overpowering forces of nature than we are today, should have personified these forces in fear and trembling. But nowadays, when we understand so many natural processes, we have no need for such solutions. I can't for the life of me see how the postulate of an Almighty God helps us in any way. What I do see is that this assumption leads to such unproductive questions as why God allows so much misery and injustice, the exploitation of the poor by the rich and all the other horrors He might have prevented. If religion is still being taught, it is by no means because its ideas still convince us, but simply because some of us want to keep the lower classes quiet. Quiet people are much easier to govern than clamorous and dissatisfied ones. They are also much easier to exploit. Religion is a kind of opium that allows a nation to lull itself into wishful dreams and so forget the injustices that are being perpetrated against the people. Hence the close alliance between those two great political forces, the State and the Church. Both need the illusion that a kindly God rewards — in heaven if not on earth — all those who have not risen up against injustice, who have done their duty quietly and uncomplainingly. That is precisely why the honest assertion that God is a mere product of the human imagination is branded as the worst of all mortal sins.

### „One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe.“

The Evolution of the Physicist's Picture of Nature (1963)

Kontextus: It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it. One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe. Our feeble attempts at mathematics enable us to understand a bit of the universe, and as we proceed to develop higher and higher mathematics we can hope to understand the universe better.

### „It seems that if one is working from the point of view of getting beauty in one's equations, and if one has really a sound insight, one is on a sure line of progress.“

The Evolution of the Physicist's Picture of Nature (1963)

Kontextus: It seems that if one is working from the point of view of getting beauty in one's equations, and if one has really a sound insight, one is on a sure line of progress. If there is not complete agreement between the results of one's work and experiment, one should not allow oneself to be too discouraged, because the discrepancy may well be due to minor features that are not properly taken into account and that will get cleared up with further development of the theory.

### „If you are receptive and humble, mathematics will lead you by the hand.“

As quoted in The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom (2009) by Graham Farmelo, p. 435

Kontextus: If you are receptive and humble, mathematics will lead you by the hand. Again and again, when I have been at a loss how to proceed, I have just had to wait until I have felt the mathematics led me by the hand. It has led me along an unexpected path, a path where new vistas open up, a path leading to new territory, where one can set up a base of operations, from which one can survey the surroundings and plan future progress.

### „It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power“

The Evolution of the Physicist's Picture of Nature (1963)

Kontextus: It seems to be one of the fundamental features of nature that fundamental physical laws are described in terms of a mathematical theory of great beauty and power, needing quite a high standard of mathematics for one to understand it. You may wonder: Why is nature constructed along these lines? One can only answer that our present knowledge seems to show that nature is so constructed. We simply have to accept it. One could perhaps describe the situation by saying that God is a mathematician of a very high order, and He used very advanced mathematics in constructing the universe. Our feeble attempts at mathematics enable us to understand a bit of the universe, and as we proceed to develop higher and higher mathematics we can hope to understand the universe better.

### „Just by studying mathematics we can hope to make a guess at the kind of mathematics that will come into the physics of the future.“

The Evolution of the Physicist's Picture of Nature (1963)

Kontextus: Just by studying mathematics we can hope to make a guess at the kind of mathematics that will come into the physics of the future. A good many people are working on the mathematical basis of quantum theory, trying to understand the theory better and to make it more powerful and more beautiful. If someone can hit on the right lines along which to make this development, it may lead to a future advance in which people will first discover the equations and then, after examining them, gradually learn how to apply them.

### „The interpretation of quantum mechanics has been dealt with by many authors, and I do not want to discuss it here. I want to deal with more fundamental things.“

P. A. M. Dirac, The inadequacies of quantum field theory, in Paul Adrien Maurice Dirac, B. N. Kursunoglu and E. P. Wigner (Cambridge University, Cambridge, 1987) p. 194

### „The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are“

Proceedings of the Royal Society of London. Series A, Containing Papers of a Mathematical and Physical Character, Vol. 123, No. 792 http://doi.org/10.1098/rspa.1929.0094 (6 April 1929)

Kontextus: The underlying physical laws necessary for the mathematical theory of a large part of physics and the whole of chemistry are thus completely known, and the difficulty is only that the exact application of these laws leads to equations much too complicated to be soluble. It therefore becomes desirable that approximate practical methods of applying quantum mechanics should be developed, which can lead to an explanation of the main features of complex atomic systems without too much computation.

### „It seems clear that the present quantum mechanics is not in its final form.“

"The Early Years of Relativity" in Albert Einstein : Historical and Cultural Perspectives : The Centennial Symposium in Jerusalem (1979) edited by Gerald James Holton and Yehuda Elkana, p. 85

Kontextus: It seems clear that the present quantum mechanics is not in its final form. Some further changes will be needed, just about as drastic as the changes made in passing from Bohr's orbit theory to quantum mechanics. Some day a new quantum mechanics, a relativistic one, will be discovered, in which we will not have these infinities occurring at all. It might very well be that the new quantum mechanics will have determinism in the way that Einstein wanted.

### „In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in the case of poetry, it's the exact opposite!“

As quoted in Brighter Than a Thousand Suns : A Personal History of the Atomic Scientists (1958) by Robert Jungk, as translated by James Cleugh, p. 22

Anecdotally, when Oppenheimer was working at Göttingen, Dirac supposedly came to him one day and said: "Oppenheimer, they tell me you are writing poetry. I do not see how a man can work on the frontiers of physics and write poetry at the same time. They are in opposition. In science you want to say something that nobody knew before, in words which everyone can understand. In poetry you are bound to say... something that everybody knows already in words that nobody can understand."

### „If there is no complete agreement between the results of one's work and the experiment, one should not allow oneself to be too discouraged.“

"The Evolution of the Physicist's Picture of Nature," Scientific American (May, 1963)

### „Causality applies only to a system which is left undisturbed. If a system is small, we cannot observe it without producing a serious disturbance and hence we cannot expect to find any causal connexion between the results of our observations. Causality will still be assumed to apply to undisturbed systems and the equations which will be set up to describe an undisturbed system will be differential equations expressing a causal connexion between conditions at one time and conditions at a later time. These equations will be in close correspondence with the equations of classical mechanics, but they will be connected only indirectly with the results of observations.“

— Paul Dirac, könyv Principles of Quantum Mechanics

I. The Principle of Superposition - 1. The Need for a Quantum Theory

The Principles of Quantum Mechanics (4th ed. 1958)

### „The measure of greatness in a scientific idea is the extent to which it stimulates thought and opens up new lines of research.“

The scientific work of Georges Lemaître (1968), P.A.M. Dirac, Commentarii (Pontifical Academy of Sciences), vol 2, 11, pp. 1–18.

### „My research work was based in pictures. I needed to visualise things and projective geometry was often most useful e. g. in figuring out how a particular quantity transforms under Lorentz transf[ormation]. When I came to publish the results I suppressed the projective geometry as the results could be expressed more concisely in analytic form.“

"Recollections of an Exciting Era," three lectures given at Varenna, 5 August 1972, quoted in Peter Galison, "The Suppressed Drawing: Paul Dirac's Hidden Geometry", Representations, No. 72 (Autumn, 2000)

### „At the beginning of time the laws of Nature were probably very different from what they are now. Thus we should consider the laws of Nature as continually changing with the epoch, instead of as holding uniformly throughout space-time. This idea was first put forward by Milne, who worked it out on… assumptions… not very satisfying… we should expect them also to depend on position in space, in order to preserve the beautiful idea of the theory of relativity [that] there is fundamental similarity between space and time.“

The Relation between Mathematics and Physics http://www.damtp.cam.ac.uk/events/strings02/dirac/speach.html (Feb. 6, 1939) Proceedings of the Royal Society (Edinburgh) Vol. 59, 1938-39, Part II, pp. 122-129.

### „Classical mechanics has been developed continuously from the time of Newton and applied to an ever-widening range of dynamical systems, including the electromagnetic field in interaction with matter. The underlying ideas and the laws governing their application form a simple and elegant scheme, which one would be inclined to think could not be seriously modified without having all its attractive features spout. Nevertheless it has been found possible to set up a new scheme, called quantum mechanics, which is more suitable for the description of phenomena on the atomic scale and which is in some respects more elegant and satisfying than the classical scheme. This possibility is due to the changes which the new scheme involves being of a very profound character and not clashing with the features of the classical theory that make it so attractive, as a result of which all these features can be incorporated in the new scheme.“

— Paul Dirac, könyv Principles of Quantum Mechanics

I. The Principle of Superposition - 1. The Need for a Quantum Theory

The Principles of Quantum Mechanics (4th ed. 1958)

### „I don't suppose that applies so much to other physicists; I think it’s a peculiarity of myself that I like to play about with equations, just looking for beautiful mathematical relations which maybe don’t have any physical meaning at all. Sometimes they do.“

Interview with Dr. P. A. M. Dirac by Thomas S. Kuhn at Dirac's home, Cambridge, England, May 7, 1963 http://www.aip.org/history/ohilist/4575_3.html