Whether you can observe a thing or not depends on the theory which you use. It is the theory which decides what can be observed.

May they not forget to keep pure the great heritage that puts them ahead of the West: the artistic configuration of life, the simplicity and modesty of personal needs, and the purity and serenity of the Japanese soul.

I have come to believe that the motion of the Earth cannot be detected by any optical experiment.

I was sitting in a chair in the patent office at Bern when all of sudden a thought occurred to me: If a person falls freely he will not feel his own weight. I was startled. This simple thought made a deep impression on me. It impelled me toward a theory of gravitation.

The only justification for our concepts and system of concepts is that they serve to represent the complex of our experiences; beyond this they have no legitimacy. I am convinced that the philosophers have had a harmful effect upon the progress of scientific thinking in removing certain fundamental concepts from the domain of empiricism, where they are under our control, to the intangible heights of the a priori. For even if it should appear that the universe of ideas cannot be deduced from experience by logical means, but is, in a sense, a creation of the human mind, without which no science is possible, nevertheless the universe of ideas is just as little independent of the nature of our experience as clothes are of the form of the human body. This is particularly true of our concepts of time and space, which physicists have been obliged by the facts to bring down from the Olympus of the a priori in order to adjust them and put them in a serviceable condition.

I do not carry such information in my mind since it is readily available in books. ...The value of a college education is not the learning of many facts but the training of the mind to think.

When a man after long years of searching chances on a thought which discloses something of the beauty of this mysterious universe, he should not therefore be personally celebrated. He is already sufficiently paid by his experience of seeking and finding. In science, moreover, the work of the individual is so bound up with that of his scientific predecessors and contemporaries that it appears almost as an impersonal product of his generation.

In Lenin I honor a man, who in total sacrifice of his own person has committed his entire energy to realizing social justice. I do not find his methods advisable. One thing is certain, however: men like him are the guardians and renewers [Erneuerer] of mankind's conscience.

The meaning of relativity has been widely misunderstood. Philosophers play with the word, like a child with a doll. Relativity, as I see it, merely denotes that certain physical and mechanical facts, which have been regarded as positive and permanent, are relative with regard to certain other facts in the sphere of physics and mechanics. It does not mean that everything in life is relative and that we have the right to turn the whole world mischievously topsy-turvy.

No man can visualize four dimensions, except mathematically ... I think in four dimensions, but only abstractly. The human mind can picture these dimensions no more than it can envisage electricity. Nevertheless, they are no less real than electro-magnetism, the force which controls our universe, within, and by which we have our being.

As a child, I received instruction both in the Bible and in the Talmud. I am a Jew, but I am enthralled by the luminous figure of the Nazarene.

I am enough of an artist to draw freely upon my imagination. Imagination is more important than knowledge. Knowledge is limited. Imagination encircles the world.

I believe in intuitions and inspirations. I sometimes feel that I am right. I do not know that I am. When two expeditions of scientists, financed by the Royal Academy, went forth to test my theory of relativity, I was convinced that their conclusions would tally with my hypothesis. I was not surprised when the eclipse of May 29, 1919, confirmed my intuitions. I would have been surprised if I had been wrong.

The only progress I can see is progress in the organization. The ordinary human being does not live long enough to draw any substantial benefit from his own experience. And no one, it seems, can benefit by the experiences of others. Being both a father and teacher, I know we can teach our children nothing. We can transmit to them neither our knowledge of life nor of mathematics. Each must learn its lesson anew.

Whereas materialistic historians and philosophers neglect psychic realities, Freud is inclined to overstress their importance. I am not a psychologist, but it seems to me fairly evident that physiological factors, especially our endocrines, control our destiny ... I am not able to venture a judgment on so important a phase of modern thought. However, it seems to me that psychoanalysis is not always salutary. It may not always be helpful to delve into the subconscious. The machinery of our legs is controlled by a hundred different muscles. Do you think it would help us to walk if we analyzed our legs and knew exactly which one of the little muscles must be employed in locomotion and the order in which they work? ... I am not prepared to accept all his [Freud's] conclusions, but I consider his work an immensely valuable contribution to the science of human behavior. I think he is even greater as a writer than as a psychologist. Freud's brilliant style is unsurpassed by anyone since Schopenhauer.

I believe with Schopenhauer: We can do what we wish, but we can only wish what we must. Practically, I am, nevertheless, compelled to act as if freedom of the will existed. If I wish to live in a civilized community, I must act as if man is a responsible being. I know that philosophically a murderer is not responsible for his crime; nevertheless, I must protect myself from unpleasant contacts. I may consider him guiltless, but I prefer not to take tea with him.

I am a determinist. As such, I do not believe in free will. The Jews believe in free will. They believe that man shapes his own life. I reject that doctrine philosophically. In that respect, I am not a Jew.

We are inclined to overemphasize the material influences in history. The Russians especially make this mistake. Intellectual values and ethnic influences, tradition and emotional factors are equally important. If this were not the case, Europe would today be a federated state, not a madhouse of nationalism.

In America, more than anywhere else, the individual is lost in the achievements of the many. America is beginning to be the world leader in a scientific investigation. American scholarship is both patient and inspiring. The Americans show an unselfish devotion to science, which is the very opposite of the conventional European view of your countrymen. Too many of us look upon Americans as dollar chasers. This is a cruel libel, even if it is reiterated thoughtlessly by the Americans themselves. It is not true that the dollar is an American fetish. The American student is not interested in dollars, not even in success as such, but in his task, the object of the search. It is his painstaking application to the study of the infinitely little and the infinitely large which accounts for his success in astronomy.

Our time is Gothic in its spirit. Unlike the Renaissance, it is not dominated by a few outstanding personalities. The twentieth century has established the democracy of the intellect. In the republic of art and science, there are many men who take an equally important part in the intellectual movements of our age. It is the epoch rather than the individual that is important. There is no one dominant personality like Galileo or Newton. Even in the nineteenth century, there were still a few giants who outtopped all others. Today the general level is much higher than ever before in the history of the world, but there are few men whose stature immediately sets them apart from all others.

Reading after a certain age diverts the mind too much from its creative pursuits. Any man who reads too much and uses his own brain too little falls into lazy habits of thinking, just as the man who spends too much time in the theater is tempted to be content with living vicariously instead of living his own life.

I refuse to make money out of my science. My laurel is not for sale like so many bales of cotton.

Sometimes one pays most for the things one gets for nothing.

Jesus is too colossal for the pen of phrasemongers, however artful. No man can dispose of Christianity with a bon mot.

I am neither a German citizen nor do I believe in anything that can be described as a "Jewish faith." But I am a Jew and glad to belong to the Jewish people, though I do not regard it in any way as chosen.

We may assume the existence of an aether; only we must give up ascribing a definite state of motion to it, i.e. we must by abstraction take from it the last mechanical characteristic which Lorentz had still left it. ... But this ether may not be thought of as endowed with the quality characteristic of ponderable media, as consisting of parts which may be tracked through time. The idea of motion may not be applied to it.

If I was not a physicist, I would probably be a musician. I often think in music. I live my daydreams in music. I see my life in terms of music. ... I cannot tell if I would have done any creative work of importance in music, but I do know that I get most joy in life out of my violin.

Everything should be made simple as possible but no simpler.

The mass of a body is a measure of its energy content.

We shall, therefore, assume the complete physical equivalence of a gravitational field and a corresponding acceleration of the reference system.

By a clock we understand anything characterized by a phenomenon passing periodically through identical phases so that we must assume, by the principle of sufficient reason, that all that happens in a given period is identical with all that happens in an arbitrary period.

...to the question whether or not the motion of the Earth in space can be made perceptible in terrestrial experiments. We have already remarked... that all attempts of this nature led to a negative result. Before the theory of relativity was put forward, it was difficult to become reconciled to this negative result.

The most beautiful fate of a physical theory is to point the way to the establishment of a more inclusive theory, in which it lives on as a limiting case.

"The physical world is real." That is supposed to be the fundamental hypothesis. What does "hypothesis" mean here? For me, a hypothesis is a statement, whose truth must be assumed for the moment, but whose meaning must be raised above all ambiguity. The above statement appears to me, however, to be, in itself, meaningless, as if one said: "The physical world is cock-a-doodle-do." It appears to me that the "real" is an intrinsically empty, meaningless category (pigeon hole), whose monstrous importance lies only in the fact that I can do certain things in it and not certain others.

I lie on the beach like a crocodile and let myself be roasted by the sun. I never see a newspaper and don't give a damn for what is called the world.

The supreme task of the physicist is to arrive at those universal elementary laws from which the cosmos can be built up by pure deduction. There is no logical path to these laws; only intuition, resting on sympathetic understanding of experience, can reach them. In this methodological uncertainty, one might suppose that there were any number of possible systems of theoretical physics all equally well justified; and this opinion is no doubt correct, theoretically. But the development of physics has shown that at any given moment, out of all conceivable constructions, a single one has always proved itself decidedly superior to all the rest.

But what can be the attraction of getting to know such a tiny section of nature thoroughly, while one leaves everything subtler and more complex shyly and timidly alone? Does the product of such a modest effort deserve to be called by the proud name of a theory of the universe? In my belief the name is justified; for the general laws on which the structure of theoretical physics is based claim to be valid for any natural phenomenon whatsoever. With them, it ought to be possible to arrive at the description, that is to say, the theory, of every natural process, including life, by means of pure deduction, if that process of deduction were not far beyond the capacity of the human intellect. The physicist's renunciation of completeness for his cosmos is therefore not a matter of fundamental principle.

Man tries to make for himself in the fashion that suits him best a simplified and intelligible picture of the world; he then tries to some extent to substitute this cosmos of his for the world of experience, and thus to overcome it. This is what the painter, the poet, the speculative philosopher, and the natural scientist do, each in his own fashion. Each makes this cosmos and its construction the pivot of his emotional life, in order to find in this way the peace and security which he cannot find in the narrow whirlpool of personal experience.

The state of mind which enables a man to do work of this kind is akin to that of the religious worshiper or the lover; the daily effort comes from no deliberate intention or program, but straight from the heart.

In the temple of science are many mansions, and various indeed are they that dwell therein and the motives that have led them thither. Many take to science out of a joyful sense of superior intellectual power; science is their own special sport to which they look for vivid experience and the satisfaction of ambition; many others are to be found in the temple who have offered the products of their brains on this altar for purely utilitarian purposes. Were an angel of the Lord to come and drive all the people belonging to these two categories out of the temple, the assemblage would be seriously depleted, but there would still be some men, of both present and past times, left inside. Our Planck is one of them, and that is why we love him. I am quite aware that we have just now lightheartedly expelled in imagination many excellent men who are largely, perhaps chiefly, responsible for the buildings of the temple of science; and in many cases, our angel would find it a pretty ticklish job to decide. But of one thing I feel sure: if the types we have just expelled were the only types there were, the temple would never have come to be, any more than a forest can grow which consists of nothing but creepers. For these people any sphere of human activity will do if it comes to a point; whether they become engineers, officers, tradesmen, or scientists depends on circumstances.Now let us have another look at those who have found favor with the angel. Most of them are somewhat odd, uncommunicative, solitary fellows, really less like each other, in spite of these common characteristics, than the hosts of the rejected. What has brought them to the temple? That is a difficult question and no single answer will cover it.

The most simple picture one can form about the creation of an empirical science is along the lines of an inductive method. Individual facts are selected and grouped together such that their lawful connection becomes clearly apparent. ... The truly great advances in our understanding of nature originated in a manner almost diametrically opposed to induction. The intuitive grasp of the essentials or a large complex of facts leads the scientist to the postulation of a hypothetical basic law, or several such basic laws. From the basic laws (system of axioms) he derives his conclusions as completely as possible in a purely logically deductive manner. These conclusions, derived from the basic laws (and often only after time-consuming developments and calculations), can then be compared to experience, and in this manner provide criteria for the justification of the assumed basic law.

I am happy because I want nothing from anyone. I do not care about money. Decorations, titles or distinctions mean nothing to me. I do not crave praise. The only thing that gives me pleasure, apart from my work, my violin, and my sailboat, is the appreciation of my fellow workers.

I claim credit for nothing. Everything is determined, the beginning as well as the end, by forces over which we have no control. It is determined for the insect as well as for the star. Human beings, vegetables or cosmic dust, we all dance to a mysterious tune, intoned in the distance by an invisible player.

Life is like riding a bicycle. To keep your balance you must keep moving.

I believe that whatever we do or live for has its causality; it is good, however, that we cannot see through to it.

The really good music, whether of the East or of the West, cannot be analyzed.

The scientific organization and comprehensive exposition in accessible form of the Talmud has a twofold importance for us Jews. It is important in the first place that the high cultural values of the Talmud should not be lost to modern minds among the Jewish people nor to science, but should operate further as a living force. In the second place, The Talmud must be made an open book to the world, in order to cut the ground from under certain malevolent attacks, of anti-Semitic origin, which borrow countenance from the obscurity and inaccessibility of certain passages in the Talmud. To support this cultural work would thus mean an important achievement for the Jewish people.

I do not think that religion is the most important element. We are held together rather by a body of tradition, handed down from father to son, which the child imbibes with his mother's milk. The atmosphere of our infancy predetermines our idiosyncrasies and predilections.

We Jews have been too adaptable. We have been too eager to sacrifice our idiosyncrasies for the sake of social conformity. ... Even in modern civilization, the Jew is most happy if he remains a Jew.

Jesus is too colossal for the pen of phrasemongers, however artful. No man can dispose of Christianity with a bon mot.