Every word or concept, clear as it may seem to be, has only a limited range of applicability.

Bohr's influence on the physics and the physicists of our century was stronger than that of anyone else, even than that of Albert Einstein.

The end of the First World War had thrown Germany's youth into great turmoil. The reins of power had fallen from the hands of a deeply disillusioned older generation, and the younger ones drew together in larger and smaller groups to blaze new paths or, at least, to discover a new star to steer by.

In America, it was decided to attempt the production of atomic bombs with an effort that would constitute a large part of the collective American war effort. In Germany, an effort one thousandth the scale of the American was applied to the problem of producing atomic energy that would drive engines.

The German physicists knew at least so much about the manufacture and construction of atomic bombs that it was clear to them that the manufacture of bombs in Germany could not succeed during the war. For this reason, they were spared the moral decision whether they should make an atomic bomb, and they had only worked on the uranium engine.

If we made atomic bombs, we would bring about a terrible change in the world. Who knows what would happen from this?

Natural science, does not simply describe and explain nature; it is part of the interplay between nature and ourselves.

Although the theory of relativity makes the greatest of demands on the ability for abstract thought, still it fulfills the traditional requirements of science insofar as it permits a division of the world into subject and object (observer and observed) and, hence, a clear formulation of the law of causality.

This proving of such and such I found to be almost like cheating. You start somewhere, and then you go into a dark tunnel, and then you come out at another place. You find that you have proved what you wanted to prove, but in the tunnel, you don't see anything.

I believe this uranium business will give the Anglo-Saxons such tremendous power that Europe will become a bloc under Anglo-Saxon domination. If that is the case, it will be a very good thing. I wonder whether Stalin will be able to stand up to the others as he has done in the past.

If the lecture is good, then everything is too smooth. That's the same in music: if the performance is too good, you really don't enjoy it, because it just goes by, and you can never penetrate into the heart of it. Sometimes a poor performance is better for enjoyment, because you can look at those things that were wrong and analyze them.

Our house was destroyed in 1943, and I moved the family to a cottage I owned before the war in the Bavarian Alps. This cottage was meant for a very few people, and at the end of the war, there were about 13 people in this very small house.

The single life is bearable to me only through my work in science, but for the long term, it would be very bad if I had to make do without a very young person next to me.

It is seen that both matter and radiation possess a remarkable duality of character, as they sometimes exhibit the properties of waves, at other times those of particles. Now, it is obvious that a thing cannot be a form of wave motion and composed of particles at the same time - the two concepts are too different.

The Anglo-Americans want the balance of power in Eurasia. The only balance of power they can achieve now is the whole of Europe against Russia. The only choice for us is either to join this Western European bloc or join in with Russia.

In 1924, I became a Dozent in Gottingen and worked out the quantum mechanics during a holiday stay on Heligoland.

I would say that I was absolutely convinced of the possibility of our making an uranium engine, but I never thought that we would make a bomb; and at the bottom of my heart, I was really glad that it was to be an engine and not a bomb.

It is generally believed that our science is empirical and that we draw our concepts and our mathematical constructs from the empirical data. If this were the whole truth, we should, when entering into a new field, introduce only such quantities as can directly be observed, and formulate natural laws only by means of these quantities.

Reports in Washington show that our reasoning was just like that of your physicists. With all this information available, at least to privileged persons, I cannot understand why it is generally held in the United States that we completely missed the basic principle of the bomb until after Hiroshima.

I had imagined doing nuclear physics and cosmic ray work in greater style in peace time. To do modern physics in a small way is of no use of all.

The problems of language here are really serious. We wish to speak in some way about the structure of the atoms. But we cannot speak about atoms in ordinary language.

The violent reaction on the recent development of modern physics can only be understood when one realises that here the foundations of physics have started moving; and that this motion has caused the feeling that the ground would be cut from science.

Not only is the universe stranger than we think it is stranger than we can think.

For Germany, the war was like an end game in chess in which she possessed one castle less than her adversary. The loss of the war was as certain as the loss of an end game under these conditions.

The uncertainty principle refers to the degree of indeterminateness in the possible present knowledge of the simultaneous values of various quantities with which the quantum theory deals; it does not restrict, for example, the exactness of a position measurement alone or a velocity measurement alone.

The uncertainty relation does not refer to the past; if the velocity of the electron is at first known and the position then exactly measured, the position for times previous to the measurement may be calculated.

One may say that in a state of science where fundamental concepts have to be changed, tradition is both the condition for progress and a hindrance. Hence, it usually takes a long time before the new concepts are generally accepted.

What we observe is not nature itself, but nature exposed to our method of questioning.

The solution of the difficulty is that the two mental pictures which experiment lead us to form - the one of the particles, the other of the waves - are both incomplete and have only the validity of analogies which are accurate only in limiting cases.

I think that if a United States of Europe were to be formed, it would be in our interests to fight for it, as all our old traditions would remain in such a united Europe, whereas if we were to start now as part of the Russian Empire, everything that had ever been in Germany would disappear.

I would like to mention astrophysics; in this field, the strange properties of the pulsars and quasars, and perhaps also the gravitational waves, can be considered as a challenge.

It is true that in quantum theory we cannot rely on strict causality. But by repeating the experiments many times, we can finally derive from the observations statistical distributions, and by repeating such series of experiments, we can arrive at objective statements concerning these distributions.

After I had written a paper or letter for Bohr, I always had the impression that I had learned something which I could use for my own work. And somehow, I never felt that I had too little time for my own work. I always found time.

Certainly, in the course of time, the splendid things will separate from the hateful.

There is a great difference between discoveries and inventions. With discoveries, one can always be skeptical, and many surprises can take place. In the case of inventions, surprises can really only occur for people who have not had anything to do with it.

Whoever dedicates his life to searching out particular connections of nature will spontaneously be confronted with the question how they harmoniously fit into the whole.