Niels Bohr

Prediction is very difficult, especially if it's about the future.

When it comes to atoms, language can be used only as in poetry. The poet, too, is not nearly so concerned with describing facts as with creating images.

Your theory is crazy, but it's not crazy enough to be true.

An expert is a man who has made all the mistakes which can be made, in a narrow field.

The best weapon of a dictatorship is secrecy, but the best weapon of a democracy should be the weapon of openness.

There are some things so serious you have to laugh at them.

Humanity will... be confronted with dangers of unprecedented character unless, in due time, measures can be taken to forestall a disastrous competition in such formidable armaments and to establish an international control of the manufacture and use of the powerful materials.

While the finish given to our picture of the world by the theory of relativity has already been absorbed into the general scientific consciousness, this has scarcely occurred to the same extent with those aspects of the general problem of knowledge which have been elucidated by the quantum theory.

No, no, you're not thinking; you're just being logical.

Technology has advanced more in the last thirty years than in the previous two thousand. The exponential increase in advancement will only continue.

Everything we call real is made of things that cannot be regarded as real.

If quantum mechanics hasn't profoundly shocked you, you haven't understood it yet.

It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we say about Nature.

Einstein, stop telling God what to do!

Never express yourself more clearly than you are able to think.

Every description of natural processes must be based on ideas which have been introduced and defined by the classical theory.

The opposite of a fact is falsehood, but the opposite of one profound truth may very well be another profound truth.

Every great and deep difficulty bears in itself its own solution. It forces us to change our thinking in order to find it.

How wonderful that we have met with a paradox. Now we have some hope of making progress.

A physicist is just an atom's way of looking at itself.

Every sentence I utter must be understood not as an affirmation, but as a question.