Those who are not shocked when they first come across quantum theory cannot possibly have understood it.

The very nature of the quantum theory ... forces us to regard the space-time coordination and the claim of causality, the union of which characterizes the classical theories, as complementary but exclusive features of the description, symbolizing the idealization of observation and description, respectively.

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

An expert is a person who has made all the mistakes that can be made in a very narrow field.

The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.

Stop telling God what to do with his dice.

I feel personally responsible for the universe's inevitable heat death.

We must be clear that 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 and establishing mental connections.[About describing atomic models in the language of classical physics:]

You must come to Copenhagen to work with us. We like people who can actually perform thought experiments!