An expert is a man who has made all the mistakes, which can be made, in a very narrow field.
How wonderful that we have met with a paradox. Now we have some hope of making progress.
Prediction is very difficult, especially about the future.
[also attributed to Mark Twain]
Those who are not shocked when they first come across quantum mechanics cannot possibly have understood it.
If anybody says he can think about quantum problems without getting giddy, that only shows he has not understood the first thing about them.
Every sentence I utter must be understood not as an affirmation, but as a question.
It is wrong to think that the task of physics is to find out how Nature is. Physics concerns what we can say about Nature.
It is, indeed, perhaps the greatest prospect of humanistic studies to contribute through an increasing knowledge of the history of cultural development to that gradual removal of prejudices which is the common aim of all science.
Never express yourself more clearly than you are able to think.
There are some things so serious that you have to laugh at them.
We are trapped by language to such a degree that every attempt to formulate insight is a play on words.
The opposite of a correct statement is a false statement. But the opposite of a profound truth may well be another profound truth.
A great truth is a truth whose opposite is also a great truth.
We are all agreed that your theory is crazy. The question which divides us is whether it is crazy enough to have a chance of being correct. My own feeling is that it is not crazy enough.
A visitor to Niels Bohr's country cottage, noticing a horseshoe hanging on the wall, teasing the eminent scientist about this ancient superstition.
Can it be true that you, of all people, believe it will bring you luck?'
'Of course not,' replied Bohr, 'but I understand it brings you luck whether you believe it or not.'