Consider the concepts referred to in the words 'where', 'when', 'why', 'being', to the elucidation of which innumerable volumes of philosophy have been devoted. We fare no better in our speculations than a fish which should strive to become clear as to what is water.

No scientist thinks in formulae.

If a theory can not be explained to a child, then the theory is probably worthless.

Science will stagnate if it is made to serve practical goals.

It should be possible to explain the laws of physics to a barmaid.

Since the mathematicians have invaded the theory of relativity I do not understand it myself any more.

[Asked about a book in which 100 Nazi professors charged him with scientific error.] Were I wrong, one professor would have been quite enough.