I never thought that others would take my theories so much more seriously than I did.

I don't know what weapons will be used in the Third World War. But I can tell you what they'll use in the Fourth - rocks!

There comes a time when the mind takes a higher plane of knowledge but can never prove how it got there.

How many people are trapped in their everyday habits: part numb, part frightened, part indifferent? To have a better life we must keep choosing how we are living.

It is a very high goal which, with our weak powers, we can reach only very inadequately, but which gives a sure foundation to our aspirations and valuations.

Playfullness is the essential feature of productive thought.

The mere formulation of a problem is far more essential than its solution, which may be merely a matter of mathematical or experimental skills. To raise new questions, new possibilities, to regard old problems from a new angle requires creative imagination and marks real advances in science.