The methods of theoretical physics should be applicable to all those branches of thought in which the essential features are expressible with numbers.

Mathematics is the tool specially suited for dealing with abstract concepts of any kind and there is no limit to its power in this field.

I found the best ideas usually came, not when one was actively striving for them, but when one was in a more relaxed state… I used to take long solitary walks on Sundays, during which I tended to review the current situation in a leisurely way. Such occasions often proved fruitful, even though (or perhaps, because) the primary purpose of the walk was relaxation and not research.

There is in my opinion a great similarity between the problems provided by the mysterious behavior of the atom and those provided by the present economic paradoxes confronting the world.

I admired Bohr very much. We had long talks together, long talks in which Bohr did practically all the talking.

Hopes are always accompanied by fears, and, in scientific research, the fears are liable to become dominant.

As time goes on, it becomes increasingly evident that the rules which the mathematician finds interesting are the same as those which Nature has chosen.