Scientific progress is measured in units of courage, not intelligence.

The aim of science is to make difficult things understandable in a simpler way; the aim of poetry is to state simple things in an incomprehensible way. The two are incompatible.

Quantum mechanics has explained all of chemistry and most of physics.

It is more important to have beauty in one's equations than to have them fit experiment.

A book on the new physics, if not purely descriptive of experimental work, must essentially be mathematical.

No. I had successfully solved the difficulty of finding a description of the electron which was consistent with both relativity and quantum mechanics. Of course, when you solve one difficulty, other new difficulties arise. You then try to sove them. You can never solve all difficulties at once.

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.