The belief in an external world independent of the perceiving subject is the basis of all natural science. Since, however, sense perception only gives information of this external world or of "physical reality" indirectly, we can only grasp the latter by speculative means. It follows from this that our notions of physical reality can never be final. We must always be ready to change these notions - that is to say, the axiomatic basis of physics - in order to do justice to perceived facts in the most perfect way.

People should be more like animals . . . they should be more intuitive; they should not be too conscious of what they do while they do it.

(Reply on what constitutes scientific proof:)"The question is much too difficult for me.

The most superior of scientific goals is to embrace a maximum of experiment with a minimum of hypotheses.

Subtle is the Lord. Malicious, He is not.

You imagine that I look back on my life's work with calm satisfaction. But from nearby it looks quite different. There is not a single concept of which I am convinced that it will stand firm, and I feel uncertain whether I am in general on the right track.

I don't try to imagine a personal God; it suffices to stand in awe at the structure of the world, insofar as it allows our inadequate senses to appreciate it.