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.

To the Master's honor all must turn, each in its track, without a sound, forever tracing Newton's ground.

I very rarely think in words at all. A thought comes, and I may try to express in words afterwards.

It may affront the military-minded person to suggest a regime that does not maintain any military secrets.

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

I recently discussed with an intelligent and well-disposed man the threat of another war, which in my opinion would seriously endanger the existence of mankind, and I remarked that only a supranational organization would offer protection from that danger. Thereupon my visitor, very calmly and coolly, said to me: "Why are you so deeply opposed to the disappearance of the human race?".

A finely tempered nature longs to escape from the personal life into the world of objective perception and thought.