The only thing we can be certain of in this life is that we can be certain of nothing.

Out yonder there is this huge world, which exists independently of us human beings and which stands before us like a great, eternal riddle, at least partially accessible to our inspection and thinking

The ordinary adult never gives a thought to space-time problems ... I, on the contrary, developed so slowly that I did not begin to wonder about space and time until I was an adult. I then delved more deeply into the problem than any other adult or child would have done.

It is not by sitting still at a grand distance and calling the human race larvae that men are to be helped.

Life isn't worth living, unless it is lived for someone else.

I have no special talent. I am only passionately curious.

Conventional words or other signs have to be sought for laboriously only in a second stage, where the associative play already referred to is sufficiently established and can be reproduced at will.