I am of the opinion that all the finer speculations in the realm of science spring from a deep religious feeling, and that without such feeling they would not be fruitful.

To raise new questions, new possibilities, to regard old problems from a new angle, requires creative imagination and marks real advance in science.

Do not grow old, no matter how long you live. Never cease to stand like curious children before the Great Mystery into which we were born.

The only mistake in life is the lesson not learned.

... one does people the best service by giving them some elevating work to do and thus indirectly elevating them.

Isn't it strange that I who have written only unpopular books should be such a popular fellow?

Science can only ascertain what is, but not what should be, and outside of its domain value judgements of all kinds remain necessary.