A theory is the more impressive the greater the simplicity of its premises is, the more different kinds of things it relates, and the more extended is its area of applicability. Therefore the deep impression which classical thermodynamics made upon me. It is the only physical theory of universal content concerning which I am convinced that within the framework of the applicability of its basic concepts, it will never be overthrown.

The human mind has first to construct forms, independently, before we can find them in things.

Life is a preparation for the future; and the best preparation for the future is to live as if there were none.

Concerning matter, we have been all wrong. What we have called matter is energy, whose vibration has been so lowered as to be perceptible to the senses. There is no matter.

Agreements about what is good or not, are usually not worth much. It is very much like art, is it not an art to lead a good life?

... on principle, it is quite wrong to try founding a theory on observable magnitudes alone. In reality the very opposite happens. It is the theory which decides what we can observe.

I came- though the child of entirely irreligious (Jewish) parents - to a deep religiousness, which, however, reached an abrupt end at the age of twelve.