When the nazis came to power, I looked to the universities that prided themselves upon their intellectual freedom, and they failed me. I looked to the German press, which prided itself on the freedom of the press, and it failed me. Until at last the churches stood alone, and that for which I once had little regard earned my respect.

I am truly a "lone traveler" and have never belonged to my country, my home, my friends, or even my immediate family, with my whole heart.

Physics is essentially an intuitive and concrete science. Mathematics is only a means for expressing the laws that govern phenomena.

By academic freedom I understand the right to search for truth and to publish and teach what one holds to be true. This right also implies a duty: one must not conceal any part of what one has recognized to be true.

The significant problems we have cannot be solved at the same level of thinking with which we created them.

It's not that I'm so smart, it's just that I stay with problems longer.

We come now to the question: what is a priori certain or necessary, respectively in geometry (doctrine of space) or its foundations? Formerly we thought everything; nowadays we think nothing. Already the distance-concept is logically arbitrary; there need be no things that correspond to it, even approximately.