Make everything as simple as possible, but not simpler.
Never argue with an artist.
I do not at all believe in human freedom in the philosophical sense. Everybody acts not only under external compulsion but also in accordance with inner necessity.
Morality is of the highest importance -- but for us, not for God.
I do not believe that civilization will be wiped out in a war fought with the atomic bomb. Perhaps two-thirds of the people of the Earth might be killed, but enough men capable of thinking, and enough books, would be left to start again, and civilization could be restored.
There are no arbitrary constants ... nature is so constituted that it is possible logically to lay down such strongly determined laws that within these laws only rationally determined constants occur (not constants, therefore, whose numerical value could be changed without destroying the theory).