Courage is never to let your actions be influenced by your fears.

History knows no scruples and no hesitation. Inert and unnering flows towards her goal. History knows herway. She makes no mistakes.

If one looks with a cold eye at the mess man has made of his history, it is difficult to avoid the conclusion that he has been afflicted by some built-in mental disorder which drives him towards self-destruction. Murder within the species on an individual or collective scale is a phenomenon unknown in the whole animal kingdom, except for man, and a few varieties of ants and rats.

Space-ships and time machines are no escape from the human condition. Let Othello subject Desdemona to a lie-detector test; his jealousy will still blind him to the evidence. Let Oedipus triumph over gravity; he won't triumph over his fate.

The real achievement in discoveries... is seeing an analogy where no one saw one before... The essence of discovery is that unlikely marriage of cabbages and kings — of previously unrelated frames of reference or universes of discourse — whose union will solve the previously insoluble problem.

In my youth I regarded the universe as an open book, printed in the language of equations, whereas now it appears to me as a text written in invisible ink, of which in our rare moments of grace we are able to decipher a small segment.