Whenever I have endured or accomplished some difficult task -- such as watching television, going out socially or sleeping -- I always look forward to rewarding myself with the small pleasure of getting back to my typewriter and writing something.

At two-tenths the speed of light, dust and atoms might not do significant damage even in a voyage of 40 years, but the faster you go, the worse it is--space begins to become abrasive. When you begin to approach the speed of light, hydrogen atoms become cosmic-ray particles, and they will fry the crew. ...So 60,000 kilometers per second may be the practical speed limit for space travel.

You can prove anything you want by coldly logical reason---if you pick the proper postulates.

You don't have to be able to lay eggs to know when one of them is rotten.

No vision of God and heaven ever experienced by the most exalted prophet can, in my opinion, match the vision of the universe as seen by Newton or Einstein

Uncertainty that comes from knowledge (knowing what you don't know) is different from uncertainty coming from ignorance.

Politically popular speech has always been protected: even the Jews were free to say ‘Heil Hitler.’