Until we get rid of religion, we won't be able to conduct the search for God.

Reading computer manuals without the hardware is as frustrating as reading sex manuals without the software.

There is a special sadness in achievement, in the knowledge that a long-desired goal has been attained at last, and that life must now be shaped toward new ends.

The numbers of distinct human societies or nations, when our race is twice its present age, may be far greater than the total number of all the men who have ever lived up to the present time.

Behind every man now alive stand thirty ghosts, for that is the ratio by which the dead outnumber the living.

Many, and some of the most pressing, of our terrestrial problems can be solved only by going into space. Long before it was a vanishing commodity, the wilderness as the preservation of the world was proclaimed by Thoreau. In the new wilderness of the Solar System may lie the future preservation of mankind.

Sometimes I think we're alone in the universe, and sometimes I think we're not. In either case the idea is quite staggering.