The difference between machines and human beings is that human beings can be reproduced by unskilled labour.

Why, Robert Singh often wondered, did we give our hearts to friends whose life spans are so much shorter than our own?

As his body became more and more defenseless, so his means of offense became steadily more frightful.

Our lifetime may be the last that will be lived out in a technological society.

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

The choice, as Wells once said, is the Universe-or nothing. . . . The challenge of the great spaces between the worlds is a stupendous one; but if we fail to meet it, the story of our race will be drawing to its close. Humanity will have turned its back upon the still untrodden heights and will be descending again the long slope that stretches, across a thousand million years of time, down to the shores of the primeval sea.

A faith that cannot survive collision with the truth is not worth many regrets.