Attempting to define science fiction is an undertaking almost as difficult, though not so popular, as trying to define pornography... In both pornography and SF, the problem lies in knowing exactly where to draw the line.

I want to be remembered most as a writer - one who entertained readers, and, hopefully, stretched their imagination as well.

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.

When you finally understand the universe, it will not only be stranger than you imagine, it will be stranger than you can imagine.

The Earth would only have to move a few million kilometers sunward-or starward-for the delicate balance of climate to be destroyed. The Antarctic icecap would melt and flood all low-lying land; or the oceans would freeze and the whole world would be locked in eternal winter. Just a nudge in either direction would be enough.

Moses Kaldor had always loved mountains; they made him feel nearer to the God whose nonexistence he still sometimes resented.

It may be that the old astrologers had the truth exactly reversed, when they believed that the stars controlled the destinies of men. The time may come when men control the destinies of stars.