I suspect that religion is a necessary evil in the childhood of our particular species. And that's one of the interesting things about contact with other intelligences: we could see what role, if any, religion plays in their development. I think that religion may be some random by-product of mammalian reproduction. If that's true, would non-mammalian aliens have a religion?

If an elderly but distinguished scientist says that something is possible, he is almost certainly right; but if he says that it is impossible, he is very probably wrong.

The space elevator will be built about 50 years after everyone stops laughing.

And because, in all the Galaxy, they had found nothing more precious than Mind, they encouraged its dawning everywhere. They became farmers in the fields of stars; they sowed, and sometimes they reaped. And sometimes, dispassionately, they had to weed.

The only way to define your limits is by going beyond them.

Almost any seat was comfortable at one-sixth of a gravity.

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