New ideas pass through three periods: 1) It can't be done. 2) It probably can be done, but it's not worth doing. 3) I knew it was a good idea all along!

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

Any technology distinguishable from magic is insufficiently advanced.

Space can be mapped and crossed and occupied without definable limit; but it can never be conquered.

My favorite definition of an intellectual: 'Someone who has been educated beyond his/her intelligence'.

You don't believe in organized religion, yet a major theme in so many of your works seems to be a quest for God.

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.