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.

The truth, as always, will be far stranger.

I've been saying for a long time that I'm hoping to find intelligent life in Washington.

I believe any malevolent supercivilisation would have rapidly self-destructed as we may be in the process of doing ourselves. If we do have contact, physical contact with aliens, I think it will be benign.

When I start on a book, I have been thinking about it and making occasional notes for some time... So I have lots of theme, locale, subjects and technical ideas... I don't worry about long periods of not doing anything. I know my subconscious is busy.

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

If we have learned one thing from the history of invention and discovery, it is that, in the long run-and often in the short one-the most daring prophecies seem laughably conservative.