I'm here to chew gum and kick some ass, and I'm all out of gum.

Not to leave planet Earth would be like castaways on a desert island not trying to escape...Sending humans to other planets ... will shape the future of the human race in ways we don't yet understand, and may determine whether we have any future at all.

It is no good getting furious if you get stuck. What I do is keep thinking about the problem but work on something else. Sometimes it is years before I see the way forward. In the case of information loss and black holes, it was 29 years.

Quiet people have the loudest minds.

Eternity is a long time, especially towards the end.

I think the next century will be the century of complexity.

A model is a good model if first it interprets a wide range of observations in terms of a simple and elegant model, and second if the model makes definite predictions that can be tested, and possibly falsified, by observation.