Any physical theory is always provisional, in the sense that it is only a hypothesis: you can never prove it. No matter how many times the results of experiments agree with some theory, you can never be sure that the next time the result will not contradict the theory.

The human race shouldn't have all its eggs in one basket, or on one planet. Let's hope we can avoid dropping the basket until we have spread the load.

One should love animals. They are so tasty.

The universe does not behave according to our pre-conceived ideas. It continues to surprise us.

For years, my early work with Roger Penrose seemed to be a disaster for science. It showed that the universe must have begun with a singularity, if Einstein's general theory of relativity is correct. That appeared to indicate that science could not predict how the universe would begin.

The fact that no one understands you doesn't mean you're an artist.

The real challenge is to work out what aliens might actually be like.