Using e-mail, I can communicate with scientists all over the world.

Time travel used to be thought of as just science fiction, but Einstein's general theory of relativity allows for the possibility that we could warp space-time so much that you could go off in a rocket and return before you set out.

There is no unique picture of reality.

Life on Earth is at the ever-increasing risk of being wiped out by a disaster, such as sudden global warming, nuclear war, a genetically engineered virus or other dangers. I think the human race has no future if it doesn't go into space. I therefore want to encourage public interest in space.

But a machine that was powerful enough to accelerate particles to the grand unification energy would have to be as big as the Solar System - and would be unlikely to be funded in the present economic climate.

If a superior alien civilization sent us a message saying, 'We'll arrive in a few decades', would we just reply, 'OK, call us when you get here - we'll leave the lights on'? Probably not - but this is more or less what is happening with AI.

The development of full artificial intelligence could spell the end of the human race.