The idea of 10 dimensions might sound exciting, but they would cause real problems if you forget where you parked your car.

Even if there is only one possible unified theory, it is just a set of rules and equations. What is it that breathes fire into the equations and makes a universe for them to describe?

I don't think the human race will survive the next thousand years, unless we spread into space. There are too many accidents that can befall life on a single planet. But I'm an optimist. We will reach out to the stars.

I think [contacting an alien civilization] would be a disaster. The extraterrestrials would probably be far in advance of us. The history of advanced races meeting more primitive people on this planet is not very happy, and they were the same species. I think we should keep our heads low.

There is a real danger that computers will develop intelligence and take over.

I believe in universal health care. And I am not afraid to say so.

If the total energy of the universe must always remain zero, and it costs energy to create a body, how can a whole universe be created from nothing?