Stephen Hawking

Observations indicate that the universe is expanding at an ever increasing rate. It will expand forever, getting emptier and darker.

Science is beautiful when it makes simple explanations of phenomena or connections between different observations. Examples include the double helix in biology and the fundamental equations of physics.

Keeping an active mind has been vital to my survival, as has been maintaining a sense of humor.

My ideal role would be a baddie in a James Bond film. I think the wheelchair and the computer voice would fit the part.

My advice to other disabled people would be, concentrate on things your disability doesn't prevent you doing well, and don't regret the things it interferes with. Don't be disabled in spirit as well as physically.

If aliens visit us, the outcome would be much as when Columbus landed in America, which didn't turn out well for the Native Americans.

My father was a research scientist in tropical medicine, so I always assumed I would be a scientist, too. I felt that medicine was too vague and inexact, so I chose physics.

I grew up thinking that a research scientist was a natural thing to be.

To my mathematical brain, the numbers alone make thinking about aliens perfectly rational. The real challenge is to work out what aliens might actually be like.

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.

It's time to commit to finding the answer, to search for life beyond Earth. Mankind has a deep need to explore, to learn, to know. We also happen to be sociable creatures. It is important for us to know if we are alone in the dark.

My three children have brought me great joy.