In Britain, like most of the developed world, stem-cell research is regarded as a great opportunity. America will be left behind if it doesn't change policy.

We each exist for but a short time, and in that time explore but a small part of the whole universe

The human capacity for guilt is such that people can always find ways to blame themselves

I put a lot of effort into writing 'A Briefer History' at a time when I was critically ill with pneumonia because I think that it's important for scientists to explain their work, particularly in cosmology. This now answers many questions once asked of religion.

One, remember to look up at the stars and not down at your feet. Two, never give up work. Work gives you meaning and purpose and life is empty without it. Three, if you are lucky enough to find love, remember it is there and don't throw it away.

It matters if you don't just give up.

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.