If we can avoid disaster for the next two centuries, our species should be safe as we spread into space. If we are the only intellegent beings in the galaxy we should make sure we survive and continue. . . . Our only chance of long-term survival is not to remain inward looking on planet Earth but to spread out into space. We have made remarkable progress in the last hundred years. But if we want to continue beyond the next hundred years, our future is in space.

Some individuals are better able than others to draw the right conclusions about the world about them and act accordingly. These individuals will be more likely to survive and reproduce so their pattern of behaviour and thought will become dominant

We only have to look at ourselves to see how intelligent life might develop into something we wouldn't want to meet.

I have sold more books on physics than Madonna has on sex.

If it [the universe] was expanding fairly slowly, the force of gravity would cause it eventually to stop expanding and then to start contracting. However, if it was expanding at more than a certain critical rate, gravity would never be strong enough to stop it, and the universe would continue to expand forever.

The doctor who diagnosed me with ALS, or motor neuron disease, told me that it would kill me in two or three years.

We won't know for a few years.