The PhD system is the real root of the evil of academic snobbery. People who have PhDs consider themselves a priesthood, and inventors generally don't have PhDs.

We do not know how much of the environmental change is due to human activities and how much [is due] to long-term natural processes over which we have no control.

The great advances in science usually result from new tools rather than from new doctrines.

Walking the streets of Tokyo with Hawking in his wheelchair ... I felt as if I were taking a walk through Galilee with Jesus Christ [as] crowds of Japanese silently streamed after us, stretching out their hands to touch Hawking's wheelchair. ... The crowds had streamed after Einstein [on Einstein's visit to Japan in 1922] as they streamed after Hawking seventy years later. ... They showed exquisite choice in their heroes. ... Somehow they understood that Einstein and Hawking were not just great scientists, but great human beings.

I think it's a big mistake to decide too soon what you're going to do with your life.

The thing that makes me most optimistic is China and India - both of them doing well.

It's us that's really amazing. As far as I can see, our concentration of different abilities in one species - there's nothing I can see that in this Darwinian evolution that could've done that. So it seems to be a miracle of some sort.