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.

Unfortunately the global warming hysteria, as I see it, is driven by politics more than by science.

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.

The reason why new concepts in any branch of science are hard to grasp is always the same; contemporary scientists try to picture the new concept in terms of ideas which existed before.

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

If we had a reliable way to label our toys good and bad, it would be easy to regulate technology wisely. But we can rarely see far enough ahead to know which road leads to damnation. Whoever concerns himself with big technology, either to push it forward or to stop it, is gambling in human lives.

There is nothing so big nor so crazy that one out of a million technological societies may not feel itself driven to do, provided it is physically possible.