It is in the long run essential to the growth of any new and high civilization that small groups of men can escape from their neighbors and from their government, to go and live as they please in the wilderness. A truly isolated, small, and creative society will never again be possible on this planet.

The purpose of thinking about the future is not to predict it but to raise people's hopes.

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

The fundamental reason why carbon dioxide in the atmosphere is critically important to biology is that there is so little of it. A field of corn growing in full sunlight in the middle of the day uses up all the carbon dioxide within a meter of the ground in about five minutes. If the air were not constantly stirred by convection currents and winds, the corn would stop growing.

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.

Intelligence may indeed be a benign influence creating isolated groups of philosopher-kings far apart in the heavens... On the other hand, intelligence may be a cancer of purposeless technological exploitation, sweeping across a galaxy as irresistibly as it has swept across our own planet.

As a working hypothesis to explain the riddle of our existence, I propose that our universe is the most interesting of all possible universes, and our fate as human beings is to make it so