In the history of science it has often happened that the majority was wrong and refused to listen to a minority that later turned out to be right.

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

The whole point of science is that most of it is uncertain. That's why science is exciting--because we don't know. Science is all about things we don't understand. The public, of course, imagines science is just a set of facts. But it's not. Science is a process of exploring, which is always partial. We explore, and we find out things that we understand. We find out things we thought we understood were wrong. That's how it makes progress.

A good cause can become bad if we fight for it with means that are indiscriminately murderous. A bad cause can become good if enough people fight for it in a spirit of comradeship and self-sacrifice. In the end it is how you fight, as much as why you fight, that makes your cause good or bad.

I think that the artificial-intelligence people are making a lot of noise recently, claiming that artificial intelligence is making huge progress and we're going to be outstripped by the machines.

So long as you have courage and a sense of humor, it is never too late to start life afresh.

If we want to go to space with humans, that's for fun not for science. Human adventures in space are just sporting events.