We should get used to the idea that we'll probably never be able to find - and confirm - a good explanation of the ultimate origin of the universe, though I see no reason to believe that we can't press much further on this question than we have managed to date.

I think many people are terribly afraid of being demoted by the Darwinian scheme from the role of authors and creators in their own right into being just places where things happen in the universe.

The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn't need its brain anymore so it eats it!

In short, we need to recover the courage we celebrate in our heroes, and in particular, the courage to tolerate, for the sake of a free society, a level of risk we hardly ever imagined in the past.

On some level, there's a limit to what the government really worries about when it comes to a guy like Ai Weiwei, who's talking to a limited audience of people. He's talking to people who more or less already agree with him.

I stayed in the astronaut program until 1993. People ask me why I left. I thought I had a lot of things to contribute that would be difficult to do if I stayed. I thought I could have a stronger voice as an advocate for space exploration. So I ended up starting my own technology consulting company.

We have something very powerful in our hands with the Internet, and we still don't really understand fully its power.

I believe in teaching as a real job. I don't think it's a substitute for anything else. It's been shown to me that teachers can help, and the writing today is just as good as it was when I started out. Technology hasn't changed that.