There was a transition going on - Baghdad being the intellectual capital of the world where major advances were made in agriculture and mathematics and engineering and medicine and astronomy, and then that all sort of collapsed. And I was trying to understand how such a intellectually fertile environment can lose its compass bearing. Because I think about the creative centers today - countries, or even regions. Will Silicon Valley always be as innovative? Will the United States be innovative, or will we become complacent?

Kids are born curious about the world. What adults primarily do in the presence of kids is unwittingly thwart the curiosity of children.

UV is bad for molecules because its high energy breaks the bonds between a molecule's constituent atoms. That's why UV is bad for you, too: it's always best to avoid things that decompose the molecules of your flesh.

People put clips of me up. There are quotes from me. I've written books, of course. I'm on Twitter. There are dozens of ways to consume my offerings, and a lecture in a large venue is really only just one of them. So I have no concerns about how much access people would have to me no matter what is the capacity of your pocketbook.

For all we know, the aliens have already done this and unwittingly concluded that there was no intelligent life on Earth. They would now be looking elsewhere. A more humbling possibility would be if aliens had become aware of the technologically proficient species that now inhabits Earth, yet they had drawn the same conclusion.

If aliens did visit us, I'd be embarrassed to tell them we still dig fossil fuels from the ground as a source of energy.

Plenty of people get excited about the universe.