We can never prove that we're alone in the universe. But the Allen Telescope Array could prove that we're not.

It's a difficult business, finding out what's true about the world, the universe.

You don't really want nonagenarians as heads of organisations which are trying to do something useful.

If a child from an Amazonian hunter-gatherer tribe comes to Boston, is raised in Boston, that child will be indistinguishable in language capacities from my children growing up here, and vice versa.

I mean, we've built a lot of products that we think are good, and will help people share photos and share videos and write messages to each other. But it's really all about how people are spreading Facebook around the world in all these different countries. And that's what's so amazing about the scale that it's at today.