The real question is not are there other forms of life in the universe, but are there other intelligent forms of life out there right now. Because the universe is not only really big but it's also really long. It's been around for a long time; it's going to be around for a long time.

The two world wars boosted American power and devastated potential rivals to an extent that could not have lasted more than a few decades.

Whether it is gun control lobby, health care lobby, or abortion, pro-choice lobby, whatever it is, people are always trying to say that it is about restricting rights and they are never really prepared to talk about what the honest tradeoffs are. One of the things we need to do a better job of is actually painting those tradeoffs.

In the nearer term, the likeliest source of risk is a conflict between China and the U.S. These are now the two largest economies in the world, and the combination of their economic interdependence, the sharp differences in their political and economic values, and the growing divergence in their interests makes this relationship potentially dangerous for everyone who might be affected by it - which means pretty much everyone.

Everything today is "transient." Technology and its ability to empower actors large and small evolve so quickly that we have to get used to living in a world that exists in a more or less constant state of flux.

I think that the environment is very a complicated question. I am very sympathetic to people who support the environment who live in the United States. I am very sympathetic to people who don't support the environment who live in a very poor country.

I think graffiti is part of Berlin culture. You think about what the Berlin wall meant and how visible that was in everyone's life. How it was a part of their very identity.