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.

I think the best way to control a population is to urbanize and to educate women. We have seen historically in many, many countries that once women are educated and have opportunities, and that happens when they live in cities and once they improve their economies, they no longer want to have eight kids.

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.

It's very hard for someone who makes $1,000 a year or some who makes less than $1 a day to care about the environment.

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 developed world should neither shelter nor militarily destabilize authoritarian regimes unless those regimes represent an imminent threat to the national security of other states. Developed states should instead work to create the conditions most favorable for a closed regime's safe passage through the least stable segment of the J curve however and whenever the slide toward instability comes. And developed states should minimize the risk these states pose the rest of the world as their transition toward modernity begins.

NASA is increasingly not the future of space exploration. I love the fact that we have private sector folks devoting a lot of money to stimulate innovation in space technology.