From a July 2006 interview  in Discover Magazine
Will physics ever be able to tackle the biggest questions�for instance, why does the universe even bother to exist?
Science is not religion. We're not going to be able to answer the "why" questions. But when you put together all of what we know about the universe, it fits together amazingly well. The fact that inflationary theory [the current model of the Big Bang] can be tested by looking at the cosmic microwave background is remarkable to me. That's not to say we can't go further. I'd like to ask: Do we live in a pocket of three-dimensional space and time? We're asking how this universe began, but maybe we should be asking how a larger, 10-dimensional universe began and how we got here from there.
This sounds like your formula for keeping science and religion from fighting with each other.
A lot of scientists take the Stephen Jay Gould approach: Religion asks questions about morals, whereas science just asks questions about the natural world. But when people try to use religion to address the natural world, science pushes back on it, and religion has to accommodate the results. Beliefs can be permanent, but beliefs can also be flexible. Personally, if I find out my belief is wrong, I change my mind. I think that's a good way to live.
So does your science leave space for untestable faith? Do you believe in God?
There's room there, and it could go either way. Faith just doesn't have anything to do with what I'm doing as a scientist. It's nice if you can believe in God, because then you see more of a purpose in things. Even if you don't, though, it doesn't mean that there's no purpose. It doesn't mean that there's no goodness. I think that there's a virtue in being good in and of itself. I think that one can work with the world we have. So I probably don't believe in God. I think it's a problem that people are considered immoral if they're not religious. That's just not true. This might earn me some enemies, but in some ways they may be even more moral. If you do something for a religious reason, you do it because you'll be rewarded in an afterlife or in this world. That's not quite as good as something you do for purely generous reasons.