“I have always believed that astrophysics should be the extrapolation of laboratory physics, that we must begin from the present universe and work our way backward to progressively more remote and uncertain epochs.”

“Given the level of anti-Americanism in the world, given the level of frustration with the United States throughout the Muslim world, you've got a homegrown attack or you have a nuclear explosion in the air that is not a test somewhere. Those are still the biggest threats out there.”