Richard Dawkins needs no introduction. Lawrence Krauss barely needs an introduction -- although we'll tell you that he's a leading voice in theoretical physics and the author of the recent book, A Universe from Nothing: Why There Is Something Rather than Nothing. (We recommend watching this lecture to get familiar with his work.) In February, the two scientists met up at Arizona State University and spent two hours in a freewheeling conversation, touching on evolution, cosmology, religion, and other topics. They spoke before a packed house, but Shirley Films was good enough to post the video online, and you can watch it above. Another conversation -- this one recorded at The Australian National University on 10 April 2012 -- can be viewed here.