This article by Sean Carroll, "A Universe from Nothing?", is a very clear explication of the two primary explanations in contemporary physics of how it is that there is something (the universe) rather than nothing. Carroll begins by referring to Lawrence Krauss's book "A Universe from Nothing: Why There Is Something Rather Than Nothing" and David Albert's negative review of Krauss's book in the New York Times. Carroll also nicely lays out how Krauss and Albert are talking past each other, as they are addressing two different versions of the questions they differ on. But the real reason to read Carroll's article is independent of its occasion (the dispute between Krauss and Albert). Even those for those with little or no background in physics, Carroll lays out the issues so clearly that you can get a sense of what possibilities are established by contemporary physical theory. I cannot recommend the article highly enough!