Why Does the World Exist? An Existential Detective Story
First, a confession: I think of the titular question as a meaningless noise. It's like asking "Why are there round things?" or "Why is there no positive integer less than one?"
Or perhaps a better analogy would be "What's north of the North Pole?" If you answered "nothing," isn't that a different kind of nothing than the nothing of "There's nothing in my pocket"? The phrase "north of the North Pole" is nugatory; it's not even wrong.
The reason that's a good analogy is that that's how cosmologists think of time and space. There's no "before the Big Bang" for the same reason that there's no "north of the North Pole": the Big Bang is where time began to exist.
Put another way, why should we assume that there's any way for the universe to not exist? There's no a priori reason, and precious little empirical support, for any such idea. Even the language is murky. I can say, with a fair degree of confidence, that there does not exist a perfect three-foot cube of solid gold with the complete works of Shakespeare translated into Sanskrit inscribed on it. That means that, as it happens, there's no such thing in the world. What would nonexistence not exist in? And, speaking of nothingness, what would it mean to say that something whose fundamental, definitional property is the property of not existing "could be the case"?
Oh, the book? I liked it very much. It's a series of clearly-written, intelligent-but-not-stuffy interviews with people on every imaginable side of the question--from those who take my point of view to religious thinkers to philosophers to the novelist John Updike--interspersed with the author's own musings. It is, in other words, a book of thought problems. As a kid I loved books full of logic puzzles; I think this is the adult equivalent.