Not at all. It has a great deal to say about "why" questions, they're perfectly legitimate scientific questions. On that particular one, for instance, which I usually think of as "why is there something rather than nothing," what we currently know of how things work indicates that "nothing" is unstable. Victor Stenger's even put a number on it; he suggests "something" is about 40% more likely than "nothing." String theory looks at some very deep "why" questions, such as, why are the masses of the elementary particles what they are, and could they have been different, why are the constants of nature what they are, could they have been something else, are they really constant, and so on. The mathematical structure of string theory suggests things like that might be predictable. The masses of elementary particles might appear as resonant vibration modes of the strings, which have a certain tension based on their energy levels, which is equivalent to mass, though the math is so difficult nobody's figured out how to do it yet. One interesting result though: string theory does require the existence of a particle with zero mass and spin 2, which quantum theory recognizes as the graviton, the hypothesized particle of the gravitational interaction. Gravity is implicit in string theory, and is completely absent from quantum theory, which is the source of the hope that string theory might show the way to the long-sought theory of everything.
But I digress, as I often do. More to the point, if god exists, he must interact with the cosmos to some degree if he's to have any meaning at all, so there must be evidence of that interaction. That makes his existence an empirical claim about the nature of reality, which is what science deals with, and science in its broadest sense, as AnnaG used the term above, offers plenty of reasons for concluding the postulated deity does not exist.
