The moon blew up without warning and for no apparent reason.
I guess in order to indulge in a bit of world-building one must destroy the world first.
Neal Stephenson is a genius. A polymath with a wide range of interests, he specializes in the big idea, and the more concrete the better. In this way he carries forward the tradition of hard science fiction, in which the best example is probably Arthur C. Clarke. Stephenson eschews FTL transportation, time travel, invading aliens, or any of the other tropes of sci-fi that cannot find a solid basis in contemporary science. Instead he takes what is known, adds what is possible, and extrapolates to what could be. His one concession to the unknown is his opening, noted at top. Although a theory or two are trotted out, we never really learn what caused the moon to explode. Consider it the MacGuffin
of the novel, the plot device that gets the action moving. I guess breaking up isn