When I read a novel by Neal Stephenson, I've come to expect a few things. I expect deep world-building, an intense layering of ideas supporting a sometimes invisible theme, andan ending that leaves me unsatisfied in terms of the novel itself. Anathem has the first two in spades (and a series of quite visible themes), but I'd say the ending was much more satisfying than usual, if still... odd.
The world-building is extraordinary, covering (in bits and pieces of history, quotation, linguistic and social constructs) millennia in time, thousands of miles in travel, various dimensions and deep discussions (quite practical to the story at hand) about mathematics, music, philosophy, technology, astronomy and belief.
The primary thing which drew me in and anchored me when the story grew cosmic is the long-running story of the “mathic” world... the cloisters, staggered and segregated by the number of years the avout who live there are closed off from the outside world, in which science is practiced as if it were religion.This could have made me twitchy, but instead it made me deliriously happy to watch science unfold in a committed, liturgical, detached atmosphere.
Which is not to say that science takes the place of religion in this world. It does so for a majority of the avout, but out in the everyday world, as well as in some of the more rarefied mathic circles, people don't merely analyze religion, they hold beliefs of their own. The book itself is hardly anti-theist; rather, it takes an intriguingly scientific approach to belief as well as to everything else.
The leap into hard scifi, about two-thirds of the way in, could have felt forced. That it doesn't may reflect the author's talents in pacing and description. Even more, I think it's related to how tightly we're tied to the first-person POV character: we experience cultural, mental and emotional shocks along with him.
And that is possible because of how the story treats time. Within the maths, time is measured daily, by seasons, by years—but even more so by Apert, by the times when the outside world is allowed in, when information maybe exchanged and new avout enter and begin their training. Outside these walls, “extramuros,” the flow of years affects the rest of the globe: cultures change, governments rise and fall, religions die and are reborn. The avout, set apart in their cloisters, see these as transitory and impermanent, compared to their buildings and libraries and theories. In some ways, they are wrong, because they are no more or less human that those outside the walls. In other ways, they are right: without their collation of millennia of information, no one on this planet would be able to cope with invaders from another dimension.