Anathem is a science fiction novel by Neal Stephenson, published in 2008. Clocking in at over nine hundred pages, it is a daunting read, but quite an interesting and thought-provoking one.
Deep breath. Okay. Let's go.
The world of Anathem is both familiar and different. At first glance, it seems to be the sort of middle-ages setting with orders of monks transcribing ancient texts and performing even more ancient rituals, locking themselves away from the rest of the world, but as you read, you realize that a) The rest of the world is at around the same technological development as we are now, b) That the rest of the world has gone through a series of occasional apocalypses, which the monks don't quite seem to care too much about, and c) the monks aren't religious, they're mathic.
And everything goes uphill from there. (Okay, maybe downhill if you're not one who enjoys multiple-page discourses on philosophical concepts such as ideal form, metaphysics, the many-worlds interpretation of quantum mechanics, alternate dimensions, phase space, epistemology, mathematical proofs, and almost everything else I like about the book. But there is a love story shafted off to the side, if you're willing to slog through it for that.)
The novel itself is about a young adult monk who is brought into the middle of a planet-wide upheaval due to the exile of his former teacher. I won't give much away apart from that plotwise, but Stephenson expertly crafts a world in which the characters live.
The monks, or avout as they are called, live in cloistered monastries called Maths. These Maths are locked from the outside world, and open once every year to the outermost circle of Unarians, once a decade to the Decarians, once a century to the Centurians, and once a millenium to the Millenarians. The gates to the walls are opened and closed through the mechanics of a clock, (similar to the thousand year clock), whose winding is the center of most of the rituals in the Maths. Technology is banned within the Maths (due to a long-winded history which is sketched out in a timeline in the introduction and throughout the story), and the avout spend their time proving theories, singing chants about the history of mathematics, stargazing, engaging each other in dialogues, and maintaining the Math.
One of the interesting things in the novel is how Stephenson draws parallels between our history and the history of their world, Arbre. Many theorems, laws, and philosophies are mentioned, all under different names from the ones we know, which becomes an interesting game to spot which schools of thought you can identify. Unfortunately, this means you have to cross-reference everything you learn in the book with real life sources to get their real names. (I'm still calling phase space Hemn space.)
If you want to read more about the world, don't worry. There's an entire wiki dedicated to figuring out what is going on.
The first half of the book is mostly these mathematical/philosophical ramblings, and letting you learn the ropes of the new world. The second half adds a bit of action (at the cost of interest and character development, in my opinion), and ends up with you scratching your head over the quantum mind-body problem.
One small problem which might irk a large number of people is the fact that the characters don't quite use proper English in speaking. Because of their altered history, some of their words have changed meaning, which is why there's a glossary at the back of the book, and definitions from the in-universe dictionary at the beginning of each new section. Although the words aren't pulled randomly. For example, schools in the novel are called suvines, becasue teacher initially taught their disciples at the edges of public squares underneath the vines, hence "sous-vines". Interesting trivia, but it doesn't crop up until you're thoroughly confused by what suvines are.
And I wasn't kidding about the multi-page discourses. Seriously. There are three appendixes (called calcas, or proofs), where Stephenson helpfully outlines some mathematical or metaphysical proof or concept. All in-narrative, of course.
All and all, a good book. It gives you lots to think about, but although it may not be the strongest in science fiction content, it still shines as a masterful piece of worldbuilding.
Also, Stephenson assembled an album based of the chants of the avouts. With songs such as "Approximating Pi" and "Sixteen Colour Prime Generating Automaton". Not bad, to say so myself.