Anathem takes place on a planet called Arbre, which is strikingly similar to the planet Earth. The Arbran civilization has also gone through a history very similar to that of human civilization, except the novel begins approximately 3,600 years from their equivalent of our present day. In Arbran history, a series of Terrible Events 3600 years before the story began wiped out much of the population. These Terrible Events were largely attributed to advances in science (at least as far as can be guessed, 3600 years is a long time) and the world civilization was entirely overhauled. All of the scientists, mathematicians, and philosophers were separated from society in Concents. Within these Concents, the scientists were further divided into groups that were allowed outside the walls of the Concent every 1, 10, 100, and 1000 years. Oners were often just members of the outside world interested in Concents, tenners were the most common members. Within the Concents, the members are further divided by their philosophical and epistemological preferences into Orders. The two major orders are based off of those who believe that words themselves contain meaning versus those who believe that only the physical concepts contain meaning. The history of philosophers in Arbre matches that of Earth. Since the Terrible Events, the Concents and the rest of the world have only interacted once, to destroy an oncoming asteroid. Approximately 1000 years before the story begins, it becomes clear that the Thousanders have developed a new form of technology that can change matter at any place on the planet, the outside world freaks out and kills nearly every member of the Concents. The three Concents that were untouchable reconvene, set up a new code of conduct, and restart.
When the book starts, it focuses on a young Tenner whose mentor is Anathematized, or removed from the Concent. As the book progresses, it becomes clear that he was removed due to an external crisis and that the world of the Concents will be forced to interact with the secular world yet again.
While it's a long read (900 pages), its engrossing and thought-bending. It includes one of the best thought out implementations of quantum mechanics in a sci-fi novel that I've ever encountered. The world(s) that he creates pull you in and keep you guessing about how it all works and what is going on, which he subsequently explains quite well. If I had to sum up Anathem in 1 sentence, I'd say that it's the only book that explains orbital mechanics in detail that I also couldn't put down.
