He said that he chose to place it on a non-Earth world to avoid having to create too much back-story to make it consistent with Earth history. The trade-off is you spend half your time trying to map arguing schools of thought in the book's world with Earth MetaPhysics yammerers.
This was definitely not my favorite book of his. May be even least-favorite (and wow drop-off ending). But still better than just about anyone else's best. Good MultiVerse mind-games, crossed with Name Of The Rose ambiance.
The Acknowledgements give lots of Earth-philosophy background
Julian Barbour's (End Of Time) footnotes and bibliographies provide enough citations to keep most readers busy for many years, however one that merits special notice here is John Stewart Bell's Speakable and Unspeakable in Quantum Mechanics (ISBN:978-0521818629), a collection of articles that includes two concise and clear explanations of the topic that, in the terminology of Anathem, passes under the name "worldtracks" or "narratives." They are to be found in the papers entitled "The measurement theory of Everett and de Broglie's pilot wave" (which, by the way, takes issue with the many-worlds interpretation) and Quantum Mechanics for Cosmologists.
Any material in Anathem that has to do with worldtracks, narratives, and "Hemn space" (which is just the Arbran term for what on Earth is called Configuration Space, Phase Space, or State Space) can be traced back directly to the works mentioned above, and their antecedents in the literature. The notion of configuration spaces dates back to Joseph Louis Lagrange's work on generalized coordinates and later refinements owed to William Rowan Hamilton. The term "Phase Space" according to Wikipedia, was introduced by Willard Gibbs in 1901; it can be taken as a further generalization of the work of Lagrange and Hamilton.
Edward N Zalta is a strong believer in formalizing philosophy, i.e., translating philosophical assertions from prose into expressions written out using the symbols of formal logic. Once this has been done, it becomes possible to compare different philosophers' ideas in the same way as a physicist might compare two different theories by writing them out as equations, then using the rules of mathematics to determine whether they contradict each other, or reduce to the same thing. It is true of both mathematics and formal logic that the rules are few and simple, but that applying them to the kinds of equations or assertions that arise in practice can become astonishingly complicated--in some cases, too complicated for humans to manage without error. Zalta has been using a computer code--an "automated reasoning system" called PROVER9--to resolve such conundrums. This strongly recalls Gottfried Leibniz's scheme for a characteristica universalis... Later in the same paper they allude to work in progress on using the system to prove theorems in Zalta's 2000 paper A (Leibnizian) Theory of Concepts, in which he reduces statements from Leibniz's metaphysics into a series of theorems expressed in formal logic. In other papers, Zalta and his collaborators Francis Jeffry Pelletier and Bernard Linsky tackle the work of Plato, Husserl, Kurt Godel, and DavidLewis, of whom more below. So this answers the question posed above ("what has been going on in the last thirty years?"). As a side note, computational metaphysics also provided the idea for some of the music that is alluded to in Anathem. Specifically, the tree-dwelling, loincloth-wearing fraas mentioned during the Aut of Inbrase at Tredegarh are carrying out--albeit very slowly--a computation along the lines of what PROVER9 does (Generative Music). They are trying to solve a deep problem in metaphysics, and it is taking them a long time because they don't have access to computers. (I think there was an old Rudy Rucker story involving music generated by theorems.)
DavidLewis wrote a book entitled On the Plurality of Worlds (ISBN:978-0631224266) ...In it, Lewis lays out a metaphysics called Modal Realism which (to sum it up very crudely) asserts that possible worlds really exist, and are as real as the world we live in (MultiVerse)... It is worth pointing out that I came to the work of Deutsch and of Zalta along completely different lines of inquiry. My interest in physics brought me to the former, my interest in the Plato-Leibniz-Husserl-Godel lineage to the latter. When both of them ended up speaking of the same philosopher, DavidLewis, I got a feeling--perhaps nothing more than self-delusion--that a circle had magically closed.