Wilber adapts the idea behind string theory (the notion that all of physics can be united under a single theory explaining the behavior of matter) to suggest that disciplines as diverse as medicine, economics, and spirituality work in the same way. Wilber sees the Western split between rational and spiritual knowledge as a dangerous mistake; he rejects, for example, Stephen Jay Gould's dualistic insistence that religion and science are "nonoverlapping realms." For Wilber, overlap is the key to the universe. He seeks to integrate all aspects of an individual, and from there a society. The book's diagrams show circular flows of knowledge: spiraling levels of selfhood, types of knowledge, variations of society.
Confused yet? The book's is not the only there are other problem. Such an ambitious project necessarily elides what people have come to regard as important differences among cultures; Wilber's chart showing Sub-Saharan Africa as an example of "horizontal" civilization over and against Euro-American "vertical meme structure" risks gross stereotyping, at best.
While some of Wilber's ideas are interesting--and readers should tip their hats to him for even trying such a project in our hyper-specialized society--it suffers from its own elephantine proportions, and misses the trees for the forest.