The most prevalent theme of The Elegant Universe is the unification of physics, which Greene argues is one of the central drives of modern physics. The search for a unifying theory that encompasses all the physical properties of the universe is the main goal and motivation for this book and for much current research in theoretical physics. This theme is so central to the book that Greene opens with Einstein’s futile search for a unifying theory in the last years of his life. As Greene explains, Einstein was so dissatisfied with the conflicts between his general theory of relativity and the emerging concepts of quantum mechanics that he became obsessed with the idea of a unifying theory “capable of describing nature’s forces within a single, all-encompassing, coherent framework” (ix).

In addition, the theme of unification is an organizing principle for the book. As Greene explains each important concept of modern physics, including relativity, quantum mechanics, and string theory, he continually returns to physicists’ tireless search for a unifying theory to combine all these concepts. Even when Greene’s discussion focuses on the ways that these concepts do not cohere, as he does throughout most of Part 2, the underlying motivation is still a push for unification.