String theory
In "Parallel Worlds", Kaku presents many of the leading theories in physics; from Newtonian physics to Relativity to Quantum Physics to String theory and even into the newest version of string theory, called M-theory. He makes available to the reader a comprehensive description of many of the more compelling theories in physics, including many interesting predictions each theory makes, what physicists, astronomers, and cosmologists are looking for now and what technology they are using in their search.