"Ever since Newton, and especially since Einstein, the goal of physics has been to find simple mathematical principles of the kind Kepler envisioned, and with them to create a unified theory of everything that would account for every detail of the matter and forces we observe in nature. ...The goal was to find not just a single theory that explains all forces but also one that explains the fundamental numbers... such as the strength of the forces and the masses and charges of the elementary particles. ...A unique theory would be unlikely to have the fine-tuning that allows us to exist. But if... we interpret Einstein's dream to be that of a unique theory that explains this and other universes, with their whole spectrum of different laws, then M-theory could be that theory."