Einstein's theory of the classical relativistic dynamics of gravity is remarkable, both in its simple elegance and in its profound statement about the nature of spacetime. Before we rush into the diverse matters which concern and motivate the search which leads to string theory and beyond, such as the nature of the quantum theory, the unification with other forces, etc., let us remind ourselves of some of the salient features of the classical theory. This will usefully foreshadow many of the concepts which we will encounter later.

The classical dynamics of geometry

Spacetime is of course a landscape of ‘events’, the points which make it up, and as such it is a classical (but of course relativistic) concept. Intuition from quantum mechanics points to a modification of this picture, and there are many concrete mechanisms in string theory which support this expectation and show that spacetime is at best a derived object or effective description. We shall see some of these mechanisms in the sequel. However, since string theory (as currently understood), seems to be devoid of a complete definition that does not require us to refer to spacetime, the language and concepts we will employ will have much in common with those used by professional practitioners of General Relativity, and of classical and quantum Field Theory. In fact, it will become clear to the newcomer that success in the physics of string theory is greatly aided by having technical facility in both of those fields.