This book aims to shed light upon the connection between the intrinsic structure of gravity and the principle of gauge invariance, which may lead to a consistent unified field theory.

The first part of the book, chapters one to six, gives a systematic account of the structure of gravity as a theory based on space / time gauge symmetries. Some basic properties of space, time and gravity are reviewed in the introductory chapter. Chapter Two deals with elements of global Poincare and conformal symmetries, which are necessary for the exposition of their localization; the structure of the corresponding gauge theories of gravity is explored in chapters three and four. Then, in chapters five and six, the book presents basic features of the constrained Hamiltonian dynamics of Poincare gauge theory, discusses the relation between gauge symmetries and conservation laws, and introduces the concept of gravitational energy and other conserved quantities.

The second part of the book treats the most promising attempts to build a unified field theory containing gravity, on the basis of the gauge principle. In chapters seven and eight, the book discusses the possibility of constructing the theory of gravity as a non-linear field theory in flat space-time. Chapters Nine, Ten and Eleven yield an exposition of the ideas of supersymmetry and supergravity, Kaluza-Klein theory and string theory.  less