There has been a revolution in our thinking about extra dimensions. A new understanding of the feasibility of localizing four dimensional gauge theories in higher dimensional spacetimes has led to a variety of phenomenologically viable models, and even to the possibility of localizing gravity. Unlike older theories of extra dimensions, much of the focus now is on extra dimensions with sizes on the order of one thousandth of a proton width or larger! Thus, there is a potential for discovery at current and soon-to-be-completed colliders, and in some cases table-top experiments. In addition there are tremendous implications for cosmology. The following topics are covered in this book:Einstein and the Fourth DimensionWaves in a Fifth DimensionString Theory and BranesExperimental Tests of Extra DimensionsThe beginnings of string theory as an attempt to understand strongly bound quarks will be reviewed initially. How string theory evolved into a theory of quantum gravity will also be covered before moving on to more recent developments including the Maldacena conjecture and it's applications to heavy ion collisions, the five dimensional Randall-Sundrum model, and a possible origin for the electron mass.Evidence has been gathering that the ordinary formulation of physics, in a space-time with three space and one time dimensions, is a clumsy way to describe our world; just like shadows on walls alone are insufficient to capture the true essence of an object in a three dimensional room. A discussion on Two-Time Physics ensues, which the author hopes will help to eliminate many of the mysteries of today's laws of physics. Two-Time Physics reveals that our physical world in 3+1 dimensions is like a shadow of a highly symmetric universe in four space and two time dimensions. Amazingly, the best understood fundamental theory in Physics, the Standard Model of Particles and Forces is reproduced, and its "strong CP problem" is solved, as a field theory in 4+2 dimensions in the context of Two-Time Physics. This point of view provides new mathematical tools and new insights for understanding our universe, and could cause many of the most basic processes in physics to need re-examination.

## 相關書籍