Gravity and Strings

TL;DR: A broad-brush review of how string theory addresses several important questions of gravitational physics can be found in this paper, where the problem of non-renormalizability is first reviewed, followed by introduction of string theory as an ultraviolet-finite theory of gravity.

Abstract: This is a broad-brush review of how string theory addresses several important questions of gravitational physics. The problem of non-renormalizability is first reviewed, followed by introduction of string theory as an ultraviolet-finite theory of gravity. String theory’s successes also include predicting both gauge theory and fermions. The difficulty of extra dimensions becomes a possible virtue, when one notes that these lead to mechanisms to explain fermion generations, as well as a means to break the large gauge symmetries of string theory. Finally, a long standing problem of string theory, that of fixing the size and shape of the extra dimensions, has recently been addressed and may shed light on the origin of the cosmological constant, the ultimate fate of our universe, as well as the question of why gravity is so weak. 1. PUZZLES OF GRAVITY In this lecture I plan to convey the basic ideas of string theory, particularly as they relate to some puzzles of gravitational physics. At my home institution, string theory is a two to three quarter class, just to teach the foundation, so the best that can be done here is to give a very impressionistic view of some of the features of the theory, introducing some of the central ideas. (For the same reason, I will only give a brief guide to the literature at the end, rather than inclusive references.) Nonetheless, I will also endeavor to bring the reader up to speed on some of the newest – and most bizarre – ideas of string theory, particularly pertaining to cosmology and the fate of the Universe. We’ll begin with the question of the day.