Superstring Cosmology: A Review
Abstract
The enhancement of superstring theory to Mtheory has profound implications for cosmology. I review the most significant aspects of the M theory cosmological picture resulting from the combined effects of (1) Mtheory's (10+1) dimensional spacetime (compared to string theory's (9+1)dimensional spacetime), (2) M theory's realization that strings have a width determined by the size of the additional spatial direction (transforming strings into membranes), and (3) the M theory prediction of spatial surfaces called Dbranes. The role of membranes and Dbranes in the preBig Bang and inflationary eras are discussed. Mtheory revisions of the original BrandenbergerVafa string inflation model are briefly summarized. The BrandenbergerVafa model offers a qualitative understanding for why only three spatial directions became large. I also discuss the RandallSundrum model and extensions of it, which offer a Dbrane explanation for the apparent weakness of gravity in our 3+1 large dimensions. A fundamental question in Mtheory is, "What is the string/Mtheory energy scale and corresponding length scale?" I review the recent astronomical measurements of John Webb et al. suggesting this scale to be much lower than the String/ (Planck) scale of 101 8 Gev. Some of the ``physical constants'' in nature, such as the fine structure constant, which specifies the strength of electromagnetic interaction, may have been varying significantly only a few billion years ago. This suggests a low energy Mtheory scale and a related long time before some compactified directions stabilized. An implication of a low energy Mtheory scale is that gravity may stop acting as a 1/r2 force at distances somewhere below a millimeter. The distance at which deviation from 1/r2 begins corresponds to the size of the eleventh dimension. Recent University of Washington experiments verify gravity as a 1/r2 force down to 0.2mm.
 Publication:

34th COSPAR Scientific Assembly
 Pub Date:
 2002
 Bibcode:
 2002cosp...34E.554C