Developments in string cosmology

The second string revolution, which begin around 1995, has led to a drastic alteration in our perception of the universe, perhaps even more so then did the first string revolution of 1984. That is, extending 10-dimensional string theory to 11-dimensional M-theory has had more profound implications than did the original extension of four-dimensional quantum mechanics and relativity to 10-dimensional string theory. After a brief review of M-theory, I discuss some implications of large extra dimensions. I then consider astronomical evidence for and constraints on large compactified dimensions. I conclude with possible string/M-theory resolutions to the apparent inconsistency between the MSSM scale and string scale in the weak coupling limit.