  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 4-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 a
possible resolution to the apparent inconsistency between the MSSM scale and
string scale in the weak coupling limit. Talk presented at COSPAR '02, Houston,
Texas, October 2002.
