String theory can explain why people go to NSync concerts.

Actually the issue here is far deeper (of course) than could be reported there. The fine structure constant is a pure number (without dimensions) that measures the strength of interaction of electric charges and light. In terms of dimensional quantities it is derived as

alpha = (e^2) / (4 PI E0 Hbar C)

where e is the electron charge, E0 is the "permittivity of the vacuum", Hbar is Planck's constant, and C is the speed of light. Of course, a change in the value of any of these would change alpha. In particular of gravity is intrinsically related to light (it is!) E0 will change with a varying gravitational field.

Dirac first investigated theories in which dimensional "constants" can change over cosmological time (the "Large Numbers Hypothesis"), and felt that the formation of dimensionless numbers out of dimensional parameters was a key to understanding the relationsip of gravity to quantum theory. The string theorists are merely aping Dirac's work, as usual, with their own spin on it.

(see interview with Dirac [link|http://www.fdavidpeat.com/interviews/dirac.htm|herein])