  Here we apply the Generalized Second Law of Thermodynamics and derive upper
limits on the variation in the fundamental constants. The maximum variation in
the electronic charge permitted for black holes accreting and emitting in the
present cosmic microwave background corresponds to a variation in the fine
structure constant of ((Delta alpha) / alpha) ~ 2 x 10^-23 per second. This
value matches the variation measured by Webb et al. using absorption lines in
the spectra of distant quasars and suggests the variation mechanism may be a
coupling between the electron and the cosmic photon background.
