  If the fine structure constant $\alpha =e^2/(\hbar c)$ were to change, then a
number of interpretations would be possible, attributing this change either to
variations in the electron charge, the dielectric constant of the vacuum, the
speed of light, or Planck's constant. All these variations should be
operationally equivalent and can be related by changes of standard units. We
show how the varying speed of light cosmology recently proposed can be
rephrased as a dielectric vacuum theory, similar to the one proposed by
Bekenstein. The cosmological problems will therefore also be solved in such a
theory.
