A simple cosmology with a varying fine structure constant

We investigate the cosmological consequences of a theory in which the electric charge e can vary. In this theory the fine structure constant, alpha, remains almost constant in the radiation era, undergoes a small increase in the matter era, but approaches a constant value when the universe starts accelerating because of a positive cosmological constant. This model satisfies geonuclear, nucleosynthesis, and cosmic microwave background constraints on time variation in a, while fitting the observed accelerating Universe and evidence for small a variations in quasar spectra. It also places specific restrictions on the nature of the dark matter. Further tests, involving stellar spectra and Eotvos experiments, are proposed.