Is it e or is it c?: Experimental tests of varying alpha

Is the recent evidence for a time-varying fine structure 'constant' alpha to be interpreted as a varying e, c, h, or a combination thereof? We consider the simplest varying electric charge and varying speed of light (VSL) theories and prove that for the same type of dark matter they predict opposite senses of variation in alpha over cosmological times. We also show that unlike varying e theories, VSL theories do not predict violations of the weak equivalence principle (VVEP). Varying e theories which explain astronomical inferences of varying alpha predict WEP violations only an order of magnitude smaller than existing Eotvos experiment limits but could be decisively tested by STEP. We finally exhibit a set of atomic-clock and related experiments for which all (hyperbolic) varying alpha theories predict non-null results. They provide independent tests of the recent astronomical evidence. (C) 2002 Elsevier Science B.V. All rights reserved.