Note that the Dirac hypothesis can also be achieved by assuming that e varies as 1∕2 t. Indeed this reflects a choice of units, either atomic or Planck units. However, there is a difference: assuming that only G varies violates the strong equivalence principle while assuming a varying e results in a theory violating the weak equivalence principle. It does not mean that we are detecting the variation of a dimensionful constant but simply that either 2 e∕ℏc or 2 Gm e∕ℏc is varying. This shows that many implementations of this idea are a priori possible.