The Pioneer riddle, the quantum vacuum and the acceleration of light

It is shown that the same phenomenological Newtonian model recently proposed, which accounts for the cosmological evolution of the fine structure constant, suggests furthermore an explanation of the unmodelled acceleration aP ≃ 8.5 × 10 −10 m/s of the Pioneer 10/11 spaceships reported by Anderson et al in 1998. In the view presented here, the permittivity and permeability of empty space are decreasing adiabatically, and the light is accelerating therefore, as a consequence of the progressive attenuation of the quantum vacuum due to the combined effect of its gravitational interaction with all the expanding universe and the fourth Heisenberg relation. It is argued that the spaceships might not have any extra acceleration (but would follow instead the unchanged Newton laws), the observed effect being due to an adiabatic acceleration of the light equal to aP, which has the same observational radio signature as the anomalous acceleration of