... in an inhomogeneous, pressurefree expanding universe. He examined geodesics to study the influence of the expansion on planetary orbits. He concluded that in this model the orbits do expand. His work will be referred to again in section 5. Interest in this topic has been renewed recently. Anderson [1] has used the method of Einstein, Infeld and Hoffmann to study a pair of gravitating particles in an Einstein–de Sitter (E–deS) universe. He concludes that the expansion does have an effect on the motion of the particles, though if they are in circular orbit it does not expand. Cooperstock et al [13] have studied the effect of the cosmic expansion on local dynamics, using Fermi normal coordinates, and conclude that ‘the expansion affects all scales, but the magnitude of the effect is essentially negligible for local systems, even at the scale of galactic clusters’. In an investigation of a different kind [10] I showed by an exact solution of the Einstein– Maxwell equations that local distributions of a certain sort of matter definitely participate in the expansion. The matter concerned was electrically counterpoised dust: this is dust carrying an electric charge density such that the grav...