Residual fluctuations in the microwave background at large angular scales: Revision of the Sachs-Wolfe effect

In this paper we revise the Sachs-Wolfe (SW) computation of large-scale anisotropies of the microwave background temperature, taking into account the properties of the metrics admitting an isotropic distribution of collisionless photons. We show that the metric used by SW belongs to the aforementioned class, and conclude that the microwave background (once the dipolar anisotropy has been subtracted) should now be isotropic at large angular scales, provided that it was isotropic on the last scattering surface and assuming that the growing mode of a pressureless Einstein–de Sitter perturbation is a good description of the metric.