Redshift and gauge choice

Abstract

We show that a specific gauge choice comes extremely close to defining a frame whose preferred observers see a dipole-free CMB. In this gauge the metric is the product of a scale factor depending on all spacetime coordinates, and a metric featuring an expansion-free geodesic timelike vector field. This setup facilitates the computation of redshift and other distance measures and explains why we can have a highly isotropic CMB despite large inhomogeneities.