Reference frames in cosmology

Abstract

In this talk a survey is given of the concept of the cosmological rest frame. To begin with one finds that the rising and setting of stars gives us the first indication that we on the Earth are living in a rotating frame of reference. Any frame accelerated relative to it requres inertial forces to be incorporated into the laws of motion. The Foucault pendulum experiment tells us how such forces can be detected on the Earth. The pendulum experiment also tells us that the local inertial frame is identical with the background of the distant stars in the sky. This led Ernst Mach to postulate his famous principle linking the property of inertia to the stellar background. This background fixes a unique cosmological rest frame. Finally, we explore how the cosmological rest frame can be identified through the somewhat confusing observations of the motions of the large scale structure in the universe and of the microwave background radiation.