When Galaxies Collide: The Search for Low-frequency Gravitational Wave Backgrounds in the Universe

Abstract

Gravitational waves (GWs) are a predicted feature of General Relativity (GR). These waves, which are tiny ripples in the fabric of space-time, appear as wavelike solutions to the vacuum Einstein equation, and are the only prediction from GR that have not yet been directly observed. In the past few decades, large scale efforts aimed at detecting these elusive waves have increasingly gained momentum: a direct observation of GWs will provide an entirely new mechanism for learning more about the structure and evolution of astrophysical objects in our universe, as well as the cosmology that underlies the universe itself.