Exploring the universe with gravitational waves

In this talk, I will present recent results about gravitational wave cosmology. I will argue that the spatial clustering of gravitational wave sources provides a wealth of invaluable information concerning the origin of binary black holes and the propagation law of gravitational waves. The former can clarify whether the observed black hole binaries are of stellar or primordial origin. The latter is important for constraining deviations from General Relativity on cosmological scales because such deviations predict modified propagation of gravitational waves compared to General Relativity. I will then explore the possibility of observed black holes having primordial origin and present its consequences for expected merger rates of such black holes and neutron stars. Time permitting, I will also summarize our recent progress made in the field of primordial gravitational waves and the implications for the inflationary models.