Recent advances in relativistic cosmology

The vast majority of the matter content in our Universe is not currently understood. On cosmological scales, our theoretical models describing this matter rely on the cosmological principle: our Universe is both homogeneous and isotropic. Yet, the theory of general relativity we use to describe gravitational interactions of this matter does not demand this. In this talk, I will describe progress modeling spacetimes without such assumptions, allowing us to test general relativity and the validity of the cosmological principle in a more general setting. This work provides some validation of our standard model, but only to a point: neglecting relativistic effects can lead to a bias in our cosmological inferences.