Observational cosmology using characteristic numerical relativity

The characteristic formalism in numerical relativity, which has been developed to study gravitational waves, and the observer metric approach in observational cosmology both make use of coordinate systems based on null cones. In this paper, these coordinate systems are compared and it is then demonstrated how characteristic numerical relativity can be used to investigate problems in observational cosmology. In a numerical experiment using the characteristic formalism, it is shown how the historical evolution of a LTB universe compares to that of the $\Lambda$CDM model given identical observational data on a local observer's past null cone. It is demonstrated that, at an earlier epoch of the LTB model, the observational data would not be consistent with that of the $\Lambda$CDM model.