How does inhomogeneity affect our interpretation of cosmological observations? It has long been wondered to what extent the observable properties of an inhomogeneous universe differ from those of a corresponding Friedman-Lemaitre-Robertson-Walker (FLRW) model, and how the inhomogeneities affect that correspondence. Here, we use numerical relativity to study the behavior of light beams traversing an inhomogeneous universe and construct the resulting Hubble diagrams. The universe that emerges exhibits an average FLRW behavior, but inhomogeneous structures contribute to deviations in observables across the observer's sky. We also investigate the relationship between angular diameter distance and the angular extent of a source, finding deviations that grow with source redshift. These departures from FLRW are important path-dependent effects with implications for using real observables in an inhomogeneous universe such as our own.
Testing homogeneity with galaxy number counts : light-cone metric and general low-redshift expansion for a central observer in a matter dominated isotropic universe without cosmological constant
The gravitational wave background induced by nonlinear interactions between isotropic inhomogeneities and anisotropic inhomogeneous density perturbations
A ready-to-fit inhomogeneous cosmological model: The axially symmetric Szekeres spacetime
Laboratoire d’étude de l’Univers et des phénomènes eXtrèmes (LUX), Observatoire de Paris-PSL, UMR 8262 CNRS, Sorbonne Université（宇宙与极端现象研究实验室（LUX），巴黎天文台-PSL，CNRS联合研究单位8262，索邦大学）
Testing the cosmological principle on gigaparsec scales
School of Physics and Astronomy, Sun Yat-sen University（中山大学物理学院）；CSST Science Center for the Guangdong-Hongkong-Macau Greater Bay Area,Sun Yat-sen University（中山大学粤港澳大湾区空间站科学中心）
