Nature: Einstein's general relativity has been used to model the expansion of the early universe, but only in a simplified form. The complexity of the equations requires the assumption that matter was uniformly distributed in the early universe, which likely does not match reality. Even after the development of supercomputers, calculations continued the simplification for models that extended beyond a small region. Now two groups have independently created full-universe simulations that include a non-uniform distribution of matter. One group—led by Eloisa Bentivegna of the University of Catania, Italy, and Marco Bruni of the University of Portsmouth, UK—developed a model to study the formation of large, superdense structures. The model developed by the other group—led by Glenn Starkman of Case Western Reserve University in Cleveland, Ohio—focuses on how the universe expands and how its curvature affects the propagation of light. Both groups' models used numerical-solution techniques that were developed for calculating the warping of spacetime caused by black hole pairs like those that created the recently detected gravitational waves.
