This image provided by the Illustris Collaboration in May 2014 shows dark matter density, left, transitioning to gas density, right, in a simulation of the evolution of the universe since the Big Bang. The new computer simulation that reproduces features — such as galaxy distribution and composition — more accurately than previous ones is described in the Thursday, May 8, 2014 issue of the journal Nature. Previous attempts have broadly reproduced the web of galaxies, but failed to create mixed populations of galaxies or predict gas and metal content. The new model correctly predicts characteristics described in observational studies, and represents a considerable step forward in modeling galaxy formation. (AP Photo/Illustris Collaboration)