Free Astronomy Magazine July-August 2014

37 COSMOLOGY another no less heavy limitation – which has systematically characterized previous cosmic simulations – and it is the adoption of the gravitational force as the only driving force (or, if not, the main one by far) of the evo- lution of the virtual universe, often applied solely to the dark matter, which constitutes 84.5% of the total matter in the universe. This simplification, if on the one hand it al- lows to adequately represent the “cosmic web”, on the other it excludes a number of factors that are central for a faithful multi- scale reproduction of the universe. It is not possible, for example, to disregard the chemical evolution of the latter, which as far as we know affects only ordinary mat- ter – especially that visible in telescopes – and that, ultimately, is precisely the one form- ing those structures that the simulations are trying to recreate and investigate. the right one was generated with Illustris. There seems to be a seamless continuity be- tween the two parts, except for a small differ- ence in focus. [Illustris Project]