宇宙中引力成团具有高度非线性，这使数值模拟成为详细追踪星系和星系团等形成结构之演化的唯一手段。然而，这需要捕获巨大的空间和时间动力学范围。例如，结构等级式并合跨越的物理尺度从星系内部的亚 kpc 尺度，一直延伸到数百兆秒差距——后者是宇宙中最大的相干尺度。在这方面，基于 $N$ 体和流体动力学技术的现代宇宙学模拟程序，最适合在结构等级式形成过程中精确追踪暗物质和气体在其全部复杂性下的联合动力学。

As a result of the high non-linearity of the gravitational clustering in the Universe, numerical simulations are the only method to follow the evolution of the forming structures like galaxies and galaxy clusters in detail. However, a huge dynamic range in space and time has to be captured. For instance, the range of physical scales over which the hierarchical assembly of structures develops spans from sub-kpc scales in galaxies up to several hundreds of megaparsecs, the latter being the largest coherent scale in the Universe. Here, modern cosmological simulation codes based on N-body and hydrodynamics techniques are best suited to accurately follow the joint dynamics of DM and gas in their full complexity, during the hierarchical build-up of these structures.

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