= Cosmic web
{wiki}
The \b[<cosmic web>] is the connected pattern of matter sheets, filaments and dense nodes surrounding <cosmic voids>. Collapse is generally anisotropic: a region can contract strongly in one direction before the others. The <Zeldovich approximation> makes this mechanism explicit through the principal directions of the initial deformation. Collapse along one, two or three directions gives the intuitive sequence of sheet, filament and compact <concentration>, although subsequent <shell crossing> and nonlinear dynamics complicate that picture.
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