Editing Shape of the universe (section)

==== Universe with negative curvature ====
A hyperbolic universe, one of a negative spatial curvature, is described by hyperbolic geometry, and can be thought of locally as a three-dimensional analog of an infinitely extended saddle shape. There are a great variety of [[hyperbolic 3-manifold]]s, and their classification is not completely understood. Those of finite volume can be understood via the [[Mostow rigidity theorem]]. For hyperbolic local geometry, many of the possible three-dimensional spaces are informally called "horn topologies", so called because of the shape of the [[pseudosphere]], a canonical model of hyperbolic geometry. An example is the [[Picard horn]], a negatively curved space, colloquially described as "funnel-shaped".<ref name="Aurich0403597">{{cite journal |last= Aurich |first= Ralf|author2=Lustig, S. |author3=Steiner, F. |author4=Then, H. |title= Hyperbolic Universes with a Horned Topology and the CMB Anisotropy |journal= [[Classical and Quantum Gravity]] |volume= 21 |issue= 21 |pages= 4901–4926 |date= 2004 |doi= 10.1088/0264-9381/21/21/010 |bibcode= 2004CQGra..21.4901A |arxiv= astro-ph/0403597|s2cid= 17619026}}</ref>