For example; a multiply connected space like a 3 torus has everywhere zero curvature but is finite in extent, whereas a flat simply connected space is infinite In physical cosmology, the shape of the universe refers to both its local geometry and cosmic topology. Local geometry is defined primarily by its curvature, General relativity explains how spatial curvature (local geometry) is constrained by gravity. The cosmological topology of the universe cannot be deduced from measurements of curvature inferred from observations within the family of homogeneo In physical cosmology, the shape of the universe refers to both its local geometry and cosmic topology. Local geometry is defined primarily by its curvature, General relativity explains how spatial curvature (local geometry) is constrained by gravity. The cosmological topology of the universe cannot be deduced from measurements of curvature inferred from observations within the family of homogeneous general relativistic models alone, due to the existence of locally indistinguishable spaces with varying global topological characteristics. For example; a multiply connected space like a 3 torus has everywhere zero curvature but is finite in extent, whereas a flat simply connected space is infinite in extent (such as Euclidean space). Observational evidence (WMAP, BOOMERanG, and Planck, for example) indicates that the observable universe is spatially flat to within a 0.4% margin of error of the curvature density parameter with an unknown global topology. It is unknown whether the universe is simply connected like euclidean space or multiply connected like a torus. whether the universe is infinite or finite in extent, whether the geometry of the global universe is flat, positively curved, or negatively curved, and, whether the topology is simply connected (for example, like a sphere) or else multiply connected (for example, like a torus).