Cosmic Microwave Background and the Curvature of Space

Cosmic Microwave Background and the Curvature of Space
Temperature variations in the early universe appear as “hot spots” in the cosmic microwave background. The apparent sizes of these spots depend on the
curvature of space. (a) In a closed universe with positive curvature, light rays from opposite sides of a hot spot bend toward each other. Hence, the hot spot
appears larger than it actually is (dashed lines). (b) The light rays do not bend in a flat universe. (c) In an open universe, light rays bend apart. The dashed
lines show that a hot spot would appear smaller than its actual size