Figure 15-17 The Geometry of the Universe The shape of the universe is either (a) closed, (b) flat, or (c) open. The curvature depends on whether the combined density of all mass and energy is greater than, equal to, or less than a critical value that is “just right.” In theory, such a curvature could be determined by seeing whether two laser beams initially parallel to each other would converge, remain parallel, or spread apart.