The Universe may have positive, negative, or zero spatial curvature depending on its total energy density.

The equations for negative spatial curvature were given by Friedmann in 1924.

Infinite expansion does not determine the spatial curvature of the universe.

One, is positive spatial curvature - that the universe is like a huge sphere.

Two, is zero spatial curvature - a so-called flat universe.

The universe seems "low density" and therefore of negative spatial curvature.

The spatial curvature of the Schwarzschild solution for can be visualized as the graphic shows.

In the 1930s, Hubble was involved in determining the distribution of galaxies and spatial curvature.

The spatial curvature of the "universe" inside the bubbles that form by this process is negative, a testable prediction.

However, it is possible that neither of these will be observed if the spatial curvature is too small and the collisions are too rare.