One of the longstanding goals of modern cosmology has been to determine the global geometry of the universe. This is the geometry of the universe at very large scales (greater than about 2 × 10⁸ light-years), at which the distribution of galaxies appears to be uniform. Determining the global geometry would answer the question of what is the curvature of space on the largest scales. (While the space-time of general relativity has four dimensions, it can be characterized by a curvature, just like a two-dimensional surface.) That is, is this space flat or curved? And, if curved, is the curvature positive (like a sphere) or negative (like a saddle-shaped surface)?