The structure of the universe—as opposed to the structure of matter in the universe—is determined by the shape of space. The shape of space can, surprisingly, be curved on a very large scale—millions or even billions of light-years across—and yet have such a tiny effect on our daily lives that we do not notice it. For decades, astronomers have tried to measure the amount of cosmic curvature. The latest data show that space is “flat,” with no curvature at all.

On smaller scales—that of planets, stars, and galaxies—the structure of the universe can be altered by massive objects. This alteration manifests itself as the curvature of space and time, as explained by the general theory of relativity.