Our Universe Has No Topological Scale

Smaller than 24 gigaparsecs—about 75 billion light years—according to a new analysis of data from the Wilkinson Microwave Anisotropy Probe. Because of conceivable hall-of-mirrors effects of spacetime, the universe might be finite in size but give us the illusion of being infinite. For example, the cosmos might be tiled with some repeating shape, around which light rays might continuously wrap themselves, somewhat like a video game in which an object might disappear off the left side of the screen and reappear on the right. In the new study, researchers looked for signs of such “wrapped” light in the form of pairs of circles, in opposite directions in the sky, that exhibit similar patterns of cosmic-microwave-background temperature fluctuations. If the universe were finite and smaller than the distance to the “surface of last scattering” (the place in deep space where the cosmic microwaves originate and that constitutes the edge of...