Our Universe Has a Topology Scale of at least 24 GPC

Our universe has a topology scale of at least 24 Gpc, or about 75 billion light years, according to a new analysis of data from the Wilkinson Microwave Anisotropy Probe (WMAP).

What does this mean? Well, because of conceivable hall-of-mirrors effects of spacetime, the universe might be finite in size but give us mortals the illusion that it is infinite. For example, the cosmos might be tiled with some repeating shape, around which light rays might wrap themselves over and over ("wrap" in the sense that, as in video games, something might disappear off the left side of the screen and reappear on the right side).

A new study by scientists from Princeton, Montana State, and Case Western looks for signs of such "wrapped " light in the form of pairs of circles, in opposite directions in the sky, with similar patterns in the temperature of the cosmic microwave background. If the universe were finite and actually smaller than the distance to the "surface of last scattering" (a distance that essentially constitutes the edge of the "visible universe," and the place in deep space whence comes the cosmic microwaves), then multiple imaging should show up in the microwave background.

But no such correspondences appeared in the analysis. The researchers are able to turn the lack of recurring patterns into the form of a lower limit on the scale of cosmic topology, equal to 24 billion parsecs, a factor of 10 larger than previous observational bounds. (Cornish, Spergel, Starkman, Komatsu, Physical Review Letters, upcoming article; contact Neil Cornish, 406-994-7986, cornish@physics.montana.edu.)