Is the Lopsided Universe an Open Universe?

The recently confirmed sky-wide asymmetry in the cosmic microwave background might be explained by assuming the Universe is slightly curved just beyond the cosmic horizon.

The density of matter and energy appears to vary more strongly on one side of the sky versus the other. That surprising assessment is based on corroborating evidence from two recent in-depth studies of the cosmic microwave background (CMB)—the thermal radiation left over from the big bang. To explain this hemispheric asymmetry, previous models [1] assumed the distribution of matter/energy fluctuations behaves differently beyond a particular distance scale, which is just a bit larger than the size of the observable Universe. However, the origin of this fundamental distance scale was left unexplained. Now, Andrew Liddle and Marina Cortês of the University of Edinburgh, UK, postulate [2] that this distance scale may represent the radius of curvature in a negatively curved (or “open”) Universe. In Physical Review Letters, the researchers show how a curvature-induced asymmetry can arise naturally if the Universe is open and was born via a process called bubble nucleation.