The Pocket Universe

A pocket universe is a concept in inflationary theory, proposed by Alan Guth. It defines a realm like the one that contains the observable universe as only one of many inflationary zones.

Astrophysicist Jean-Luc Lehners, of the Princeton Center for Theoretical Science, has argued that an inflationary universe does produce pockets. As he wrote in 2012, "Eternal inflation produces pocket universes with all physically allowed vacuum and histories. Some of these pocket universes might contain a phase of slow-roll inflation, some might undergo cycles of cosmological evolution, and some might look like the Galilean genesis or other 'emergent' universe scenarios. Which one of these types of universe we are most likely to inhabit depends on the measure we choose in order to regulate the infinities inherent in eternal inflation."

But, Lehners continues, "the current leading measure proposals&mdash;namely, the global light-cone cutoff and its local counterpart, the causal diamond measure&mdash;as well as closely related proposals, all predict that we should live in a pocket universe that starts out with a small Hubble rate, thus favoring emergent and cyclic models." Lehners adds, deadpan, "Pocket universes which undergo cycles are further preferred, because they produce habitable conditions repeatedly inside each pocket."