Many worlds in one

Abstract

A generic prediction of inflation is that the thermalized region we inhabit is spatially infinite. Thus, it contains an infinite number of regions of the same size as our observable universe, which we shall denote as $\mathcal{O}$ regions. We argue that the number of possible histories which may take place inside of an $\mathcal{O}$ region, from the time of recombination up to the present time, is finite. Hence, there are an infinite number of $\mathcal{O}$ regions with identical histories up to the present, but which need not be identical in the future. Moreover, all histories which are not forbidden by conservation laws will occur in a finite fraction of all $\mathcal{O}$ regions. The ensemble of $\mathcal{O}$ regions is reminiscent of the ensemble of universes in the many-world picture of quantum mechanics. An important difference, however, is that other $\mathcal{O}$ regions are unquestionably real.