Open universes from bubbles: an introduction and update

This is an introduction to models of open universes originating from bubbles, including a summary of recent theoretical results for the power spectrum. To appear in the Proceedings of the XXXI Moriond meeting, “Microwave Background Anisotropies.” PACS numbers 98.80Bp, 98.80Cq A flat (Ωtot = 1) universe has long been considered a generic prediction of inflationary [1] models. It has recently been demonstrated that inflation can also produce viable open (Ω < 1) universes [2]. As the data on Ω has not yet converged, further investigation of these models is worthwhile. In the following, why and how bubbles give open universes is reviewed, the main features of the new models are outlined and current results and questions are summarized. Due to space limitations, this is necessarily just an overview, and readers are referred to the cited papers and their references for more in depth discussion and comprehensive referencing. The basic reason bubbles give an open universe can be illustrated with empty Minkowski space, which does not have a unique coordinate system leading to a metric of the form ds = dη − a(η)dσ . (1) [email protected]