Assessing Direct Observational Signatures of Eternal Inflation

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

In the inflation scenario of how the early universe evolved, the universe undergoes a period of accelerated expansion which ensures that the present universe is homogenous and isotropic on large scales, and lays down the primordial perturbation spectrum that sources the temperature anisotropies of the Cosmic Microwave Background (CMB), and the formation of galaxies (and their associated large scale structure in the universe). Eternal inflation arises when the inflationary growth does not end globally, but only in a sub-regions or pockets of the overall spacetime. In this case, one typically has an infinite number of pockets, each of which effectively comprises the entire 'visible universe' of any observer that live inside a pocket. Many well-known models of inflation predict that inflation is eternal, but this possibility has usually been regarded as on the fringe of philosophy, since any given observer is unable to see anything outside their own pocket, and the eternal nature of inflation thus does not seem to have an immediately observable consequences. This proposal challenges that view and gives arguments that one can find direct experimental consequences of eternal inflation. The key component of this proposal is that one should study the collisions between different pockets shortly after their formation, which would generically lead to anisotropies visible from inside a single pocket. Since they are not generically expected in inflationary scenarios, these anisotropies would allow one to define specific signatures of eternal inflation that could then be compared to observational data. Specifically The PI proposes to study the detailed outcome of a generic bubble collision using exact solutions to Einstein?s equations. The then intends to do a linear analysis of the effect of perturbations on the bubble wall, and finally he intends to perform numerical simulations of bubble collisions, initially in fixed Minkowski and de Sitter backgrounds, then in full general relativity. The PI will attempt to connect these results to, on the one hand, our observed CMB sky, and, on the other hand, the underlying picture of eternal inflation with many minima. The proposed research will greatly increase the understanding of open inflation and bubble collisions, which are of great current relevance in inflationary cosmology; further, it may well suggest other avenues of observationally testing both eternal inflation and the string landscape. The PI will be involved in several outreach efforts including public talks, presentations and programs as part of the SCIPP/UCSC Physics outreach program, and outreach online through blogging and other activities