Detecting topology in a nearly flat hyperbolic universe

Abstract

Cosmic microwave background data shows the observable universe to be nearly flat, but leaves open the question of whether it is simply or multiply connected. Several authors have investigated whether the topology of a multiply connect hyperbolic universe would be detectable when 0.9 < Omega < 1. However, the possibility of detecting a given topology varies depending on the location of the observer within the space. Recent studies have assumed the observer sits at a favorable location. The present paper extends that work to consider observers at all points in the space, and (for given values of Omega_m and Omega_Lambda and a given topology) computes the probability that a randomly placed observer could detect the topology. The computations show that when Omega = 0.98 a randomly placed observer has a reasonable chance (~50%) of detecting a hyperbolic topology, but when Omega = 0.99 the chances are low (<10%) and decrease still further as Omega approaches one.