I read here, http://www.space.com/24781-big-bang-theory-alternatives-infographic.html , that, "What we call the "observable universe" (or the "Hubble Volume") is the spherical region, about 90 billion light-years in diameter, that is centered on any given observer. This is the only part of the universe in which light has had time to reach the observer in the 13.8 billion years since the universe began. " How on earth is it possible to be centered on any given observer?? How can the observable universe for an observer near the boundary of the Hubble Volume also be a 90 billion light-year diameter sphere where that observer is the center??