A Cyclic Model of the Universe

Why is the Universe homogeneous and isotropic on large scales? Why is it spatially flat? How did the inhomogeneities in the Universe arise that lead to the formation of galaxies and the fluctuations in the cosmic microwave background? Inflationary cosmology answers these three important questions by introducing a brief period of extraordinary cosmic acceleration during the first $10^{-30}$ seconds after the big bang. However, there are other deep questions of cosmology which inflation does not resolve: How old is the Universe? How big is the Universe? What occurred at the initial singularity? What is the ultimate fate of the Universe? What is the role of the dark energy and the recently observed low-energy cosmic acceleration? Does time, and the arrow of time, exist before the big bang? We introduce a cyclic model of the Universe that addresses all of these questions and does so without introducing the extraordinarily rapid acceleration that characterizes inflationary models. In this picture, the Universe undergoes an endless sequence of cosmic cycles each of which begins with the Universe expanding from a `big bang' and ends with the Universe contracting to a `big crunch.' Each big bang proceeds through a period of radiation and matter domination consistent with the standard cosmology. The Universe then begins an exceedingly long period of slow cosmic acceleration (as detected in recent observations) which ultimately empties the Universe of entropy and black holes produced in the preceding cycle and triggers the onset of contraction to a big crunch.