Beyond inflation: A cyclic universe scenario

Neil Turok, Paul J. Steinhardt

Research output: Contribution to journalConference articlepeer-review

23 Scopus citations


Inflation has been the leading early universe scenario for two decades, and has become an accepted element of the successful 'cosmic concordance' model. However, there are many puzzling features of the resulting theory. It requires both high energy and low energy inflation, with energy densities differing by a hundred orders of magnitude. The questions of why the universe started out undergoing high energy inflation, and why it will end up in low energy inflation, are unanswered. Rather than resort to anthropic arguments, we have developed an alternative cosmology, the cyclic universe, in which the universe exists in a very long-lived attractor state determined by the laws of physics. The model shares inflation's phenomenological successes without requiring an epoch of high energy inflation. Instead, the universe is made homogeneous and flat, and scale-invariant adiabatic perturbations are generated during an epoch of low energy acceleration like that seen today, but preceding the last big bang. Unlike inflation, the model requires low energy acceleration in order for a periodic attractor state to exist. The key challenge facing the scenario is that of passing through the cosmic singularity at t = 0. Substantial progress has been made at the level of linearised gravity, which is reviewed here. The challenge of extending this to nonlinear gravity and string theory remains.

Original languageEnglish (US)
Pages (from-to)76-85
Number of pages10
JournalPhysica Scripta T
StatePublished - 2005
EventNobel Symposium 127 on String Theory and Cosmology - Sigtuna, Sweden
Duration: Aug 14 2003Aug 19 2003

All Science Journal Classification (ASJC) codes

  • Atomic and Molecular Physics, and Optics
  • Mathematical Physics
  • Condensed Matter Physics


Dive into the research topics of 'Beyond inflation: A cyclic universe scenario'. Together they form a unique fingerprint.

Cite this