Bouncing cosmology made simple

Anna Ijjas, Paul J. Steinhardt

Research output: Contribution to journalReview articlepeer-review

79 Scopus citations


We introduce the 'wedge diagram', an intuitive way to illustrate how cosmological models with a classical (non-singular) bounce generically resolve fundamental problems in cosmology. These include the well-known horizon, flatness, and inhomogeneity problems; the small tensor-to-scalar ratio observed in the cosmic microwave background; the low entropy at the beginning of a hot, expanding phase; and the avoidance of quantum runaway. The same diagrammatic approach can be used to compare with other cosmological scenarios.

Original languageEnglish (US)
Article number135004
JournalClassical and Quantum Gravity
Issue number13
StatePublished - Jun 1 2018

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)


  • bouncing cosmology
  • ekyprotic universe
  • flatness problem
  • homogeneity problem
  • singularity problem


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