Implications of Planck2015 for inflationary, ekpyrotic and anamorphic bouncing cosmologies

Anna Ijjas, Paul J. Steinhardt

Research output: Contribution to journalArticlepeer-review

47 Scopus citations


The results from Planck2015, when combined with earlier observations from the Wilkinson Microwave Anisotropy Probe, Atacama Cosmology Telescope, South Pole Telescope and other experiments, were the first observations to disfavor the 'classic' inflationary paradigm. To satisfy the observational constraints, inflationary theorists have been forced to consider plateau-like inflaton potentials that introduce more parameters and more fine-tuning, problematic initial conditions, multiverse-unpredictability issues, and a new 'unlikeliness problem'. Some propose turning instead to a 'postmodern' inflationary paradigm in which the cosmological properties in our observable Universe are only locally valid and set randomly, with completely different properties (and perhaps even different physical laws) existing in most regions outside our horizon. By contrast, the new results are consistent with the simplest versions of ekpyrotic cyclic models in which the Universe is smoothed and flattened during a period of slow contraction followed by a bounce, and another promising bouncing theory, anamorphic cosmology, has been proposed that can produce distinctive predictions.

Original languageEnglish (US)
Article number044001
JournalClassical and Quantum Gravity
Issue number4
StatePublished - Jan 27 2016

All Science Journal Classification (ASJC) codes

  • Physics and Astronomy (miscellaneous)


  • Planck2015
  • anamorphic cosmology
  • ekpyrotic cosmology
  • eternal inflation and multiverse
  • inflation
  • unlikeliness problem


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