A regime of linear stability for the Einstein-scalar field system with applications to nonlinear Big Bang formation

Igor Rodnianski, Jared Speck

Research output: Contribution to journalArticlepeer-review

27 Scopus citations


We linearize the Einstein-scalar field equations, expressed relative to constant mean curvature (CMC)-transported spatial coordinates gauge, around members of the well-known family of Kasner solutions on (0;∞) × T3. The Kasner solutions model a spatially uniform scalar field evolving in a (typically) spatially anisotropic spacetime that expands towards the future and that has a "Big Bang" singularity at (t = 0). We place initial data for the linearized system along (t = 1) ≃ T3 and study the linear solution's behavior in the collapsing direction t ↓ 0. Our first main result is the proof of an approximate L2 monotonicity identity for the linear solutions. Using it, we prove a linear stability result that holds when the background Kasner solution is sufficiently close to the Friedmann-Lemaĭtre-Robertson-Walker (FLRW) solution. In particular, we show that as t ↓ 0, various time- rescaled components of the linear solution converge to regular functions defined along (t = 0). In addition, we motivate the preferred direction of the approximate monotonicity by showing that the CMC-transported spatial coordinates gauge can be viewed as a limiting version of a family of parabolic gauges for the lapse variable; an approximate monotonicity identity and corresponding linear stability results also hold in the para-bolic gauges, but the corresponding parabolic PDEs are locally well posed only in the direction t ↓ 0. Finally, based on the linear stability results, we outline a proof of the following result, whose complete proof will appear elsewhere: the FLRW solution is globally nonlinearly stable in the collapsing direction t↓ 0 under small perturbations of its data at (t = 1).

Original languageEnglish (US)
Pages (from-to)65-156
Number of pages92
JournalAnnals of Mathematics
Issue number1
StatePublished - Jan 1 2018

All Science Journal Classification (ASJC) codes

  • Statistics and Probability
  • Statistics, Probability and Uncertainty


  • BKL conjectures
  • Constant mean curvature
  • FLRW
  • Kasner solution
  • Monotonicity
  • Parabolic gauge
  • Quiescent cosmology
  • Spatial harmonic coordinates
  • Stable blowup
  • Strong cosmic censorship
  • Transported spatial coordinates


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