Is de Sitter space stable against infrared quantum back-reaction?
In plain words
In an expanding universe with a cosmological constant, quantum fluctuations of light fields and gravitons can accumulate over time. Some argue that this slowly screens or destabilizes the expansion; others argue the effect is an artifact of the calculation.
Precise statement
For massless minimally coupled scalars and perturbative gravitons on de Sitter space with Hubble rate H, loop corrections to correlators and to $\langle T_{ab}\rangle$ grow secularly as powers of H t or $\ln a$, with a the scale factor (Tsamis and Woodard; Polyakov 2012). Determine whether, after infrared resummation and in terms of gauge-invariant observables, back-reaction changes the local expansion rate or produces an instability, or whether the secular terms are gauge or resummation artifacts. An answer is a gauge-invariant computation of a local expansion observable with controlled infrared resummation and its late-time limit.
What would settle it
A gauge-invariant, infrared-resummed calculation of the late-time local expansion rate including graviton loops.
Status in the literature
Unverified note
Stochastic resummation controls scalar secular growth; the graviton case and Polyakov's instability claim remain disputed as of 2026.