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Title: Is de Sitter space stable against infrared quantum back-reaction?
Plain: 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: 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.
Settled by: A gauge-invariant, infrared-resummed calculation of the late-time local expansion rate including graviton loops.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: contested
Status note: Stochastic resummation controls scalar secular growth; the graviton case and Polyakov's instability claim remain disputed as of 2026.
Posed since: (empty)