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Safely smoothing spacetime: backreaction in relativistic cosmological simulations
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A persistent theme in the study of dark energy is the question of whether it really exists or not. It is often claimed hat we are mis-calculating the cosmological model by neglecting the effects associated with averaging over large-scale structures. In the Newtonian approximation this is clear: there is no effect. Within the full relativistic picture this remains an important open question however, owing to the complex mathematics involved. We study this issue using particle numerical simulations which account for all relevant relativistic effects without any problems from shell crossing. In this context we show for the first time that the backreaction from structure can differ by many orders of magnitude depending upon the slicing of spacetime one chooses to average over. In the worst case, where smoothing is carried out in synchronous spatial surfaces, the corrections can reach ten percent and more. However, when smoothing on the constant time hypersurface of the Newtonian gauge, backreaction contributions remain 3-5 orders of magnitude smaller.
Forward citations
Cited by 4 Pith papers
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Evolving Dark Energy from the Back-Reaction of Cosmological Perturbations
Back-reaction of cosmological inhomogeneities can make an effective dark energy with a time-dependent equation of state and no phantom crossing, even for a global average.
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Impact of inhomogeneous curvature on growth rate measurements from magnitude fluctuations
Full-GR simulations find that inhomogeneous curvature produces only sub-dominant systematic offsets in growth-rate measurements from magnitude fluctuations at z ≲ 0.2 relative to current statistical errors.
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Little ado about everything II: an `emergent' dark energy from structure formation to rule cosmic tensions
An ensemble-averaged stochastic cosmology with a 'little ado' noise term produces an emergent dark energy that fits late-time data and claims to relieve the H0 and f sigma8 tensions.
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Les Houches on Dark Universe 2025: Elements of cosmology beyond FLRW
A lecture-notes review arguing that inhomogeneities cause only negligible backreaction and fitting corrections, leaving FLRW-based cosmology intact under the cosmological principle.
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