EFFECTS OF STRUCTURE FORMATION ON THE APPARENT EXPANSION RATE OF THE UNIVERSE: A REALISTIC ESTIMATE BASED UPON N-BODY SIMULATIONS

摘要

General relativistic corrections to the Friedmann expansion rate arise when the Einstein equations are averaged over a spatial volume in a locally inhomogeneous cosmology. It has been suggested that these corrections may contribute to the observed present cosmic acceleration. Here, we describe a new scheme based upon detailed numerical simulations to make a realistic estimate of the magnitude of these corrections for general inhomogeneities in (3+1) spacetime. We use these simulations to quantitatively calculate the volume averaged expansion rate using N-body large scale structure simulations and compare it with the expansion rate in a standard FRW cosmology. We find that in the weak-field limit, the corrections are slightly larger than previous claimed 10~(-5) level, but not large enough to mimic the proposed dark energy to drive current cosmic acceleration. Moreover, at the highest resolution the corrections are of the wrong sign to induce acceleration. Nevertheless, the cumulative effect of the growth of strong-field sources needs to be further investigated.