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A key result of isotropic loop quantum cosmology is the existence of aquantum bounce which occurs when the energy density of the matter fieldapproaches a universal maximum close to the Planck density. Though the bouncehas been exhibited in various matter models, due to severe computationalchallenges some important questions have so far remained unaddressed. Theseinclude the demonstration of the bounce for widely spread states, its detailedproperties for the states when matter field probes regions close to the Planckvolume and the reliability of the continuum effective spacetime description ingeneral. In this manuscript we rigorously answer these questions using theChimera numerical scheme for the isotropic spatially flat model sourced with amassless scalar field. We show that as expected from an exactly solvable model,the quantum bounce is a generic feature of states even with a very wide spread,and for those which bounce much closer to the Planck volume. We perform adetailed analysis of the departures from the effective description and findsome expected, and some surprising results. At a coarse level of description,the effective dynamics can be regarded as a good approximation to theunderlying quantum dynamics unless the states correspond to small scalar fieldmomenta, in which case they bounce closer to the Planck volume, or are verywidely spread. Quantifying the amount of discrepancy between the quantum andthe effective dynamics, we find that the departure between them depends in asubtle and non-monotonic way on the field momentum and different fluctuations.Interestingly, the departures are generically found to be such that theeffective dynamics overestimates the spacetime curvature, and underestimatesthe volume at the bounce.

Numerical simulations of a loop quantum cosmos: robustness of the quantum bounce and the validity of effective dynamics