우주 팽창률에서의 밀도 섭동의 영향

Abstract

Our universe, though homogeneous and isotropic globally, is filled with irregularities at various length scales. The shape of these irregularities varies with time as the universe expands. This, in turn, affects the local as well as global structure of spacetime metric. It is considered to be a very complicated job to analyze fluctuations within the general relativistic framework beyond first-order approximations. Here we present a way to calculate the magnitudes of spatially averaged quantities such as energy density and pressure up to second-order without explicitly solving second-order equations. Especially we discuss our frameworks in the context of Friedmann-Robertson-Walker cosmology.