标题： 通过空间平均的显式宇宙学粗粒化 显示英文标题

标题： Explicit Cosmological Coarse Graining via Spatial Averaging

摘要： 宇宙当前的物质密度，在小尺度上高度不均匀，但在大尺度上表现出近似均匀性。 我们提出，尽管使用弗里德曼-勒梅特-罗伯特森-沃尔克（FLRW）线元（描述一个完全均匀和各向同性的宇宙）作为模板来构建光度距离以将观测结果与理论进行比较是合理的，但在此构造中尺度因子的演化必须由布赫尔特[7, 8]在宇宙学空间平均背景下推导出的修改后的弗里德曼方程来支配，而不是由标准的FLRW度规的爱因斯坦方程来支配。 此外，我们认为，如果平均区域的大小与宇宙学均匀性出现的尺度一致，那么这种在空间平均宇宙学中定义的尺度因子将对应于有效FLRW度规。 这在原则上允许我们以标准方式（例如通过计算光度距离与红移的关系）将空间平均宇宙学的预测与观测结果进行比较。 空间平均宇宙学的预测通常会与标准FLRW宇宙学不同，因为此时尺度因子遵循修改后的FLRW方程。 这可能有助于通过与观测结果的比较，确定宇宙不均匀性是否可以作为观测到的宇宙加速膨胀的替代解释。 显示英文摘要

摘要： The present matter density of the Universe, while highly inhomogeneous on small scales, displays approximate homogeneity on large scales. We propose that whereas it is justified to use the Friedmann-Lemaitre-Robertson-Walker (FLRW) line element (which describes an exactly homogeneous and isotropic universe) as a template to construct luminosity distances in order to compare observations with theory, the evolution of the scale factor in such a construction must be governed not by the standard Einstein equations for the FLRW metric, but by the modified Friedmann equations derived by Buchert [7, 8] in the context of spatial averaging in Cosmology. Furthermore, we argue that this scale factor, defined in the spatially averaged cosmology, will correspond to the effective FLRW metric provided the size of the averaging domain coincides with the scale at which cosmological homogeneity arises. This allows us, in principle, to compare predictions of a spatially averaged cosmology with observations, in the standard manner, for instance by computing the luminosity distance versus red-shift relation. The predictions of the spatially averaged cosmology would in general differ from standard FLRW cosmology, because the scale-factor now obeys the modified FLRW equations. This could help determine, by comparing with observations, whether or not cosmological inhomogeneities are an alternative explanation for the observed cosmic acceleration.