Local and nonlocal measures of acceleration in cosmology
Local and nonlocal measures of acceleration in cosmology
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DOI：
10.1103/physrevd.85.103512
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发表时间：
2012-03
影响因子：
5
通讯作者：
P. Bull;T. Clifton
中科院分区：
文献类型：
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作者：
P. Bull;T. Clifton
目前的宇宙学观测，当在均匀各向同性的Friedmann-Lemaitre-Robertson-Walker(FLRW)模型框架内解释时，强烈表明宇宙正在进入加速膨胀时期。这通常被认为意味着空间本身的扩张正在加速。然而，在一般的时空中，这不一定是真的。我们试图通过考虑各种非均匀宇宙模型中的一些局部和非局部加速度测量来澄清这一点。所选择的每一种测量都对应于以前用于研究宇宙学中的加速度的一种理论或观测过程，并且在精确的空间均匀性和各向同性的限制下，所有测量都减少到相同的量。在统计均匀和各向同性的时空中，我们发现由距离-红移关系的观测得到的加速度与空间平均宇宙的加速度密切相关，但不一定与时空本身的局部加速度的平均值有任何相似之处。然而，对于不表现出统计齐次和各向同性的非均匀时空，我们发现从观测中推断的加速度与平均时空的加速度之间几乎没有相关性。这表明，在一个不均匀的宇宙中进行的观测可以暗示在没有暗能量存在的情况下加速。
Current cosmological observations, when interpreted within the framework of a homogeneous and isotropic Friedmann-Lemaitre-Robertson-Walker (FLRW) model, strongly suggest that the Universe is entering a period of accelerating expansion. This is often taken to mean that the expansion of space itself is accelerating. In a general spacetime, however, this is not necessarily true. We attempt to clarify this point by considering a handful of local and non-local measures of acceleration in a variety of inhomogeneous cosmological models. Each of the chosen measures corresponds to a theoretical or observational procedure that has previously been used to study acceleration in cosmology, and all measures reduce to the same quantity in the limit of exact spatial homogeneity and isotropy. In statistically homogeneous and isotropic spacetimes, we find that the acceleration inferred from observations of the distance-redshift relation is closely related to the acceleration of the spatially averaged universe, but does not necessarily bear any resemblance to the average of the local acceleration of spacetime itself. For inhomogeneous spacetimes that do not display statistical homogeneity and isotropy, however, we find little correlation between acceleration inferred from observations and the acceleration of the averaged spacetime. This shows that observations made in an inhomogeneous universe can imply acceleration without the existence of dark energy.