Cosmic backreaction as an additional source of the expansion of the universe has been a debate topic since the discovery of cosmic acceleration. The major concern is whether the self interaction of small-scale nonlinear structures would source gravity on very large scales. Gregory Ryskin argued against the additional inclusion of gravitational interaction energy of astronomical objects, whose masses are mostly inferred from gravitational effects and hence should already contain all sources with long-range gravity forces. Ryskin proposed that the backreaction contribution to the energy momentum tensor is instead from the rest of the universe beyond the observable patch. Ryskin's model elegantly solves the fine-tuning problem and is in good agreement with the Hubble diagram of Type Ia supernovae. In this article we revisit Ryskin's model and show that it is {\it inconsistent} with at least one of the following statements: (i) the universe is matter-dominated at low redshift ($z\lesssim 2$); (ii) the universe is radiation-dominated at sufficiently high redshift; (iii) matter density fluctuations are tiny ($\lesssim 10^{-4}$) at the recombination epoch.

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重新审视 Ryskin 的宇宙加速模型

自从发现宇宙加速以来，作为宇宙膨胀的另一个来源的宇宙逆反应一直是一个争论的话题。主要关注的是小尺度非线性结构的自相互作用是否会在非常大的尺度上产生重力。Gregory Ryskin 反对额外包含天文物体的引力相互作用能，这些天体的质量主要是从引力效应中推断出来的，因此应该已经包含了所有具有远程引力的来源。Ryskin 提出，对能量动量张量的反向反应贡献来自可观测斑块之外的宇宙其他部分。Ryskin 的模型优雅地解决了微调问题，与 Ia 型超新星的哈勃图非常吻合。在这篇文章中，我们重新审视了 Ryskin' s 模型并证明它与以下陈述中的至少一项{\it 不一致}：（i）宇宙在低红移（$z\lesssim 2$）时以物质为主；(ii) 宇宙在足够高的红移处以辐射为主；(iii) 在重组时期，物质密度波动很小（$\lesssim 10^{-4}$）。