We discuss Manchak (2009a)'s result that there are locally (but not globally) isometric universes observationally indistinguishable from our own. This theorem makes the epistemic predicament of modern cosmology particularly problematic and the prospects of ever gaining knowledge of the global structure of the universe rather unlikely in the context of general relativity. We argue however that this conclusion is too quick; indeed, Manchak's theorem deploys spacetimes which are not physically reasonable, since they have features which are not the product of any physical process. This ultimately rests on the fact that local isometry between two spacetimes is not sufficient to guarantee that they are both physically reasonable. We propose an additional condition to properly define when a spacetime is physically reasonable, and we show that Manchak's spacetimes do not satisfy this further demand.

我们讨论了 Manchak (2009a) 的结果，即存在局部（但不是全球）等距宇宙，在观测上与我们自己的宇宙无法区分。这个定理使得现代宇宙学的认知困境特别成问题，而且在广义相对论的背景下，获得宇宙整体结构知识的前景也不太可能。然而，我们认为这个结论太快了。事实上，曼恰克定理部署了在物理上不合理的时空，因为它们具有不是任何物理过程产物的特征。这最终取决于这样一个事实，即两个时空之间的局部等距不足以保证它们在物理上都是合理的。我们提出了一个附加条件来正确定义时空何时在物理上是合理的，