▪The Hubble parameter, H0, is not an univocally defined quantity: It relates redshifts to distances in the near Universe, but it is also a key parameter of the ΛCDM standard cosmological model. As such, H0 affects several physical processes at different cosmic epochs and multiple observables. We have counted more than a dozen H0s that are expected to agree if (a) there are no significant systematics in the data and their interpretation and (b) the adopted cosmological model is correct.▪With few exceptions (proverbially confirming the rule), these determinations do not agree at high statistical significance; their values cluster around two camps: the low (68 km s1 Mpc1) and high (73 km s1 Mpc1) camps. It appears to be a matter of anchors. The shape of the Universe expansion history agrees with the model; it is the normalizations that disagree.▪Beyond systematics in the data/analysis, if the model is incorrect, there are only two viable ways to “fix” it: by changing the early time (z ≳ 1,100) physics and, thus, the early time normalization or by a global modification, possibly touching the model's fundamental assumptions (e.g., homogeneity, isotropy, gravity). None of these three options has the consensus of the community.▪The research community has been actively looking for deviations from ΛCDM for two decades; the one we might have found makes us wish we could put the genie back in the bottle.

中文翻译：

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许多 H0 的故事


▪哈勃参数H0不是一个明确定义的量：它将红移与近处宇宙的距离联系起来，但它也是ΛCDM标准宇宙学模型的关键参数。因此，H0 影响不同宇宙时期和多个可观测值的多个物理过程。我们统计了十多个 H0，如果 (a) 数据及其解释不存在显着的系统性，并且 (b) 采用的宇宙学模型是正确的，则这些 H0 预计会达成一致。▪ 除了少数例外（众所周知，证实了该规则），这些测定结果在统计显着性上不一致；它们的值集中在两个阵营：低阵营（68 km s1 Mpc1）和高阵营（73 km s1 Mpc1）。这似乎是锚的问题。宇宙膨胀历史的形状与模型相符； ▪ 除了数据/分析中的系统学之外，如果模型不正确，只有两种可行的方法来“修复”它：通过改变早期 (z ≳ 1,100) 物理学，从而改变早期归一化或通过全局修改，可能会触及模型的基本假设（例如均匀性、各向同性、重力）。这三个选项都没有得到社区的共识。 ▪ 研究社区二十年来一直在积极寻找与ΛCDM 的偏差；我们可能发现的那个让我们希望能够把精灵放回瓶子里。