Over the past decade, the disparity between the value of the cosmic expansion rate determined directly from measurements of distance and redshift and that determined instead from the standard Lambda cold dark matter (ΛCDM) cosmological model, calibrated by measurements from the early Universe, has grown to a level of significance requiring a solution. Proposed systematic errors are not supported by the breadth of available data (and unknown errors are untestable by lack of definition). Simple theoretical explanations for this Hubble tension that are consistent with the majority of the data have been surprisingly hard to come by, but in recent years, attention has focused increasingly on models that alter the early or pre-recombination physics of ΛCDM as the most feasible. Here, we describe the nature of this tension and emphasize recent developments on the observational side. We then explain why early-Universe solutions are currently favored and the constraints that any such model must satisfy. We discuss one workable example, early dark energy, and describe how it can be tested with future measurements. Given an assortment of more extended recent reviews on specific aspects of the problem, the discussion is intended to be fairly general and understandable to a broad audience.

中文翻译：

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哈勃张力和早期暗能量


在过去的十年中，直接由距离和红移测量确定的宇宙膨胀率值与由标准 Lambda 冷暗物质 （ΛCDM） 宇宙学模型确定的宇宙膨胀率值之间的差异，由早期宇宙的测量校准，已经发展到需要解决方案的重要水平。所提出的系统误差没有得到可用数据的广度的支持（并且由于缺乏定义而无法检验未知错误）。对这种哈勃张力的简单理论解释与大多数数据一致，出乎意料地难以获得，但近年来，人们的注意力越来越多地集中在将 ΛCDM 的早期或前复合物理改变为最可行的模型上。在这里，我们描述了这种紧张局势的性质，并强调了观察方面的最新发展。然后，我们解释了为什么目前支持早期宇宙解，以及任何此类模型必须满足的约束条件。我们讨论了一个可行的例子，早期暗能量，并描述了如何用未来的测量来测试它。鉴于最近对问题特定方面的各种更深入的评论，该讨论旨在对广大受众相当笼统和易于理解。