Since the expansion of the universe was first established by Edwin Hubble and Georges Lemaître about a century ago, the Hubble constant \(H_0\) which measures its rate has been of great interest to astronomers. Besides being interesting in its own right, few properties of the universe can be deduced without it. In the last decade, a significant gap has emerged between different methods of measuring it, some anchored in the nearby universe, others at cosmological distances. The SH0ES team has found \(H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\) locally, whereas the value found for the early universe by the Planck Collaboration is \(H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\) from measurements of the cosmic microwave background. Is this gap a sign that the well-established \({\varLambda} {\text{CDM}}\) cosmological model is somehow incomplete? Or are there unknown systematics? And more practically, how should humble astronomers pick between competing claims if they need to assume a value for a certain purpose? In this article, we review results and what changes to the cosmological model could be needed to accommodate them all. For astronomers in a hurry, we provide a buyer’s guide to the results, and make recommendations.

自从大约一个世纪前埃德温·哈勃和乔治·勒梅特首次确立宇宙膨胀以来，测量宇宙膨胀速度的哈勃常数\(H_0\)一直引起天文学家的极大兴趣。除了它本身很有趣之外，没有它就无法推断出宇宙的一些性质。在过去的十年中，不同的测量方法之间出现了巨大的差距，一些方法基于附近的宇宙，另一些方法则基于宇宙学距离。 SH0ES 团队在本地找到了\(H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\) ，而找到的值普朗克合作组织的早期宇宙是\(H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\)宇宙微波背景。这个差距是否表明完善的\({\varLambda} {\text{CDM}}\)宇宙学模型在某种程度上是不完整的？还是有未知的系统学？更实际的是，如果谦虚的天文学家需要为某种目的假设一个值，他们应该如何在相互竞争的主张之间做出选择？在本文中，我们回顾了结果以及可能需要对宇宙学模型进行哪些改变才能适应所有这些结果。对于赶时间的天文学家，我们提供结果购买指南，并提出建议。