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·勒梅特首次建立宇宙膨胀以来，测量其速率的哈勃常数\(H_0\)一直引起天文学家的极大兴趣。除了本身很有趣之外，没有它就可以推断出很少的宇宙属性。在过去的十年里，不同的测量方法之间出现了巨大的差距，一些方法锚定在附近的宇宙中，另一些方法则在宇宙学距离上。SH0ES 团队在本地找到了\(H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\)，而为普朗克合作的早期宇宙是\(H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}\)来自宇宙微波背景的测量。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，如果谦逊的天文学家需要为某个目的假设一个值，他们应该如何在相互竞争的主张之间进行选择？在本文中，我们回顾了结果，以及为了适应所有这些可能需要对宇宙模型进行哪些更改。对于赶时间的天文学家，我们提供购买者的结果指南，并提出建议。