The speed of the expansion of the universe is governed by the Hubble constant. Discordance tells of its troubled 100-year history, from tentative steps to measure the distances of nearby stars to orbiting telescopes peering into the far reaches of space. But recent results hint at more trouble ahead...

The speed of the expansion of the universe is governed by the Hubble constant. Discordance tells of its troubled 100-year history, from tentative steps to measure the distances of nearby stars to orbiting telescopes peering into the far reaches of space. But recent results hint at more trouble ahead: the 'Hubble tension'. The story is not over yet.