What explains the Hubble tension in cosmology?

[Natalie.J]

I've been reading about the new measurements of the universe's expansion rate, and I'm confused about how the Hubble tension between local and early-universe measurements can be so persistent. If both sets of observations are so precise, what fundamental thing are we not accounting for in our cosmological models?

[Brian.R]

The Hubble tension bugs me because the local distance ladder and the early universe data both look precise yet disagree.

[RobertVG]

I spent weeks chasing a small calibration error in Cepheid brightness on a project and the shift was tiny but enough to move the result a bit.

[Kenneth29]

Could it be that the real issue is measurement bias and not new physics after all?

[James_A]

We tried a different supernova calibration set and the H0 value stayed stubbornly high even when I expected it to move.