Dillon Brout, Adam Riess and Dan Scolnic talk about the latest SH0ES measurement of the Hubble parameter, making use of the new Pantheon+ supernovae data set.

The measurement accuracy has reached ± 1.0 km s⁻¹ Mpc⁻¹, and they analysed the data in 67 different possible ways and every time reach a result that is in significant tension with Planck + ΛCDM. Their baseline analysis, the one with the best χ² with the fewest free parameters, is now in 5σ tension, on its own, with Planck.

It isn’t clear where the solution to the Hubble tension will come from, but the fact that all local measurements of H₀ come in above Planck, and that the most accurate measurement is now in 5σ tension is very interesting. It’s worth also noting that the prediction from the early universe + ΛCDM doesn’t rely uniquely on Planck. Other CMB experiments give the same small value, and even just Big Bang Nucleosynthesis and local Baryon Acoustic Oscillation measurements, combined with ΛCDM give a small value of H₀.

So, if this isn’t evidence of new physics in cosmology, it will be a very strange series of errors that is causing it.

Dillon: http://djbrout.github.io/
Adam: https://physics-astronomy.jhu.edu/directory/adam-riess/
Dan: https://scholars.duke.edu/person/dscolnic

The paper (SH0ES): https://arxiv.org/abs/2112.04510
The paper (Pantheon+ data): https://arxiv.org/abs/2112.03863