Solving the Hubble tension \`a la Ellis & Stoeger 1987

Understand

The discrepancy between the value of the Hubble constant $H_0$ in the late, local universe and the one obtained from the Planck collaboration representing an all-sky value for the early universe reached the 5-$\sigma$ level.

• Approaches to alleviate the tension contain a wide range of ansatzes: increasing uncertainties in data acquisition, reducing biases in the astrophysical models that underly the probes, or taking into account observer-dependent variances in the parameters of the cosmological background model.
• Yet, early and late universe probes are often treated as independent, they live on different length scales, and require different perturbations to be subtracted.
• Hence, fitting a flat Friedmann-Lema\^itre-Robertson-Walker cosmology to different probes at different cosmic epochs can yield different sets of cosmological parameter values.