Ending the Hubble Tension

Abstract If primordial black holes of mass 10 −19 M ⊙ formed in the early universe, their Hawking radiation would have delayed recombination and increased the cosmic microwave background Hubble Constant by 10%. The hypothesis that the ionization history of the universe is locked to the thermal history is too precarious an assumption to hang the expansion rate on. It is better to measure H 0 at z < 1.