Abstract
The distance ladder using supernovae yields higher values of the Hubble constant than those inferred from measurements of the cosmic microwave background (CMB) and galaxy surveys, a discrepancy that has come to be known as the “Hubble tension”. This has motivated the exploration of extensions to the standard cosmological model in which higher values of can be obtained from CMB measurements and galaxy surveys. The trouble, however, goes beyond ; such modifications affect other quantities, too. In particular, their effects on cosmic times are usually neglected. We explore here the implications that measurements of the age of the Universe, such as a recent inference from the age of the oldest globular clusters, can have for potential solutions to the tension. The value of inferred from the CMB and galaxy surveys is related to the sound horizon at CMB decoupling (or at radiation drag), but it is also related to the matter density and to . Given this observation, we show how model-independent measurements may support or disfavor proposed new-physics solutions to the Hubble tension. Finally, we argue that cosmological measurements today provide constraints that, within a given cosmological model, represent an overconstrained system, offering a powerful diagnostic tool of consistency. We propose the use of ternary plots to simultaneously visualize independent constraints on key quantities related to like , the sound horizon at radiation drag, and the matter density parameter. We envision that this representation will help find a solution to the trouble of and beyond .
- Received 15 February 2021
- Accepted 8 April 2021
DOI:https://doi.org/10.1103/PhysRevD.103.103533
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