English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The Hubble tension has now grown to a level of significance which can nolonger be ignored and calls for a solution which, despite a huge number ofattempts, has so far eluded us. Significant efforts in the literature havefocused on early-time modifications of $\Lambda$CDM, introducing new physicsoperating prior to recombination and reducing the sound horizon. In thisopinion paper I argue that early-time new physics alone will always fall shortof fully solving the Hubble tension. I base my arguments on seven independenthints, related to 1) the ages of the oldest astrophysical objects, 2)considerations on the sound horizon-Hubble constant degeneracy directions incosmological data, 3) the important role of cosmic chronometers, 4) a number of``descending trends'' observed in a wide variety of low-redshift datasets, 5)the early integrated Sachs-Wolfe effect as an early-time consistency test of$\Lambda$CDM, 6) early-Universe physics insensitive and uncalibrated cosmicstandard constraints on the matter density, and finally 7) equalitywavenumber-based constraints on the Hubble constant from galaxy power spectrummeasurements. I argue that a promising way forward should ultimately involve acombination of early- and late-time (but non-local -- in a cosmological sense,i.e. at high redshift) new physics, as well as local (i.e. at $z \sim 0$) newphysics, and I conclude by providing reflections with regards to potentiallyinteresting models which may also help with the $S_8$ tension.

Seven hints that early-time new physics alone is not sufficient to solve the Hubble tension