A buyer’s guide to the Hubble constant

Abstract

Since the expansion of the universe was first established by Edwin Hubble and Georges Lemaître about a century ago, the Hubble constant $$H_0$$ H 0 which measures its rate has been of great interest to astronomers. Besides being interesting in its own right, few properties of the universe can be deduced without it. In the last decade, a significant gap has emerged between different methods of measuring it, some anchored in the nearby universe, others at cosmological distances. The SH0ES team has found $$H_0 = 73.2 \pm 1.3 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 73.2 ± 1.3 kms - 1 Mpc - 1 locally, whereas the value found for the early universe by the Planck Collaboration is $$H_0 = 67.4 \pm 0.5 \; \;\,\hbox {kms}^{-1} \,\hbox {Mpc}^{-1}$$ H 0 = 67.4 ± 0.5 kms - 1 Mpc - 1 from measurements of the cosmic microwave background. Is this gap a sign that the well-established $${\varLambda} {\text{CDM}}$$ Λ CDM cosmological model is somehow incomplete? Or are there unknown systematics? And more practically, how should humble astronomers pick between competing claims if they need to assume a value for a certain purpose? In this article, we review results and what changes to the cosmological model could be needed to accommodate them all. For astronomers in a hurry, we provide a buyer’s guide to the results, and make recommendations.

Cosmological direct detection of dark energy: non-linear structure formation signatures of dark energy scattering with visible matter

“…One important example, covered in a large and growing body of literature, is that of so-called coupled DE models, which involve non-gravitational interactions between DM and DE (Wang et al 2016). 2 From the observational perspective instead, mismatches between independent measurements of the Hubble constant H 0 (the "Hubble tension", see Verde et al 2019;Di Valentino et al 2021a,c;Perivolaropoulos & Skara 2021;Shah et al 2021) might be pointing towards a more complex DE sector, potentially featuring non-trivial DE dynamics both at late (Poulin et al 2018;Banihashemi et al 2020;Guo et al 2019;Vagnozzi 2020;Pan et al 2020a;Akarsu et al 2020;Yang et al 2020b;Alestas et al 2020;Marra & Perivolaropoulos 2021;Vagnozzi et al 2021a) and especially early times (Bernal et al 2016;Mörtsell & Dhawan 2018;Poulin et al 2019;Knox & Millea 2020;Niedermann & Sloth 2021;Sakstein & Trodden 2020;Zumalacarregui 2020;Hill et al 2020;Vagnozzi 2021;Schöneberg et al 2021).…”

Revisiting the quasi-molecular mechanism of recombination

“…Solà Peracaula et al 2019;Raveri 2020;Yan et al 2020;Solà Peracaula et al 2020), primordial magnetic fields (Jedamzik & Pogosian 2020), and non-standard recombination (Chiang & Slosar 2018;Liu et al 2020;Ye & Piao 2020;Sekiguchi & Takahashi 2021). See Verde et al (2019); Knox & Millea (2020); Di Valentino et al (2021); Shah et al (2021); Cai et al (2022a,b) for recent reviews.…”

Kaniadakis holographic dark energy: observational constraints and global dynamics

“…In addition, recent observations developed by the collaboration Supernova H 0 for the Equation of State (SH0ES) [7] show a discrepancy for the obtained value of H 0 when compared to Planck observations based on the Λ Cold Dark Matter (ΛCDM) model [8]. This generates a tension of 4.2σ between the mentioned experiments, bringing a new crisis and the need for new ways to tackle the problem [9], as long as this discrepancy is not related to unknown systematic errors affecting the measurements [10][11][12][13][14]. Is in this vein that the community has been proposing other alternatives to address the problem of the Universe acceleration.…”