ICCUB news: Astrophysicists suggest a potential crack in the Standard Model of Cosmology

Title
Diferences in the values of the Hubble constant between early (right) and late (left) universe.
Credits
Image: NASA/JPL-Caltech/ESA/and the Planck Collaboration
Area
Cosmology

Astrophysicists point to a crack in the standard model of Cosmology. The precision of new observational results on the early and late Universe have increased and researchers suggest the requirement of new physics to fit the new data. This is the main conclusion of a study published in Nature Astronomy and signed by researchers from the University of Barcelona, the University of California (United States) and the Johns Hopkins University (Maryland, United States).

The standard cosmological model describes many observations from different periods of the Universe, from the primordial nucleosynthesis to the accelerating expansion of the present day.  However, the cosmological parameters of this model are nowadays being determined with unprecedented precision and researchers cannot guarantee the same model to fit anymore the more precise observation of the different cosmic epochs.

“As precision increases one may wonder if cracks may be appearing in the Standard Model” explains Licia Verde, ICREA researcher at the Institute of Cosmos Sciences of the University of Barcelona (ICCUB). “Discrepancies developing between observations at early and late cosmological time, if they persist, may require an expansion of the standard model, and may lead to the discovery of new physics” adds Verde.

There is increasing evidence for these discrepancies, primarily in the value of the Hubble constant. In a science meeting in July, researchers presented the different observational results of this parameter –obtained via two techniques: cepheids, strong lensing time delays, top of the red giant branch, megamasers, oxygen-rich Mira and surface brightness fluctuations (SBF) resulting in a set of six new ones in the last several months. In the published by Nature Astronomy, the astrophysicists present a summary of such data to show that, by combining three independent approaches to measure the Hubble constant (H0) in the late universe yields substantial differences with the early Universe values (between 4.0 σ and 5.8 σ), when the universe was 1,100 times smaller than now, that is, before the matter recombination and after the microwave cosmic background, when the universe was half its size today.

“This controversy began in 2013 but almost nobody paid attention to it. Now we are in the "magic" 5 σ of difference so now researchers are in a panic state. On the other hand, this shows that the discrepancy does not appear to be dependent on the use of any one method, team, or source. Therefore, theoretical ideas to explain the discrepancy focused on new physics in the decade of expansion preceding recombination could be the most plausible” concludes Licia Verde.

Article reference:
L. Verde, T. Treu, A. G. Riess. “Tensions between the Early and the Late Universe”. Nature Astronomy, September 2019. Doi: 10.1038/s41550-019-0902-0

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