When data lead the way to unveiling dark energy

A slice through the 3D map of galaxies from the first few months of the Dark Energy Spectroscopic Instrument (DESI). The Earth is at the center, with the furthest galaxies plotted at distances of 10 billion light years. Each point represents one galaxy, and the color scheme has been created to simplify visualization. This version of the DESI map shows a subset of 400,000 of the 35 million galaxies that will be in the final map. Credit: D. Schlegel/Berkeley Lab using data from DESI, Acknowledgment: M. Zamani (NSF’s NOIRLab)

Understanding whether dark energy evolves over time is one of the key challenges in today's cosmology. Dark energy is an obscure ingredient of our universe, filling ~70% of its energy budget, that drives the current accelerated expansion universe. In its commonly accepted description it is described by a cosmological constant (constant over time). However, recent data from the Dark Energy Spectroscopic Instrument (DESI) clearly suggest a preference in the data for a time evolving Dark Energy component, in contrast with the simple cosmological constant model. In this recent paper, which attracted the attention of the scientific community and has been selected as "Editor's suggestion" by Physical Review D, a group of researchers, including Emilio Bellini currently SMASH fellow at the University of Nova Gorica, reanalyse public DESI data in a model independent way, letting the data speak for themselves. Model-independent reconstruction methods offer a way to allow observations to directly guide the evolution of the Dark Energy density, without imposing our favourite cosmological model on them. This approach opens a path to testing the nature of Dark Energy with minimal theoretical assumptions. Their agnostic reconstruction finds a significant deviation from a cosmological constant, that confirms in a more robust way the deviations found with standard model-dependent strategies. The analysis reveals hints of complex evolution over cosmic history, with a density of Dark Energy that increases as the universe expands. If confirmed by future data, this trend disfavours the cosmological constant model, as well as other simple theories without exotic gravitational interactions. A revision of Einstein’s General Relativity on cosmological scales may then become necessary.

More on SMASH:

SMASH is a multidisciplinary programme, financed by the European Commission through the Horizon Europe programme, Marie Skłodowska-Curie COFUND action, and it connects researchers from five excellent research institutions in Slovenia, 25 associated partners, Slovene companies and research institutions all over the world.

The aim of the SMASH network is the research in which the use of the artificial intelligence and machine learning methods create new approaches in contemporary science, with a special emphasis on data science, environmental science, personalised medicine, fundamental physics (particle physics, astrophysics, cosmology) and linguistics.

Links:
https://journals.aps.org/prd/abstract/10.1103/dj3k-84v4
SMASH: https://smash.ung.si/