New DESI results: Evidence mounts for evolving dark energy

(Press-News.org) A new analysis of data collected over three years by the Dark Energy Spectroscopic Instrument (DESI) collaboration provides even stronger evidence than the group’s previous datasets that dark energy, long thought to be a “cosmological constant,” might be evolving over time in unexpected ways.

Dr. Mustapha Ishak-Boushaki, professor of physics at The University of Texas at Dallas, is co-chair of the DESI working group that interprets cosmological survey data gathered by the international collaboration, which includes more than 900 researchers from over 70 institutions around the world. In April 2024 at a meeting of the American Physical Society, Ishak-Boushaki represented the collaboration in presenting analyses of its first year of data, which revealed the first hints that dark energy might be evolving over time.

Although it is not well understood, dark energy is thought by many scientists to play a key role in the observed accelerated expansion of the universe. 

The new DESI data analysis, paired with other measurements, contributes to mounting indications that the impact of dark energy may be weakening over time — and that the standard model of how the universe works might need to be updated.

Those other measurements include the light left over from the dawn of the universe (the cosmic microwave background, or CMB), exploding stars (supernovae), and how light from distant galaxies is warped by gravity (weak gravitational lensing).

The collaboration shared its findings March 19 in multiple papers posted on the online repository arXiv and in a presentation at the American Physical Society’s Global Physics Summit in Anaheim, California.

Researchers said that so far, the preference for an evolving dark energy has not yet risen to a statistical significance of 5 sigma, the gold standard in physics that represents the threshold for a discovery. However, different combinations of DESI data mixed with the CMB, supernovae and weak lensing measurements set the range from 2.8 sigma to 4.2 sigma.

“With a 4.2 sigma significance, I think we are getting to the point of no return,” Ishak-Boushaki said. “In this new analysis, not only have we confirmed our previous findings that dark energy is likely evolving over time, but we are increasing their significance. The point that I find the most exciting is that the evidence is coming from different datasets.

“I’ve worked on the question of cosmic acceleration for 25 years, and my perspective is, if the evidence continues to grow, and it is likely to, then this will be huge for cosmology and all of physics.”

DESI is one of the most extensive surveys of the cosmos ever conducted. The state-of-the-art instrument can capture light from 5,000 galaxies simultaneously. The experiment is now in its fourth year surveying the sky and aims to measure roughly 50 million galaxies and quasars by the time the project ends.

The new analysis uses data from the first three years of observations of nearly 15 million galaxies and quasars.

DESI was constructed and is operated with funding from the Department of Energy (DOE) Office of Science and sits atop the National Science Foundation’s (NSF) Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory, which is operated by the NSF’s NOIRLab. The DOE’s Lawrence Berkeley National Laboratory manages the DESI experiment.

DESI also is supported by the National Energy Research Scientific Computing Center, a DOE Office of Science national user facility. Additional support for DESI is provided by the NSF; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Alternative Energies and Atomic Energy Commission; the National Council of Humanities, Sciences, and Technologies of Mexico; the Ministry of Science and Innovation of Spain; and DESI member institutions.

The DESI collaboration is honored to be permitted to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain with particular significance to the Tohono O’odham Nation.

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