DESI’s latest measurements suggest dark energy may be changing over time: Study

In their work, authors Swagat Saurav Mishra — who did his PhD from Inter-University Centre for Astronomy and Astrophysics, Pune and is now at School of Physics and Astronomy, University of Nottingham, UK; Prof Varun Sahni from IUCAA, William L Matthewson, Arman Shafieloo, and Yuri Shtanov present a simple explanation for why DESI’s latest measurements suggest that dark energy may be changing over time.

“DESI has been operational since 2021 and is carrying out a five-year programme to map the positions and distances of more than 40 million galaxies. Its latest results suggest that dark energy, the mysterious force driving cosmic acceleration, may not be constant after all. Instead, it could be dynamical, gradually changing with time. More specifically, DESI’s observations indicate that dark energy was increasing in density in the distant past, but around 5 billion years ago it began to decay and slowly dilute. If confirmed, this behaviour would challenge the long-standing “cosmological constant” model and open the door to entirely new physics. Although the Universe appears to be accelerating today, a decaying dark energy component would have profound implications for its future — very different from the standard scenario in which a constant dark energy density drives eternal acceleration and suppresses the formation of new cosmic structures,” Mishra said.

Its most recent Data Release (DR2), based on the first two years of observations, contains precise measurements from nearly 15 million cosmic objects, producing the most detailed 3-D map of the Universe ever created. Some of these galaxies lie over 15 billion light years away, enabling DESI to probe the expansion history deep into cosmic time. The second data release (DR2), the most precise measurement yet of cosmic expansion, points to models in which the density of dark energy gradually evolves as the Universe expands,” Prof Mishra added.

Study authors explained that these predictions will be scrutinised further by DESI’s upcoming data releases, as well as by new space missions such as Euclid and the Roman Space Telescope. If the model’s predictions continue to hold,it could provide the first observational hints that our Universe possesses more dimensions than the ones we directly perceive — a discovery with far-reaching implications for fundamental physics,” Prof Mishra also said.

Way forward

DESI has opened an exciting new window. For the first time, large-scale observations may be pointing beyond the long-standing cosmological constant. Study authors said that with another DESI data release (DR3) expected in 2026, the current evidence remains preliminary, but the implications are striking. “A time-varying dark energy component could fundamentally reshape our understanding of how the cosmos will evolve: whether expansion will continue indefinitely, slow down, or take a completely different turn. In response, a major global theoretical effort is now underway to develop physical models of dark energy that can naturally explain DESI’s hints and offer clear, testable predictions for upcoming surveys,” Prof Mishra observed