New data hints dark energy in the universe is evolving
On March 19, 2025, scientists published the results of a new analysis using the Dark Energy Spectroscopic Instrument (DESI), mounted on the Nicholas U. Mayall 4-meter Telescope at Kitt Peak National Observatory in Arizona. With the first three years of data involving some 15 million galaxies and quasars, they’ve found hints that dark energy changes over time. Dark energy, which makes up some 70% of the universe, is a mysterious force that drives the accelerating expansion of our universe.
DESI helped create the largest yet 3D map of our universe. With this map, scientists could see how dark energy has influenced our universe over the past 11 billion years. And what they found was that this influence has not been a cosmological constant, but it has changed over time.
The DESI collaboration published their peer-reviewed findings on March 19, 2025, in multiple papers that you can read on the DESI collaboration website. The scientists also presented their findings at the American Physical Society’s Global Physics Summit in Anaheim, California.
Dark energy may be weakening over time
The findings draw upon the data from DESI and also earlier studies of the cosmic microwave background, supernovas and weak lensing. The press release said:
Taken alone, DESI’s data are consistent with our standard model of the universe: Lambda CDM, where CDM is cold dark matter and lambda represents the simplest case of dark energy, where it acts as a cosmological constant. However, when paired with other measurements, there are mounting indications that the impact of dark energy may be weakening over time and that other models may be a better fit.
In order for scientists to declare a discovery, their findings should reach a 5-sigma level. This is the gold standard for the threshold of discovery. At the moment, the analysis of the new data is around 2.8 to 4.2 sigma.
An animation of the largest 3D map of our universe. It traces the location of matter, with Earth at the center and the darker blues denoting the most distant objects. Animation via DESI Collaboration/ DOE/ KPNO/ NOIRLab/ NSF/ AURA/ R. Proctor.
DESI data available to the public
DESI can look at 5,000 galaxies at one time. And it tracks the influence of dark energy by noting where matter exists across our universe. There are patterns left behind from the early universe known as Baryon Acoustic Oscillations (BAO). The pattern in these oscillations provide scientists with a ruler. And the ruler allows scientists to measure the peaks in the oscillating waves and how much they get stretched over time.
Michael Levi, DESI director and a scientist at Berkeley Lab, said:
Whatever the nature of dark energy is, it will shape the future of our universe. It’s pretty remarkable that we can look up at the sky with our telescopes and try to answer one of the biggest questions that humanity has ever asked.
The dataset is now available to astronomers and the public alike. This wealth of data has information on 18.7 million objects. That’s about 4 million stars, 13.1 million galaxies and 1.6 million quasars. Eventually, DESI will provide us with precise distances to millions of galaxies.
Chris Davis, NSF program director for NSF NOIRLab, said:
These are remarkable results from an incredibly successful project. The potent combination of the National Science Foundation’s Mayall Telescope and Department of Engery’s Dark Energy Spectroscopic Instrument shows the benefits of federal agencies working together on fundamental science that improves our understanding of the universe.
Bottom line: A new data release from the Dark Energy Spectroscopic Instrument hints that the universe’s dark energy is not constant and may be weakening over time.
Source: Dark Energy Survey: implications for cosmological expansion models from the final DES Baryon Acoustic Oscillation and Supernova data
Via NOIRLab