Largest Ever Map Could Change What We Know About the Universe's Fate

The largest-ever three-dimensional map of the cosmos, plotting out some 15 million celestial objects, could help reveal the ultimate fate of the universe.

Astrophysicists know that the universe is expanding at an accelerated rate—and have proposed a hidden phenomenon dubbed "dark energy" to explain this.

Exactly how the universe continues to expand will affect how it ends, whether the universe undergoes heat death, is ripped apart, or even collapses back into a "big crunch."

Dark energy has long been thought to be fixed: a "cosmological constant." In fact, this is a tenet of our standard model of the universe, "Lambda CDM".

However, observations by the Dark Energy Spectroscopic Instrument (DESI) at the Kitt Peak National Observatory in Arizona are increasingly hinting that dark energy may in fact be weakening over time, suggesting we may need to change the way we think about the universe.

Such a conclusion has also been hinted at by measurements of supernovae, the cosmic microwave background and the gravitation distortion of light from distant galaxies.

At present, the evidence in favor of evolving dark energy has not met the "5 sigma" statistical threshold for a discovery—and falls around 2.8–4.2 sigma, meaning more data will be needed to either support or disprove the hypothesis.

"We're in the business of letting the universe tell us how it works, and maybe the universe is telling us it's more complicated than we thought it was," said observational cosmologist Andrei Cuceu of Berkeley Lab in a statement.

"It's interesting and gives us more confidence to see that many different lines of evidence are pointing in the same direction."

DESI—which began operating in May 2021—is presently in the penultimate year of its main survey, which will cover some 50 million galaxies and quasars (extremely bright active galactic nuclei powered by supermassive black holes) by its conclusion.

The survey is able to study the influence of dark energy by determining how matter is spread across the universe.

Astronomers use patterns in the structure of matter left over from the universe's infancy as a sort of ruler; by measuring the ruler at different distances (and therefore different points back in time), it's possible to determine how strong dark energy was at different points in time.

The new study was conducted on data from DESI's first three years of observations—covering some 15 million of the survey's best-measured targets—improving on the prior analysis, which was based only on one year of data collection.

"It's not just that the data continue to show a preference for evolving dark energy, but that the evidence is stronger now than it was," said cosmologist professor Seshadri Nadathur of the University of Portsmouth, England, who is co-chair of DESI's Galaxy and Quasar Clustering working group.

"We've also performed many additional tests compared to the first year, and they're making us confident that the results aren't driven by some unknown effect in the data that we haven't accounted for."

With their latest dark energy study complete, the DESI collaboration will continue to analyze the data collected to date and resume their five-year sky survey.

(In addition, the collaboration has also made its first 13 months of survey data publicly available—a wealth of information covering millions of celestial objects.)

"Our results are a fertile ground for our theory colleagues as they look at new and existing models—and we're excited to see what they come up with," said DESI director and physicist Michael Levi of Berkeley Lab in a statement.

He concluded: "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 humanity has ever asked."

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References

DESI Collaboration, Karim, M. A., Aguilar, J., Ahlen, S., Alam, S., Allen, L., Prieto, C. A., Alves, O., Anand, A., Andrade, U., Armengaud, E., Aviles, A., Bailey, S., Baltay, C., Bansal, P., Bault, A., Behera, J., BenZvi, S., Bianchi, D., ... Zou, H. (2025a). DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints (No. arXiv:2503.14738). arXiv. https://doi.org/10.48550/arXiv.2503.14738

DESI Collaboration, Karim, M. A., Aguilar, J., Ahlen, S., Prieto, C. A., Alves, O., Anand, A., Andrade, U., Armengaud, E., Aviles, A., Bailey, S., Bault, A., BenZvi, S., Bianchi, D., Blake, C., Brodzeller, A., Brooks, D., Buckley-Geer, E., Burtin, E., ... Zou, H. (2025b). DESI DR2 Results I: Baryon Acoustic Oscillations from the Lyman Alpha Forest (No. arXiv:2503.14739). arXiv. https://doi.org/10.48550/arXiv.2503.14739