Universe may have already begun slowing, new study suggests

ISTANBUL

The universe may no longer be racing apart, and cosmic expansion could already be slowing down—overturning one of modern cosmology’s most fundamental assumptions, according to a new study.

The study was published Thursday in the Monthly Notices of the Royal Astronomical Society.

“Our study shows that the universe has already entered a phase of decelerated expansion at the present epoch and that dark energy evolves with time much more rapidly than previously thought,” said Professor Young-Wook Lee of Yonsei University in South Korea, who led the research.

“If these results are confirmed, it would mark a major paradigm shift in cosmology since the discovery of dark energy 27 years ago,” he added.

For nearly three decades, scientists have believed the universe’s expansion was accelerating due to dark energy—a mysterious force that earned the 2011 Nobel Prize in Physics. But Lee’s team found no convincing evidence of continued acceleration.

By analyzing data from 300 galaxies, the researchers discovered that the supernovae used to measure cosmic distances—once thought to be reliable “standard candles”—actually vary in brightness depending on the age of their host stars.

After correcting for the bias, the data no longer supported the standard cosmological model (ΛCDM) but rather matched findings from the Dark Energy Spectroscopic Instrument (DESI) project, which indicate dark energy is weakening over time.

“In the DESI project, results showed the universe would decelerate in the future,” Lee said. “By contrast, our analysis shows it has already entered a decelerating phase today.”

The team plans further tests using upcoming data from the Vera C. Rubin Observatory in Chile, which will identify tens of thousands of new supernovae in the next few years.

As research co-lead Chul Chung put it, “Precise age measurements will allow for a far more robust and definitive test of supernova cosmology.”

If confirmed, the findings could force scientists to rewrite what they know about dark energy—and the ultimate fate of the universe itself.