The expansion of our universe may be slowing down. What does this mean for dark energy?

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As if dark energy wasn’t mysterious and confusing enough, new research suggests that this unknown force may no longer be tearing galaxies apart at an ever-increasing rate.

This remarkable result comes from research that shows that the expansion of the Universe has already begun to slow down, contrary to the current belief that dark energy is still accelerating the expansion of space. The discovery also ties in with results from last year’s Dark Energy Spectroscopy Instrument (DESI). showed that dark energy is weakening.

In addition to changing our understanding of the universe as it is today, this research could offer clues about how our cosmos will end up. If dark energy has already lost its battle with gravity, the next step after the deceleration of cosmic expansion could be the contraction of space, which could mean the end of the universe Big Crunch scenario similar to the Big Bang played in reverse.

Researchers of the discovery are already hailing it as a potential paradigm shift in how we think about the very nature of the universe. “Our study shows that the Universe has already entered a decelerated expansion phase in the current epoch, and that dark energy is evolving over time much faster than previously thought,” team leader and researcher Young-Wook Lee of Yonsei University in South Korea said in a statement. “If confirmed, these results would represent a major paradigm shift in cosmology since the discovery of dark energy 27 years ago.

Dark energy is evolving

The existence of dark energy was first proposed in 1998 when two separate teams of astronomers observed a distant Type Ia supernovaealso called “standard candles” because their uniform light can be used to measure cosmic distances. This revealed that the further away the galaxy was, the faster it was moving away. This was shown to two teams in 2011. who received the Nobel Prize in Physics for the discovery that the rate of expansion of the universe is increasing. Dark energy has been introduced as a placeholder force to explain this accelerating expansion.

Over the next three decades, although scientists could not definitively determine what dark energy was, they determined that this force was dominant, accounting for approximately 68% of the total energy and matter budget of the Universe. The researchers also found that dark energy wasn’t always dominant — it seemed to take control and accelerate the expansion of the universe around 5 billion years ago, or about 9 billion years after the Big Bang.

The first indication that dark energy may not be as dominant as previously thought came from DESI’s first results in 2024. in the spring This new chink in the dark energy armor comes after Lee and colleagues at Yonsei University discovered that a Type Ia supernova might not be so standard. This is because their brightness can be strongly affected by the age of the progenitor stars of these explosive events. In fact, this team found that, even after standardizing the light from Type Ia supernovae, Type Ia supernovae from younger stellar populations were fainter than those from older stellar populations.

Using a sample of 300 galaxies, the study found that the dimming of distant Type Ia supernovae can be 99.99 percent. Correcting for bias, the team found that their results reject the currently favored model of cosmic evolution, the Standard Model of cosmology, or the Lambda Cold Dark Matter (LCDM) model and its dark energy recipe.

However, the main result of this study is that the Universe is not expanding rapidly, but has already entered a state of deceleration. This is even more so than DESI’s hints at the weakening of dark energy.

“The main results of the DESI project were to combine uncorrected supernova data with measurements of baryonic acoustic oscillations, suggesting that even though the Universe will slow down in the future, it is still accelerating,” explained Lee. “In contrast, our age-bias-corrected analysis suggests that the universe today has already entered a deceleration phase.

The team’s next step will be to confirm these results in a “no-evolution test” using only young Type Ia supernovae from young galaxies at various distances. The Vera C. Rubin Observatory, which has just begun observing space with the world’s largest digital camera from its site on Cerro Pachón in Chile, is poised to play a major role in this research.

“With the Vera C. Rubin Observatory discovering more than 20,000 new supernova host galaxies over the next five years, precise age measurements will provide a much more reliable and precise test of supernova cosmology,” said Chul Chung, a team member and researcher at Yonsei University.

The team’s research was published Wednesday (November 5) in the journal Monthly Notices of the Royal Astronomical Society.