For nearly 30 years, scientists have believed that the universe is expanding at an accelerating pace, heading towards a cold, desolate end. However, a new study from researchers at Yonsei University in South Korea challenges this long-held assumption, suggesting that we may have misinterpreted the cosmic speed at which the universe expands. Their research posits that instead of continuously accelerating, the universe might actually be in a phase of decelerating expansion, possibly heading towards a gravitational collapse known as the ‘Big Crunch.’
Professor Young-Wook Lee, the lead author of the study, stated that their findings indicate the universe has already started to slow down. “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,” he explained. If validated, these results could lead to a significant shift in cosmological understanding, marking a major development since dark energy was first identified 27 years ago.
Since 1998, astronomers have used Type Ia supernovae-bright, exploding stars believed to have consistent brightness-to measure cosmic distances. These supernovae have been referred to as “standard candles.” A dimmer appearance indicated a greater distance, suggesting faster expansion fueled by dark energy. However, the Yonsei team identified a flaw in this method.
Upon studying 300 host galaxies, the researchers discovered that the brightness of a supernova is actually related to the age of its progenitor stars. Their findings revealed that older stars tend to produce brighter explosions, while younger stars emit fainter ones. This implies that the dimness seen in distant supernovae may not solely be due to the universe’s acceleration, but rather the age of the stars themselves, suggesting the standards for measuring cosmic distances change over time.
“This new analysis, based on a considerably larger sample size of 300 galaxies, confirms this effect with extremely high statistical significance (99.999 percent confidence), indicating that the fading of distant supernovae stems from both cosmological and stellar factors,” the researchers noted.
The traditional “Standard Model” of cosmology presumed dark energy to be a constant force. Yet, once adjusted for age bias, the data shows otherwise. The new evidence indicates that dark energy may not be a constant pressure. Instead, it seems to diminish over time. This updated view corroborates measurements of the Cosmic Microwave Background-the remnant glow from the Big Bang-and Baryonic Acoustic Oscillations, ancient sound waves preserved in space. By combining various cosmic data sources, the research challenges the long-accepted “cosmological constant” theory, positing that the universe’s expansion mechanism is losing momentum.
“Our analysis, which includes correct age-bias considerations, shows that the universe has already entered a decelerating phase today. Remarkably, this aligns with predictions derived from BAO-only or BAO-CMB analyses, although this aspect has been largely overlooked,” Lee added.
To further investigate their findings, the Yonsei team is conducting an “evolution-free test,” isolating supernovae from galaxies of similar ages. The conclusive evidence may soon come from the Vera C. Rubin Observatory in Chile, where the world’s most powerful digital camera is expected to uncover 20,000 new supernova hosts over the next five years. The study has been published in the Monthly Notices of the Royal Astronomical Society.
Original Source: https://interestingengineering.com/space/universe-expansion-slowing-down
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Publish Date: 2025-12-29 13:59:00
