Study reaffirms universe’s expansion is accelerating

The expansion of the universe is still accelerating, according to a new study that rebuts claims made late last year suggesting the cosmos had entered a phase of deceleration. The paper, published on June 11 in the Monthly Notices of the Royal Astronomical Society, was led by the University of Southampton and includes Nobel Prize-winning astrophysicists Adam Riess and Brian Schmidt among its authors.miragenews+1

A Crisis Averted

In late 2025, a team of South Korean researchers from Yonsei University published findings claiming that dark energy — the mysterious force thought to drive the universe apart — was weakening over time and that the expansion of the universe was no longer accelerating. The claim, if true, would have upended nearly three decades of astronomical progress and undermined the Nobel Prize-winning discovery that Riess, Schmidt, and Saul Perlmutter made in the late 1990s.eurekalert+3

The new study, titled "Still Accelerating: Type Ia supernova cosmology is robust to host galaxy age evolution," re-evaluated the data and found the universe is behaving exactly as expected. Lead author Phil Wiseman of the University of Southampton said the debate was the result of a scientific misunderstanding. "The previous and well accepted measurements were, in fact, fine and our current understanding of the fate of the universe remains robust," Wiseman said. "By proving our measurements are correct, we can get back to trying to understand what dark energy actually is, rather than wondering if it exists at all."miragenews+1

Where the Error Lay

The 2025 study had argued that Type Ia supernovae — luminous white dwarf star explosions used to measure cosmic distances — had different maximum brightnesses as the universe aged, creating the illusion of acceleration. The Southampton-led team found the error lay in how the age of these stars was estimated. The earlier paper incorrectly assumed the age of a host galaxy was the same as the age of the star that exploded and failed to account for the mass of host galaxies, a standard correction in modern cosmology.eurekalert+1

Riess said: "Extraordinary claims require especially careful testing. What we find is that when we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent."eurekalert

The Mystery Remains

While the study confirms that dark energy continues to drive cosmic acceleration, the deeper question of what dark energy actually is remains unanswered. Mark Sullivan, also from the University of Southampton, said the episode was still productive: "Although this idea did not turn out correct, it has opened up new ways of thinking about how supernovae explode and how we can measure dark energy more accurately."eurekalert