An anonymous reader shared this report from CNN:
The universe’s expansion might not be accelerating but slowing down, a new study suggests. If confirmed, the finding would upend decades of established astronomical assumptions and rewrite our understanding of dark energy, the elusive force that counters the inward pull of gravity in our universe…
Last year, a consortium of hundreds of researchers using data from the Dark Energy Spectroscopic Instrument (DESI) in Arizona, developed the largest ever 3D map of the universe. The observations hinted at the fact that dark energy may be weakening over time, indicating that the universe’s rate of expansion could eventually slow. Now, a study published November 6 in the journal Monthly Notices of the Royal Astronomical Society provides further evidence that dark energy might not be pushing on the universe with the same strength it used to. The DESI project’s findings last year represented “a major, major paradigm change … and our result, in some sense, agrees well with that,” said Young-Wook Lee, a professor of astrophysics at Yonsei University in South Korea and lead researcher for the new study….
To reach their conclusions, the researchers analyzed a sample of 300 galaxies containing Type 1a supernovas and posited that the dimming of distant exploding stars was not only due to their moving farther away from Earth, but also due to the progenitor star’s age… [Study coauthor Junhyuk Son, a doctoral candidate of astronomy at Yonsei University, said] “we found that their luminosity actually depends on the age of the stars that produce them — younger progenitors yield slightly dimmer supernovae, while older ones are brighter.” Son said the team has a high statistical confidence — 99.99% — about this age-brightness relation, allowing them to use Type 1a supernovas more accurately than before to assess the universe’s expansion… Eventually, if the expansion continues to slow down, the universe could begin to contract, ending in what astronomers imagine may be the opposite of the big bang — the big crunch. “That is certainly a possibility,” Lee said. “Even two years ago, the Big Crunch was out of the question. But we need more work to see whether it could actually happen.”
The new research proposes a radical revision of accepted knowledge, so, understandably, it is being met with skepticism. “This study rests on a flawed premise,” Adam Riess, a professor of physics and astronomy at the Johns Hopkins University and one of the recipients of the 2011 Nobel Prize in physics, said in an email. “It suggests supernovae have aged with the Universe, yet observations show the opposite — today’s supernovae occur where young stars form. The same idea was proposed years ago and refuted then, and there appears to be nothing new in this version.” Lee, however, said Riess’ claim is incorrect. “Even in the present-day Universe, Type Ia supernovae are found just as frequently in old, quiescent elliptical galaxies as in young, star-forming ones — which clearly shows that this comment is mistaken. The so-called paper that ‘refuted’ our earlier result relied on deeply flawed data with enormous uncertainties,” he said, adding that the age-brightness correlation has been independently confirmed by two separate teams in the United States and China… “Extraordinary claims require extraordinary evidence,” Dragan Huterer, a professor of physics at the University of Michigan in Ann Arbor, said in an email, noting that he does not feel the new research “rises to the threshold to overturn the currently favored model….”
The new Vera C. Rubin Observatory, which started operating this year, is set to help settle the debate with the early 2026 launch of the Legacy Survey of Space and Time, an ultrawide and ultra-high-definition time-lapse record of the universe made by scanning the entire sky every few nights over 10 years to capture a compilation of asteroids and comets, exploding stars, and distant galaxies as they change.