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An international team of researchers has challenged a study published last year that claimed the expansion of the universe may be slowing, saying the standard model of an accelerating universe remains robust.
The new study, published in Monthly Notices of the Royal Astronomical Society, argues that the earlier findings resulted from problems in the analysis rather than evidence that the prevailing understanding of the universe had broken down.
The research team includes Nobel laureates Adam Riess and Brian Schmidt, who shared the 2011 Nobel Prize in Physics for work showing that the expansion of the universe is accelerating.
The latest analysis responds to a South Korean study that suggested dark energy—the mysterious force thought to drive the accelerated expansion of the universe—could be weakening over time.
Lead author Dr Phil Wiseman of the University of Southampton said previous measurements supporting cosmic acceleration remain valid.
“Our current understanding of the fate of the universe remains robust,” Wiseman said, adding that the findings allow scientists to focus again on understanding the nature of dark energy rather than questioning its existence.
The original evidence for accelerating expansion came from observations of Type Ia supernovae, extremely bright stellar explosions that serve as important cosmic distance markers. Astronomers found that distant supernovae indicated that the universe was expanding at an accelerating rate.
The South Korean study challenged this interpretation by suggesting that Type Ia supernovae may not have had identical peak brightness throughout cosmic history. If true, this could have affected estimates of cosmic expansion.
However, the new research identified problems with the earlier analysis, particularly its treatment of the ages of exploding stars. The researchers said it had effectively treated the age of a galaxy as equivalent to the age of the individual star that eventually exploded.
They also said the earlier study did not adequately account for the mass of the galaxies hosting the supernovae, an important factor in modern cosmological analyses.
Professor Riess said that after accounting for differences in host galaxies and stellar populations, evidence for accelerating expansion remained strong.
The researchers stressed that the debate was nevertheless valuable, prompting closer examination of supernova explosions and ways to improve measurements of dark energy.
Professor Mark Sullivan of Southampton said challenging established ideas was an essential part of scientific progress, while co-author Dr Brodie Popovic said the controversy had created an opportunity to reassess assumptions underlying cosmological measurements.