New Analysis Confirms the Universe's Expansion Is Still Accelerating

An international team of astrophysicists, including two Nobel Prize-winning scientists, has concluded that the universe is still expanding at an accelerating rate, challenging a study published last November that argued cosmic expansion might be slowing down. The new findings, led by Dr. Phil Wiseman of the University of Southampton, were published in the journal Monthly Notices of the Royal Astronomical Society.

The debate traces back to 2011, when Adam Riess, Brian Schmidt and Saul Perlmutter won the Nobel Prize in Physics for showing, through observations of Type Ia supernovae — bright explosions of white dwarf stars — that the universe's expansion is accelerating, driven by a mysterious force called dark energy. That conclusion has remained the standard explanation ever since.

Last November, a team in South Korea argued that Type Ia supernovae may not have had the same maximum brightness throughout cosmic history, meaning astronomers could have mistaken a slowing universe for an accelerating one. Wiseman's team says that claim rested on an error: the earlier study treated the age of a galaxy as the same as the age of the star that later exploded within it, and did not apply a standard correction for the mass of the supernovae's host galaxies.

"Extraordinary claims require especially careful testing," said Riess, one of the paper's co-authors. "When we calibrate these supernovae, accounting for different host environments and populations, the evidence for cosmic acceleration remains remarkably consistent." Wiseman said the earlier measurements were fine, and that why the universe's expansion continues to accelerate remains unexplained.