For decades, astronomers have believed that the universe is not only expanding, but doing so at an ever-increasing rate.<\/p>\n
This acceleration has become one of the pillars of modern cosmology, attributed to a mysterious force known as dark energy that appeared to be pulling galaxies apart faster and faster.<\/p>\n
A new study has challenged that picture. It argues that the expansion of the universe may in fact be slowing down, not speeding up. The results, if borne out, might mean that the universe\u2019s expansion will one day halt and reverse, culminating in a cosmos-ending \u201cbig crunch\u201d.<\/p>\n
\u2022 Never mind the Big Bang, universe could end with a big crunch<\/a><\/p>\n The study focuses on \u201ctype Ia supernovae\u201d \u2014 exploding stars that have been used as cosmic mileposts. These blasts were long thought to reach the same peak brightness wherever they occurred. If that were true, their brightness when viewed from Earth would reveal how far away they are. In the 1990s, distant supernovae appeared unexpectedly faint, leading to the conclusion that the universe\u2019s expansion was accelerating.<\/p>\n The new research, from a team at Yonsei University in South Korea, asks a simple question: what if some supernovae are naturally dimmer than others?<\/p>\n The authors argue that supernovae in younger galaxies are slightly fainter than those in older ones, possibly because younger galaxies contain more light-scattering dust. This matters because observing very distant galaxies means looking back in time: their light has taken billions of years to reach us. The young, far-away supernovae used to infer acceleration may have been dimmer to begin with, not necessarily farther away.<\/p>\n When the team corrected for this \u201cage effect\u201d, the supernova data told a different story. Instead of an accelerating universe, the corrected results lined up closely with another, completely independent measure of cosmic expansion: baryonic acoustic oscillations, or BAO \u2014 vast, faint ripples in the distribution of galaxies, left behind in the immediate aftermath of the Big Bang. <\/p>\n