In 2025, Yonsei University’s Professor Young-Wook Lee and colleagues shocked the space community with claims that the evidence of dark energy was weakening such that the expansion is no longer accelerating.

They suggested the methods used to measure the Universe’s expansion using supernovae were fundamentally flawed.
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“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.”

To measure the Universe, the authors looked closely at Type Ia supernovae to calculate vast cosmic distances.

The 2025 study had claimed that, as the Universe aged, these supernovae had different maximum brightnesses, tricking astronomers into thinking the cosmos was accelerating when it was slowing.

However, the new study found the error lay in how the age of these stars was estimated.

They proved that the previous findings incorrectly assumed the age of a galaxy was the same as the age of the star that exploded.

They also said the 2025 paper failed to account for the mass of host galaxies, a standard correction used in modern cosmology to prove accuracy.

“Challenging accepted theories and observations is fundamental to science,” said University of Southampton’s Professor Mark Sullivan, co-author of the study.

“This is how progress is made. 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.”