Watch this pace

In 1998, three American astrophysicists shocked the astrophysics community by announcing that the universe was expanding at a faster rate every instant. Till then, astronomers had thought the universe would expand at an increasingly slower rate because gravity would keep pulling the galaxies back. It took the astronomy community a while to accept the findings. The three astronomers — Saul Perlmutter, Adam Riess and Brian Schmidt — got the Nobel Prize in 2011 as several independent methods seemed to confirm their finding. Astronomers turned their focus on the precise cause of this expansion. Then, some scientists began to question the current cosmological model.

In a series of recent papers, scientists have affirmed or questioned the acceleration of the universe. The first hint came from observations by the Dark Energy Spectroscopic Instrument (DESI) in April 2024. This multinational collaboration, which measured the velocities of several million galaxies over time, found a small deviation from predictions of the prevailing cosmological model. The first set of DESI results had evoked some disbelief in the community as it hinted that dark energy was slowly decaying. The next set of results, announced in October 2025, came with a stronger degree of confidence. It was still not good enough, but surprises came from other quarters as well.