Imagine inflating a balloon. At first, it expands slowly; then someone gives a sharp blast of air, and it swells faster. But as the airflow weakens, the balloon's growth slows again. According to a new study, the Universe has behaved much the same way: after the Big Bang, it expanded, then suddenly accelerated, and now that acceleration is fading.
The authors started with spacetime curvature gravity, but instead of the usual geometry, they used a slightly different mathematical framework, so-called $f(T)$ gravity. Into this, they added dark energy (the mysterious force pushing galaxies apart) with properties that evolve over time. Using data on how galaxies aged at different cosmic epochs and on supernova explosions, they pinned down the model's parameters. It turned out that acceleration wasn't eternal: it peaked and is now declining.
This scenario matches what we observe today: dark energy behaves like 'quintessence'—something between a constant force and a vanishing one. The model passed thermodynamic checks and gave a Universe age of about 13.8 billion years — close to astronomers' estimates.
If acceleration continued forever, distant galaxies would eventually vanish beyond the cosmic horizon, making the Universe seem empty. In this model, they might stay visible.
In Isaac Asimov's 'The Last Question,' humanity watches the Universe expand and then contract — here, we see acceleration give way to deceleration without a collapse.