Our universe might have an expiry date and it's sooner than we thought

Time of India

27-07-2025

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The universe may not be heading for an eternal stretch into emptiness, as once assumed. According to new findings from two of the largest astronomical surveys — the Dark Energy Survey (DES) and the Dark Energy Spectroscopic Instrument (DESI) — the mysterious force known as dark energy could be changing.That shift, if real, has serious consequences. Instead of expanding forever, the universe might one day contract. Scientists now believe a complete reversal could start within 10 billion years, ending in a collapse known as the Big Crunch These conclusions come from a new theoretical study, currently in preprint and awaiting peer review, that presents a bold reinterpretation of how cosmic forces work.For years, physicists assumed dark energy was steady and uniform, based on a simple number called the cosmological constant in Einstein's general relativity. But the latest analysis challenges that view.The study, reported by Space.com, introduces two components behind dark energy: the cosmological constant and a particle known as the axion. Axions are hypothetical ultralight particles that rarely interact with matter. Yet, they could fill the universe and account for much of its current accelerated expansion.The cosmological constant, by contrast, is a fixed energy value in empty space. But in this model, it's not positive. It's negative.The team behind the research explained their reasoning clearly. 'We are living in a temporary period of accelerated expansion,' they wrote. 'It is heavily driven by the axion field.'Right now, axions are doing most of the work in keeping the universe expanding. But over time, these particles are expected to lose their influence. Once they fade, the negative cosmological constant will begin to dominate. This shift would decelerate the universe's expansion.Eventually, expansion could not only stop but reverse.What happens next? According to the model, gravity would begin to pull everything back in. Galaxies would start to draw closer, merge, and collapse into each other. Temperatures would rise. Space would grow smaller, hotter, and denser.In the final act, all matter and energy would compress into a single point — a singularity.This collapse, termed the Big Crunch, is effectively the reverse of the Big Bang The study predicts the beginning of this reversal could occur in 10 billion years. The contraction would then take another 10 billion years to complete. The full lifespan of the universe, under this model, would be about 33.3 billion years.We're already 13.8 billion years into that timeline.The DES and DESI surveys have mapped millions of galaxies to measure how the universe expands over time. These surveys are central to modern cosmology, offering one of the most detailed views of the universe's large-scale structure.Until recently, all observations supported the idea that dark energy was constant. But the new data show signs that it might be evolving.This insight gave rise to the axion-dark energy model, or aDE, a theoretical framework that incorporates both axions and a changing cosmological constant.As explained by Space.com, 'One of the most striking findings in the new study is the possibility that the cosmological constant — which reflects the energy density of space itself — may be negative.'The study's authors are careful not to overstate their findings. The model, while compelling, is still under review and not confirmed.'These are preliminary findings,' the researchers acknowledged. They stress that deeper space surveys and next-generation telescopes will be crucial for testing whether dark energy really does evolve with time.Still, the idea is already sparking serious debate among physicists. If it holds, it would force scientists to rethink the universe's timeline — and its ending.Some theories go further. They suggest the Big Crunch might not be the absolute end.Instead, that final singularity could trigger another Big Bang. A fresh cycle. A new universe. Though these ideas remain speculative, they reflect just how much we still don't understand about the nature of reality.For now, the only certainty is that the universe might be less predictable than once believed. As astronomers dig deeper into the skies, the answers we get may continue to surprise us.