Dark energy, the mysterious force driving the expansion of the universe, appears to be weakening, according to research that could fundamentally change the current scientific understanding of the fate of the cosmos.

If confirmed, the results from a team using the Dark Energy Spectroscopic Investigation Instrument (DESI) at the Kitt Peak National Observatory in Arizona, USA, could have broad implications for theories about the evolution of the universe.

They raise the possibility that the current expansion of the universe could reverse into a process known as the Big Contraction.

"What we're discovering is incredibly intriguing. It's exciting to think that we could be on the verge of a major discovery about dark energy and the fundamental nature of our universe," said Professor Alexie Leauthaud-Harnett, a spokesperson for the DESI team and a cosmologist at the University of California, Santa Cruz.

Dark energy was first discovered in the late 1990s, when astronomers studied distant supernova explosions to investigate how the expansion rate of the universe changed over time.

Gravity was expected to slow down the expansion that has occurred since the Big Bang, but instead, data showed that the universe is actually expanding faster, meaning it is being driven by an unknown force called dark energy.

It has until now been considered constant, meaning the universe would end in a scenario known as the Big Freeze, when galaxies would drift so far apart that even light would no longer be able to cross the gap. The new data, presented at the Global Physics Summit, calls this theory into question.

The DESI instrument, which uses 5000 optical fibers to map the universe with unprecedented precision, in its latest survey included 15 million galaxies, covering a period of 11 billion years of cosmological history. This data allowed scientists to create the most detailed three-dimensional map of the universe to date.

The results suggest that dark energy was strongest when the universe was about 70% of its current age, but that it has weakened by about 10% since then. In other words, the universe is still expanding at an accelerating rate, but dark energy is gradually fading away.

"What we're finding is that there really is something that's pushing galaxies apart, but this force is not constant. It's weakening," said Professor Carlos Frenk, a cosmologist at Durham University and a member of the DESI team.

The data still doesn't meet the five-sigma threshold of statistical confidence, which is the gold standard in physics for confirming discoveries. But many scientists on the DESI team have moved from initial skepticism to confidence in the accuracy of the data in recent months.

"I have no more doubts. I have studied the data in detail. This is a solid result. We are witnessing the collapse of an old paradigm and the emergence of a new one," Frenk said.

Professor John Peacock, a cosmologist at the University of Edinburgh, was sceptical last year about the theory that dark energy is changing, but now admits he has changed his mind.

"Extreme claims require extreme evidence. Almost nothing in science is certain enough to bet on, but I wouldn't mind putting £1000 on this outcome," he said.

Others, however, are more cautious. Professor George Efstathiou of the University of Cambridge, who was not involved in the research, said: "My conclusion from this analysis is that the measurements do not yet provide definitive evidence of variable dark energy. Perhaps they will when DESI collects more data."

If dark energy continues to weaken to the point where it becomes negative, the universe could end up in a reverse Big Bang, a scenario known as the Big Crunch. In that case, the expansion of the universe would not only slow down, but would begin to reverse, until it collapses in on itself, writes the Guardian, reports KosovaPress.

Scientists still don't know why dark energy is weakening. It is generally estimated to make up about 70% of the universe, with the rest being dark matter and ordinary matter. It is possible that this discovery points to fundamental changes in the laws of physics or suggests that a key piece of the puzzle is still missing from our understanding of the universe.