The universe could stop expanding remarkably soon, study suggests

After nearly 13.8 billion years of nonstop expansion, the universe
could soon grind to a standstill, then slowly start to contract, new
research published in the journal Proceedings of the National
Academy of Sciences suggests (https://bit.ly/39Plnl8).
In the new paper, three scientists attempt to model the nature of
dark energy - a mysterious force that seems to be causing the
universe to expand ever faster - based on past observations of
cosmic expansion. In the team's model, dark energy is not a constant
force of nature, but an entity called quintessence, which can decay
over time.
The researchers found that, even though the expansion of the universe
has been accelerating for billions of years, the repellent force of
dark energy may be weakening. According to their model, the
acceleration of the universe could rapidly end within the next
65 million years - then, within 100 million years, the universe could
stop expanding altogether, and instead it could enter an era of slow
contraction that ends billions of years from now with the death - or
perhaps the rebirth - of time and space.
And this could all happen "remarkably" quickly, said study co-author
Paul Steinhardt, Director of the Princeton Center for Theoretical
Science at Princeton University in New Jersey.
"Going back in time 65 million years, that's when the Chicxulub
asteroid hit the Earth and eliminated the dinosaurs," Steinhardt told
Live Science. "On a cosmic scale, 65 million years is remarkably
short."
Nothing about this theory is controversial or implausible, Gary
Hinshaw, a professor of physics and astronomy at the University
of British Columbia who was not involved in the study, told Live
Science. However, because the model hinges on past observations
of expansion alone - and because the present nature of dark energy
in the universe is such a mystery - the predictions in this paper are
currently impossible to test. For now, they can only remain theories.