After nearly 13.8 billion years of nonstop expansion, the universe may soon come to a standstill, then slowly begin to contract, new research published in the journal Proceedings of the National Academy of Sciences suggests.
In the new paper, three scientists attempt to model the nature of dark energy – a mysterious force that appears to be causing the universe to expand faster than ever – based on previous observations of expansion. of the universe. In the group’s model, dark energy is not an immutable force of nature, but an entity called an elite, which can decay over time.
The researchers found that, although the expansion of the universe has been accelerating for billions of years, the repulsion of dark energy may be waning. According to their model, the universe’s acceleration could quickly 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 rebirth – of time and space.
Study co-author Paul Steinhardt, director of the Princeton Center for Theoretical Science at Princeton University in New Jersey, said all of this could happen “significantly” quickly.
Steinhardt told Live Science: “Back in time 65 million years, that’s when the asteroid Chicxulub hit Earth and eliminated the dinosaurs. “On a cosmic scale, 65 million years is remarkably short.”
Gary Hinshaw, a professor of physics and astronomy at the University of British Columbia who was not involved in the study, told Live Science that there is nothing about the theory that is controversial or implausible. However, because the model focuses only on previous observations of expansion – and because the current nature of dark energy in the universe is a mystery – the predictions in this paper are currently impossible. can be checked. For now, they can only be theories.
Energy of the void
Since the 1990s, scientists have understood that the expansion of the universe is accelerating; Intergalactic space is now expanding faster than it was billions of years ago. Scientists have named this mysterious source of accelerating dark energy – an invisible entity that seems to work in opposition to gravity, pushing the universe’s heaviest objects apart rather than pulling them. close together.
Although dark energy makes up about 70% of the total mass-energy of the universe, its properties remain a mystery. A popular theory, put forward by Albert Einstein, is that dark energy is a cosmological constant – an unchanging form of energy woven into the fabric of space-time. If that were the case, and the force exerted by dark energy could never change, then the universe would continue to expand (and accelerate) forever.
However, one competing theory holds that dark energy does not need to be stable to match observations of past cosmic expansion. Rather, dark energy might be what’s called an elite – a dynamic field that changes over time. (Steinhardt was one of three scientists who introduced the idea in a 1998 paper in the journal Physical Review Letters.)
Unlike the cosmological constant, a crystal can be either repulsive or attractive, depending on the ratio of its kinetic and potential energy at a given time. Over the past 14 billion years, the elite has been pushed back. However, for most of that time, it contributed less to the expansion of the universe than radiation and matter, Steinhardt said. That changed about 5 billion years ago when the quintessence became the dominant ingredient and its gravitational repulsion caused the expansion of the universe to accelerate.
“The question we are asking in this paper is, ‘Does this acceleration last forever? “. “And if not, what are the alternatives, and how long could things change?”
The death of dark energy
In their study, Steinhardt and his colleagues, Anna Ijjas of New York University and Cosmin Andrei of Princeton, predicted how the properties of the elite might change over the next few billion years. To do this, the team created a physical model of the quintessence, showing its overwhelming and attractive strength over time, to match previous observations of the expansion. of the universe. Once the team’s model was able to reliably reproduce the expansion history of the universe, they extended their prediction into the future.
“To their surprise, the dark energy in their model could decay over time,” Hinshaw said. “Its power can wane. And if it does so in some way, eventually the antigravity property of dark energy will disappear and it will revert back to something like ordinary matter. than.”
According to the team’s model, the dark energy’s repulsion may be in a phase of rapid decline that likely began billions of years ago.
In this scenario, the accelerated expansion of the universe today is slowing down. Before long, perhaps in about 65 million years, that acceleration could stop completely – then, within 100 million years from now, dark energy could become gravitational, causing the entire universe to become more intense. the universe began to shrink. In other words, after nearly 14 billion years of growth, space may begin to shrink.
“This is going to be a very special type of contraction that we call slow contraction,” says Steinhardt. “Instead of expanding, space shrinks very, very slowly.”
Initially, the universe’s contraction would be so slow that any hypothetical humans still alive on Earth wouldn’t even notice the change, Steinhardt said. According to the team’s model, it would take several billion years of slow contraction for the universe to reach half its size.
The end of the universe?
From there, one of two things can happen, Steinhardt said. Either the universe shrinks until it collapses on its own in a massive “crumbling”, ending space-time as we know it – or, the universe shrank just enough to return to a state similar to that of conditions. its beginning, and another Big Bang – or a big “bounce” – occurred, creating a new universe from the ashes of the old one.
In that second scenario (which Steinhardt and another colleague described in a 2019 paper in the journal Physics Letters B), the universe follows a pattern of periodic expansion and contraction, brittleness, and bounce. , repeatedly crash and redo it. If that’s true, then our current universe may not be the first or only universe, but just the latest in an infinite series of universes that have expanded and contracted before us, Steinhardt said. And it all revolves around the mutable nature of dark energy.
How reasonable is all of this? Hinshaw said the new paper’s quintessential interpretation is a “completely reasonable assumption for what dark energy is.” Because all of our observations of the expansion of the universe have come from objects millions to billions of light-years from Earth, current data can only inform scientists about the process. the past of the universe, not its present or future, he added. So the universe is most likely headed for a breakup, and we won’t have any way of knowing until long after the contraction begins.
“I think it really boils down to how compelling you find the theory to be, and more importantly, how testable do you find it?” Hinshaw added.
Unfortunately, there’s no good way to test whether the elves are real, or whether the universe’s expansion has begun to slow, Steinhardt admits. For now, it’s just a matter of matching the theory with past observations – and the authors do just that amazingly in their new paper. Whether a future of endless growth or rapid decay awaits our universe, only time will tell.
Originally published on Live Science.
https://www.space.com/end-cosmic-expansion Cosmic expansion could soon reverse