After about 13.8 billion years of continuous expansion, the universe may soon reach a steady state and then slowly begin to shrink, according to new research published in the Journal of the National Academy of Sciences.
In the new study published by ScienceAlert, three scientists tried to simulate the nature of dark energy – a mysterious force that appears to be causing the universe to expand faster – based on previous observations of cosmic expansion.
In the team’s model, dark energy is not a constant natural force, but an entity called an essence, which can decay over time.
The researchers found that although the expansion of the universe has been accelerating for billions of years, the repulsive force of dark energy may be weakening.
According to their model, the acceleration of the universe could end “quickly” within the next 65 years, then within a hundred million years, the universe could completely stop expanding, and may instead enter an era of slow contraction that could lead billions of years from now to The death or rebirth of spacetime.
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 “remarkably” quickly.
He added, “If we want to go back in time sixty-five million years, we reach the period in which the asteroid Chicxulub struck the Earth and wiped out the dinosaurs… When we talk on a cosmic level, sixty-five million years is a remarkably short period.”
However, because the model is based only on previous observations of expansion—and because the current nature of dark energy in the universe remains a mystery—it’s currently impossible to test what the study predicts, and its findings remain just theories.
vacuum energy
Since the 1990s, scientists have realized that the universe is expanding at an accelerating pace, with the distance between galaxies growing faster now than it was billions of years ago.
Scientists have dubbed the mysterious source of this acceleration as dark energy – an invisible entity that appears to work against gravity, pushing huge objects in the universe apart rather than bringing them closer together.
Although dark energy makes up nearly 70 percent of the universe’s total energy, its properties remain a complete mystery.
A popular theory, advanced by Albert Einstein, says that dark energy is a cosmological constant – a constant form of energy embedded in the fabric of spacetime. If that is the case, and the force exerted by dark energy can never change, then the universe must continue to expand (and accelerate) forever.
However, a different theory suggests that dark energy does not need to be constant to accommodate the previously observed cosmic expansion.
Alternatively, dark energy might be something called a core – a dynamic field that changes over time.
In contrast to the cosmological constant, a substance can be repulsive or attractive, depending on the ratio between its kinetic and potential energy at a given time. For the past fourteen billion years, the essence has been expelling.
For most of that period, his contribution to the expansion of the universe was negligible compared to radiation and matter. That changed about five billion years ago, when the core became the dominant component and the effect of gravitational repulsion accelerated the expansion of the universe.
“The question we ask in this study is should this acceleration continue forever? If not, what are the alternatives, and how quickly can things change?” Steinhardt said.
Dark Energy Death
In their study, Steinhardt and his colleagues, Anna Egas of New York University and Cosmin Andre of Princeton University, predict how the properties of the substance might change over the next few billion years.
To do this, the team created a physical model of the core, showing its repulsive and attractive force over time, to match previous observations of the expansion of the universe. Once the team’s model could reliably reconstruct the history of the expansion of the universe, the researchers withdrew their predictions for the future.
Gary Henshaw, a professor of physics and astronomy at the University of British Columbia, who was not involved in the study, said: “The researchers were amazed that the dark energy in their model could decay over time… it could weaken its strength. And if this happens in a certain way, the dark energy property Antigravity eventually disappears and turns back into something resembling ordinary matter.”
According to the team’s model, the repulsive force of dark energy could have begun to decline rapidly billions of years ago.
In this scenario, the accelerating expansion of the universe is already slowing down today. Soon, perhaps in sixty-five million years, this acceleration could stop completely, and then in a hundred million years from now dark energy could become attractive, causing the entire universe to begin to shrink.
In other words, after a growth of about fourteen billion years, the universe could begin to shrink.
But this contraction would be so slow at first that any human being who is still alive on Earth would not even notice any change, and it would take the universe a few billion years of slow contraction to reach half its size today.
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Is this the end of the universe?
Steinhardt said, there are two possibilities after the universe begins to shrink: Either the universe shrinks until it collapses completely and the spacetime we know runs out, or it shrinks enough to return to a state similar to its original conditions, and thus another Big Bang occurs – or a large “rebound” that leads to the creation of the universe A new remnant of the old universe.
In this second scenario, the universe follows a recurring cycle of expansion, contraction, fading and regression, as it continually collapses and reshapes itself.
If this is true, our current universe may not be the first or only universe, but rather the latest in an endless chain of universes that expanded and contracted before ours. And it all depends on the changing nature of dark energy.
The new study’s explanation for the core, Henshaw said, is “a perfectly reasonable assumption of what dark energy is.”
He added that since all our observations of cosmic expansion come from objects millions to billions of light years away from Earth, the current data can only give scientists an idea of the universe’s past, not its present or future.
So, the universe could be on its way to collapse, and we won’t have any way of knowing until long after the contraction phase begins.
“I think it just boils down to how convinced you are of that theory and, more importantly, how testable are you?” Henshaw said.
Unfortunately, Steinhardt admitted, there’s no good way to test whether the essence is real, or whether the cosmic expansion has begun to slow.
Whether a future of endless growth or rapid decay awaits our universe, we will only know with time.