After nearly 13.8 billion years of uninterrupted expansion, the universe could soon come to a stop and then begin slowly contracting, according to new research published in the journal. Proceedings of the National Academy of Sciences suggests.
In the new article, three scientists attempt to model the nature of dark energy – a mysterious force that appears to be causing the universe to expand faster and faster – based on past observations of cosmic expansion. In the team’s model, dark energy is not a constant force of nature, but rather 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 repelling force of dark energy may be weakening. According to their model, the acceleration of the universe could quickly end within the next 65 million years; then 100 million years from now, the universe could stop expanding altogether and instead enter a slow-contracting era that ends billions of years later. now with the death—or perhaps the rebirth—of time and space.
And all of this could happen “remarkably” quickly, said study co-author Paul Steinhardt, director of the Princeton Center for Theoretical Sciences at Princeton University in New Jersey.
“Going back in time 65 million years, that’s when the Chicxulub asteroid it hit Earth and wiped out the dinosaurs,” Steinhardt told WordsSideKick.com. “On a cosmic scale, 65 million years is remarkably short.”
nothing of 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 depends only on past 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 to test. For now, they can only remain in theories.
Since the 1990s, scientists have understood that the expansion of the universe is accelerating; the space between galaxies is expanding faster now than it was billions of years ago. Scientists named the mysterious source of this accelerating dark energy: an unseen entity that appears to work contrary to gravitypushing the most massive objects in the universe farther apart instead of pulling them together.
Although dark energy makes up about 70% of the total mass-energy in the universe, its properties remain a total mystery. A popular theory, introduced by Albert Einsteinis that dark energy is a cosmological constant — an unchanging form of energy that is woven into the fabric of space time. If that’s the case, and the force exerted by dark energy can never change, then the universe should continue to expand (and speed up) forever.
However, a competing theory suggests that dark energy need not be constant to fit observations of past cosmic expansion. Rather, dark energy may be something called quintessence, a dynamic field that changes over time. (Steinhardt was one of three scientists who introduced the idea in a 1998 article in the journal Physical Review Letters.)
Unlike the cosmological constant, quintessence can be repulsive or attractive, depending on the ratio of its kinetic and potential energy at a given moment. In the early universe, quintessence was attractive and cosmic expansion was slowing down; later, perhaps about 10 billion years ago, Steinhardt has suggested — the balance of matter and energy in the universe changed, and the quintessence became repellent, accelerating cosmic expansion.
“The question we pose in this paper is: ‘Does this acceleration have to last forever?'” Steinhardt said. “And if not, what are the alternatives and how soon could things change?”
The death of dark energy.
In their study, Steinhardt and colleagues predicted how the properties of the quintessence might change in the next few billion years. To do this, the team created a physical model of quintessence, showing its attractive and repellent power over time, to fit with 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 predictions into the future.
“To their surprise, the dark energy in their model can decay over time,” said Hinshaw. “Its strength can weaken. And if you do it a certain way, eventually the antigravity property of dark energy wears off and it reverts back to something that looks more like ordinary matter.”
Based on the team’s model, the repelling force of dark energy could be in the midst of a rapid decline that potentially began millions of years ago.
In this scenario, the accelerating expansion of the universe is already slowing down today. Soon, perhaps in about 65 million years, that acceleration could stop altogether; then, just 100 million years from now, dark energy could become attractive again, causing the entire universe to start contracting. In other words, after almost 14 billion years of growth, space could begin to shrink.
“This would be a very special kind of twitch that we call a slow twitch,” Steinhardt said. “Instead of expanding, space is contracting very, very slowly.”
Initially, the contraction of the universe would be so slow that any hypothetical human still alive in land you wouldn’t even notice a change, Steinhardt said. According to the team’s model, it would take a few billion years of slow contraction for the universe to become about half the size it is today.
The end of the universe?
From there, one of two things could happen, Steinhardt said. Either the universe contracts until it collapses in on itself in one big “crunch,” ending space-time as we know it, or the universe contracts enough to return to a state similar to its original conditions, and another. big Bang – or a big “rebound” – occurs, creating a new universe from the ashes of the old one.
In that second scenario (which Steinhardt and another colleague described in a 2019 article in the journal Physics letters B), the universe follows a cyclical pattern of expansion and contraction, creaking and bouncing, constantly collapsing and remaking 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 ours, Steinhardt said. And it all depends on the changing nature of dark energy.
How plausible is all this? Hinshaw said the new paper’s interpretation of quintessence is a “perfectly reasonable guess at what dark energy is.” Because all of our observations of cosmic expansion come from objects that are millions to billions of light-years away from Earth, the current data can only tell scientists about the universe’s past, not its present or future, he added. So the universe could very well be hurtling toward a crunch, and we’d have no way of knowing until long after the contraction phase began.
“I think it really comes down to how convincing you think this theory is, and more importantly, how testable you think it is.” Hinshaw added.
Unfortunately, there’s no good way to test whether the quintessence is real or whether the cosmic expansion has started to slow down, Steinhardt admitted. For now, it’s just a matter of fitting the theory to earlier observations, and the authors cleverly do so in his new paper. Whether a future of endless growth or rapid decline awaits our universe, only weather will tell
Originally published on Live Science.