May 29, 2022

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Scientists say the universe could start to shrink "significantly" soon

Scientists say the universe could start to shrink “significantly” soon

After nearly 13.8 billion years of continuous expansion, the universe could soon come to a standstill, then slowly begin to shrink, according to new research published in the journal Science. Proceedings of the National Academy of Sciences It suggests.

In the new paper, three scientists attempt to model a nature 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 model, dark energy It is not an immutable force of nature, but an entity called Essence, which can disintegrate over time.

Researchers have found that although the expansion of the universe has accelerated for billions of years, the repulsive force of dark energy may be weakening.

According to their model, the acceleration of the universe could end rapidly within the next 65 million years — then, in 100 million years, the universe could stop completely, and instead could enter an era of slow contraction that ends billions of years from now with death — or Perhaps rebirth – time and place.

All of this can 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, then Asteroid Chicxulub Hit the ground and eliminate dinosaursSteinhardt for Live Science. On a cosmic scale, 65 million years are remarkably short. “

Nothing about this theory It’s controversial or implausible, Gary Henshaw, 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 previous observations of expansion alone – and because the current nature of dark energy in the universe is a mystery – it is currently impossible to test the predictions in this paper. For now, they can only remain theories.

vacuum energy

Since the 1990s, scientists have recognized that the expansion of the universe is accelerating; The distance between galaxies is expanding faster now than it was billions of years ago.

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Scientists have dubbed the mysterious source of this acceleration dark energy – an invisible entity that appears to work in reverse gravitywhich pushes the largest objects in the universe away from each other rather than clustered together.

Although dark energy makes up nearly 70 percent of the universe’s total energy, its properties remain a total mystery.

popular theory, presented by Albert EinsteinIs this dark energy a cosmic constant – A constant form of energy woven into a fabric Spare time. If so, and the force exerted by dark energy can never change, then the universe must continue to expand (and accelerate) forever.

However, a competing theory suggests that dark energy does not need to be static to accommodate previous cosmic expansion observations.

Alternatively, the dark energy might be something called a core – a dynamic field that changes over time. (Steinhardt was one of three scientists who proposed the idea in a 1998 paper published in the journal Physical Review Letters.)

Unlike the cosmological constant, a substance can be repulsive or attractive, depending on the ratio of its kinetic energy and potential energy at a given time. For the past 14 billion years, the essence has been disgusting.

For most of that period, radiation and matter contributed insignificantly to the expansion of the universe. 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 paper is, should this acceleration continue forever?” Steinhardt said. “And if not, what are the alternatives, and when might things change soon?”

Dark energy death

In their study, Steinhardt and 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 several billion years.

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To do this, the team created a physical model of the core, which shows its repulsive and attractive strengths over time, to match previous observations of the expansion of the universe. Once the team’s model could reliably reproduce the history of the expansion of the universe, they expanded their predictions for the future.

“To their surprise, the dark energy in their model can decay over time,” Henshaw said. “It can weaken its power. And if you do it in a certain way, the anti-gravitational property of dark energy eventually disappears and turns back into something resembling ordinary matter.”

According to the team’s model, the centrifugal force of dark energy in the midst of a rapid decline could have begun billions of years ago.

In this scenario, the accelerating expansion of the universe is already slowing down today. Soon, perhaps in 65 million years, this acceleration could stop completely — then, in 100 million years from now, dark energy could become attractive, causing the entire universe to begin to shrink.

In other words, after nearly 14 billion years of growth, space could begin to shrink.

“This is going to be a very special kind of contraction that we call a slow contraction,” Steinhardt said. “Instead of expanding, space is shrinking very, very slowly.”

At first, the contraction of the universe will be so slow that any hypothetical human being is still alive Land He wouldn’t even notice the change, Steinhardt said. According to the team’s model, it would take the universe a few billion years of slow contraction to reach half its size today.

the end of the universe?

From there, Steinhardt said, one of two things can happen. Either the universe shrinks until it collapses in on itself in a major “crisis”, and space-time as we know it comes to an end—or, the universe shrinks enough to return to a state similar to its original conditions, and another the great explosion – or a major “bounce” – takes place, forming a new universe from the ashes of the old universe.

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In that second scenario (described by Steinhardt and another colleague in a 2019 paper published in the journal Physics Letters B), the universe follows a periodic pattern of expansion and contraction, crunches and bounces, which is constantly collapsing and reshaping.

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.

How reasonable is all of this? Henshaw said the new paper’s interpretation of the core is a “completely reasonable assumption of what dark energy is.”

He added that since all of our observations of cosmic expansion come from objects millions to billions of light years away from Earth, current data can only inform scientists of the universe’s past, not its present or future.

Therefore, the universe could be on its way to a crisis, and we will have no way of knowing until long after the contraction phase begins.

“I guess it just boils down to how convincing you are of this theory and, more importantly, how testable do you find it?” Hinshaw has been added.

Unfortunately, there’s no good way to test whether the essence is real, or whether the cosmic expansion is starting to slow, Steinhardt admitted. For now, it’s just a matter of aligning the theory with previous observations – and the authors do so ably in their new paper.

Whether a future of endless growth or rapid decay awaits our universe, only the time will tell.

This article was originally published by Live Science. Read the The original article is here.