Wednesday, March 29, 2023

Universe may soon start shrinking ‘remarkably’, scientists say

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 Science gives suggestions.

In the new paper, three scientists attempt to model the nature of dark energy — a mysterious force that causes the universe to rapidly expand — based on previous 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 over billions of years, the repelling power of dark energy may be weakening.

According to his model, within the next 65 million years the acceleration of the universe may end rapidly – ​​then, within 100 million years, the universe may stop expanding altogether, and instead it may enter an era of slow contraction. that lasts for billions of years. Now with death – or perhaps rebirth – of time and space.

And it can all happen “remarkably” quickly, said study co-author Paul Steinhardt, director of the Princeton Center for Theoretical Sciences at Princeton University in New Jersey.

“At the time 65 million years ago, when the Chicxulub asteroid hit Earth and wiped out the dinosaurs,” Steinhardt told Live Science. “On a cosmic scale, 65 million years is remarkably short.”

There is nothing controversial or impossible about this theory, 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 previous observations of expansion alone – and because the current nature of dark energy in the universe is such a mystery – it is impossible to test the predictions in this paper. For now, they can remain only theory.

zero energy

Since the 1990s, scientists have understood that the universe is expanding rapidly; The space between galaxies is expanding faster now than it was billions of years ago.

Scientists have named the mysterious source of this acceleration dark energy – an invisible entity that acts opposite to gravity, pulling the universe’s most massive objects together rather than pushing them away.

Although dark energy makes up about 70 percent of the total mass-energy of the universe, its properties remain a total mystery.

A popular theory put forward by Albert Einstein is that dark energy is a cosmological constant—an immutable form of energy that is woven into the fabric of space-time. 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 competing theory suggests that dark energy does not need to remain constant in order to fit in with observations of past cosmic expansion.

Rather, dark energy can be called quintessence – 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 paper,

In contrast to the cosmological constant, quintessence can be either repulsive or attractive, depending on the ratio of its kinetic and potential energy at a given time. In the past 14 billion years, quintessence was repulsive.

For much of that period, however, it contributed negligible compared to radiation and matter to the expansion of the universe. This changed about five billion years ago, when the supergiant became the dominant component and its gravitational repulsion effect accelerated the expansion of the universe.

“The question we’re raising in this paper is, ‘Is this acceleration going to last forever?'” Steinhardt said. “And if not, what are the alternatives, and how quickly can things change?”

death of dark energy

In their study, Steinhardt and her colleagues, Anna Izzas of New York University and Kosmin Andrei of Princeton, predicted how the properties of quintessence might change over the next several billion years.

To do this, the team built a physical model of the quinine, showing its repulsive and attractive power over time, to fit with previous observations of the expansion of the universe. Once the team’s model could reliably reproduce the expansion history of the universe, they expanded their predictions into the future.

“To their surprise, the dark energy in their model can decay over time,” Hinshaw said. “Its strength can weaken. And if it does so in a certain way, eventually the antigravitational property of dark energy wears off and it turns back into something that’s like normal matter.”

According to the team’s model, the repelling power of dark energy may be in the middle of a rapid decline that potentially began billions of years ago.

In this scenario, the accelerated expansion of the universe is already slowing down today. Soon, perhaps within about 65 million years, that acceleration may stop altogether—then, within at least 100 million years from now, dark energy could be lucrative, causing the entire universe to shrink.

In other words, after about 14 billion years of evolution, space may begin to shrink.

“It would be a very special type of contraction that we call a slow contraction,” Steinhardt said. “Instead of expanding, space very slowly shrinks.”

Initially, the contraction of the universe would be so slow that even a hypothetical human still alive on Earth would not notice the change, Steinhardt said. According to the team’s model, it would take a few billion years of slow contraction for the universe to reach about half the size it is today.

end of the universe?

From there, one of two things can happen, Steinhardt said. Either the universe shrinks until it collapses on itself in a large “crunch”, ending space-time as we know it – or, the universe is set to return to a state similar to its original conditions. contracts, and another Big Bang – or a bigger “bounce” – 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 paper in the journal physics letter b), the universe follows a cyclical pattern of expansion and contraction, crunches and bounces, constantly collapsing and remaking it.

If this is true, then our current universe may not be the first or only universe, but the latest in an infinite series of universes that expanded and contracted before us, Steinhardt said. And it all hinges on the mutable nature of dark energy.

How admirable is all this? Hinshaw said the new paper’s quintessential interpretation is a “perfectly reasonable approximation for dark energy.”

Because all our observations of cosmic expansion come from objects that are millions to billions of light-years away from Earth, current data can only inform scientists about the universe’s past, not its present or future, they said. said.

So, the universe may very well be headed for a crunch, and we’ll have no way of knowing until long after the contraction phase begins.

“I guess it really just boils down to how compelling you find this theory and more importantly, how testable do you find it?” Hinshaw added.

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

Only time will tell if a future of endless evolution or rapid decay awaits our universe.

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

Nation World News Desk
Nation World News Desk
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