New research has suggested that after nearly 13.8 billion years of nonstop development, the Universe might soon reach a standstill, then slowly begin to contract.
Three scientists attempt to model the nature ofdark energy, a mysterious force that appears to be causing the Universe to expand even faster using previous observations of cosmic expansion.
Dark energy is not a constant force of nature, but a form of quintessence, which can decay over time in the team''s model.
Despite the evolution of the Universe, researchers discovered that the repellent force of dark energy might be weakening.
According to their models, the Universe''s acceleration might quickly close within the next 65 million years then, within 100 million years, the Universe may stop expanding altogether, and instead it might enter a halt to a long period of contraction that ends billions of years from now with the death or perhaps the rebirth of time and space.
According to Paul Steinhardt, the director of the Princeton Center for Theoretical Science at Princeton University in New Jersey, the whole thing might happen "remarkably."
"On a cosmic scale, 65 million years is relatively short," Steinhardt said of theChicxulub asteroid hitting the Earth and eliminating the dinosaurs.
Gary Hinshaw, a British Columbia professor of physics and astronomy who was not involved in the study, said there was no controversy or implausible about thistheoryis.
Despite the fact that the model focuses on previous expansion only, and because the present nature of dark energy in the Universe is so a mystery, these predictions are currently impossible to test. For the time being, they can only remain theories.
Energy of the void
Scientists have understood that the expansion of the Universe is speeding up, and that the space between galaxies is expanding faster today than it was billions of years ago.
Scientists identified the mysterious source of this acceleration dark energy as a hidden entity that appears to work contrary to gravity, pushing the Universe''s most significant objects farther apart rather than drawing them together.
While dark energy is thought to be around 70 percent of the world''s total mass-energy, its properties remain a mystery.
According to Albert Einstein, dark energy is a cosmic constant, an unchanging form of energy that''s woven into the fabric of space-time. If the theory is true, then the Universe should continue expanding (and continuing) forever.
Despite the difference, a theory suggests that dark energy isn''t required to be constant in order to be compatible with previous cosmic expansion estimates.
Dark energy may be a substrational field that changes over time, according to one of three scientists. (Steinhardt was one of three people who introduced the idea in a 1998 paper in the journalPhysical Review Letters.)
Like the cosmological constant, a quintessence may be repulsive or attractive depending on the amount of its kinetic and potential energy at a given time. Over the last 14 billions years, it was repulsive.
For the majority of the period, it tended to be insignificantly related to radiation and matter in the Universe''s expansion. That changed five billion years ago, when quintessence became the dominant component, and its gravitational repulsion effect caused the universe''s expansion to accelerate.
"Does this acceleration have to last forever," Steinhardt said. "And if not, what are the solutions, and how soon might things change?"
The death of dark energy
In their research, Steinhardt and his colleagues, Anna Ijjas of New York University and Cosmin Andrei of Princeton, forecast how the properties of quintessence might change in the next several billion years.
The team grew the scale of quintessence by exhibiting its repellent and attractive power over time, suited to the Universe''s expansion history. Once the team''s model constituted the Universe''s expansion history, it extended its predictions to the future.
"And if dark energy in their model fails in a certain way, then it''s time to destroy it, thus making it more like ordinary matter." Hinshaw said he believes the dark energy in their model has a tendency to decay with time.
According to the team''s model, the repellent force of dark energy might be in the midst of a rapid decline that might begin billions of years ago.
The universe''s accelerated expansion is already slowing down today. Depending on how long it takes to accelerate this acceleration then, dark energy might become attractive in within about 100 million years, causing the entire universe to begin contracting.
In other words, space may start to shrink after almost 14 billion years of growth.
"This would be a very different form of contraction, which we call slow contraction," Steinhardt said. "Instead of expanding, space contracts very, very slowly."
The Universe''s contraction would be so slow that any hypothetical humans still alive onEarthwouldn''t even notice a change, according to Steinhardt. According to the team''s model, it would take a few billion years of slow contraction to reach roughly half the size it is today.
The end of the Universe?
One of two things might happen, according to Steinhardt. Either the Universe contracts until it collapses in on itself in a big "crunch," ending space-time as we know it, or the Universe contracts only enough to return to a state similar to its original conditions, and anotherBig Bang or a big "bounce" occurs, generating a new Universe from the ashes of the old one.
In this second situation (which Steinhardt and his another colleague described in a 2019 paper in the journalPhysics Letters B), the Universe follows a cyclical pattern of expansion and contraction, crunches and bounces, which constantly collapse and remake it.
If that''s true, then our current Universe may not be the first or only Universe, but it''s just the latest in a long line of Universes that have expanded and contracted before ours, according to Steinhardt. It all depends on the changeable nature of dark energy.
How logical is all of that? Hinshaw said the new paper''s craze of quintessence is a "perfectly reasonable assumption for what''s dark energy."
Because all of our cosmic expansion observations are made from objects that are million to billions of light-years away from Earth, current information can only inform scientists about the Universe''s past, not its present or future, according to him.
So, the Universe might be rushing towards a crisis, and we''d have no way of knowing until long after the contraction phase began.
"It''s really just down to how compelling do you find this theory to be and, most importantly, how testable do you find it to be," Hinshaw added.
There is no good way to determine whether quintessence is real or whether cosmic expansion has begun to slow, according to Steinhardt. For the time being, it''s only a matter of fitting the theory with previous observations, and the authors do that capably in their new paper.
Onlytimewill tell whether our Universe will have a future of endless growth or rapid decay.
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