After nearly 13.8 billion years of nonstop expansion, the universe could
soon grind to a standstill, then slowly start to contract, new research
published in the journal Proceedings of the
National Academy of Sciences
suggests.
In the new paper, three scientists attempt to model the nature of dark
energy — a mysterious force that seems to be causing the universe to expand
ever faster — based on past 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 for billions of years, the repellent force of dark energy
may be weakening. According to their model, the acceleration of the universe
could rapidly end within the next 65 million years — then, within 100
million years, the universe could stop expanding altogether, and instead it
could enter an era of slow contraction that ends billions of years from now
with the death — or perhaps the rebirth — of time and space.
And this could all 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, that's when the Chicxulub asteroid hit
the Earth and eliminated the dinosaurs," Steinhardt told Live Science. "On a
cosmic scale, 65 million years is remarkably short."
Nothing about 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
hinges on past observations of expansion alone — and because the present
nature of dark energy in the universe is such a mystery — the predictions in
this paper are currently impossible to test. For now, they can only remain
theories.
Energy of the void
Since the 1990s, scientists have understood that the expansion of the
universe is speeding up; the space between galaxies is widening faster now
than it was billions of years ago. Scientists named the mysterious source of
this acceleration dark energy — an invisible entity that seems to work
contrary to gravity, pushing the universe's most massive objects farther
apart rather than drawing them together.
Though dark energy makes up approximately 70% of the total mass-energy of
the universe, its properties remain a total mystery. A popular theory,
introduced by Albert Einstein, is that dark energy is a cosmological
constant — an unchanging form of energy that's 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 expanding (and accelerating)
forever.
However, a competing theory suggests that dark energy doesn't need to be
constant in order to fit with 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 paper in the journal
Physical Review Letters.)
Unlike the cosmological constant, quintessence can be either repulsive or
attractive, depending on the ratio of its kinetic and potential energy at a
given time. Over the last 14 billions years, quintessence was
repulsive. For most of that period, though, it contributed
insignificantly compared to radiation and matter to the expansion of the
universe. That changed about five billion years when quintessence became the
dominant component and its gravitational repulsion effect caused the
expansion of the universe to speed up.
"The question we're raising 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 his colleagues, Anna Ijjas of New York
University and Cosmin Andrei of Princeton, predicted how the properties of
quintessence could change over the next several billion years. To do this,
the team created a physical model of quintessence, showing its repellent and
attractive power over time, to fit with past observations of the universe's
expansion. Once the team's model could reliably reproduce the universe's
expansion history, they extended their predictions into the future.
"To their surprise, dark energy in their model can decay with time," Hinshaw
said. "Its strength can weaken. And if it does so in a certain way, then
eventually the antigravitational property of dark energy goes away and it
transitions back into something that's more like ordinary matter."
According to the team's model, the repellent force of dark energy could be
in the midst 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 could stop altogether — then, within as few as 100 million
years from now, dark energy could become attractive, causing the entire
universe to start contracting. In other words, after nearly 14 billion years
of growth, space could start to shrink.
"This would be a very special kind of contraction that we call slow
contraction," Steinhardt said. "Instead of expanding, space contracts very,
very slowly."
Initially, the contraction of the universe would be so slow that any
hypothetical humans still alive on Earth 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 reach 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 a big "crunch," ending
space-time as we know it — or, the universe contracts just enough to return
to a state similar to its original conditions, and another Big Bang — or a
big "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 Letters B), the universe follows a cyclical pattern of expansion and contraction,
crunches and bounces, that constantly collapse and remake 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 hinges on the changeable
nature of dark energy.
How plausible is all this? Hinshaw said the new paper's interpretation of
quintessence is a "perfectly reasonable supposition for what the 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, current data
can only inform scientists about the universe's past, not its present or
future, he added. So, the universe could very well be barreling toward a
crunch, and we'd have no way of knowing until long after the contraction
phase began.
"I think it really just boils down to how compelling do you find this theory
to be and, more importantly, how testable do you find it to be?" Hinshaw
added.
Unfortunately, there is no good way to test whether quintessence is real, or
whether cosmic expansion has started to slow, Steinhardt admitted. For now,
it's just a matter of fitting the theory with past observations — and the
authors do that capably in their new paper. Whether a future of endless
growth or rapid decay awaits our universe, only time will tell.
Originally published on
Live Science.
Tags:
Space & Astrophysics
In the beginning it was void and the energy of God movd in the void...behold the universe were folded like a scroll. ..then.. I saw a new universe and old has passed away....
ReplyDeleteThe universe will melt in fervent heat (not cold death)
In my opinion,
ReplyDeleteIf we want to understand the expansion of the universe and dark energy, it is necessary to change the model of the universe a little bit.
There really is no such thing as dark energy.
What exists is a completely natural phenomenon.
Current universe models describe the Big Bang as the release of all baryonic energy from a dimensionless singular point. The expansion is also based on this.
However, if we consider Space (the part which has no Time) as a sea composed of neutral=non-vibrating energy units (quantum), the model to be obtained produces the same results.
The Big Bang would be defined as the breaking of symmetry as a result of a forceful impact (by an unknown reason), in a point in this sea.
As the shock wave of this impact propagates spherically-symmetrically, it will mobilize the stagnant energy units in the Space (Still there is no The Time). Each unit will occupy a larger area with its vibration. This will be the initial impetus for expansion.
This global expansion will be transformed with increasing violence (as more units will join this new system).
Secondly, the energy density of the area where the symmetry is broken will increase. This shows us two different densities of media.
Thus, a denser medium will begin to expand into a field of less density.
(If they want to test this as an experiment, let them hold a water tanker full of pure water under light pressure for a while. When the water molecules reach the lowest entropy, let them pump one beat of high heat-energy from a central point.
I think, If we watch the movement of the heated water molecules, similar results can observe. (If the temperature is too high, the first spherical expansion will turn into a torus expansion to maintain the surface-to-volume ratio.)
If the medium change of a shock wave is examined, it is seen that a reflection wave goes backwards during the transition. The frequency and wavelength of this wave are equivalent to the expanding wave. Only the amplitude and phase are different.
(I think the same thing will happen in a heat shock wave propagating in water. A water molecule vibration field width will be wavelength of the wavefront of propagating impact as the same.)
These reflected echo waves will have a concave slope as they travel. That is, as they progress, their energy per unit field will increase.
When they reach the center, they will create a driving source that will support the expansion.
These echo waves will also preserve the integrity of the particles that condensed and solidify (tiny ice) during the first symmetry breaking.
In our universe, I think these waves are the equivalent of Time. Space and Time became should be intertwined in this way.
I have some explanations about various subjects (such as; Special relativity, dark matter, antimatter, gravity, etc.) compatible with this assumption in my answers at the quora site.
Another thing to worry about! I'm going to line my house with aluminum foil to protect myself from any bad effects from this.
ReplyDelete