Will the universe end in a bang or a whimper? A pair of theoretical physicists have proposed a third path: perhaps the universe will never end.
In a study that attempts to define the nature of dark energy — a mysterious phenomenon thought to be causing the universe to expand faster and faster every moment — the physicists find that cosmic expansion isn't always a given.
Rather, they write, dark energy may periodically "switch" on and off, sometimes growing the cosmos, sometimes shrinking it down until the conditions are right for a new Big Bang to occur — and for a new universe to be born.
Related: What is the Big Bang Theory?
The great escape
Our universe is currently experiencing a phase of runaway expansion: The cosmos is getting bigger faster with every passing moment. Cosmologists do not understand the cause of this acceleration, which they name dark energy. If this acceleration persists, then our universe will eventually expand into oblivion, with all matter and radiation torn apart.
This wouldn't be the first period of runaway growth. In the earliest moments of the Big Bang, the energies and densities were so extreme that existing physics cannot cope — it predicts a singularity, a point of infinite density where the math breaks down. After that, the universe experienced a period of incredibly rapid expansion known as inflation, which is also poorly understood.
Astronomers have long wondered if these two phases of accelerated expansion — one in the earliest moments of the Big Bang and one in the present epoch — are connected to each other, and whether an entity that drives both of them avoids the problem of the big bang singularity.
To answer that, a pair of theoretical physicists published a study Feb. 7 in the preprint database arXiv (opens in new tab) which examined a model of the universe where dark energy has always played a role. Previous research modeled dark energy "switching on" at various times to drive cosmic expansion, but the new research proposes a more realistic model that includes matter and radiation.
They wanted to see if dark energy can avoid a Big Bang singularity, drive inflation, and accelerate the late universe. To avoid that initial singularity, the universe can't begin from a point of infinite density. Instead, the universe we live in would have to be one in an infinite series of repeated "Big Bounces."
In this scenario, dark energy drives the universe until it reaches a certain size. But then the dark energy transforms itself, forcing the universe to contract. The cosmos then suffers a big crunch, but right before reaching a state of infinite density, dark energy turns around again, driving a period of incredibly rapid inflation and starting the cycle anew.
A finely tuned mechanism
The researchers found a model of dark energy that performed the trifecta. But crucially, matter and radiation could not be present in the extremely early universe, otherwise they spoiled inflation. Instead, matter and radiation had to appear just after inflation, as a portion of the dark energy decayed away, flooding the universe with light and matter.
While initially successful, the researchers weren't able to find a generic class of dark energy models that could always lead to the same results. Instead, they had to artificially put in a smaller value for the present-day accelerated expansion than quantum mechanics predicts in order to get the exact right outcome.
However, this new research does point in a promising direction, providing a viable platform for further exploring models like this. Humans are not necessarily destined to live in a cold, empty cosmos, because dark energy might behave differently in the far future. Only continued research will uncover our ultimate fate.
Originally published on LiveScience.
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The universe may have started with a dark Big Bang, https://phys.org/news/2023-03-universe-dark-big.html
Dark Matter and Gravity Waves from a Dark Big Bang, https://arxiv.org/abs/2302.11579, 22-Feb-2023.
My observation. The 46-page PDF report tackles the problem of explaining the origin of DM in the BB model and provides information on redshift changes too. This is from page 3.
“We have been particularly interested in answering the following question: what is the latest time at which the Dark Big Bang could take place in the history of the Universe? Clearly, for purely gravitational couplings between the dark and visible sectors, the Dark Big Bang can occur after BBN without spoiling the light element abundances. But another key issue is that the dark matter must pick up the right adiabatic perturbations required for structure formation. Indeed, we will show that the leading constraints on the time of the Dark Big Bang arise from structure formation and allow for a Dark Big Bang as late as O(month) after the Hot Big Bang (corresponding to a redshift of z ~ 3 x 10^6). We note, however, that the Dark Big Bang cannot be pushed to an epoch as late as matter-radiation equality at z = 3500 (as preferred by early dark energy solutions to the Hubble tension ) without spoiling Lyman-alpha and CMB observations.”
My note. We have redshifts 3 x 10^6 and 3500 for z values here. The postulated redshift for the origin of the CMBR is about 1100, z=3500, the universe age then could be 48,772 years old after the BB event using H0 69 km/s/Mpc and cosmology calculators. What the paper shows, there are more epochs in BB cosmology with much larger redshifts than 1100 for the origin of the CMBR. BB cosmology and modeling is very flexible :) Now we can know for sure how we evolved from a tiny area into such a large universe, filled with much dark matter too 😊
The other report cited in post #2 has fine-tuning problems too. How many fine-tuning problems are now known in science and where are they all listed, shown clearly to the public?
They seem to just have to have it a naked singularity of string stringing out. No paralleling at all, much less an infinity and eternity of paralleling. A constant of 'white hole' Big Bang Beginning, a constant of paralleling black hole ends (a constant of black hole end). A constant of brackets bracketing Hawking's "life zone" (the paralleling infinities of Hawking's "life zones').
Our whole universe is already the vertical constant (as opposed to the constant of 'horizontal' infinitely flat universe) of one big 'black hole' . . . vertically the largest black hole of them all (and, per Chaos Theory, as to infinite vertical "zoom" levels of it, even it parallels (vertically) . . . there being no limit to detached (as opposed to attached) acceleration (+) / deceleration (-) . . . (+/- 'c').
It's a three-dimensional “wrapping” around a four-dimensional black hole's event horizon. What we see is the 4D reality in 3 dimensions.
"our universe will eventually expand into oblivion, with all matter and radiation torn apart. "
All information I have found on the expansion of our universe specifically states that space within the bounds of gravitational systems like galaxies or even galaxy clusters is not expanding.
This means that, no, all matter and radiation will not be torn apart unless you have an example of space accelerating apart within the gravitational influence of galaxy clusters or within galaxies.
I am amazed at the state of our sciences these days. Everyone has a different theory, and half the time they don't jive with what we already know.
This "proposal" seems very suppositional. But, if the expansion rate did vary dramatically and at different times, there should be ways to test for it. The Lyman-alpha Forest is one possible test, but finding their distance would be very difficult, I assume.
It would help explain the relatively small difference between the two values for the H-L constant since the slower rate was found from the CMBR from 13.8 billion year ago, and the faster rate established as today's rate.
I'm doubtful their capricious view of DE explains the difference.