In a study trying to define the nature of dark energy – a mysterious phenomenon believed to cause the universe to expand faster and faster every moment – physicists find that cosmic expansion is not always a given.Rather, they write, dark energy can periodically “switch” on and off, sometimes growing the cosmos, sometimes shrinking, 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 each passing moment. Cosmologists do not understand the cause of this acceleration, which they call dark energy. If this acceleration continues, then our universe will eventually expand into oblivion, with all matter and radiation torn apart.
This would not 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 handle it—it predicts a singularity, a point of infinite density where the mathematics 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 whether these two phases of accelerated expansion—one in the earliest moments of the Big Bang and one in the present epoch—are connected, and whether an entity driving them both avoids the big bang singularity problem .
To answer that, a pair of theoretical physicists published a study Feb. 7 in the preprint database arXiv (opens in new tab) which investigated a model of the universe in which dark energy has always played a role. Previous research modeled dark energy “ignition” at different times to drive cosmic expansion, but the new research suggests 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 this initial singularity, the universe cannot begin from a point of infinite density. Instead, the universe we live in should 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 and forces the universe to contract. The cosmos then suffers a big crunch, but just before it reaches a state of infinite density, dark energy reverses again, driving a period of incredibly rapid inflation and starting the cycle all over again.
A fine-tuned mechanism
The researchers found a model of dark energy that performed the trifecta. But it is crucial that 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, when some of the dark energy decayed and flooded the universe with light and matter.
Although initially successful, the researchers were unable to find a generic class of dark energy models that could always lead to the same results. Instead, they had to artificially insert a smaller value for the current accelerated expansion than quantum mechanics predicts to get the exact right result.
However, this new research points in a promising direction that provides a viable platform to further explore models like this. Humans are not necessarily destined to live in a cold, empty cosmos because dark energy may behave differently in the distant future. Only continued research will uncover our ultimate destiny.
Originally published on LiveScience.
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