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September 19th, 2023 
Awake Goy 
Something unknown appears to be suppressing the growth of the gargantuan structures that connect the universe in a cosmic web, a finding that challenges our current understanding of physics, according to a new study.
Scientists have presented new observational evidence that large-scale structures, which are enormous filaments and nodes made of gas and dark matter, are growing at a slower rate than predicted by the standard model of cosmology. The growth of these structures may have slowed down in the later eras of the universe, a scenario that could help to explain a major cosmic mystery known as the sigma-8 tension.
The cosmic web is a network of large-scale structures that stretch for hundreds of millions of light years and intersect at points called nodes. These structures are primarily made of dark matter, an unidentified substance that accounts for most of the mass of the universe. The cosmic web influences the distribution of gas and galaxies; matter travels along the filaments and accumulates into dense regions at the nodes.
The standard model, also known as the Lambda cold dark matter model (ΛCDM), offers predictions about the long-scale evolution of these structures, which have mostly been validated by observations. However, some observations seem to defy the model, such as the value of sigma-8, which is a term used to describe the distribution of matter in the universe.
Now, scientists led by Minh Nguyen, an astrophysicist and cosmologist at the University of Michigan, suggest that the growth of large-scale structures has been suppressed in the modern universe, even as the overall expansion of the universe has accelerated over time, due to a mysterious force known as dark energy. The researchers concluded that some “cosmological tensions can be interpreted as evidence of growth suppression” and that the sigma-8 tension could be effectively resolved by their hypothesis, according to a new study published in Physical Review Letters.
“Throughout the cosmic time, an initially small clump of mass attracts and accumulates more and more matter from its local region through gravitational interaction,” said Nguyen in a statement. “As the region becomes denser and denser, it eventually collapses under its own gravity.”
“As they collapse, the clumps grow denser,” he said. “That is what we mean by growth. It’s like a fabric loom where one-, two- and three-dimensional collapses look like a sheet, a filament and a node. The reality is a mixture of all three cases, and you have galaxies living along the filaments while galaxy clusters—groups of thousands of galaxies, the most massive objects in our universe bounded by gravity—sit at the nodes.”
Scientists have developed a few techniques to clock the growth of large-scale structures over the course of the universe’s 13.8-billion-year lifetime. The oldest light in the universe, known as the cosmic microwave background, reveals insights about the cosmic web in the deep past. Scientists also use a cosmic effect called gravitational lensing, in which light is warped and brightened by massive objects as it moves through space, to map out the distribution of matter in the more recent “dark-energy-dominated” universe, which began about four billion years ago.
Nguyen and his colleagues created a timeline of large-scale structure evolution that incorporates both of these techniques, as well as movements of local galaxies to help fill in more recent growth patterns. The results suggest that cosmic growth rates have been suppressed in the dark-energy-dominated era, hinting at the possibility of physics beyond the standard model.
“The difference in these growth rates that we have potentially discovered becomes more prominent as we approach the present day,” Nguyen said. “These different probes individually and collectively indicate a growth suppression. Either we are missing some systematic errors in each of these probes, or we are missing some new, late-time physics in our standard model.”
It’s not clear what might be driving this apparent suppression of growth, assuming it is not an observational error. But if future studies were to corroborate the findings, scientists could potentially resolve the finicky sigma-8 tension.
This cosmological problem arises from the fact that measurements using the CMB, gravitational lensing, and other techniques return different values of sigma-8. Nguyen and his colleagues suggest this is simply because the growth, or “clumpiness,” of large-scale structures is actually different over the course of the universe’s lifetime. But the researchers note that it will take more research and observation to build on their findings, and figure out exactly what it means for our understanding of reality.
“In this era of high-precision large-scale structure and CMB measurements, joint analyses of these data sets will hold the key to confirming any evidence for physics beyond the standard model,” the team concluded in the study.
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