Scientists have unveiled an unprecedented map of all the matter in the universe using two very different telescopes, an effort that revealed weird inconsistencies between our observations and models of the so-called “cosmic web” that links the cosmos, according to new research.
The results suggest that our universe appears to be slightly less “clumpy” than expected based on our best models, an anomaly that might be resolved by future precision measurements or could potentially point to deeper problems in our understanding of the cosmic web.
In the moments after the Big Bang, the universe was an utterly chaotic soup of hot subatomic particles that seems unrecognizable from our modern vantagepoint. But as this inferno cooled, familiar forms of matter emerged and began to coalesce into “clumps” that evolved into the cosmic web, a network of large-scale structures that plays a role in the evolution of galaxies.
Mapping out the distribution of matter across the cosmos is a major quest in astronomy that could help resolve many mysteries about the evolution and current structure of our universe.
Now, an international team of more than 150 scientists has produced one of the most precise maps of cosmic matter ever created by combining observations from the Dark Energy Survey (DES), which observes distant galaxies from its perch in Chile, and the South Pole Telescope (SPT), which captures the oldest light in the universe, called the cosmic microwave background, from Antarctica.
This approach enabled the researchers to “cross-correlate” our view of cosmic matter with very different datasets, allowing them “to extract information stored in the large-scale structure” of the universe, according to a trio of studies about the new map that was published on Tuesday in the journal Physical Review D.
For the most part, the new map neatly lined up with the predictions of the standard model of cosmology, which is a theoretical framework that accounts for many phenomena in our universe.
However, the team also reported the “unexpected discovery” of discrepancies in a cosmic property called “sigma-8,” which measures the fluctuations in density across the universe, according to the study. In other words, sigma-8 describes the clumpiness of the cosmos across vast distances. The DES and SPT observations reveal a universe that is less clumped together, and more evenly spaced out, than scientists expect based on the standard model, which is an anomaly that has also popped up in previous studies.
It may be that the uncertainty is the result of biases in these new observational techniques, which are probing some of the most elusive structures in the universe. As these methods become even more precise in the coming years, the well-documented tension over sigma-8 might eventually vanish.
However, it’s also possible that the discrepancy points to new physics that are not encompassed by the standard model, which is also known as the cold dark matter model (ΛCDM). If the next iteration of cosmic matter maps continues to show the sigma-8 tension, it could mean that we are missing fundamental insights about the universe.
“There is no known physical explanation for this discrepancy,” the researchers said in one of their studies. “This tension could result from physics beyond the standard cosmological constant and cold dark matter model (ΛCDM), or it could result from systematic biases in the analyses.”
“Looking farther forward, cross-correlations between surveys such as the Vera Rubin Observatory Legacy Survey of Space and Time, the Nancy Grace Roman Space Telescope, the [European Space Agency] Euclid mission, Simons Observatory, and CMB-S4 will enable significantly more powerful cross-correlation studies that will deliver some of the most precise and accurate cosmological constraints, and that will allow us to continue stress-testing the concordance ΛCDM model,” the team concluded.