New research has integrated data from two significant surveys that explore the universe’s evolution and has uncovered indications that it might be less clumped in certain areas than earlier assumptions suggested. The results imply that as the universe ages, it becomes more intricate.
Throughout cosmic history, tremendous forces have influenced matter, reshaping the universe into an increasingly intricate web of structures.
A fresh study spearheaded by Joshua Kim and Mathew Madhavacheril from the University of Pennsylvania, including collaborators from Lawrence Berkeley National Laboratory, indicates that our universe has become “messier and more complicated” over its approximate 13.8 billion-year history, suggesting that matter distribution is not as “clumpy” as previously thought.
“Our research involved cross-referencing two distinct datasets from complementary surveys,” explains Madhavacheril. “We found that, for the most part, the narrative of structure formation aligns closely with predictions based on Einstein’s theories of gravity. However, we did observe a slight discrepancy regarding the expected clumpiness from around four billion years ago, which may be worth investigating.”
The research findings, which are published in the Journal of Cosmology and Astroparticle Physics and the preprint server arXiv, utilize final data from the Atacama Cosmology Telescope (ACT) and Year 1 data from the Dark Energy Spectroscopic Instrument (DESI). Madhavacheril notes that combining these datasets allows the team to layer cosmic time, akin to stacking transparencies of ancient cosmic images over more recent ones for a multidimensional view of the universe.
“ACT, observing about 23% of the sky, depicts the universe’s early years using faint, distant light that has been traveling since the Big Bang,” notes Joshua Kim, the paper’s lead author and a graduate researcher in the Madhavacheril Group. “This light, formally known as the Cosmic Microwave Background (CMB), acts like a baby picture of the universe, providing a glimpse of it when it was roughly 380,000 years old.”
According to Kim, the journey of this ancient light through time has been complex. Gravitational forces from large, dense structures like galaxy clusters have warped the CMB’s path, compared to an image getting distorted when viewed through glasses. This phenomenon, known as “gravitational lensing,” was predicted by Einstein over a century ago and serves as a critical tool for cosmologists in inferring properties such as matter distribution and the age of the universe.
Conversely, DESI’s data offers a more current depiction of the cosmos. Located at the Kitt Peak National Observatory in Arizona and run by Lawrence Berkeley National Laboratory, DESI is charting the universe’s three-dimensional layout by analyzing the distribution of millions of galaxies, especially luminous red galaxies (LRGs). These galaxies serve as cosmic markers, allowing scientists to trace how matter has evolved over billions of years.
“The LRGs from DESI provide a newer perspective of the universe, illustrating how galaxies are spread out at various distances,” Kim adds, comparing this data to the universe’s high school yearbook photo. “It’s a robust method to observe how structures have changed from the CMB map to the current positions of galaxies.”
By merging the lensing maps derived from ACT’s CMB data with that of DESI’s LRGs, the team established an extraordinary overlap between ancient and recent cosmic histories, allowing direct comparisons of measurements from both early and late phases of the universe. “This process operates similarly to a cosmic CT scan,” Madhavacheril notes, “where we can examine different slices of cosmic time and observe how matter clustered in various epochs, providing direct insight into how the gravitational effects of matter evolved over billions of years.”
During this analysis, they identified a minor discrepancy: the anticipated clumpiness, or density fluctuations, for later epochs did not entirely align with predictions. The metric known as Sigma 8 (σ8), which gauges the intensity of matter density fluctuations, is particularly important, Kim explains. Lower σ8 values signify less clumping than expected, implying that cosmic structures may not have developed according to early-universe models and hinting at a slowing growth of the universe’s structures in ways that our current models do not completely account for.
Kim explains that this slight divergence from expectations “isn’t strong enough to definitively suggest new physics—it is still possible that this discrepancy is coincidental.”
However, if this deviation proves genuine, it may signal the influence of some unexplained physics on how structures develop and change over cosmic timescales, potentially implicating dark energy—the enigmatic force believed to drive the universe’s acceleration—in structuring formation to a greater extent than previously recognized.
Looking ahead, the research team plans to collaborate with more advanced telescopes, such as the upcoming Simons Observatory, to enhance measurements with greater accuracy and achieve a clearer understanding of cosmic structures.
