The DESI collaboration is conducting a groundbreaking experiment to understand the expansion and acceleration of the universe. Their work with the DESI instrument allowed them to map the universe from its early stages to the present day, challenging existing models of the universe. Initial findings suggest there may be more to discover about dark energy and cosmic acceleration. The project’s innovative approach, including fully blinded analysis, ensures that their conclusions are based on unbiased data, paving the way for future discoveries in astrophysics. Credit: SciTechDaily.com
The DESI The collaboration explores the accelerating expansion of the universe through comprehensive mapping from its early stages to the present. Their findings challenge traditional cosmic models and suggest new perspectives on dark energy, all while using pioneering and unbiased research methods.
A team of researchers, including an astrophysicist from the University of Texas at Dallas, as part of the Dark Energy Spectroscopic Instrument (DESI) collaboration is leading a groundbreaking experiment aimed at investigating the expansion and acceleration of the universe.
Dr. Mustapha Ishak-Boushaki, professor of physics in the School of Natural Sciences and Mathematics (NSM) at UT Dallas, is a member of the DESI collaboration, an international group of more than 900 researchers from more than 70 institutions around the world engaged in a multiyear experiment to increase understanding of the history and the fate of the universe.
On April 4, Ishak-Boushaki presented analyzes of the first year of data collected by the DESI experiment at the American Physical Society meeting in Sacramento, California, along with two other DESI scientists. Ishak-Boushaki presented cosmology results derived from DESI data and their implications for the universe. The researchers also shared results from the first year of data collection in several papers published on the arXiv preprint page.
The role of the DESI tool
The DESI instrument, located at Kitt Peak National Observatory (KPNO) in Arizona, collects light from the most distant parts of the universe, allowing scientists to map the universe as it was young and trace its evolution to what is observed today. Understanding how the universe evolved is linked to how it ends, and to one of physics’ greatest mysteries: What accounts for the observation that the expansion of the universe is accelerating?
Analysis of DESI’s first year of data collection has confirmed the foundations of what scientists believe is the best model of the universe, but also suggests that more needs to be learned about the underlying cause or causes of cosmic acceleration, the discovery of which led to the 2011 Nobel Prize in Physics.
DESI has created the largest 3D map of our universe to date. Earth is in the center of this thin slice of the entire map. In a magnified section, it is easy to see the basic structure of matter in our universe. Credit: Claire Lamman/DESI collaboration; custom color map pack from cmastro
Cosmic acceleration is problematic because it counteracts how gravity, which causes massive objects to be pulled together, works in our solar system and the nearby universe.
“Gravity pulls matter toward itself, so when we throw a ball up in the air, Earth’s gravity pulls it down toward the planet,” Ishak-Boushaki said. “But on the largest scale, the universe behaves differently. It acts as if there is something repulsive pushing the universe apart and accelerating its expansion. This is a big mystery and we are investigating it on several fronts. Is it the unknown dark energy in the universe, or is it a modification of Albert Einstein’s theory of gravity on cosmological scales?
Exploring dark energy and the expansion of the universe
Many scientists think that dark energy plays a key role in accelerating the universe, but it is not well understood. Some believe it’s a cosmological constant—an intrinsic property of space that drives the acceleration.
To study the effects of dark energy over the past 11 billion years, the DESI group has created the largest 3D map of the universe ever created using the most precise measurements to date. It is the first time scientists have measured the expansion history of the young universe with an accuracy of better than 1%.
The leading model of the universe is known as Lambda-CDM. It includes both ordinary matter and a rare interacting type of matter called cold dark matter (CDM) and dark energy, known as Lambda. Both matter and dark energy shape how the universe expands, but in opposite ways. Through gravitational attraction, matter and dark matter slow down the expansion, while dark energy speeds it up. The amount of each affects how the universe evolves. The model is effective in validating the results of previous experiments and describing what the universe looks like over time, Ishak-Boushaki said.
This animation shows how baryon acoustic oscillations act as a cosmic ruler to measure the expansion of the universe. Credit: Collaboration of Claire Lamman/DESI and Jenny Nuss/Berkeley Lab
However, when DESI’s first-year results are combined with data from other studies, there are some subtle differences from what the Lambda-CDM model would predict.
“Our results show some interesting deviations from the standard model of the universe that could indicate that dark energy evolves over time,” Ishak-Boushaki said. “The more data we collect, the better equipped we will be to determine whether this finding holds. With more data, we could identify or confirm different explanations for the result we observe. If it persists, such a result will shed some light on what causes cosmic acceleration and provide a huge step forward in understanding the evolution of our universe.”
More data will also improve other early DESI results, which weigh in on the Hubble constant — a measure of how fast the universe is expanding today — and the mass of particles called neutrinos.
The importance of blind analysis in research
DESI is the first spectroscopic experiment to perform a completely blinded analysis, hiding the actual result from the scientists to avoid any subconscious confirmation bias. The researchers work “blind” with the edited data and write computer code to analyze their findings. Once everything is complete, they apply their analysis to the original data to uncover the real answer.
“Dr. Ishak-Boushaki’s research and his collaboration with scientists from approximately 70 institutions are revealing important insights about our universe, and the results are fascinating,” said Dr. David Hyndman, NSM Dean and Francis S. and Maurine G. Johnson Distinguished University Chair. “It’s inspiring to have such world-class research programs at UT Dallas and to see our scientists play a key role in major discoveries.”
Reference: “Year 1 Cosmology Results” by DESI Collaboration et al., 4 April 2024.
DESI was constructed and is operated with funding from the Department of Energy’s (DOE) Office of Science and is located on the NSF-operated Nicholas U. Mayall 4-meter telescope at KPNO. NOIRLab. DOE’s Lawrence Berkeley National Laboratory manages the DESI experiment.
DESI also supports the National Energy Research Scientific Computing Center, the primary computing facility for DOE’s Office of Science. Additional support for DESI is provided by the NSF; UK Science and Technology Facilities Council; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; French Commission for Alternative Energies and Atomic Energy; National Humanities, Sciences and Technologies Council of Mexico; Ministry of Science and Innovation of Spain; and DESI member institutions.
The DESI Collaboration is honored to conduct scientific research on Iolkam Du’ag (Kitt Peak), a mountain of special significance to the Tohono O’odham Nation.