The DESI collaboration explores the accelerating expansion of the universe through extensive mapping from its early stages to the present. Their findings challenge traditional cosmic models and suggest new insights into dark energy, while using groundbreaking, unbiased research methods.
As part of the Dark Energy Spectroscopic Instrument (DESI) collaboration, a team of researchers, including an astrophysicist from the University of Texas at Dallas, are 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 multi-year experiment to advance understanding of the history and fate of the cosmos.
On April 4, Ishak-Boushaki presented analyzes of the first year of data collected by the DESI experiment at a meeting of the American Physical Society in Sacramento, California, along with two other DESI scientists. Ishak-Boushaki presented the cosmological results derived from DESI data and their implications for the universe. Researchers also shared the results of the first year of data collected in multiple articles posted on the preprint site arXiv.
The role of the DESI instrument
The DESI instrument, based at Kitt Peak National Observatory (KPNO) in Arizona, collects light from the most remote parts of the universe, allowing scientists to map the cosmos as it was in its youth and trace its evolution to what is observed today. Understanding how the universe evolved is linked to how it ends and to one of the greatest mysteries in physics: what’s behind the observation that the universe’s expansion is accelerating?
The analysis of DESI’s first year of data collection confirmed the basic principles of what scientists consider the best model of the universe, but it also indicates that there is more to learn about the underlying cause, or causes, of cosmic acceleration that led to its discovery won the Nobel Prize for Physics in 2011.
Cosmic acceleration is problematic because it contradicts the action of gravity, which pulls objects with mass together in our solar system and nearby space.
“Gravity pulls matter together, so that when we throw a ball in the air, Earth’s gravity pulls it down toward the planet,” Ishak-Boushaki said. “But on the largest scales, the universe behaves differently. It behaves as if there is something disgusting that is driving the universe apart and accelerating its expansion. This is a big mystery and we are investigating it on several fronts. Is it an unknown dark energy in the universe, or is it a modification of Albert Einstein’s theory of gravity on a cosmological scale?”
Research into dark energy and the expansion of the universe
Many scientists believe that dark energy plays a key role in cosmic acceleration, but this is not yet well understood. Some theorize that it is 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 cosmos ever created using the most accurate measurements to date. This is the first time that scientists have measured the expansion history of the early universe with an accuracy of better than 1%.
The guiding model of the universe is known as Lambda-CDM. It includes both ordinary matter and a rarely interacting type of matter called cold dark matter (CDM) and dark energy known as Lambda. Both matter and dark energy determine how the universe expands, but in opposite ways. Due to gravity, matter and dark matter slow down the expansion, while dark energy accelerates it. The amount of each affects how the universe evolves. This model is effective at validating results from previous experiments and describing what the universe looks like through time, Ishak-Boushaki said.
This animation shows how acoustic oscillations of baryons act as a cosmic ruler for measuring the expansion of the universe. Credit: collaboration 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,” says Ishak-Boushaki. “The more data we collect, the better we will be able to determine whether this finding holds up. With more data we can identify different explanations for the result we observe or confirm. If this holds, such a result will shed some light on what is causing the cosmic acceleration and represent a huge step forward in understanding the evolution of our universe.”
More data will also improve DESI’s other early results, which weigh on Hubble’s constant — a measure of how fast the universe is expanding today — and the mass of particles called neutrinos.
Importance of blind analysis in research
DESI is the first spectroscopic experiment to perform a completely blinded analysis, which hides the true result from the scientists to prevent any unconscious confirmation bias. Researchers work ‘blind’ with modified data and write computer code to analyze their findings. Once everything is finalized, they apply their analysis to the original data to reveal the actual answer.
“Dr. Ishak-Boushaki’s research and his collaboration with scientists from some 70 institutions are revealing important insights about our universe, and the results are fascinating,” said Dr. David Hyndman, Dean of NSM and the Francis S. and Maurine G. Johnson Distinguished University Chair. . “It is inspiring to have such world-class research programs at UT Dallas and to see our scientists playing a key role in fundamental discoveries.”
Reference: “Year 1 Cosmology Results” by DESI Collaboration et al., April 4, 2024.
Built and operated with funding from the Department of Energy (DOE) Office of Science, DESI is located atop the National Science Foundation’s (NSF) Nicholas U. Mayall 4-meter Telescope at KPNO, which is managed by the NSF’s NOIRLab. The DOE’s Lawrence Berkeley National Laboratory is managing the DESI experiment.
DESI is also supported by the National Energy Research Scientific Computing Center, the primary computing facility for the DOE Office of Science. Additional support for DESI is provided by the NSF; the Science and Technology Facilities Council of the United Kingdom; the Gordon and Betty Moore Foundation; the Heising-Simons Foundation; the French Commission for Alternative Energy and Atomic Energy; the National Council for Humanities, Sciences and Technologies of Mexico; the 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.