On March 19, the Dark Energy Spectroscopic Instrument (DESI) collaboration shared its findings in multiple papers posted on arXiv and in a presentation at the American Physical Society's Global Physics Summit in Anaheim, California. Researchers analyzed three years of observations by DESI at Kitt Peak National Observatory, which included nearly 15 million of the best-measured galaxies and quasars. The team identified patterns suggesting that dark energy has not remained constant over time, providing stronger evidence that dark energy might be evolving.
If confirmed, the findings of varying dark energy could fundamentally alter our understanding of the universe and challenge the standard cosmological model, including the Lambda-CDM model, which has been the cornerstone of modern cosmology and may need to be modified. Currently, the conclusion of variable dark energy is at a confidence level between 2.8 and 4.2 sigma, which is just shy of the 5-sigma threshold typically required for a discovery.
The predominant cosmological model, known as Lambda-CDM, holds that the observable universe is composed of approximately 68% dark energy, 27% dark matter, and 5% ordinary matter. Dark energy, thought to be a property of space itself, is one of the universe's great mysteries, and its physical nature is presently unknown.
"What we are seeing is deeply intriguing. It is exciting to think that we may be on the cusp of a major discovery about dark energy and the fundamental nature of our universe," said Alexie Leauthaud-Harnett, co-spokesperson for DESI.
"Our findings in DESI that the dark energy is evolving in time and is not the cosmological constant is probably the most important result about cosmic acceleration since its discovery in 1998 that led to the Nobel Prize in physics in 2011," said Mustapha Ishak, a cosmologist at the University of Texas at Dallas and co-chair of the working group that analyzed the DESI data, as reported by Reuters.
"Whatever the nature of dark energy is, it will shape the future of our universe. It's pretty remarkable that we can look up at the sky with our telescopes and try to answer one of the biggest questions that humanity has ever asked," said Michael Levi, DESI director and a scientist at Berkeley Lab.
Some dramatic scenarios become more plausible, such as the big crunch, where the cosmos starts contracting instead of expanding and eventually collapses in on itself. The fate of the universe may be at stake, particularly regarding whether its expansion will continue accelerating eternally, and the exact future of the universe remains an open question.
"The DESI results tantalizingly hint at an evolving dark energy," said Arjun Dey, an astrophysicist at the U.S. National Science Foundation's NOIRLab, aligning with findings from other cosmologists, as reported by Reuters.
"Something has to break somewhere," said cosmologist Claire Lamman, a graduate student at the Center for Astrophysics Harvard & Smithsonian, according to Scientific American.
Despite countless observations of dark energy and dark matter, scientists are still unsure where they came from or what they even are. Dark energy is responsible for the acceleration of the universe's expansion, acting as a sort of anti-gravity that permeates the entirety of space.
Other experiments will soon weigh in on dark energy, adding to the ongoing investigation into its nature. The European Space Agency's Euclid mission, launched in 2023, has released early data observing 26 million galaxies, which will contribute valuable insights into the universe's expansion and dark energy.
"Our results are truly remarkable. We are seeing even stronger evidence for a fundamental shift in how we think about dark energy," said Klaus Honscheid, lead scientist of DESI instrument operations and a physics professor at The Ohio State University.
Researchers are hopeful that the new insights could point them toward a sturdier model, and other models may be a better fit than the standard model based on these findings. If it is confirmed that dark energy is dynamic, scientists will have to explore alternative theories to explain the evolution of the universe, which may include a very different future for the cosmos.
The DESI project will observe over 40 million galaxies at different distance ranges over its planned five years of service, continuing to take data over the next two years to measure roughly 50 million galaxies and other bright objects. The DESI collaboration includes more than 900 researchers from over 70 institutions around the world.
The article was written with the assistance of a news analysis system.