In a groundbreaking study released on November 20, 2024, an international team of over 900 researchers from the DESI (Dark Energy Spectroscopic Instrument) collaboration confirmed that gravity behaves as predicted by Einstein's theory of general relativity. This significant finding not only validates our primary model of the universe but also narrows down alternative theories regarding modified gravity, which have been proposed to explain the universe's accelerating expansion, often attributed to dark energy.
Pauline Zarrouk, a cosmologist at the French National Center for Scientific Research, emphasized the importance of testing general relativity on a larger scale, stating, "Studying the rate at which galaxies formed lets us directly test our theories, and so far, we're lining up with what general relativity predicts at cosmological scales." This research utilized nearly 6 million galaxies and quasars, allowing scientists to peer back 11 billion years into the universe's past.
Additionally, the study established new upper limits on neutrino masses, the only fundamental particles whose masses remain poorly defined. The results indicate that the total mass of the three types of neutrinos should be less than 0.071 eV/c², refining previous measurements and leaving a narrow margin for future exploration.
DESI's innovative techniques have enabled the creation of the largest 3D map of the universe to date. The collaboration's recent findings extend previous analyses and enhance understanding of how galaxies and matter are distributed across various scales. Dragan Huterer, a professor at the University of Michigan, remarked, "This is the first time that DESI has looked at the growth of cosmic structure. We're showing a tremendous new ability to probe modified gravity and improve constraints on models of dark energy."
The instrument, capable of capturing light from 5,000 galaxies simultaneously, is currently in its fourth year of a five-year survey, with plans to analyze approximately 40 million galaxies and quasars by the project's conclusion. The collaboration anticipates presenting updated measurements of dark energy and the universe's expansion history in spring 2025, further deepening our understanding of these cosmic mysteries.
Mark Maus, a PhD student involved in the project, encapsulated the excitement surrounding the research, stating, "The idea that we can take pictures of the universe and tackle these big, fundamental questions is mind-blowing." The implications of this work could lead to advancements in our understanding of dark matter and dark energy, which together constitute about 95% of the universe, yet remain largely enigmatic.