DESI Data Suggests Dark Energy May Be Evolving

The Dark Energy Spectroscopic Instrument (DESI) has released its second analysis of initial data, revealing a potential deviation in the nature of dark energy that could fundamentally reshape modern cosmology. This finding, based on approximately one-third of the instrument’s projected total dataset, suggests that the equation of state parameter for dark energy may not be constant over time. The results indicate a significance between 2.8 and 4.2 sigma, a level that does not yet meet the conventional 5-sigma threshold required for a definitive scientific discovery. However, if confirmed with additional data, this observation could represent a transformation as significant as the original discovery of cosmic acceleration in 1999. The analysis challenges the standard cosmological constant model, which has long been the prevailing explanation for the universe’s accelerating expansion.

For over two decades, the scientific community has operated under the assumption that dark energy is a cosmological constant, a uniform energy density that remains unchanged throughout cosmic history. In this standard model, the equation of state parameter, denoted as w, is exactly equal to negative one. This value implies that the pressure of dark energy is constant relative to its density, driving the expansion of the universe at an accelerating rate. The discovery of this acceleration by two independent research teams in 1999, the High-Z Supernova Search Team and the Supernova Cosmology Project, earned Saul Perlmutter, Brian Schmidt, and Adam Riess the 2011 Nobel Prize in Physics. The DESI findings now introduce the possibility that w may evolve, potentially crossing the negative one boundary, which would necessitate a reevaluation of fundamental physical laws.

The DESI instrument is a groundbreaking spectroscopic device capable of measuring the optical spectra of 5,000 galaxies simultaneously. By analyzing the spectral fingerprints of these galaxies, scientists can determine their precise distances using redshifts, which measure the stretching of light wavelengths due to cosmic expansion. This technical capability allows for the creation of a three-dimensional map of the universe that spans vast cosmic distances and lookback times. The current results are derived from three years of DESI operations, with the collaboration now having completed four years of observations. The team is actively analyzing this expanded dataset to refine their measurements and improve the precision of their constraints on dark energy properties.

The potential evolution of dark energy suggested by DESI data presents a complex theoretical scenario. The measurements indicate that the universe may be transitioning from an accelerating phase toward a decelerating one in the future, a stark contrast to the standard model’s prediction of continued acceleration. Furthermore, the data hints that the equation of state parameter w may cross the negative one boundary. When w is greater than negative one, the density of dark energy decreases over time, a behavior that can be explained by scalar field models. Conversely, when w is less than negative one, the density increases, leading to theoretical challenges known as phantom scenarios. A transition across this boundary cannot be explained by single-field theories, implying the need for more complex multi-field frameworks.

If the deviation from w equals negative one is confirmed at higher significance, the implications for theoretical physics would be profound. Such a finding would rule out the cosmological constant as the sole explanation for dark energy. Moreover, a crossing of the phantom divide would necessitate the development of more complex theories, potentially involving quantum gravity or modifications to Einstein’s general relativity. These developments represent a critical frontier in physics, where astronomical observations provide crucial insights into the fundamental nature of space, time, and energy. The DESI survey is expected to be completed and fully analyzed by 2027, providing significantly improved constraints that may lead to a more complete theory of gravity and cosmic evolution.

Complementary experiments are also underway to verify these findings using independent techniques. The space telescope Euclid and the Vera C. Rubin Observatory are among the projects that will enhance our understanding of dark energy.

In a separate development within the physics community, the Physical Society of Japan (JPS) has announced the winners of the 6th Fumiko Yonezawa Memorial Prize for 2025. This prize honors the legacy of the late Fumiko Yonezawa, an emeritus professor at Keio University who made major contributions to physics, including the development of the coherent potential approximation. Prof. Yonezawa was also the first female president of the JPS and served as president of the Society for Women Scientists for a Bright Future, where she actively promoted the participation of women in science. The prize is designed to celebrate her achievements and encourage the activities of female members of the JPS.

The 2025 recipients of the Fumiko Yonezawa Memorial Prize include Dr. Miho Katsuragawa, Dr. Natsuki Tomida, and Dr. Sachiko Nakamura. Dr. Katsuragawa, an Assistant Professor at Kyoto University, has pioneered innovative approaches in nondestructive elemental analysis and cancer radiation therapy. She utilized a hard-X-ray detector originally designed for an X-ray astronomy satellite to achieve a positional resolution of one millimeter in elemental analysis using negative muons. This technology has already led to industrial applications, such as studying the distribution of lithium in Li-ion batteries, and has attracted significant attention from medical researchers for its potential in visualizing radiopharmaceuticals within tumors.

Dr. Natsuki Tomida, also an Assistant Professor at Kyoto University, was recognized for her work on the origin of hadron masses and the development of large-area, high-time-resolution detectors. She achieved remarkable accomplishments in the search for eta-prime bound nuclei at the SPRING-8 LEPS2 facility. Her introduction of a novel method involving proton-eta-prime coincidence significantly reduced background noise in experiments. Additionally, Dr. Tomida developed high-performance resistive plate chambers (RPCs) with the world’s highest timing resolution for large-area detectors. These detectors have been adopted at J-PARC and major international research institutes, establishing her as a leader in the international collaboration for next-generation RPC development.

Dr. Sachiko Nakamura, an Associate Professor at Kyushu University, was honored for her novel studies on superconducting dynamics using nonlinear terahertz spectroscopy. She has broken new ground in observing Higgs modes in superconductors by combining low-temperature experimental techniques with terahertz waves. Dr. Nakamura demonstrated that under supercurrent injection, Higgs modes can be observed via linear coupling with terahertz waves, a method that expands the range of applicable superconductors compared to previous nonlinear optical responses. Her work revealed that the flux core mass in certain superconductors is comparable to the electron mass, contrary to previous theoretical predictions, providing important insights into ultrafast dynamics and the mechanism of superconducting breakdown.

Another significant event in the physics community was the academic seminar held on March 20, 2025, to honor Academician Junhao Chu of the Chinese Academy of Sciences. The seminar, titled “Advancements and Perspectives in China’s Infrared Science,” was held at the Crowne Plaza Shanghai Fudan Hotel and attended by more than 200 researchers, educators, and industry representatives. Academician Chu is widely recognized for his contributions to infrared physics, including the resolution of a long-standing problem concerning the intrinsic optical absorption spectrum of mercury cadmium telluride. He also derived the “CXT formula,” which remains a fundamental reference for assessing infrared detector materials. The seminar featured technical presentations on augmented reality displays, space-based infrared detectors, and induced photoelectric effects, highlighting the strategic importance of Chu’s research in aligning scientific inquiry with national needs.

The 25th Asian Physics Olympiad was successfully organized in Dhahran, Saudi Arabia, from May 4 to 12, 2025. Supported by the Ministry of Education, Saudi Arabia, Mawhiba, and the King Fahd University of Petroleum and Minerals, the event brought together 224 students from 30 countries or territories. Hyeokjoon Lee from South Korea was awarded the absolute winner or first place, followed by Zhang Jingsong and Han Yicao from China in second and third places, respectively. Mazen Zaid Alshakhs from Saudi Arabia received the APhO president’s Book Prize for the best participant from the host nation.

The Association of Asia Pacific Physical Society (AAPPS) also provided an award for the best girl student, which was given to Yegenbergenova Nurgul from Kazakhstan. This award is endorsed by the Working Group 5 of the International Union of Pure and Applied Physics (IUPAP) on Women in Physics and the Women in Physics Working Group of AAPPS.

Subject of Research: Cosmological observations of dark energy evolution and recent awards in physics

Article Title: News and views (5&6)

Article References: AAPPS Bulletin (2025). News and views (5&6). AAPPS Bulletin, 35(1), Article 15. https://doi.org/10.1007/s43673-025-00155-9

Image Credits: AI Generated

DOI: 10.1007/s43673-025-00155-9

Keywords: dark energy, DESI, cosmology, equation of state, Fumiko Yonezawa Memorial Prize, Asian Physics Olympiad, infrared science, superconductivity, particle physics, X-ray astronomy, News, views