Dark energy's shifting role explored through advanced supercomputer simulations

Dark energy's shifting role explored through advanced supercomputer simulations
by Riko Seibo
Tokyo, Japan (SPX) Oct 06, 2025

Since the early 20th century, scientists have known that the Universe is expanding at an accelerating pace. This acceleration has been attributed to dark energy, a mysterious property of spacetime that counteracts gravity. Traditionally, cosmologists have treated dark energy as constant under the Lambda Cold Dark Matter (LCDM) model, but new data are challenging this assumption.

Recent findings from the Dark Energy Spectroscopic Instrument (DESI) indicate that dark energy may not be constant, suggesting a dynamic dark energy (DDE) component that changes over time. This discovery raises major questions about how such time variation could affect the formation and evolution of large-scale cosmic structures.

To explore these effects, a team led by Associate Professor Tomoaki Ishiyama from Chiba University's Digital Transformation Enhancement Council conducted one of the largest cosmological simulations ever run. Working with Francisco Prada from the Instituto de Astrofisica de Andalucia, Spain, and Anatoly A. Klypin from New Mexico State University, USA, the researchers published their study in Physical Review D on August 4, 2025.

Using Japan's Fugaku supercomputer, the team performed three massive N-body simulations, each eight times larger in volume than previous efforts. One represented the standard Planck-2018 LCDM Universe, while two others incorporated dynamic dark energy. By comparing models, the researchers isolated the effects of DDE and examined how changes in cosmological parameters influenced results.

When they adjusted the matter density in the DDE model based on DESI data - about 10 percent higher than standard values - they found striking results. A denser Universe amplified gravitational forces, leading to earlier and more efficient formation of massive galaxy clusters. The DESI-derived DDE model predicted up to 70 percent more massive clusters during the early Universe.

The team also analyzed baryonic acoustic oscillations (BAOs) - the cosmic imprints of ancient sound waves used to measure distances. The DDE simulations showed a 3.71 percent shift in the BAO peak toward smaller scales, consistent with DESI observations.

Further examination of galaxy clustering revealed that the DESI-derived DDE model produced stronger clustering signals at smaller scales, again aligning with observational data. "Our large simulations demonstrate that variations in cosmological parameters, particularly the matter density in the Universe, have a greater influence on structure formation than the DDE component alone," explains Dr. Ishiyama.

Looking ahead, upcoming surveys such as those from the Subaru Prime Focus Spectrograph and DESI will provide even finer detail, helping refine our understanding of dark energy's true nature. "This study provides a theoretical basis for interpreting such upcoming data," adds Dr. Ishiyama.

Research Report:Evolution of clustering in cosmological models with time-varying dark energy