A team of scientists from Japan, Spain, and the US has utilized one of the world’s fastest supercomputers, Fugaku, to better understand the impact of dark energy throughout the cosmos.
During the experiment, the supercomputer, which uses over 150,000 CPUs to achieve over 442 petaflops of computing power, conducted one of the largest cosmological simulations to date.
This allowed the team of scientists to investigate the effects of time-varying dark energy on the Universe’s evolution. Their paper challenges the standard Lambda Cold Dark Matter (ΛCDM) model, which assumes that the effects of dark energy remain constant.
Exploring dark energy
Dark energy is responsible for the Universe’s accelerating expansion. However, the energy, which makes up roughly 70 percent of the Universe, largely remains a mystery.
Scientists have long assumed that dark energy is a constant, unchanging entity. However, recent Dark Energy Spectroscopic Instrument (DESI) data has hinted at another possibility. What if dark energy were a time-varying property of the Universe? The first DESI findings, released in 2023, suggested that dark energy is, in fact, weakening over time, meaning it is not a constant.
This allowed for the emergence of models of the cosmos that include a type of dark energy that evolves over time – a dynamical dark energy (DDE).
Led by Associate Professor Tomoaki Ishiyama from Chiba University, a team set out to investigate the impact of DDE in various scenarios, using the power of Fugaku. The team’s simulations showed that, while DDE has modest effects on its own, variations in parameters like matter density significantly influence galaxy formation and cosmic structure.
The team used Fugaku to run three high-resolution N-body simulations, each eight times larger in volume than previous studies. One simulation modeled the standard ΛCDM Universe, while two incorporated DDE. One of the two DDE simulations used fixed parameters to isolate the influence of the time-varying dark energy component. The other used parameters derived from DESI’s year one findings, including a 10% higher matter density.
The impact of dynamical dark energy
The team’s results showed that DDE by itself has a minimal impact on cosmic structure. However, the DESI-derived model, with increased matter density, did show significant effects. According to the researchers, this model predicted up to 70 percent more massive galaxy clusters in the Universe’s early epochs due to stronger gravitational forces.
Crucially, the researchers closely studied the DDE model’s predictions, showing that they aligned with observational data from DESI. This lends weight to the idea that dark energy is not a constant.
“In the near future, large-scale galaxy surveys from the Subaru Prime Focus Spectrograph and DESI are expected to significantly improve measurements of cosmological parameters,” Dr. Ishiyama explained in a press statement. “This study provides a theoretical basis for interpreting such upcoming data.”
Japan’s Fugaku was the world’s fastest supercomputer, until it was overtaken by the United States’ Frontier supercomputerin 2022. Now, the nation is aiming to overtake Frontier, having invested $750 million to develop FugakuNEXT. This next-generation supercomputer is designed to supercharge the nation’s AI and scientific research.
The paper was published in the journal Physical Review D.