You may have noticed that the universe is pretty big—in fact, possibly infinite. These immense scales offer a challenge for scientists who seek to model the “cosmic web,” a network of large-scale structures that link the universe and intersect at nodes where galaxies accumulate into clusters.
That’s why researchers led by Marco Bonici, a cosmologist at the University of Waterloo, have developed an emulator called Effort.jl that can parse cosmic data much faster than traditional models. This approach will accelerate the pace of discoveries about the mysterious cosmic web and help test fundamental theories about the nature of spacetime.
The tool achieves “exceptional computational performance without sacrificing accuracy,” according to the team’s study, which was published last week in the Journal of Cosmology and Astroparticle Physics.
“An emulator is a mimic, in a sense,” Bonici said in a call with 404 Media. “It basically lets you do the same kind of analysis that you would do on a supercomputer in a few days of time, in a bunch of hours on your laptop.”
Emulators can imitate the predictions of more complex models by training on their outputs, he added, without getting bogged down in the underlying physics and repetitive calculations.
“Of course, there is a trade-off in precision,” Bonici said. “This is an approximate method. The goal of my study was to show that for some scenarios, we are able to recover the final result of an analysis, even with the emulator. In this way, we can show that the error that we are introducing is negligible.”
The new emulator is designed to probe the Effective Field Theory of Large-Scale Structure (EFTofLSS), a well-corroborated theoretical model of the universe. Bonici first started developing Effort.jl—an abbreviation of “effective field theory surrogate”—during his work on the European Space Agency’s Euclid space telescope, which launched in 2023.
Euclid, along with the Dark Energy Spectroscopic Instrument (DESI) in Arizona, are producing a flood of exciting new observations about the cosmic web, dark matter, and dark energy that may overturn longstanding assumptions about the universe. Ejjort.jl aims to help interpret these findings more quickly.
Dark matter is an unidentified substance that accounts for most matter in the universe and forms the basis of the cosmic web, while dark energy is the term for whatever the heck is causing the universe to expand at an accelerating rate.
The concept of dark energy dates back to Albert Einstein, who proposed that a “cosmological constant” acts as an anti-gravity force to keep the universe in a static state, preventing it from collapsing under its own gravity. Einstein famously called the constant his “greatest blunder” after Edwin Hubble discovered that the universe was not static, but was rather expanding.
However, the cosmological constant was later repurposed into the standard model of cosmology, also called the Lambda-cold dark matter model (ΛCDM), where Lambda stands for the constant. This constant describes the accelerating expansion of the universe and is now closely associated with dark energy.
This complicated tale now has another exciting twist: DESI’s observations strongly suggest that this constant is not all that constant across the universe’s history. In other words, the effect of dark energy on the universe may change over time, a finding that could upend our basic assumptions about this strange cosmos we inhabit (this seems to happen a lot).
“With DESI’s first data release, we had the first hint that was pointing towards this deviation from the cosmological constant,” Bonici said. “With the second release, that hint was still there.”
“If we have an independent confirmation that this is actually correct, then this will be the first evidence for a behavior beyond the standard model of cosmology,” he continued. “It would be a huge revolution.”
The standard model is still highly accurate in describing cosmic phenomena, but scientists have long wondered about weak spots in its armor, including the unexplained nature of dark matter and dark energy. As Euclid and DESI gather real observations of the cosmic web, these underlying mysteries of our universe will come into sharper focus.
Bonici and his colleagues hope Effort.jl can speed up the process of evaluating the enormous reams of incoming data, acting as a complement to more resource-intensive models that require supercomputers and other expensive and time-consuming approaches.
Though Bonici’s work on the emulator requires a painstaking focus on lines of code, he does occasionally get an opportunity to step back and consider the broad implications of his field. To that end, he recalled that one of his colleagues opened his PhD thesis with the wry observation: “Cosmology is that humble branch of physics which wants to explain the universe as a whole.”
“We are describing literally everything in the universe,” Bonici said. “Most of the time, I just focus on the small details, but when I look at the big picture, to me, it is always exciting to think about, and mind blowing.”