A New Study Says We May Be Living in a Variable Universe

Dark energy’s grip on the cosmos could be more fickle than scientists once believed.

• The standard cosmological model known as Lambda-CDM (ΛCDM) proposes that dark energy is a constant force in the universe.
• However, an early “hint” in a new detailed map from the Dark Energy Spectroscopic Instrument shows that dark energy can actually grow stronger and weaker over time.
• While this evidence isn’t enough to be considered a discovery, it does call into question some underlying assumptions about how the universe formed and is expanding.

Understanding the universe and our place in it is the great journey of human science, and right now the best theory of… well… everything is a concept known as the Lambda-CDM (ΛCDM) model. With observable matter only making up roughly 5 percent of the universe, this model represents dark energy (Λ) and cold dark matter (CDM), which together are believed to make up everything else. There’s just one problem—dark matter and dark energy are invisible, and only weakly interacts with gravity.

So, in other words, there’s more than a few mysteries where dark matter and dark energy are concerned. And now, a new cosmological map developed by the Dark Energy Spectroscopic Instrument (DESI) is creating a few more. DESI—outfitted at Kitt Peak National Observatory in Tucson, Arizona—just commenced a five-year effort to make the most detailed map of the known universe, including 40 million galaxies stretched across 11 billion years. The first data release, just recently published online, is already showing that the cosmological model is pretty good, but can’t quite predict everything that the instrument is seeing.

“So far, we’re seeing basic agreement with our best model of the universe, but we’re also seeing some potentially interesting differences that could indicate that dark energy is evolving with time,” Michael Levi, DESI director and a scientist at the Department of Energy’s Lawrence Berkeley National Laboratory, said in a press statement. “Those may or may not go away with more data, so we’re excited to start analyzing our three-year dataset soon.”

Those differences are in reference to the cosmological constant, an idea—first put forward by Albert Einstein in 1915— that suggests the universe is expanding at a constant rate. This is thought to be powered by the unceasing, and unchanging work of dark energy, and has led astronomers to believe that, eventually, the universe will simply expand indefinitely until even the very last atoms are ripped apart. However, DESI’s initial results contradict this idea. Instead, they indicate that dark energy appears to grow stronger and weaker over time.

DESI gathered this data by focusing on Baryon Acoustic Oscillations (BAOs)—“bubbles” formed from the explosive early moments of the universe. Because things were so hot and heavy (literally) when the universe formed, subatomic particles were moving too fast for atoms to form. So, the nuclei of hydrogen and helium—known as baryons—were pervasive on their own. These baryons formed acoustic waves that eventually froze in place when the universe thinned and cooled.

Scientists use these BAOs as a “cosmic ruler,” which allows them to measure the growth of the universe at different times in the past based on their distances. And so far, this technique has found that the cosmological constant isn’t very constant at all.

“We do see, indeed, [see] a hint that the properties of dark energy would not correspond to a simple cosmological constant,” astrophysicist at the Lawrence Berkeley lab Palanque-Delabrouille told The New York Times. “And this is the first time we have that…[but] I wouldn’t call it evidence yet. It’s too, too weak.”

This new data comes at an important time for cosmology’s investigations into the underpinning of everything—and it’s also not the cosmological model’s only competitor. This week, a meeting at London’s Royal Society will question this standard view, with astronomers bringing evidence of the universe’s “lopsidedness” along with groundbreaking (and perplexing) data from the James Webb Space Telescope. All of this comes in preparation for large sky surveys scheduled to come online in the next couple years, including the Vera C. Rubin Observatory and Nancy Grace Roman Space Telescope.

“We are in the golden era of cosmology, with large-scale surveys ongoing and about to be started, and new techniques being developed to make the best use of these datasets,” Arnaud de Mattia, co-leader of DESI’s group interpreting the cosmological data, said in a press statement. “We’re all really motivated to see whether new data will confirm the features we saw in our first-year sample and build a better understanding of the dynamics of our universe.”

Some 2,600 years in the making, that great human journey of universal understanding is entering a new era.