The Mayall Telescope Star Trail in Arizona houses dark energy spectroscopy equipment
Luke Tyas/Berkeley Lab
Dark energy is one of the most mysterious features of our universe. We don’t know what it is, but it controls how the universe is expanding and its ultimate destiny. Now, the study of millions of heavenly objects reveals that they may have been thinking about all the wrong things that could potentially have dramatic consequences in the universe.
“This is the biggest hint we have about the nature of dark energy in the roughly 25 years since we discovered it,” he says. Adam Reese at Johns Hopkins University in Maryland.
The results come from three years of data collected by Arizona’s Dark Energy Spectroscopy (DESI). By combining this data with other measurements such as background radiation in cosmic microwaves and maps of supernovas, the DESI team concluded that dark energy may have changed over time.
“This is the cutting edge of human knowledge,” says a member of the DigiTeam. It’ll be Percival At the University of Waterloo, Canada. “We see amazing things throughout the universe.”
Desi is attached to a telescope and works by measuring the “redshift” of light emitted from a distant galaxy, or how that wavelength of light extends as it travels through space. From now on, researchers can determine how much the universe has expanded during the journey of light and calculate how this expansion is changing. So far, the team has analyzed light from nearly 15 million galaxies and other bright objects in the sky.
For decades, physicists have agreed that the universe is expanding at a fixed acceleration. This is a cosmological constant known as the lambda, interpreted as the driving force of dark energy. However, in April 2024, Desi’s measurements provide the first hint that the universe may actually be decreasing faster over time, with the cosmological constants not so constant.
Riess, who is not part of the Desi team, says at the time they were not sure if the discovery would last with more data. In fact, it’s just getting stronger. “It’s very exciting for me to see that. [the team] After another year and after they added more data, no issues were found in the analysis. If anything, the outcome is more important,” he says.
That being said, this discovery still does not meet the “5-sigma” statistical levels traditionally used by physicists to discover it as authentic, rather than as a statistical fluke. Current analysis reaches a maximum of 4.2 sigma, but team members Mustafa Ishak Bouzaki At the University of Texas and Dallas, the team says they believe the results will reach five sigma within two years as Digi continues to acquire the data. “This outcome with dark energy is something we never thought it would happen in our lifetime,” he says.
One of the relief, according to Ishak-Boushaki, is that the discovery relies on Desi’s data as well as several other investigations in the universe. Riess compares the situation with a multi-legged stool. With this stool, breaking one leg or deleting one dataset will not completely break your conclusion.
Assuming the feet are held, the universe looks very different from the current photographs. As dark energy continues to weaken, the universe may reach a state of expansion at a constant speed rather than faster, says Ishak Bouzaki. Some dramatic scenarios, such as “big crunches,” can also be plausible. There, instead of expanding, Cosmos begins a contract, and ultimately collapses on its own.
The exact future of the universe is an open question, not the only tool researchers use to answer it. Riess points to several other investigations in the universe, including NASA’s Nancy Gray Sloman Space Telescope and the Belarubin Observatory in Chile.
While mathematical models of the universe with changes in dark energy must keep up with these observations, Percival says he hopes future theoretical research will help design more experiments that will directly test our assumptions about this mystical power.
“When it comes to theoretical models, Pandora’s box just opened. I was stuck with the cosmological constant,” says Ishak Bouzaki. “We’re not stuck anymore.”
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