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It\u2019s looking more and more as if dark energy, the mysterious factor that scientists say is behind the accelerating expansion of the universe, isn\u2019t as constant as they once thought.<\/p>\n
The latest findings from the Dark Energy Spectroscopic Instrument, or DESI, don\u2019t quite yet come up to the level of a confirmed discovery, but they\u2019re leading scientists to rethink their views on the evolution of the universe \u2014 and how it might end.<\/p>\n
Readings from DESI\u2019s Data Release 2, published on March 19, suggest dark energy\u2019s influence isn\u2019t as strong as it used to be. Scientists had thought that the universe\u2019s endless expansion would eventually lead to a state of cosmic stasis known as the \u201cBig Chill.\u201d But if dark energy fizzles out, billions or trillions of years from now, the universe may fall back on itself and end up in a reverse Big Bang, or \u201cBig Crunch.\u201d<\/p>\n
\u201cWhat we are seeing is deeply intriguing,\u201d Alexie Leauthaud-Harnett, co-spokesperson for DESI and a professor at the University of California at Santa Cruz, said in a news release. \u201cIt is exciting to think that we may be on the cusp of a major discovery about dark energy and the fundamental nature of our universe.\u201d<\/p>\n
DESI uses the 4-meter Mayall Telescope at Kitt Peak National Observatory in Arizona to map the universe in 3D, going back 11 billion years in time. The international effort is managed by the U.S. Department of Energy\u2019s Berkeley National Lab. During the first three years of its five-year mission, DESI mapped nearly 15 million galaxies and quasars \u2014 and those are the readings that were released this week.<\/p>\n
The readings confirm preliminary results that were released last year. Both sets of findings add a new layer of complexity to the debate over dark energy, which is thought to account for about 70 percent of the universe\u2019s cosmic contents.<\/p>\n
Dark energy\u2019s influence has been compared to the effect of blowing up a polka-dotted balloon. As the balloon gets bigger, the polka dots spread farther apart. In a similar way, galaxies and galaxy clusters have been expanding farther apart on the fabric of spacetime.<\/p>\n
A quarter-century ago, scientists analyzed data about the distance of supernovae during different eras of the universe\u2019s history \u2014 and determined that the spreading effect seemed to be accelerating over time. Their findings earned them the Nobel Prize in physics in 2011.<\/p>\n
Some scientists noted that dark energy\u2019s effects could be explained most easily by invoking a cosmological constant. Such a constant wouldn\u2019t explain what dark energy is. It would, however, balance out the equations describing the nature of the universe.\u00a0 Theoretical physicist Albert Einstein first came up with the idea in 1917, but he later abandoned the concept and was said to have called it his \u201cbiggest blunder.\u201d Decades later, the idea was revived for dark energy.<\/p>\n
DESI was designed to bring a higher level of precision to measurements of dark matter\u2019s effects over time. The telescope\u2019s readings were analyzed to focus in on subtle patterns known as baryon acoustic oscillations, which can reveal the distribution of matter at different epochs in the history of the universe. Such readings serve as a \u201cstandard ruler\u201d for measuring the strength of dark energy.<\/p>\n<\/p><\/div>\n
The latest findings, released in conjunction with this week\u2019s meeting of the American Physical Society, are based on DESI\u2019s data as well as other types of measurements. Taken together, they suggest that dark matter began making its mark on the universe\u2019s evolution earlier than previously thought, and that those effects are now weaker than what had been predicted.<\/p>\n
\u201cIt\u2019s not just that the data continue to show a preference for evolving dark energy, but that the evidence is stronger now than it was,\u201d said the University of Portsmouth\u2019s Seshadri Nadathur, co-chair of DESI\u2019s Galaxy and Quasar Clustering working group. \u201cWe\u2019ve also performed many additional tests compared to the first year, and they\u2019re making us confident that the results aren\u2019t driven by some unknown effect in the data that we haven\u2019t accounted for.\u201d<\/p>\n
To explain what they\u2019re seeing, physicists may need to add new twists to theories relating to the origin and evolution of the universe.<\/p>\n
\u201cFor a couple of decades, we\u2019ve had this standard model of cosmology that is really impressive,\u201d said Willem Elbers, a postdoctoral researcher at Durham University and co-chair of DESI\u2019s Cosmological Parameter Estimation working group. \u201cAs our data are getting more and more precise, we\u2019re finding potential cracks in the model and realizing we may need something new to explain all the results together.\u201d<\/p>\n
But don\u2019t resign yourself to the universe\u2019s eventual collapse just yet. The findings haven\u2019t yet reached the level of confidence that\u2019s required for a confirmed discovery just yet. In statistical terms, that level is known as 5 sigma. That means there\u2019s only a 1-in-3.5 million chance that the measurements are the result of a fluke.<\/p>\n
In contrast, the findings that rely on DESI\u2019s readings and other observations are in the range of 2.8 to 4.2 sigma \u2014 and a 3-sigma event has a 0.3% chance of being a statistical fluke. That\u2019s a small chance, to be sure, but more data will be needed to make sure the DESI team\u2019s claims are rock-solid.<\/p>\n
Fresh waves of data are sure to come from DESI, which is still in the midst of its sky survey. Other instruments \u2014 including the European Space Agency\u2019s Euclid space telescope, NASA\u2019s newly launched SPHEREx observatory and the Vera C. Rubin Observatory in Chile \u2014 are likely to contribute data as well.<\/p>\n
In the meantime, theoretical physicists will be putting in long hours.<\/p>\n
\u201cOur results are fertile ground for our theory colleagues as they look at new and existing models, and we\u2019re excited to see what they come up with,\u201d said Michael Levi, DESI director and a scientist at Berkeley Lab. \u201cWhatever the nature of dark energy is, it will shape the future of our universe.\u201d<\/p>\n
A version of this report was published on Alan Boyle’s Cosmic Log. The view that dark energy can change over time also received a boost from supercomputer simulations that looked at how different theoretical models would be expected to affect the large-scale evolution of the universe. Read about the research.<\/em><\/p>\n<\/p><\/div>\n