Space Telescope Data Reignites Debate Over How Fast Our Universe Is Expanding

"A new front has opened in the longstanding debate over how fast the universe is expanding," writes Science magazine:For years astronomers have argued over a gulf between the expansion rate as measured from galaxies in the local universe and as calculated from studies of the cosmic microwave background (CMB), the afterglow of the Big Bang. The disparity was so large and persistent that some astronomers thought the standard theory of the universe might have to be tweaked. But over the past week, results from NASA's new James Webb Space Telescope orbiting observatory suggest the problem may be more mundane: some systematic error in the strategies used to measure the distance to nearby galaxies. "The evidence based on these data does not suggest the need for additional physics," says Wendy Freedman of the University of Chicago, who leads [the Carnegie-Chicago Hubble Program, or CCHP] that calculated the expansion rate from JWST data using three different galactic distance measurements and released the results on the arXiv preprint server. (The papers have not yet been peer reviewed.) The methods disagreed about the expansion rate, known as the Hubble constant, or H0, and two were close to the CMB prediction. Specifically, the team used JWST to measure the distance to 10 local galaxies using three stars with a predictable brightness: Cepheids, the brightest red giant stars, and carbon stars. Science notes that the last two methods "agreed to about 1%, but differed from the Cepheid-based distance by 2.5% to 4%." Combining all three methods the team derived a value "just shy of 70 km/s per Mpc," according to the article - leading the University of Chicago's Freedman to say "There's something systematic in the measurements. Until we can establish unambiguously where the issue lies in the nearby universe, we can't be claiming that there's additional physics in the distant universe." But the controversy continues, according to Adam Riess of Johns Hopkins University (leader of a team of Hubble Constant researchers known as SH0ES).Riess points out that other teams have used JWST to measure distances with all three methods separately and have come up with values closer to the original SH0ES result. He also questions why CCHP excluded data from telescopes other than JWST. "I don't see a compelling justification for excluding the data they do," he says. Thanks to long-time Slashdot reader sciencehabit for sharing the article.

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