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This week, leading experts at clocking one of the most contested numbers in the cosmos—the Hubble constant, the rate at which the universe expands—gathered in hopes that new measurements could point the way out of a brewing storm in cosmology.
No luck so far. A hotly anticipated new cosmic yardstick, reliant on red giants, has served only to muddle the debate about the actual value of the constant, and other measurements brought no resolution. “It was the craziest conference I’ve been to,” said Daniel Scolnic, an astrophysicist at Duke University in Durham, North Carolina. “Everyone felt like they were on this rollercoaster.”
Meeting - Kavli - Institute - Theoretical - Physics
The meeting, at the Kavli Institute for Theoretical Physics in Santa Barbara, California, was the latest episode in a saga stretching back to the 1920s, when Edwin Hubble established that the farther one looks into space, the faster galaxies are speeding away from Earth. Since then, scientists have devoted entire careers to refining the rate of that flow, Hubble’s eponymous constant, or H0. But recently, the problem has hardened into a transdisciplinary dispute.
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On one side are cosmologists who gather data from the greatest distances, such as a map of the big bang’s afterglow recorded by the European satellite Planck. They compare the apparent size of features in that afterglow with their actual size, as predicted by theory, to calculate an H0 of about 67. That means distant galaxies should be flying away from the Milky Way 67 kilometers per second faster for every additional megaparsec astronomers gaze out into space.
Astronomers - Galaxies - Chains - Inferences - Universe
But when astronomers look at actual galaxies, using delicate chains of inferences to make up for the universe’s frustrating lack of tick marks, they get a different number. Over the past few years, a team led by...
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