In DepthAstrophysics

New tactics clash on speed of expanding universe

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Science  26 Jul 2019:
Vol. 365, Issue 6451, pp. 306-307
DOI: 10.1126/science.365.6451.306

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Summary

Last 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. 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: Cosmologists, looking at the most ancient universe, calculate a lower H0 than astronomers, looking out from the neighborhood of the Milky Way.

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