Conflicting Values For Hubble Constant Not Due To Measurement Error, Study Finds

Jennifer Ouellette reports via Ars Technica: Astronomers have made new measurements of the Hubble Constant, a measure of how quickly the Universe is expanding, by combining data from the Hubble Space Telescope and the James Webb Space Telescope. Their results confirmed the accuracy of Hubble's earlier measurement of the constant's value, according to their recent paper published in The Astrophysical Journal Letters, with implications for a long-standing discrepancy in values obtained by different observational methods known as the "Hubble tension." There was a time when scientists believed the Universe was static, but that changed with Albert Einstein's general theory of relativity. Alexander Friedmann published a set of equations showing that the Universe might actually be expanding in 1922, with Georges Lemaitre later making an independent derivation to arrive at that same conclusion. Edwin Hubble confirmed this expansion with observational data in 1929. Prior to this, Einstein had been trying to modify general relativity by adding a cosmological constant in order to get a static universe from his theory; after Hubble's discovery, legend has it, he referred to that effort as his biggest blunder. The article notes how scientists have employed different methods to calculate the Hubble Constant, including observing nearby celestial objects, analyzing gravitational waves from cosmic events, and examining the Cosmic Microwave Background (CMB). However, these approaches yield differing values, highlighting the challenge in pinning down the constant precisely. A recent effort involved making additional observations of Cepheid variable stars, correlating them with the Hubble data. The results further confirmed the accuracy of the Hubble data. "We've now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence," said co-author and team leader Adam Riess, a physicist at Johns Hopkins University. "Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder. With measurement errors negated, what remains is the real and exciting possibility that we have misunderstood the Universe."

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