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Clocking the universe’s expansion
Conflicting estimates of the Hubble constant — a measure of the speed of the universe’s expansion — have sparked debate among cosmologists. The discrepancy in data from the Planck satellite with data from other methods may be just a mistake, or it may require adjusting the cosmological model of the universe, as Tom Siegfried explained in “Cosmic question mark” (SN: 4/5/14, p. 18).
“I think I’m missing something,” reader Michael Herzog wrote in an e-mail. “If dark energy is causing the expansion of the universe to accelerate, wouldn’t we expect the value of the Hubble constant derived from the early universe (the Planck results) to be smaller than the current value?”