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