writes: Astronomers have measured the universe's current expansion rate (a value known as the Hubble constant) at about 44.7 miles (71.9 kilometers) per second per megaparsec (3.26 million light-years). This is consistent with a calculation that was announced last year by a research team, but it's considerably higher than the rate that was estimated by the European Space Agency's Planck satellite mission in 2015 -- about 41.6 miles (66.9 km) per second per megaparsec. The cause of this discrepancy is unclear. "The expansion rate of the universe is now starting to be measured in different ways with such high precision that actual discrepancies may possibly point towards new physics beyond our current knowledge of the universe," a researcher said.
Mike Wall writes via Space.com: "The differences in the Hubble constant estimates may reflect something that astronomers don't understand about the early universe, or something that has changed since that long-ago epoch, scientists have said. For example, it's possible that dark energy -- the mysterious force that's thought to be driving the universe's accelerating expansion -- has grown in strength over the eons, members of Riess' team said last year. The discrepancy could also indicate that dark matter -- the strange, invisible stuff that astronomers think vastly outweighs 'normal' matter throughout the universe -- has as-yet-unappreciated characteristics, or that Einstein's theory of gravity has some holes, they added."