The Struggle to Measure Cosmic Expansion

The New York Times : This spring, in what he called “a triumph of metrology,” Adam Riess from Johns Hopkins University and Lucas Macri of Texas A&M University,announced they had used the Hubble Space Telescope to make the newest and most precise measurement yet of the Hubble constant-- the measure that tells astronomers how fast the universe is growing, how big it is and how old it is.