What is the expansion history of the universe? That is what the Canadian Hydrogen Intensity Mapping Experiment (CHIME) is designed to determine. Located at the Dominion Radio Astrophysical Observatory about 400 km northeast of Vancouver, British Columbia, CHIME is slated to begin operating in late 2015.
Unlike other approaches to mapping the structure of the universe as a function of time (see, for instance, the article by Josh Frieman in Physics Today, April 2014, page 28), CHIME won’t look for details about individual galaxies. Instead, the idea is to measure the 21-cm line of neutral hydrogen, which traces the positions of galaxies and, in turn, the distribution of matter. The experiment is sensitive over the redshift range of 0.8–2.5, which corresponds to the period from about 7 billion to 11 billion years ago.
CHIME will consist of five parallel, parabolic, cylindrical, mesh reflectors, each 100 m long and...
