Sitting in the high Andean desert of northern Chile at an altitude of 5100 meters, the Cosmic Background Imager (CBI) has been scrutinizing the random microkelvin anisotropies of the cosmic microwave background (CMB) since the beginning of 2000. CBI is an interferometric microwave telescope operated by a collaboration of institutions in the US, Canada, and Chile, headed by Anthony Readhead and Stephen Padin at Caltech. The collaboration has now reported the results of its first full year of observing. 1  

The new microwave interferometer’s special claim to fame is its ability to map fluctuations in the CMB with an unprecedented angular resolution of 4 arc minutes. The older microwave telescopes that have mapped the CMB in impressive detail in the last few years—Boomerang, Maxima, and DASI—were limited to resolutions coarser than 10 or 15 arc min (see Physics Today, Physics Today 0031-9228 54

 July 2001,...

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