Although it was discovered less than 40 years ago, the cosmic microwave background (CMB) radiation has been around a lot longer than that. A relic from the early days of the Universe more than 14 billion years ago, the CMB is the oldest radiation on record. Current cosmological models posit that the CMB should be slightly polarized but this property has never been observed--until now. Researchers have successfully detected the CMB's polarization and found that it agrees with the theoretical estimates.

Erik Leitch and John Kovac of the University of Chicago and their colleagues used the Degree Angular Scale Interferometer (DASI), which is located at the Amundsen-Scott South Pole Station, to study the CMB radiation. Over a two-year period, this array of radio telescopes collected radiation signals coming from deep space in two patches of blank sky. The resulting 271 days worth of useable data revealed the light's polarization (the direction in which the light's field oscillates as it travels toward an observer on the ground). Writing in the journal Nature, the scientists report that the CMB radiation's level and spatial distribution are in excellent agreement with the predictions of the standard theory. "If the light hadn't been polarized, that would mean that we would have to throw out our whole model of how we understand the physics of the early universe," Leitch notes. In an accompanying commentary, Matias Zaldarriaga of New York University calls the findings "both a remarkable technical achievement and a wonderful consistency check for the theory."