Arno Allan Penzias

Arno Allan Penzias and Robert Woodrow Wilson discovered an unexplained microwave antenna signal at Bell Laboratories. Their measurement compared a horn-reflector antenna with a cooled reference and separately estimated atmospheric emission, instrumental losses and ground pickup.

The remaining excess was approximately isotropic, unpolarized and seasonally stable. Those checks made a purely local instrumental explanation less plausible. Interpreted as cosmic microwave background, the signal connected a calibrated radio-noise measurement to the thermal history of the cosmos; the original single-frequency result did not yet establish the full blackbody spectrum.^[ref]