well in the CBR case, the signal that Penzias and Wilson were looking for was a signal coming from the center of the Milky way galaxy. What they measured was a homogeneous noise coming from everywhere (isotropic). This noise was also adiabatic and Gaussian. A noise at 2.7 degrees K coming from everywhere, very uniform, very Guassian, a nearly prefect blackbody radiation. Penzias and Willson had no idea what it was but it was everywhere, day and night, summer and winter, unvarying, homogenious, isotropic noise.
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