Television snow is mostly local. Although an analog set tuned between stations can pick up radiation left over from the early universe, its flickering screen owes far more to nearby interference and noise generated inside the receiver itself. The cosmic contribution is small. That distinction makes the familiar claim less spectacular, but more interesting.
The machinery deserves more credit. Inside a receiver, thermal noise arises from the random motion of electrical charges, while the antenna collects unwanted radio signals whose sources can include electrical equipment and other transmitters. The screen mixes these inputs. Without a strong broadcast signal to organize the picture, the television's circuitry turns fluctuations into shifting speckles, rather than displaying a recognizable image of whatever produced them. Attribution is the difficult part. How much each source contributes depends on the antenna, reception frequency, receiver design and surroundings, which is why a universal percentage for the cosmic share promises more precision than the equipment supports.
The smaller claim is stranger. The cosmic microwave background is radiation released when the early universe became transparent, its wavelengths stretched by cosmic expansion until the radiation cooled to about 2.7 kelvin. Its reach includes television frequencies. A suitable receiving system can therefore admit a faint contribution, though ordinary television snow cannot isolate it or establish its origin without specialized measurements and careful accounting for other noise. The screen offers no labels. Across the restless glass, the household and the ancient universe can leave marks that look exactly alike.
