380,000 years after the Big Bang, 13 and a half billion years ago...
WHite noise on television screen.
380,000 years after the Big Bang, the temperature of the universe fell to 2700 °C while reaching a diameter still a hundred times smaller than that of the visible universe today.
At this temperature, the forming atoms have captured the electrons, which stop interacting permanently with the photons. These can then circulate freely: the light is visible, the universe becomes transparent.
It is this light that we receive today in the form of radiation: the cosmic microwave background or fossil radiation.
Indeed, continuing to extend and therefore to cool since then, the photons of that time have lost energy and reach us with frequencies a thousand times lower than at the origin: they are microwaves which do not are more visible in the light spectrum but only in time as electromagnetic radiation.
The discovery of this radiation was accidental. It was while trying a new type of antenna, that two researchers of the Bell laboratories (Arno Penzias and Robert Wilson) identified a parasitic noise which they did not find the origin and which they tried to suppress.
It was actually the discovery of fossil radiation from the beginnings of the universe, as predicted by the Big Bang theory, discovery for which the two researchers were awarded the Nobel Prize in 1978.
The "snow" visible on an analog television when it is not set is due for a tiny part (less than 1%) to this fossil radiation, embedded among the parasites of the electronic circuits.
The image of this "snow" on a television does not represent a distribution of noise in space, unlike the targeted measurements of this radiation that they sweep the space to obtain a spatial map of this cosmic microwave background.
