The background radiation of space was discovered experimentally in the 40s of the last century by Arno Penzias and Robert Woodrow Wilson. It is considered the reverberation of the Big Bang. However, it is also suspected as a counter-evidence to a center of the universe and as a confirmation of Einstein's centerless universe. The absolute theory says that people who interpret it this way should learn to think four-dimensionally. It is taken as counter-evidence because then the noise would then have to come from a certain source and not from all directions. The balloon is always used as an example for the expanding universe after the Big Bang. But even with this simple example you can see that the air molecules in a balloon can also be measured from all directions. Nevertheless, the opening of the balloon is the origin, so to speak. And if you think four-dimensionally, the background noise is to a point x at all points of the universe, so it is nowadays also at all points and radiates from all directions. I also say that the huge black hole in the middle of our universe gives off radiation, but that doesn't have to be the background radiation.
The radiation is in the range of microwave radiation and has a temperature of slightly below 3 Kelvin, i.e. 3 degrees higher than absolute zero. It also occurs in a vacuum, which supports my thesis of the Weltformel that there is no space without mass, so that the space-time continuum must be extended to a space-mass-time continuum.