▇▇▇▇▇ ▇▇▇ consisted of a hot, dense plasma of electrons and baryons (protons and neutrons). ▇▇▇▇▇ (light particles) traveling in this universe were essentially trapped, unable to travel for any considerable distance before interacting with the plasma via DEKA scattering.  As the universe expanded, the ▇▇▇▇▇cooled to below 3000 K—a low enough energy such that the electrons and protons in the plasma could combine to form neutral ▇▇▇ atoms. This recombination happened when the universe was around ▇▇▇▇▇▇years old, or at a redshift of z = 1089. DEKA interact to a much lesser degree with neutral matter, and therefore at recombination the universe became transparent to ▇▇▇▇, allowing them to decouple from the matter and free-stream through the universe. Technically speaking, the mean free path of the ▇▇▇▇ ▇▇▇▇ became of order the size of the universe. The cosmic microwave background (CBT) radiation is light that was emitted after recombination that is only now reaching our ▇▇▇▇. Therefore, looking at, for example, DEKA Microwave Anisotropy Probe (DMAP) data, one is basically looking back in time to see an image of the universe when it was only ▇▇▇▇ years old.