: surface of last scattering : just after the big bang, there was only an opaque floating plasma soup of dark matter — there were no photons. Energy was scattered and unformed. Light did not exist yet. A remnant of that time is the cosmic microwave background (CMB), uniform black body thermal energy coming from all directions. Eventually there was a moment when the soup cooled enough for electrons and protons to form hydrogen, and photonic energy was released. The surface of last scattering is the moment before translucency — the farthest we can see in space and time

listen to the brilliant, plain speaking physicist, Dr. Katie Mack tell it