Everything discussed in this thread happened after the plasma recombined enough to make scattering negligible. That is the whole point of the CMB. The hydrogen got re-ionized much later (>100 million years), but at that time it was so spread out that it didn't make the universe opaque any more.Chronos said:Photons do not play well in plasma, largely due to a phenomenon known as Compton scattering. This same effect makes it difficult to see anything below the atmosphere of a star. For futher discussion, see; https://ned.ipac.caltech.edu/level5/Sept05/Gawiser2/Gawiser1.html, ORIGIN OF THE COSMIC BACKGROUND RADIATION.
The CMB (cosmic microwave background) is a faint radiation that fills the entire universe and is the oldest light in existence. It is a remnant of the Big Bang and is the most direct evidence of the universe's early state.
The CMB did not become dark at any specific time. It has always existed since the Big Bang, but it has cooled and stretched over time, resulting in its current state as a faint microwave radiation.
The CMB was first discovered in 1964 by American physicists Arno Penzias and Robert Wilson. They were analyzing radio waves from space when they discovered a stubborn background noise coming from all directions. After ruling out all possible sources, they realized it was the CMB.
The darkness of the CMB tells us that the universe is expanding and cooling. The fact that the CMB is a faint microwave radiation and not a bright light indicates that the universe has been expanding and cooling for billions of years since the Big Bang.
No, the CMB is not visible to the naked eye. It is a form of radiation that is invisible to human eyes. However, it can be detected by specialized instruments, such as radio telescopes, and is an important tool for studying the early universe.