What is cosmic microwave background radiation?

What they had accidentally discovered was radiation left over from the beginning of the universe. However, this description is not entirely accurate. As we look further back in time, the universe becomes progressively hotter. If we go back far enough, the universe was so hot that it could ionise the hydrogen produced in the Big Bang. For hydrogen, ionisation means that the electron and proton out of which it is comprised break apart and can travel freely without being bound together as an atom. Any light travelling through space at this time, would very quickly encounter an electron or proton from the ionised hydrogen and scatter, sending it travelling in a different direction. As a result, the universe was opaque, because light was unable to travel any significant distance before being scattered in a new direction. <a href="https://richardvnd.medium.com/what-is-cosmic-microwave-background-radiation-61bdaf0fbc6d">Click Here</a>