What happened 3800000000 years after the big bang?

Answer 1

Approximately 377,000 years after the end of inflation, the density and temperature of the proton / electron / photon "soup" had decreased to the point where, on the average, photons would no longer blast electrons from protons, when the former went into an orbital near the latter. When this happened, photons were de-coupled from the other two, and could then move freely throughout our Universe. Following that event, photons began to move from all parts of our Universe towards all other parts of the our Universe.

As the photons continued to move for the next 13.7 billion years or so, space continued to expand. Thus, the wavelengths of these photons grew. At this time in the history of our Universe, all such photons have had their wavelengths expand such that they are now all microwave photons. This why all parts of our Universe now experience an almost perfectly isotopic microwave background radiaion.

Answer 2

Around 3800000000 years after the Big Bang, the universe was primarily made up of hydrogen and helium with some trace amounts of lithium. Galaxies were beginning to form and stars were igniting, leading to the start of the cosmic dawn era. This period marked a significant shift in the evolution of the universe as structures began to emerge.