At its earliest moments of around time sec, the Universe was extremely hot and dense and was expanding. K. It was a Universe full of light. The photons were so energetic that they could combine to make basic particles of matter, such as protons, neutrons, and electrons. This provides an important observational test of the Big Bang model.
Studies indicate in the affirmative.
Now the photons are so weak they cannot even ionize Hydrogen atoms. This is referred to as the decoupling era. So the photons from that time just amble along through space participating in the expansion of the Universe. At billion years, galaxies begin to form. Using the Hubble Telescope, astronomers stared at a small piece of sky for 10 days to image the faintest, furthest, and yougest galaxies ever seen.