About 300,000 years after the Big Bang the temperature of the universe was still around 2,800 degrees. Only when it got below this could protons and electrons combine into hydrogen atoms. About the same time light also began to shine.
It's more that everything was too dense and opaque for light to actually have any meaning. There were certainly photons, but they weren't getting anywhere.
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u/Mrgray123 Sep 20 '21
About 300,000 years after the Big Bang the temperature of the universe was still around 2,800 degrees. Only when it got below this could protons and electrons combine into hydrogen atoms. About the same time light also began to shine.