When and how did the universe become transparent to radiation?

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Request for Question Clarification by funkywizard-ga on 04 Dec 2002 17:03 PST

I'm not sure exactly what you are looking for. I would think that the
empty space in the universe has always been transparent to radiation,
and the various materials that are in the universe are transparent to
different kinds of radiation. Other than the first few years the
universe existed, I doubt that the density of matter was great enough
for radiation to be fully absorbed by the matter in the universe. I
suppose I don't understand the intent of your question. Could you
clarify it at all?