No need for dark matter. As it states in explanation paragraph, according to big bang theory, in the beginning stages there were light everywhere and the universe was not even transparent. So according to this, when we look at the sky now we should see that light if we look far enough. But we don't. Reason for that is that as universe expanded, that light emitted from the early stages got "stretched out" and shifted from visible light to microwave length. That's what we call cosmic microwave background. So it's not a possibility - it's fact.