If the entire body of the deep underwent nucleosynthesis and energy radiated from every particle in existence, then there ought to be an even distribution of radiation and elementary particles. There's your CMBR.
"Let light be, and light was" is normally translated as "let there be light, and there was light." We (that's me and the Holy spirit) develop the logic of how God caused light to appear.
The Bible accounts for the Big Bang nucleosynthesis. Popular science (SciPop) grudgingly arrived at this conclusion but it has no cause for it or source for the material used. The Bible gives us both.
Detection of the CMBR is taken to be support for the Big Bang Theory, although using the CMBR in this way only amounts to an inductive rationalization of circumstantial evidence to fit a premise.
Let Light Be Nucleosynthesis (LLBN), and the conditions described in Genesis 1:2-3, would cause a cosmic microwave background radiation (CMBR). Therefore, detection of the CMBR proves that Genesis is true.