Or (3), God both stretches the heavens out and bestows on the substance of the heavens a property such as what is postulated today as dark energy by some astronomers. The result is the expansion of space and what I have said in (1) above. Personally, I’m not to sure about this idea of dark energy especially in those models about the expansion of the heavens going on forever. Presently from what I understand, all that can be said about the idea of the expansion of space is that it may have happened in the past but we don’t know if it is still going on. It could take hundreds or thousands of years of observations of redshift galaxies to see if there is any change in the redshift if indeed the redshift is caused by the expansion of space at all rather than a Doppler effect or some unknown cause.
Sorry for such a long post. The creation of light in verse 3 and day one of the Genesis narrative seems to be allied in some manner with the creation of the sun, moon, and stars on day 4 for we have the same terms as light and darkness, night and day, and the separation of each. The making of the firmament on day 2 could be intertwined in this as well if the firmament of day 2 is understood to be the starry heaven for on day 4 it is said that God set the two great lights and the stars in the firmament of the heavens. It seems to me that the creation of light on day one is when God began or produced some further formation of the heavens and the corporeal world at large in the form of the galaxies and stars, the end result looking like this picture of an estimated I believe 10,000 galaxies in a very small region of space from Hubble Ultra Deep Field:
“And God separated the light from the darkness” (Gen. 1: 4)