1. Here are the verses:
6 And God said, Let there be a firmament in the midst of the waters, and let it divide the waters from the waters. 7 And God made the firmament, and divided the waters which were under the firmament from the waters which were above the firmament: and it was so.
The firmament was the solid boundary of Adam's world. When God put it in the middle of the water, it divided the waters above the firmament from the waters below the firmament, just a ANY solid object divides water from water.
8 And God called the firmament Heaven. And the evening and the morning were the second day.
This was on the 2nd Day and God called the firmament "Heaven".
4 These are the generations of the heavens and of the earth when they were created, in the day that the Lord God made the earth and the heavens,
This verse shows that on the 3rd Day, God made other Heavens. We know it's the 3rd Day because that is the Day when Adam's EARTH was made. Gen 1:10 One heaven made on the 2nd Day PLUS other HeavenS made on the 3rd Day means that at least 3 Heavens were made by the 3rd Day. This agrees with other Scripture which shows the THIRD Heaven. ll Corinthians 12:2
2. A Multiverse is composed of at least 2 HeavenS or 2 Universes. Amen?