I am assuming God made the stars in the firmament. Above this was water. Below this was water. The opening that existed and were opened by God in the flood brought the water from above. So if you think God used a big plastic straw to pipe in the water, fine. Don't accuse others of doing what you do, make stuff up.
It was above. So you could make up someplace the waters came from, or admit we don't know. There is another place some chapters back where it talks about waters above. It is reasonable to assume those waters came down in the flood. But assume whatever you like. There is no other options available as far as the bible goes. You either admit not knowing, or assume that probably the waters God created above were brought down. Do feel free to plead ignorance. Do not feel free to mock His word or make stuff up.
There is nothing beyond that. God opened windows up there to bring water from somewhere. Are you suggesting the water was right there in space or the sky above where the windows opened up? Or are you just in disbelief, period?
The simple answer is that by "in the firmament", the isrealites meant that stars were "in" the dome, much like a thumb tack is "in" a cork board. They were not aware of what stars actually were, and more importantly, they did not understand how far away they were. (again, we can't blame them, they had not yet invented telescopes or trigonometry to gauge distances via the Pythagorean theorem.)
To the naked eye, they are equidistant lights. Moving in synchronization with the rotating planet, they would appear "pinned" in the firmament. As the firmament or expanse that was stretched out, as it rotated, so too did all the stars "in" it. Though now in modern times we know that stars aren't actually "in" anything. But you have to put yourself into their shoes and think about what they saw and how they experienced things before modern technology.
Would this not be a common sense approach as opposed to your radical idea of wormholes of water traveling billions of light years through space?
You really think that water traveling from other dimensions is more likely than the far more simple and straight forward explanation that perhaps the isrealites who had yet to master space travel, might not actually know what stars are?
Turn off all the extra-biblical wormhole miracle thoughts for just a moment and just imagine what it was like 3,000+ years ago in the eyes of the ancient Hebrews. And once you do this, all of Genesis then becomes 100% perfectly clear and fully 100% biblical.
1. How did the firmament separate waters from waters? Because it had limited thickness and stood over the land, but underneath the blue sky which had an appearance of water.
2. How did birds fly across the [flat] face of the firmament? Because the firmament was viewed much like a flat expanded sheet of metal in that it had flat sides (though curved in a bowl shape). This word used for expanse is the same word used for metal that was spread in ancient times. There's a reason isreals anti missile system is called the iron "dome". It's a play on words referring to the Torahs description of the firmament.
3. How could there be windows in the firmament? Windows or gates can be in any flat object.
4. Where did the water above the firmament come from? Not from intergalactic space, but from the blue sky which resembles water which the flat firmament held up and separated.
5. How is it possible for stars to be in the firmament where there are also windows? Does this mean that water was traveling through space worm holes?
NO! Of course not. And scripture doesn't say that. The stars all appeared equidistant and because they all moved together, it looked like they were stuck "in" something. "In" the flat, expanded, stretched thin, firmament.
Its biblical, it's literal, it aligns with everything we know about beliefs of all societies of that time, it doesn't involve any alternative extra-biblical wild miracles like wormholes. It's also simple and rational.
The ancient Hebrews weren't ubergalactic super-brains who knew advanced futuristic wormhole astrophysics. No.
there's no evidence that they were. Not in scripture, not in historical writings. And to say otherwise is just unbiblical and imaginary.