There was an analogy of balloon to the BB.
if you only focus on the surface area of the balloon, you would notice that balloon deflated of air, will have small surface area. By slowly balloon with air, the surface area will slowly increase. It will double from its original size, triple, quadruple, etc, the surface area of the balloon will also increase, as it being inflated.
The balloon expanded, as it was being inflated. Sure, the inflating balloon will take up some space around the balloon, but I just wanted you to only focus on the balloon itself. The balloon will expand or contract, as it being inflated or deflated, respectively. It size and shape will increase or decrease.
Now, imagine the universe being like a balloon in the above analogy. The size of the universe will expand or contract. The Big Bang theory is just focusing on the observable universe, not whatever outside of the observations.
Unlike the universe, the balloon has critical limits as to the size it can reach, so the balloon will pop. There are still a lot of mysteries about the universe, things we don’t know about, nor understand.
We don’t if the universe have any limit. It might continually expand infinitely. Or it might one day start to contract, thereby the universe would collapse upon itself. We simply don’t know.
While the technology, like the Voyager 1 & 2, Hubble, WMAP, Planck, JWST, etc, provide us with enormous numbers of discoveries , and providing insights about universe, these technologies all have their limits, so it often come with more questions than answers.
Your assertions that the universe must expand either to “something”, or to “nothing”, is one of those questions that are outside the scope of the Big Bang theory…and not really relevant, especially when you considered that the universe is expanding faster than what our limited technology can observe.
Meaning, if we don’t build even better technology than the JWST, then the very distant galaxies that we can observe today with the JWST, might not be there 20 or 50 years from now, because the expansion of the universe will push these galaxies beyond our sight.
while the universe appears to have no limits (for expansion), there are limits to our technology.
