I had defined natural as “something as part of our 3 dimensional space-time that is empirically detectable”. Extranatural is something that is not part of our 3 dimensional space-time or something that is not empirically detectable.
With the idea of the space-time fabric expanding, there are multiple levels of the extranatural being introduced.
One is if our 3-D space fabric is expanding, it must be “expanding” into something. There must be a higher order dimension for it to expand into. There must be 3 higher order dimensions for each of our 3-dimensional space to expand into. So, there must exist at least 6 dimensions total. Of course, these additional dimensions would be extranatural.
With the expansion of our space-time fabric, there would exist parts of the universe that would be beyond any way for us to empirically detect it. This is called the unobservable universe. By its very nature, the unobservable universe is impossible to access. Since the unobservable universe cannot be empirically measured, it would fall under being extranatural.
Both popular and professional research articles in cosmology often use the term “universe” to mean “observable universe”. This can be justified on the grounds that we can never know anything by direct experimentation about any part of the universe that is causally disconnected from the Earth, although many credible theories require a total universe much larger than the observable universe.
There are various estimates to the size of the unobservable universe. All of them are massive.
This means the unobservable Universe, assuming there’s no topological weirdness, must be at least 23 trillion light years in diameter, and contain a volume of space that’s over 15 million times as large as the volume we can observe.
at present the entire universe’s size is at least 1.5×10^34 light-years—at least 3×10^23 times the radius of the observable universe
Based on what we currently think about inflation, this means that the Universe is at least 10^(10^30) times the size of our observable Universe!
Even to an infinite size.
The size of the whole universe is unknown, and it might be infinite in extent.
So, our natural world (the observable universe) would be vastly smaller than the extranatural world (the unobservable universe).