If space is a substance rather than plain nothingness as has been traditionally thought, it should have a universal composition and nature that would in a way be comparable to quantum structures. If inflation is an expansion of space rather than some other cause, because more space substance seems to be created and fills an increasing volume, that seems opposed to the idea of nothingness expanding.
Nothingness as space in the absolute sense should neither be created or destroyed. It ought logically to have existed infinitely forever and isn’t capable of increasing or decreasing. Space as a substance on the other hand could have been initially finite to alternatively infinite and existing within the underlying host of nothingness.
There are several definitions of space as well as Universe these days that help to confuse the topics one is addressing for others. There are logical modal universes and alternate universes such as one finds in multi-universe theories derived from eternal inflation.
I wanted to point out that if inflation of space occurs forever as a localized process that moves on leaving nonexpanding space in its wake, that it is just as likely that the boundaries of substance-space move on through already existing infinite space, or bring more substance space within its moving boundary region as that substance space itself upsurges into being from nothingness. Of course one might infer that if substance space upsurges into being that it must be from somewhere other than the present region of its expansion.
The Universe is everything that exists. It is generally regarded as being made of energy or converted to mass, yet it is everything and logically infinite. Modern science has provided a wealth of confusion concerning what formerly was simple and given humanity the ‘multiverse’.
When I was a kid the Hoyle hypothesis was still hanging on although heavily tattered. Einstein believed in a static universe. I would guess he believed it infinite as did I when I first learned about those things at age 6 or 7. The profusion of Multiverse jargon since then has required a rethinking, yet ultimately the meaning of Universe remains intact as everything that exists rather than one part of a vast structure with an infinite number of others similar to it connected by space or even juxtaposed in Hilbert space with infinite dimensions. Just because scientists discover new facts about the Universe concerning its structure that doesn’t mean they have discovered alternate Universes; it just indicates they did not know what the structure was of the Universe they were in. The Universe is everything that exists including a goggleplex of other units inconveniently named universe 1 through infinity.
Most people including scientists didn’t know the real structure of the Universe in 1950 yet most people probably assumed it was infinite and unbounded. When cosmologists, theoretical physicists and astronomers inducted, discovered and theorized about an expansion of their knowledge of the Universe and extrapolated about other regions of space forming from inflation proceeding the Big Bang that may have continued after this observed Universe formed some 13.3 billion years ago more or less as the crow flies they choose to call those hypothetical regions of unobservable space universes too; primarily because they lacked a term for a meta-universe or greater universe that included all possible hypothetical universes of which there might be an infinite number. Basically they lacked a name for the new units of universe so they called it a Multiverse; and that was a bad choice though convenient for scientists at that time.
Most people had an existing concept of an infinite unbounded Universe already yet lacked knowledge of its distant structure. Modern cosmology has been mapping in fact and with theory, hypothetical structures of space that include possibly an unlimited number of regions of space like the one scientists knew before the rise of Multiverse theory. In a way a universe has been downgraded comparatively to the status of a galaxy. It as if scientists believed there was just one galaxy (Universe) and having found more or hypothesized about more existing galaxies existing they have developed multigalaxy theory. That is fine for galaxies yet doesn’t work with a Universe that should rightly be defined as everything that exists including that which cannot be observed. Plainly there isn’t a word existing presently for the unit that includes all of the galaxies and mass existing in a contingent expanded spacetime from an inflation or big bang that would disambiguate it from the infinite other potential units like itself. The Universe that includes all the universe-like units could be called the Metaverse reasonably well yet it would be better to name it the Universe and find a named for structures that are like the observable universe humanity lives in. One could call them big units, big bang units, second tier units, temporal verses, boroughs, legally defined regions of largest scale, etc however about any serviceable designation would be better than calling them universes. A universe is a good concept to retain. It is simple and suitable for an infinite and unbounded structure that is unmapped and perhaps unmappable. One day people may find a way to journey transcendentally beyond the boundaries of physical spacetime before death, and if so it might be useful to still regard oneself as being in the Universe when relocating to another unit.
For an example of the circumstance, compare the Universe to a chess board. A chess board has sixty-four squares and the grid coordinates are labeled columns A through H and rows 1 through 8. Consider that in the past humanity lived in square A1 and thought of themselves as being located in the center of the universe in the middle of square A1. Though their knowledge of the chess board universe did not exceed beyond square A1 the popular belief was that the Universe square had no limits and was infinite in extant (some humans did have other beliefs). After a few thousand years- within the past century and a half, scientists have learned more about the chess board and have observed the visible horizon limits of square A1 where they lived and developed theories concerning a vast number of squares like their own existing beyond the edge or boundaries of A1. They call those new squares universes instead of regarding them as distant and almost inaccessible areas of the infinite Universe. It would have been useful to rename the new squares or theoretical squares as different areas of a universe without limits or for this analogy, a chessboard in Hilbert space with infinite dimensions and without an edge for-itself although it hosts/contains all space-time unit big banged squares.
Physical space and energy quanta plus fields may not be the sole form of being; scientists seem willing to believe so though because it is observable and spirit or divine content generally aren’t. The Universe or Metaverse could be a though in the mind of God; who can say? Human language should at least keep a word to define everything that exists and not regressively dispose of a word (Universe) for the all-encompassing Universe though it can have complex, distant and infinite areas difficult to map with different physical laws and non-contiguous space-time content events. Reducing the Universe comparable to meaning a small county amidst an infinite number of counties makes it challenging for people to understand the actual state of things of cosmology.