There is only one universe. QM and GR are about the same subject matter, but they are like two different languages. Better not mix them up.
Let’s start out with the word universe. It is very easy to hold it inside our minds, but that single word is actually not an entity; it is a phenomenon.
Space is infinite; it has no borders. Therefore, it cannot be a something. Only matter within is finite and as far as we understand today, the divergent motion of all matter started somewhere 13+ billion years ago. That is as much space as it has moved through since. The space did not move out of the way or anything; it already was nothing but space. Space is a phenomenon.
The material universe is also not a single entity. Next to the divergent action at the collective level, there is the convergent action as we see with planets and stars. Where the divergent action involves the collective, the convergent action can only occur at the ‘local’ level and not the collective level.
In plain English: divergent means separation, and convergent is probably best understood with grouping. Separation is not a something; it is a phenomenon. Grouping involves the real deal and we can build upon it.
The largest universal entities involved with convergent action are galaxies. There are no larger agglomerations of matter than galaxies in the universe. There is nothing larger in the universe than the largest galaxy.
Understand that divergent action and convergent action cannot be made one; one cannot add separation to grouping and end up with a single outcome.
Let discuss GR and QM as if it were something else. Let’s make QM like statistics and let’s make GR be about biology.
From statistics, one can gather data from about 1,000+ people and find out things to a high degree of accuracy about their biology, for instance, the height distribution in an entire population. But put an individual inside a box and not even the best statistician can declare how tall that person is.
From biology, a doctor can investigate the physical realities of a person, even to the point of having fully accurate and scientific knowledge about that person. But ask that doctor if she can tell you anything about the neighbor living next door to the one she investigated, and she will tell you she doesn’t have a glass ball.
Two realms. Two sets of certainties. Somehow indeed the same subject matter. But both languages are not linked. The results among both languages need to be understood, not fully linked as if they are one language.
A universe is not a something; it is a spatial phenomenon. The subject matter we most care about is matter. We can know a thing or two about matter. We cannot make the spatial setting and matter singular. As above, not so below.
