Can the Universe be seen from an outside?
v. 2 n. 41
The reader is outside the cover image "universe" looking in because it is framed, has a (rough gray) boundary. Before the title question is addressed, though, it should be discussed what the Universe is:
As an aside, the latter point can be exemplified by "The Neverending Story," a charming fantasy where the "universe of possibilities" is bounded by a dearth of dedicated readership because of widespread electronics, where the "nothing" impinges further and further on "existence of possibilities." While this point is colorful and mind-bending, let's continue with the first three.
The first point is astronomy and astrophysics, and the second is theoretical cosmology. According to General Relativity, acceleration cannot be distinguished from gravity. If this is so in all cases -- if acceleration and gravity are not only equivalent but also identical -- the Universe is accelerating because of gravity. And, on the large scale gravity is repulsive? ...
Conventional "dark energy" is a label for an unknown; it does not have the status of an inference, let alone an explanation for the acceleration of the Universe.
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Also conventionally, all that now physically is -- space, time, mass/energy -- emerged from a small region, according to General Relativity because space(time) and gravity or mass/energy are identical, or at least equivalent. Shrink space, and mass/energy is the same but in less space. Then there is the usual question of what the Universe expands into; a boundary is built into this way of seeing cosmology. The boundary is between what is and what is not, which requires boundary conditions, which are unknown. Therefore, this interpretation of the emergence of the Universe is mathematically/physically unsolvable, requiring assumed boundary conditions.
There are two ways of considering the contraction/expansion of the space of General Relativity. The first has been introduced above. It is also possible to assume a contraction of a subspace from a more encompassing space, where there is no boundary between the two. One region contracts, and an adjacent region expands so that mass/energy is constant in this pair; if not constant, any other mass/energy must be accounted for if the conservation of mass/energy is to hold. No boundary conditions are required in this interpretation, no unknowns. The Universe at ever larger scales beyond the known might be essentially the same -- self-similar, "wheels within wheels." This is a way of describing a wave in a space that is larger than the known Universe. Since it is a wave and of space, it might be described as a rather conventional gravitational wave, small versions of which are observed.
The view of space below is unbounded compared with that of the cover image, and therefore seen from inside the Universe. Image credit: imgflip.com
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cover image caption: Does the Universe have a boundary?