The observable universe exists inside a black hole created by the total mass present in the observable universe.
1.Black hole cosmology
If we find the size at which the mass distribution with the average mass density of the present universe forms a black hole.
R=2GM/c^2
R_UB=(3c^2/8πGρ)^(1/2)=14.3Gly
The above expression means that if the present universe has a critical mass density ρ_c(the order of 5~6 hydrogen atoms per 1/m^3) value and
the size is approximately R_UB=14.3Gly or more, this region becomes a black hole.
Currently, we estimate that the size of the observable universe is larger than 14.3 Gly, and the entire universe is estimated to be larger than the observable universe 46.5Gly, so our observable universe inevitably exists inside a huge black hole called the universe.
Black hole cosmology holds true if the following four things are true.
1)Finite Universe
We do not yet know whether the universe is finite or infinite. However, in my personal opinion, infinity is a mathematical notion, and there seems to be no infinite in physical reality. Even flat space-time does not guarantee an infinite universe (infinite mass-energy distribution). Since the age of the universe is finite and the propagation velocity of the field is also finite, the mass distribution is considered to be finite. Therefore, if we exclude the infinite universe, we face the problems 2)~4).
2)Schwarzschild's radius equation R=2GM/c^2
3)Observed average density
4)The observable universe 46.5Gly, the entire universe much larger than the observable universe.
The Black Hole Cosmology is the inevitable conclusion of the above 4 items. 2) is an equation that has been verified in two different theoretical systems (Newtonian mechanics and general relativity), 3) and 4) is on a very solid foundation, and even if 3) and 4) have some errors, the entire universe is estimated to be much larger than the observable universe. Even if the average density is lower than the current observation, the much larger entire universe inevitably renders the universe a black hole. This is because when the universe becomes R times larger, the density required to become a black hole decreases by 1/R^2.
2.Weaknesses of the Black Hole Cosmology
1) In a black hole, all matter is compressed into a singularity, so there is no space for humans to live. There is no almost flat space-time that could contain the observable universe inside a black hole.
2) In the black hole, singularity exist in the future, and in the universe, singularity exist in the past. Black hole and the universe are opposites.
3) The universe is expanding. Inside a black hole, all matter must contract at a singularity. The two models show opposite phenomena. It is difficult to explain the expansion of the universe inside a black hole.
Problems such as strong tidal force enough to disintegrate people, the movement of all matter in the direction of the singularity, and the expanding universe have been pointed out as fatal weaknesses of the Black Hole Cosmology. If our universe was a black hole, all galaxies should have collapsed into a singularity or exhibit motion in the direction of the singularity, but the real universe does not exhibit such motion characteristics. Therefore, the Black Hole Cosmology was judged to be inconsistent with the current observations, and the Black Hole Cosmology did not become a mainstream cosmological model.
A singularity exists inside a black hole, and all matter falls to the singularity and is destroyed.
In other words, if we were inside a black hole now, it would have collapsed due to gravity as a singularity, so we would not have been able to form the current structure of the galaxy or the solar system, and we could not exist.
Although this objection(Weaknesses) appears to be clear and well-grounded, in fact, this objection also has its own weaknesses.
1) The proposed weakness does not break the argument 2)~4) of the Black Hole Cosmology.
Whatever the weakness , if 1) ~ 4) does not collapse, the Black Hole Cosmology is very likely to hold.
2) Most physicists and astronomers believe that the singularity problem will be solved either using quantum mechanics or in some unknown way, so there will be no singularity.
In other words,
in the process of solving the singularity problem, there is a possibility that the singularity problem of the Black Hole Cosmology will also be solved.
3) Since the singularity exists in the Schwarzschild solution, the Schwarzschild solution must be changed for the singularity problem to disappear. That is, among the elements constituting the Black Hole Cosmology, the 2)Schwarzschild radius equation is affected.
For the singularity to disappear, there must be a repulsive force inside the black hole. Due to this repulsive force, an uncompressed region inevitably exists inside the black hole.
The remaining problem is, "Could an incompressible region be larger than the observable universe?"
Solutions to the problems of Black Hole Cosmology
Fatal weakness: 1) In a black hole, all matter is compressed into a singularity, so there is no space for humans to live. There is no almost flat space-time that could contain the observable universe inside a black hole
1. Gravitational self-energy
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U_gs=-(3/5)GM^2/R
In the generality of cases, the value of gravitational self-energy is small enough to be negligible, compared to mass energy mc^2. So generally, there was no need to consider gravitational self-energy. However the smaller R becomes, the higher the absolute value of U_gs. For this reason, we can see that U_gs is likely to offset the mass energy in a certain radius.
Thus, looking for the size in which gravitational self-energy becomes equal to rest mass energy by comparing both,
This equation means that if mass M is uniformly distributed within the radius R_gs, gravitational self-energy for such an object equals mass energy in size. So, in case of such an object, (positive) mass energy and (negative) gravitational self-energy can be completely offset while total energy is zero. Since total energy of such an object is 0, gravity exercised on another object outside is also 0.
Comparing R_gs with R_S, the radius of Schwarzschild black hole,
This means that there exists the point where negative gravitational self-energy becomes equal to positive mass energy within the radius of black hole, and that, supposing a uniform distribution, the value exists at the point 0.3R_S, about 30% level of the black hole radius.
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Fig.x. Internal structure of the black hole. a)Existing model b)New model. If, over time, the black hole stabilizes,the black hole does not have a singularity in the center, but it has a zero (total) energy zone.
2. Inside a sufficiently large black hole, there is enough space for intelligent life to exist
A black hole has no singularity, has a Zero Energy Zone with a total energy of zero, and this region is very large, reaching 15% ~ 30% of the radius of the black hole. It suggests an internal structure of a black hole that is completely different from the existing model. Inside the huge black hole, there is an area where intelligent life can live.
For example,
if the masses are distributed approximately 46.5Gly with the average density of the current universe, the size of the black hole created by this mass distribution will be 491.6Gly, and the size of the Zero Energy Zone will be approximately 73.7Gly ~147.5Gly. In other words, there is no strong tidal force and a region with almost flat space-time that can form a stable galaxy structure is much larger than the observable range of 46.5 Gly. The entire universe is estimated to be much larger than the observable universe, so it may not be at all unusual for us to observe only the Zero Energy Zone (nearly flat space-time).
Fatal weakness: 2) In the black hole, singularity exist in the future, and in the universe, singularity exist in the past. Black hole and the universe are opposites
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Fatal weakness: 3) The problem of cosmic expansion inside a black hole. The universe is expanding. It is difficult to explain the distance between galaxies inside a black hole
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#Problems and Solutions of Black Hole Cosmology
https://www.researchgate.net/publication/359192496