Draft:Black Hole Universe

• Comment: This is an interesting and notable topic. With additional work I think the article could be accepted. I review under the assumption that the goal is solid article and not an attempt to set an agenda.
  The only requirements to accept this draft are reliable sources verifying notability and removal of any unacceptable material. I will include suggestions for improvements as well.
  * The introduction should be a summary of the article with only broad secondary sources or none. Specifically the 2025 source is inappropriate in the summary.
  * The History should be based on secondary sources, not primary sources. The primary sources are not needed, but nice to have. The reason is simply that historical perspective is needed and it should not be supplied by wikipedia editors. We summarize, not analyze.
  * The History should not have "For an overview, see". The History should be an overview. The source "Lemaître model and cosmic mass" source is not appropriate: history sources should be about the article topic. Similarly the "Chinese universe" article seems related but does not verify any historical content.
  * The focus on the Gaztañaga sources is inappropriate. If the topic is notable, it will have a broad number of sources. Other approaches need to be discussed in a balanced way. The Zhang work is inappropriate.
  There are many other sources on this topic.
  * Yoo, C. M., Okawa, H., & Nakao, K. I. (2013). Black-hole universe: time evolution. Physical Review Letters, 111(16), 161102.
  * Pathria, R. K. (1972). The universe as a black hole. Nature, 240(5379), 298-299.
  * Lineweaver, C. H., & Patel, V. M. (2023). All objects and some questions. American Journal of Physics, 91(10), 819-825.
  * Knutsen, H. (2009). The idea of the universe as a black hole revisited. Gravitation and Cosmology, 15(3), 273-277.
  * Doran, R., Lobo, F. S., & Crawford, P. (2008). Interior of a Schwarzschild black hole revisited. Foundations of Physics, 38(2), 160-187. Johnjbarton (talk) 23:27, 14 July 2025 (UTC)

• Comment: seems very notable and interesting-however more editors should take a look first, thank you Ozzie10aaaa (talk) 16:58, 11 July 2025 (UTC)

• Comment: Interesting, but many paragraphs are unsourced. GoldRomean (talk) 02:00, 7 July 2025 (UTC)

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Diagram comparing the Big Bang expansion (left) to the Black Hole Universe one (right). A finite region of homogeneous matter collapses and bounces without forming a singularity, leading to expansion. The interior follows FLRW evolution; the exterior is empty Schwarzschild.

The Black Hole Universe (BHU) is a cosmological model proposing that the observable universe originates from the gravitational collapse—and subsequent bounce—of a large cloud of matter formed in a parent universe. The model incorporates an exact solution to Einstein's field equations that includes quantum degeneracy pressure, resulting in non-singular black hole formation and a bounce followed by expansion. It provides an alternative to classical big bang singularity models and accounts for both early- and late-time cosmic acceleration without modifying general relativity or introducing additional hypothetical components.

History

Early precursors to the BHU include the models of Georges Lemaître (1933) (the original interpretation of cosmic expansion), Richard C. Tolman (1934), and J. Robert Oppenheimer and Hartland Snyder (1939), which describe the gravitational collapse of a finite, homogeneous, spherically symmetric cloud. These models apply a FLRW metric in the interior matched to an external Schwarzschild vacuum solution. Although they describe both expanding and collapsing solutions, all lead inevitably to a past or future singularity.

Related works include those of Bondi (1947), Misner & Sharp (1964), Vaidya (1968), and Hawking (1968), among many others. For an overview, see:

In the 1970s, Raj Kumar Pathria and I. J. Good independently proposed that our expanding universe might lie inside a black hole. While suggestive, these ideas were not based on exact solutions and remained speculative.

Further developments explored nonsingular bounces in modified gravity theories. Other speculative approaches, such as Zhang's Black Hole Universe, use non-standard assumptions for General Relativity (GR).

Stuckey (1994) proposed an exact GR solution for expansion inside a black hole, although with singularities and without a cosmological constant.

Exact Solution

A modern version of the BHU model was introduced in 2021–2025. It presents an exact analytical FLRW solution with quantum degeneracy pressure that avoids singularities and explains cosmic inflation as part of the same purely gravitational process. Close to the bounce point ($\tau =0$), the physical radius $R(\tau )$ of the collapsing cloud as a function of comoving time $\tau$ follows:

$R(\tau )=R_{B}\cosh {\left({\frac {\tau }{R_{B}}}\right)}={\frac {R_{B}}{2}}\left[e^{-\tau /R_{B}}+e^{+\tau /R_{B}}\right],$

with $R_{B}\equiv {\sqrt {\frac {3}{8\pi G\rho _{G}}}}$, where $\rho _{G}$ is the ground-state density of degenerate matter, comparable to the nuclear saturation density of a neutron star. After the bounce, this solution reproduces cosmic inflation ($R\sim e^{+\tau /R_{B}}$) without requiring any additional fields or mechanisms. The accelerated expansion naturally drives the system away from the ground state, thereby ending the inflationary phase.

The BHU assumes that the FLRW metric describes a finite, spherical overdensity embedded within a larger background spacetime. In this context, the overdensity leads to positive spatial curvature (as gravity curves spacetime). As a result, the interior spatial hypersurfaces are compact, violating one of the key assumptions of the Penrose–Hawking singularity theorems, which require a non-compact Cauchy surface. This geometric feature allows the solution to avoid singularity formation and enables a non-singular bounce.

The bounce remains entirely confined within the initial gravitational radius, $r_{S}=2GM$, which acts effectively as a cosmological constant $\Lambda$ for interior observers. Inside this radius, the geometry satisfies $r_{S}={\sqrt {3/\Lambda }}$, while to external observers in the parent universe, the structure appears as a Schwarzschild black hole. Due to the presence of the $\Lambda$ term, the boundary of the collapsing cloud lies beyond the observable horizon for any comoving observer inside, ensuring that no background anisotropies are visible from within.

Geometry and dynamics

The BHU uses a closed FLRW metric for the interior and a Schwarzschild vacuum for the exterior. The boundary is an apparent horizon, and the bounce occurs entirely within it. The solution is time-symmetric near the bounce, so the thermodynamic arrow of time is well-defined. This addresses the entropy problem raised by Roger Penrose (see also Past hypothesis), who noted that the low entropy of the Big Bang is not explained by inflation alone. However, note that the BHU is not cyclic, as the expansion asymptotically approaches a de Sitter phase, which corresponds to a static universe from the perspective of a rest-frame (non-comoving) observer.

Implications

The BHU implies that black holes might give rise to new universes, suggesting a recursive cosmological hierarchy. It avoids cosmological singularities and provides a geometric origin for inflation and dark energy without invoking exotic matter, dark energy or modifications to general relativity. In contrast to the standard (ΛCDM) model, BHU predicts small positive spatial curvature and a cutoff in the scale-invariant spectrum of density perturbations which can be observed as anysotropies in the CMB super horizon perturbations. The rotation of the black hole could impart a preferred spin direction to all matter within, leading to a majority of galaxies rotating the same way.

Popular coverage

A summary of the BHU model appeared in *The Conversation* in June 2025. [1] and in Scientific American in April 2025.[2] among many other news outlets [3][4]

See also

• Friedmann–Lemaître–Robertson–Walker metric
• Cosmic inflation
• Black hole cosmology
• Penrose–Hawking singularity theorems
• Past hypothesis
• Big Bounce

External links

This page will be placed in the following categories if it is moved to the article namespace.

Categories:

• Cosmology
• General relativity
• Black holes
• Theoretical physics
• Physical cosmology