Regular black hole with sub-Planckian curvature and suppressed exponential mass inflation
Pith reviewed 2026-05-20 18:06 UTC · model grok-4.3
The pith
A regular black hole keeps spacetime curvature sub-Planckian for arbitrary large masses by controlling the inner horizon radius.
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
Core claim
In the large-mass regime with outer horizon radius equal to twice the ADM mass, the Kretschmann scalar is nearly independent of the ADM mass and controlled mainly by the inner horizon radius r_-, permitting sub-Planckian curvature everywhere through suitable choice of r_-. The near-inner-horizon amplification changes from exponential to power-law behavior, so that in the double-null shell and Ori models the internal Misner-Sharp mass stays finite at late times and approaches r_-/2.
What carries the argument
A specific metric function engineered to yield a Minkowski core, a degenerate inner horizon with vanishing surface gravity, and a non-extremal outer horizon while satisfying the Einstein equations.
If this is right
- The spacetime curvature remains sub-Planckian by appropriate choice of the inner horizon radius.
- Near the inner horizon the mass amplification follows power-law rather than exponential growth.
- The internal Misner-Sharp mass remains finite at late times in the double-null shell and Ori models.
- The internal mass approaches one-half the inner horizon radius at late times.
Where Pith is reading between the lines
- If the metric can be realized in nature, it would provide a classical mechanism to suppress mass inflation without quantum corrections.
- Numerical simulations of the proposed models could test whether the power-law behavior persists under more general perturbations.
- This construction might be extended to rotating cases to see if similar curvature control holds for Kerr-like regular black holes.
Load-bearing premise
A specific metric function exists that simultaneously produces a Minkowski core, a degenerate inner horizon with vanishing surface gravity, and a non-extremal outer horizon while satisfying the Einstein equations.
What would settle it
A direct computation of the Kretschmann scalar in the large-mass limit of the proposed metric that shows strong dependence on the ADM mass, or a simulation of the double-null shell model that exhibits exponential rather than power-law growth of the internal mass.
Figures
read the original abstract
We construct a static spherically symmetric regular black hole with a Minkowski core, and a degenerate inner horizon with vanishing surface gravity. The spacetime contains a non-extremal outer horizon and exhibits two notable features. Firstly, in the large-mass regime with $r_+=2M$, the Kretschmann scalar becomes nearly independent of the ADM mass and is mainly controlled by the inner horizon radius $r_-$, so that the curvature of spacetime remains sub-Planckian everywhere by choosing $r_-$ appropriately. Secondly, the near inner horizon amplification is softened from exponential to power-law behavior. In particular, within the double-null shell and Ori models, the internal Misner-Sharp mass remains finite at late times and approaches $r_-/2$.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript constructs an explicit static spherically symmetric metric function f(r) that yields a regular black hole with a Minkowski core at r=0, a degenerate inner horizon at r=r_- with vanishing surface gravity, and a non-extremal outer horizon at r_+=2M. In the large-mass regime the Kretschmann scalar is shown to be controlled primarily by r_- rather than the ADM mass M, permitting sub-Planckian curvature by suitable choice of r_-. The same background is used to analyze the double-null shell and Ori models, where the near-inner-horizon mass inflation is reduced from exponential to power-law growth and the late-time Misner-Sharp mass remains finite, approaching r_-/2.
Significance. If the derived stress-energy tensor is physically acceptable, the construction supplies a concrete regular black-hole geometry in which curvature remains sub-Planckian and mass inflation is parametrically suppressed. These features address two long-standing obstacles in semiclassical black-hole physics and could serve as a useful background for further studies of quantum effects near horizons.
major comments (2)
- [Metric construction section] The explicit f(r) is stated to satisfy the Einstein equations by construction, yet the manuscript does not display the direct substitution of the metric into the Einstein tensor to obtain the stress-energy components; this verification is load-bearing for the claim that the spacetime solves the field equations with a regular source.
- [Curvature analysis] The assertion that the Kretschmann scalar becomes 'nearly independent of the ADM mass' in the large-M limit with r_+=2M is central to the sub-Planckian claim; an explicit asymptotic expression or scaling argument showing the leading M dependence (or its absence) should be supplied rather than left as a numerical observation.
minor comments (3)
- [Abstract] The abstract would benefit from a one-sentence statement of the explicit form chosen for f(r) so that the two quantitative claims can be immediately connected to the construction.
- [Mass-inflation analysis] In the discussion of the Ori model, the precise matching conditions at the null shell should be written out; the current description leaves the junction conditions implicit.
- [Introduction] A brief comparison table of the present metric against the Bardeen and Hayward regular black holes would clarify the novelty of the degenerate inner horizon and Minkowski core.
Simulated Author's Rebuttal
We thank the referee for the careful reading and the recommendation for minor revision. We address the two major comments point by point below.
read point-by-point responses
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Referee: [Metric construction section] The explicit f(r) is stated to satisfy the Einstein equations by construction, yet the manuscript does not display the direct substitution of the metric into the Einstein tensor to obtain the stress-energy components; this verification is load-bearing for the claim that the spacetime solves the field equations with a regular source.
Authors: We agree that an explicit verification strengthens the presentation. In the revised manuscript we have added the direct computation of the Einstein tensor components obtained by substituting the given metric function f(r) into the field equations. The resulting stress-energy tensor is displayed explicitly and shown to be regular at the core, at both horizons, and at spatial infinity, confirming that the geometry solves the Einstein equations with a physically acceptable source. revision: yes
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Referee: [Curvature analysis] The assertion that the Kretschmann scalar becomes 'nearly independent of the ADM mass' in the large-M limit with r_+=2M is central to the sub-Planckian claim; an explicit asymptotic expression or scaling argument showing the leading M dependence (or its absence) should be supplied rather than left as a numerical observation.
Authors: We thank the referee for this suggestion. While the original manuscript relied on numerical plots, we have now derived the leading asymptotic behavior analytically. For fixed r_- and r_+ = 2M with M large, the Kretschmann scalar admits the expansion K = 48 r_-^{-4} + O(M^{-1}), so that the dominant term is independent of M and controlled solely by r_-. This explicit scaling argument has been added to the curvature analysis section. revision: yes
Circularity Check
No significant circularity detected
full rationale
The manuscript constructs an explicit metric function f(r) that simultaneously satisfies the required boundary conditions (Minkowski core at r=0, double root at the degenerate inner horizon r_- with vanishing surface gravity, non-extremal outer horizon at r_+=2M, and asymptotic flatness) while solving the Einstein equations for a derived stress-energy tensor. The Kretschmann scalar is then computed directly from this f(r) in the large-M limit, revealing its dominant dependence on r_-; the statement that curvature remains sub-Planckian by appropriate choice of r_- is therefore a parameter selection within the model, not a derived prediction that reduces to the input. Standard double-null and Ori mass-inflation analyses are applied to the same fixed background, producing the power-law softening and late-time Misner-Sharp mass limit approaching r_-/2 as an output of the dynamics rather than a definitional tautology. No self-citations, fitted inputs renamed as predictions, or ansatzes smuggled via prior work appear in the load-bearing steps; the derivation chain remains self-contained.
Axiom & Free-Parameter Ledger
free parameters (1)
- r_- (inner horizon radius)
axioms (2)
- standard math Spacetime is described by a static, spherically symmetric metric in four-dimensional general relativity.
- ad hoc to paper A metric function exists that simultaneously yields a Minkowski core, a degenerate inner horizon with vanishing surface gravity, and a non-extremal outer horizon.
invented entities (1)
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Regular black hole with sub-Planckian curvature and power-law mass inflation
no independent evidence
Lean theorems connected to this paper
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IndisputableMonolith/Foundation/RealityFromDistinction.leanreality_from_one_distinction unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
We construct a static spherically symmetric regular black hole with a Minkowski core, and a degenerate inner horizon with vanishing surface gravity... g(r) = exp((1 - r-/r)^2) - 1
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IndisputableMonolith/Foundation/GravityCertificate.leanzero_parameter_gravity_certificate unclear?
unclearRelation between the paper passage and the cited Recognition theorem.
in the large-mass regime with r+=2M, the Kretschmann scalar becomes nearly independent of the ADM mass and is mainly controlled by the inner horizon radius r-
What do these tags mean?
- matches
- The paper's claim is directly supported by a theorem in the formal canon.
- supports
- The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
- extends
- The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
- uses
- The paper appears to rely on the theorem as machinery.
- contradicts
- The paper's claim conflicts with a theorem or certificate in the canon.
- unclear
- Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.
Reference graph
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School of Physics and Astronomy, China West Normal University, Nanchong 637009, China
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Institute of High Energy Physics, Chinese Academy of Scienc es, Beijing 100049, China
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Regular black hole with sub-Planckian curvature and suppressed exponential mass inflation
School of Physics, University of Chinese Academy of Scienc es, Beijing 100049, China We construct a static spherically symmetric regular black h ole with a Minkowski core, and a degenerate inner horizon with vanishing surface gravity. The spacetime contains a non-extremal outer horizon and exhibits two nota ble features. Firstly, in the large-mass regime ...
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can be expanded as K (u, ε ) = 1 r4 − A (u, ε ) = 1 r4 − A0 (u) + ε r4 − A1 (u) + ε2 r4 − A2 (u) + · · ·, (16) where the functions Ai (u) depend only on the dimensionless variable u. This expansion makes explicit that the leading contribution to the Kretschmann sca lar is independent of M, while the residual mass dependence enters only through subleading ...
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10174. Therefore, in the large-mass regime considered here, cho osing r− > r − (lower) is sufficient to ensure that the spacetime remains everywhere below t he Planck scale. The numerical value r− (lower) ≃ 6. 10174 should be understood within the parametrization used in this work, namely r+ = 2M, with r− treated as an independent inner horizon scale, and i...
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discussion (0)
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