Push $ m $ further still—beyond stars, beyond comprehension—until the gradient becomes so extreme
that the landscape itself folds inward.
This is not merely steep curvature. This is terminal curvature:
a point where the cost function becomes undefined for external observers.
$$ m \to M_{\text{critical}} \;\;\Longrightarrow\;\; r \to r_s = \frac{2GM}{c^2} $$
At the Schwarzschild radius $ r_s $, the geometry ceases to permit outbound trajectories.
Not because of force, but because all geodesics point inward.
The Ledger That Cannot Be Audited
In our economic metaphor, the black hole is an account that accepts deposits but issues no receipts.
Information crosses the event horizon, paying the energy cost $ E = mc^2 $, but the transaction
cannot be reversed or verified from outside.
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Inside $ r_s $: Time and space exchange roles.
The "future" points toward the singularity with the same inevitability that the past recedes from us.
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At $ r_s $: Latency becomes formally infinite for external observers.
A photon emitted at the horizon takes infinite coordinate time to escape—which is to say, it doesn't.
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Beyond $ r_s $: The gradient is steep but traversable.
You can still climb out—barely—if you pay the energy cost.
$$ \text{Curvature at } r_s: \quad \lim_{r \to r_s^+} \left(1 - \frac{r_s}{r}\right)^{-1} = \infty $$
This is the point where the cost function diverges. No amount of energy suffices to escape.
The exchange rate becomes undefined.
Optimization Collapse: No Gradient to Descend
In the language of gradient descent, a black hole represents a region where the loss landscape
has collapsed into a well with vertical walls.
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For a star, the gradient is steep but finite. Descent is rapid but possible in reverse (with sufficient energy).
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For a black hole, the gradient at $ r_s $ is discontinuous.
Inside, there is no gradient pointing outward. The only direction is down.
$$ \nabla_{\text{outward}} = 0 \quad \text{for } r < r_s $$
You cannot optimize your way out. The terraforming is complete and irreversible.
The Singularity: Where the Ledger Itself Breaks
At $ r = 0 $, curvature becomes infinite—not just steep, but singular.
The equations fail. Geometry loses meaning. The cost function has no domain.
This is not a feature. It is a boundary condition signaling that our current framework—General Relativity—
requires completion. Likely by quantum gravity, where the ledger is kept at Planck scale and the concept of
"position" itself becomes probabilistic.
$$ r \to 0 \quad \Longrightarrow \quad R_{\mu\nu\rho\sigma} \to \infty \quad \text{(breakdown)} $$
The singularity is where the raindrop metaphor ends.
Not because the raindrop vanishes, but because the landscape itself ceases to exist as a continuum.
What the Black Hole Teaches Us
A black hole is not an object. It is a threshold in the cost function of spacetime.
- It is the point where latency becomes absolute.
- It is the region where all paths converge to a single inevitable endpoint.
- It is the limit case of terraforming: geometry so extreme it permits no return.
In optimization terms: it is a loss well so deep that gradient descent cannot climb out,
no matter the learning rate, no matter the batch size, no matter the architecture.
The black hole does not pull.
It finalizes.