Jacob Bekenstein and Stephen Hawking showed that black holes store hidden information — entropy. But how exactly does it arise? Inside a black hole, there is no point of infinite density — instead, there exists a core resembling a tiny universe. This core can behave in two ways. If it expands (expansion parameter \(H\) positive), entropy accumulates like heat in an oven. If it contracts (\(H\) negative), entropy becomes negative — not a debt, but rather an antipode of ordinary heat, which when summed with the horizon entropy gives zero. Thus, a black hole gravastar has zero total entropy.
From the perspective of quantum gravity, the compass-core can switch between modes via a quantum jump, like a needle flipping. These transitions leave traces — a series of gravitational waves that detectors may register in the future.
For an astrophysical black hole of 10 M☉, the semiclassical description of collapse breaks down at n ~ 0.01—well before the classical Minkowski violation (n=0). In this regime, the inner horizon’s temperature surpasses the Planck temperature, and the geometry turns into a quantum foam.