← openxiv:gr-qc.2026.00002 · gr-qc
Second-law check through the inner Cauchy horizon of regular black holes with nonlocal fakeon-regulated mass inflation
Explainer at the level of a curious high-schooler. Read the original paper.
Plain language. Few jargon words; every one is defined inline.
Black holes can have an inner horizon deep inside. If this horizon is disturbed, the mass inside can grow out of control—a problem called mass inflation. To study this, researchers used a new mathematical tool called a fakeon regulator. It keeps the mass growth from becoming infinite. They then tested whether the second law of thermodynamics still holds. The second law says that entropy, a measure of disorder, must always increase. They calculated the total entropy from both the outer and inner horizons. The outer horizon’s entropy increases, but the inner horizon’s decreases. So it wasn’t obvious if total entropy would increase. By running many calculations for different black hole sizes, they found that total entropy always increases. This confirms the second law for these black holes. They did not study one particular method (S4) in this work.
Explainers are best-effort summaries — they round corners. For the authoritative claims, read the paper itself.