Black Holes Never Shrink: Testing the Area Law ✛ ✦
A black hole is a region where curved spacetime doesn't let even light escape. Its horizon is like a one-way membrane, and its area is linked to entropy — the hidden disorder inside. Jacob Bekenstein and Stephen Hawking realized: just as disorder in a house only ever grows, so the horizon area cannot shrink. This was tested in the merger of two black holes. The collision creates gravitational ripples, and LIGO detectors pick them up like ultra-sensitive microphones. The brief ringdown right after the merger, distorted by time dilation near the horizon, holds a clue to the spin. By breaking this ringdown into tones, scientists calculated the mass and spin, and from them — the area of the new black hole. The value matched the theory: the area only grew, as if the disorder after the merger became larger than the sum of the two separate ones. By the way, in a fraction of a second, the merger released more energy in ripples than all the stars in the universe emit in that same time — yet even this outburst didn't allow the horizon to shrink.
The horizon area of the black hole GW250114 is about 40,000 square kilometers — roughly the size of the Netherlands, squeezed into the volume of a medium-sized city.
In Carl Sagan's novel "Contact" and the film "Interstellar", characters tried to extract data from signals coming from the vicinity of black holes — a similar idea, but there it was science fiction, and here it's real physics.