# MIT physicists observationally confirm Stephen Hawking's area theorem

Back in 1971, Stephen Hawking proposed the area theorem having to do with black holes. Hawking's area theorem predicted that the total area of the black hole's event horizon should never decrease. Physicists from MIT have now observationally confirmed that theorem for the first time. The study shows evidence-based on gravitational waves to show the total area of a black hole's event horizon can never decrease.

While much about black holes is a mystery, the central law predicted that black holes should never be able to shrink the area of their event horizon. The event horizon is the boundary beyond which nothing can escape the gravitational pull of the black hole. The law is described as Hawking's area theorem, and five decades after Hawking proposed the theorem, it has now been confirmed for the first time.

In the study, researchers at MIT and elsewhere looked closely at GW150914, which is the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory in 2015. The signal was produced by a pair of inspiraling black holes that generated a new black hole and a massive amount of energy. Researchers say if Hawking's area theorem holds, the horizon area of the new black hole shouldn't be smaller than the total horizon area of the parent black holes.

In the study, the signal was reanalyzed before and after the cosmic collision, and physicists found that the total event horizon area did not decrease after the merger. The team says they have 95 percent confidence in their findings. The findings marked the first direct observational confirmation of Hawking's area theorem, which had previously been proven mathematically but never observed in nature.

Researchers on the project intend to test future gravitational wave signals to see if they also confirm Hawking's theorem. Researcher Maximiliano Isi says this isn't something you test once, and it's over. Testing it once is only the beginning.