Hawking's Area Law: How Black Holes Test Quantum Gravity ✎ express
When two black holes merge, their event horizons – surfaces of 'no return' – combine like two pieces of sticky film. The total area never decreases. This is the law discovered by Stephen Hawking in the 1970s.
The LIGO and Virgo detectors, which pick up gravitational waves, confirmed the rule in practice. Then physicists went further: they took the law as absolute and demanded that quantum gravity theories obey it. It turned out to be a strict filter – only those constructs survive where extra mathematical add-ons vanish, and curved spacetime is free of hidden instabilities. An unexpected bonus: strictly following the law automatically leads to the formula first proposed by Jacob Bekenstein, S = A/4, linking entropy and area, and even hints that a black hole's horizon might not be a perfect sphere but could have microscopic wrinkles. Such simplifications weed out many complex theories and bring us closer to solving the quantum nature of gravity.
If the horizon area could shrink, you could endlessly extract energy from a black hole – but the universe's design forbids it.