In a stunning confirmation of one of physics' most audacious predictions, scientists have detected the echoes of a cataclysmic black hole merger from across the cosmos, providing the first direct proof of a theory Stephen Hawking proposed over 50 years ago: black holes can never, ever get smaller.
More than half a century ago, long before we had the technology to even imagine verifying it, the legendary physicist Stephen Hawking made a bold claim. He proposed a simple, elegant rule governing the universe's most mysterious objects. The event horizon of a black hole its ghostly point of no return has a surface area that can only increase. It is a one-way street; black holes only grow.
Now, in a study published in Physical Review Letters, scientists have announced they finally have the proof. On January 14, 2025, the laser arms of the LIGO gravitational-wave observatory "heard" a ghostly chirp from deep space—the unmistakable sound of two behemoths colliding. This was the moment Hawking’s long-contested idea was cemented into the bedrock of cosmic law.
A Symphony in Spacetime
The event, cataloged as GW250114, involved the violent merger of two massive black holes. As they spiraled into each other at nearly the speed of light, they warped the very fabric of reality, sending powerful gravitational waves rippling across the universe. These ripples are what LIGO detected, and within their complex signal was the data scientists had been waiting for.
Before their final, destructive dance, the two individual black holes had event horizons whose areas, when added together, spanned a surface roughly the size of Oregon—about 93,700 square miles (243,000 square km).
When they collided, they merged into a single, more massive black hole. As the chaos subsided, the new, unified event horizon was measured. It stretched across a staggering 154,500 square miles (400,000 square km), an area comparable to the state of California.
The result was unequivocal. The final surface area was not just the sum of the two parts; it was significantly larger, perfectly obeying the cosmic censorship that Hawking's Area Law demanded.
The Laws of Nature in Harmony
This principle is formally known as the "second law of black hole mechanics," and its beauty lies in its uncanny resemblance to one of the most fundamental laws of physics: the second law of thermodynamics. Just as the entropy (disorder) in the universe can only increase, Hawking theorized that the surface area of a black hole's event horizon must also always increase.
This confirmation does more than just prove a 50-year-old theory correct. It powerfully strengthens the profound and mysterious link between the laws of gravity (governing black holes), thermodynamics (governing heat and energy), and quantum mechanics. It hints that these cosmic monsters are not just gravitational oddities but may hold the key to a unified "Theory of Everything" that can finally explain all the forces of nature.
As if to add a final, poetic flourish, the newly formed black hole "rang" like a struck bell. In the moments after the merger, the distorted object quivered, shedding its imperfections by radiating away gravitational waves in a characteristic pattern. This "ringdown" signal not only allowed scientists to precisely measure the new black hole's final size and shape, but it also perfectly matched the predictions of what a post-merger object should look like according to both Einstein's and Hawking's theories.
Stephen Hawking’s brilliant insight, once a purely theoretical concept born from pen and paper, has now been heard and verified across billions of light-years. His legacy is once again proven to be as vast and enduring as the cosmic phenomena he dedicated his life to understanding.
Read the Study: "GW250114: Testing Hawking’s Area Law and the Kerr Nature of Black Holes." Physical Review Letters, 10 Sep 2025.
Credit: Aurore Simonnet (SSU/EdEon)/LVK/URI
