Particles linked across the boundary may be the key to Hawking radiation itself.
In the quiet of a laboratory, physicists have done what cosmology alone could never permit: they have held the edge of a black hole in their hands. Using a chain of atoms as a stand-in for one of the universe's most extreme objects, researchers at the University of Amsterdam detected faint thermal radiation matching what Stephen Hawking predicted half a century ago would leak from the boundary of a real black hole. The experiment does not resolve the long-standing tension between general relativity and quantum mechanics, but it offers a rare and tangible foothold in the search for a unified theory of quantum gravity.
- Physics has long been caught between two irreconcilable masterworks — general relativity and quantum mechanics — and black holes sit precisely at the fault line where both theories break down.
- Hawking radiation, the theoretical thermal glow predicted to escape a black hole's event horizon, has never been directly observed in nature, leaving one of physics' most consequential predictions unconfirmed for fifty years.
- Lotte Mertens and her team engineered an artificial event horizon inside a one-dimensional atomic chain, tuning electron behavior until the system mimicked the quantum boundary conditions of a real black hole.
- The thermal signature they measured matched theoretical predictions — but only when part of the chain crossed the artificial horizon, pointing to quantum entanglement across that boundary as the likely engine of Hawking radiation.
- The experiment's elegant simplicity means it can be reproduced and adapted across many condensed matter systems, opening a practical laboratory pathway into the physics of curved spacetime.
In November 2022, a team led by Lotte Mertens at the University of Amsterdam built something that physics had long confined to the realm of pure abstraction: a working black hole analog, constructed from a single chain of atoms. It was not a real black hole — that would be catastrophic — but it was real enough to glow.
The experiment was designed to confront one of physics' most enduring impasses. General relativity describes gravity as the smooth warping of spacetime. Quantum mechanics describes reality as a probabilistic dance of discrete particles. Both are extraordinarily successful in their own domains, yet near a black hole — where gravity is extreme and quantum effects are unavoidable — they collide without resolution. A unified theory of quantum gravity has remained elusive precisely because no laboratory has ever been able to test the boundary conditions where both theories must somehow coexist.
Black holes are the natural site of this collision. In 1974, Stephen Hawking predicted mathematically that quantum fluctuations at a black hole's event horizon should produce a slow thermal leak of radiation. No one has ever observed it directly — real black holes are too distant, and their Hawking radiation too faint against the noise of the cosmos. But its properties, Mertens reasoned, could be studied in miniature.
Her team engineered an artificial event horizon by tuning how easily electrons could hop between atoms in a one-dimensional chain. At a certain point along the chain, the wave-like behavior of the electrons was disrupted — a boundary that functioned, mathematically, like the edge of a real black hole. When they measured the system's temperature, it rose in precise agreement with Hawking's theoretical predictions. Critically, this thermal signature only emerged when part of the chain extended beyond the artificial horizon, suggesting that quantum entanglement across that boundary may be the very mechanism that generates Hawking radiation.
The work, published in Physical Review Research, does not close the gap between general relativity and quantum mechanics. But its simplicity is its power. The model is flexible enough to be adapted across many different experimental systems, offering physicists a controlled, repeatable way to probe the quantum foundations of gravity — one atomic chain at a time.
In November 2022, physicists working in a laboratory did something that seemed to belong in the realm of pure theory: they built a black hole. Not a real one—that would be catastrophic—but a working model made from a chain of atoms arranged in a single line. And then, as if on cue, it began to glow with the faint thermal signature that Stephen Hawking predicted nearly fifty years earlier should emanate from the edge of any black hole's event horizon.
The experiment, led by Lotte Mertens at the University of Amsterdam, was an attempt to probe one of physics' most stubborn puzzles: the fact that our two best descriptions of reality refuse to play nicely together. General relativity explains gravity as a warping of spacetime itself, a smooth and continuous fabric. Quantum mechanics describes the universe as a collection of discrete particles governed by probability. Both theories work brilliantly in their domains. But near a black hole—where gravity becomes extreme and quantum effects matter—they collide. A unified theory of quantum gravity would require them to somehow reconcile, but so far, that reconciliation has remained elusive.
Black holes are the natural laboratory for this problem. They are the most extreme objects known to exist: so dense that nothing, not even light, can escape once it crosses a boundary called the event horizon. In 1974, Hawking showed mathematically that quantum fluctuations at this boundary should produce a type of radiation—thermal radiation, like heat—that slowly leaks away from the black hole. This radiation has never been directly observed. Real black holes are too distant, and any Hawking radiation they emit is drowned out by the noise of the universe. But its properties could be studied in miniature, using laboratory analogs.
Mertens and her team took a different approach than previous attempts. They created a one-dimensional chain of atoms and tuned the ease with which electrons could hop from one atom to the next. By adjusting this hopping rate, they could engineer a kind of artificial event horizon—a point in the chain where the wave-like nature of the electrons was disrupted, mimicking the boundary of a real black hole. When they measured the temperature of the system, they found it rose in a way that matched the theoretical predictions for Hawking radiation. Crucially, this thermal signature only appeared when part of the atomic chain extended beyond the artificial event horizon.
This detail matters. It suggests that the entanglement of particles—their quantum connection across the boundary—may be the mechanism that generates Hawking radiation in the first place. The radiation was only thermal within a specific range of hopping rates and when the simulated spacetime was flat, suggesting that Hawking radiation itself may only behave thermally under certain conditions, particularly when spacetime is warped by gravity.
What this means for quantum gravity remains an open question. But the beauty of the approach is its simplicity and flexibility. Because the model is so straightforward, it can be adapted and deployed in many different experimental settings. Researchers can now study how quantum mechanics and gravity interact without the overwhelming complexity of an actual black hole formation. The work, published in Physical Review Research, opens a door to exploring the quantum mechanical foundations of gravity in controlled laboratory environments—a small step, perhaps, but one that might eventually help bridge the gap between the two theories that describe our universe.
Notable Quotes
This can open a venue for exploring fundamental quantum-mechanical aspects alongside gravity and curved spacetimes in various condensed matter settings.— The research team
The Hearth Conversation Another angle on the story
Why does it matter that they saw this glow? Hawking predicted it decades ago.
Because prediction and observation are different things. Hawking showed it mathematically, but we've never actually seen it happen, even in a real black hole. This lab version lets us test whether his math holds up when we can actually measure it.
But it's not a real black hole. How do we know the fake version tells us anything true?
That's the right skepticism. The answer is that the physics of the event horizon—the boundary—should be the same whether it's made of atoms or spacetime itself. They're testing the principle, not the object.
And what did they find that was surprising?
That the radiation only appeared when particles straddled the boundary. That suggests entanglement—quantum connection—is doing the work. It's not just about the boundary existing; it's about particles being linked across it.
So this helps with the quantum gravity problem how?
It gives us a way to study how quantum mechanics and gravity interact without needing an actual black hole. We can run experiments, tweak variables, see what happens. That's how you build a unified theory—by testing pieces of it in controlled ways.
What happens next?
Other labs will adapt this model, test it in different ways, push it further. Eventually, the patterns they find might point toward the deeper theory that makes both quantum mechanics and relativity work together.