A new type of black hole analog might tell us a thing or two about an elusive radiation theoretically emitted by the real thing.
Using a chain of atoms in a single file to simulate the event horizon of a black hole, a team of physicists has observed the equivalent of what we call Hawking radiation: particles born from perturbations in quantum fluctuations caused by the rupture of the black hole in space-time. .
This, they say, could help resolve the tension between two currently irreconcilable frameworks for describing the Universe: general relativity, which describes the behavior of gravity as a continuous field known as spacetime; and quantum mechanics, which describes the behavior of discrete particles using the mathematics of probability.
For a unified theory of quantum gravity to be universally applicable, these two immiscible theories must somehow find a way to get along.
This is where black holes come into play, possibly the strangest and most extreme objects in the Universe. These massive objects are so incredibly dense that, at a certain distance from the black hole’s center of mass, no velocity in the Universe is sufficient to escape. Not even the speed of light.
This distance, which varies depending on the mass of the black hole, is called the event horizon. Once an object crosses its boundary we can only imagine what happens, as nothing comes back with vital information about its fate. But in 1974, Stephen Hawking proposed that disruptions of quantum fluctuations caused by the event horizon give rise to a type of radiation very similar to thermal radiation.
If this Hawking radiation exists, it is too weak for us to detect it yet. We may never get it out of the hissing static of the Universe. But we can investigate their properties by creating black hole analogues in laboratory settings.
This has been done before, but now a team led by Lotte Mertens from the University of Amsterdam in the Netherlands has done something new.
A one-dimensional chain of atoms served as a path for electrons to “jump” from one position to another. By adjusting how easily this jump can occur, physicists could make certain properties disappear, effectively creating a kind of event horizon that interfered with the wave nature of electrons.
The effect of this false event horizon produced a temperature increase that matched theoretical expectations for an equivalent black hole system, the team said, but only when part of the chain it extended beyond the event horizon.
This could mean that the entanglement of particles straddling the event horizon is critical to generating Hawking radiation.
The simulated Hawking radiation was only thermal for a certain range of jump amplitudes, and in simulations that started by mimicking a kind of spacetime considered “flat”. This suggests that Hawking radiation can only be thermal in a number of situations, and when there is a change in the warping of spacetime due to gravity.
It is not clear what this means for quantum gravity, but the model offers a way to study the emergence of Hawking radiation in an environment that is not influenced by the wild dynamics of black hole formation. And because it’s so simple, it can be put to work in a wide range of experimental settings, the researchers said.
“This may open a venue for exploring fundamental aspects of quantum mechanics along with gravity and curved spacetime in various condensed matter environments,” the researchers write.
The research has been published in Physical Review Research.