Radiant Black Holes
To achieve this goal, we should look at what manages to escape black holes, not what gets swallowed. The event horizon is an immaterial boundary around every black hole beyond which there is no path. However, Stephen Hawking famously discovered that every black hole must emit a small amount of thermal radiation due to small quantum fluctuations around its horizon.
Unfortunately, this radiation has never been directly detected. The amount of Hawking radiation emanating from each black hole is predicted to be so small that it is impossible (with current technology) to detect it among the radiation from all other cosmic objects.
Alternatively, we could investigate the mechanism underlying the emergence of Hawking radiation right here Earth? Researchers from the University of Amsterdam and IFW Dresden went on a search. And the answer is an exciting “yes”.
Black holes in the laboratory
“We wanted to use the powerful tools of condensed matter physics to study the unattainable physics of these incredible objects: black holes,” says the author Lotte Mertens.
To do this, the researchers examined a model based on a one-dimensional chain of atoms in which electrons can “hop” from one atomic location to the next. The distortion of space-time due to the presence of a black hole is mimicked by adjusting how easily electrons can bounce between locations.
With the right variation in jump probability along the chain, an electron moving from one end of the chain to the other behaves just like a piece of matter approaching the horizon of a black hole. And analogous to Hawking radiation, the model system has measurable thermal excitations in the presence of a synthetic horizon.
Learning by analogy
Despite the lack of actual gravity in the model system, including this synthetic horizon gives important insights into black hole physics. For example, the fact that the simulated Hawking radiation is thermal only for a certain choice of spatial variation in the jump probability (meaning that the system appears to be at a fixed temperature) suggests that the real Hawking radiation is also thermal in certain situations can only be purely thermal.
Furthermore, the Hawking radiation only occurs when the model system starts out with no spatial variation in jump probabilities, mimicking a flat spacetime with no horizon before converting to one that hosts a synthetic black hole. The emergence of Hawking radiation therefore requires a change in the space-time warp, or a change in the perception of that warp by an observer looking for the radiation.
Finally, Hawking radiation requires part of the chain to exist beyond the synthetic horizon. This means that the existence of thermal radiation is closely related to the quantum mechanical property of entanglement between objects on either side of the horizon.
Because the model is so simple, it can be implemented in a variety of experimental designs. These can be tunable electronic systems, spin chains, ultracold atoms or optical experiments. Bringing black holes into the lab can bring us a step closer to understanding the interplay between gravity and quantum mechanics and towards a theory of quantum gravity.