Understanding black holes is the key to unraveling the most fundamental laws that govern the cosmos.
The most extreme objects in the universe are black holes, which are so densely packed into such a small space that nothing, not even light, can escape their gravitational pull once it’s close enough.
Understanding black holes is the key to unraveling the most fundamental laws governing the cosmos because they represent the limits of two of the most well-proven theories of physics: the theory of general relativity, which describes gravity as a result of warping (on a large scale). of space-time by massive objects, and the theory of quantum mechanics, which describes physics at the smallest length scales.
To fully describe black holes, these two theories must come together to form a theory of quantum gravity.
Radiant black holes
To achieve this goal, we might want to look at what manages to escape from black holes, rather than what gets swallowed up. The event horizon is an intangible boundary around each black hole, beyond which there is no way out. However, Stephen Hawking discovered that each 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 coming from each black hole is predicted to be so small that it is impossible to detect (with current technology) among the radiation coming from all other cosmic objects.
Alternatively, could we study the mechanism underlying the appearance of Hawking radiation right here on Earth? This is what researchers from the University of Amsterdam and IFW Dresden set out to investigate. And the answer is an exciting “yes.”
Black holes in the lab
“We wanted to use the powerful tools of condensed matter physics to investigate the unreachable physics of these incredible objects: black holes,” says author Lotte Mertens.
To do this, the researchers studied a model based on a one-dimensional chain of atoms, in which electrons can “jump” from one atomic site to another. The warping of spacetime due to the presence of a black hole is mimicked by adjusting how easily electrons can jump between each site.
With the correct variation of the hopping probability along the chain, an electron moving from one end of the chain to the other will behave exactly 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 real gravity in the model system, considering this synthetic horizon gives important insight into the physics of black holes. For example, the fact that the simulated Hawking radiation is thermal (that is, the system appears to have a fixed temperature) only for a specific choice of spatial variation of the jump probability suggests that the real Hawking radiation may also be purely thermal in certain situations. .
Furthermore, Hawking radiation only occurs when the model system starts with no spatial variation of the jump probabilities, mimicking flat spacetime without any horizon, before becoming one that hosts a synthetic black hole. Therefore, the appearance of Hawking radiation requires a change in the warping of spacetime, or a change in the way an observer looking for the radiation perceives that warping.
Finally, Hawking radiation requires some part of the chain to exist beyond the synthetic horizon. This means that the existence of thermal radiation is intimately connected with 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 number of experimental settings. This could include tunable electronic systems, spin chains, ultracold atoms or optical experiments. Bringing black holes into the lab may bring us one step closer to understanding the interplay between gravity and quantum mechanics, and on our way to a theory of quantum gravity.