A hot chain of atoms lined up in a row behaves like a tiny black hole. Such a chain is a series of particles, each resembling a tiny magnet. At normal temperatures, the little magnets flip randomly, but when cooled, they align in a uniform order. Physicists have discovered that when heated, this simple system reproduces the strange properties of black holes.
The key point is a signal sent along the chain. In a cold chain, it travels freely from one end to the other. But once heated, the signal starts to 'get stuck': part of it is absorbed, like light falling into a black hole. The higher the temperature, the stronger the absorption. This is the first sign that an analog of an event horizon, a boundary from which nothing returns, appears in the system.
The second sign is damping. If you pluck a heated chain, it won't oscillate forever but will settle down according to a special law — exponentially, like the fading ring of a bell. Black holes have similar 'rings'—quasinormal modes: after a disturbance, a black hole 'rings' and then quiets down. The chain follows the same damping law, and its rate depends on temperature.
The third sign is an entropy jump. Entropy is a measure of disorder. A black hole has a famous phase transition: at a certain temperature, its properties change abruptly. In the chain, when heated, entropy also changes abruptly, and the temperature of this jump matches the transition temperature for a black hole.
Thus, a simple system of little magnets becomes a bridge between the quantum world and the world of black holes. It lets us 'feel' a black hole in the lab without venturing into deep space. Perhaps such chains will help unravel the quantum nature of space and time.
The entropy of a black hole depends not on its volume but on the surface area of its horizon, as if all the information about the hole is written on its shell, not inside.
In the movie 'Interstellar', the black hole Gargantua warps time — quantum chains could be a first step toward understanding such physics in the lab.