
A laboratory system that mimics the event horizon and physics of a gravitational black hole.An analog black hole is a laboratory system that reproduces the essential physics of a gravitational black hole's event horizon using a different medium, such as flowing water, ultracold atomic clouds, or optical fibers. The idea is that the mathematical description of a horizon—where the flow speed exceeds the local wave speed—applies to any system with waves, not just gravity. These analogs allow researchers to study Hawking radiation and other horizon effects in a controlled setting, since real black holes are impossible to observe directly.
The concept was proposed by William Unruh in 1981, who noted the mathematical analogy between sound waves in moving fluids and scalar fields near a black hole.
In a typical setup, a fluid (or a Bose-Einstein condensate) is made to flow faster than the speed of sound in a localized region. Sound waves traveling against the flow are swept downstream, creating a sonic horizon. Quantum fluctuations near this horizon produce phonon pairs, one escaping and one trapped, mirroring Hawking radiation. In optical analogs, a pulse of light in a nonlinear medium creates a refractive index change that acts as a horizon for other light waves.
Used to test predictions of quantum field theory in curved spacetime, such as Hawking radiation and the thermodynamics of horizons, without needing a real black hole.
The first laboratory observation of a sonic analog of Hawking radiation was reported in 2016 using a Bose-Einstein condensate of rubidium atoms.









