Vibrating mirrors of light create analog of a black hole event horizon

Vibrating one of two light "mirrors" in an optical cavity concentrates a diffuse cloud of ultracold atoms into a tight packet. The experiment, conducted by David Weld and colleagues at the University of California, Santa Barbara, confirmed a theoretical prediction that light waves in a cavity should bunch together into short, intense pulses when the distance between mirrors is changed rapidly. The results mimic the physics of curved spacetime, similar to what is observed near the event horizon of a black hole or its counterpart, a "white hole." The team used atoms, which behave like waves at ultracold temperatures, to test the prediction. The atoms were confined using laser light and moved back and forth at a controlled rate, creating a repeating path that followed the theoretical model.

The experiment involved a grid of laser light that forced the atoms to travel at nearly constant speed, and the moving light sheet transformed the initially diffuse cloud into a tight packet of atoms. The packets followed a stable path, mimicking the one-way motion predicted to occur near black hole event horizons. By doubling the driving frequency, the researchers produced two concentrated packets, each following its own path. Swapping the stable and unstable paths allowed them to reverse the packets' motion. The results show that the cavity behaves in ways that mimic the strange physics of curved spacetime, and the setup could lead to new ways of compressing and decompressing optical signals in solid materials.

The findings suggest that the optical cavity can be used to explore fundamental predictions about spacetime, such as how pairs of light particles can be created from empty space between rapidly moving mirrors. The experiment demonstrates that the behavior of matter waves in a cavity can replicate the physics of black holes, providing a new way to study these phenomena. The results have been published in Physical Review Letters, and the setup could help physicists explore other predictions related to quantum mechanics and spacetime.

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