Indirect Evidence of Hawking Radiation From Acoustic Black Hole

I suspect this is a ways from "sealing the deal" for Hawking Radiation from an actual black hole, but it's still a pretty cool sounding experiment.

To test this prediction, Steinhauer created an analogue black hole using extremely cold atoms trapped in a laser beam.

When he applied a second laser beam, it made a sort of step that the atoms could flow over, kind of like a waterfall. As the atoms poured over the step, they accelerated, reaching supersonic speeds (faster than the speed of sound).

This created an acoustic black hole — sound waves inside the supersonic region couldn't escape because the condensate was flowing faster than the sound particles, or phonons, could travel.

It's like trying to swim against a river, Steinhauer told Business Insider. If the river is flowing faster than you can swim, then you can't move forward — you go back. That's like this phonon trying to escape the black hole.

When pairs of phonons were created near the analogue black hole, Steinhauer observed one particle falling in and the other escaping. This, he said, is analogous to a photon escaping a real black hole.

In 2014, Steinhauer observed this Hawking radiation, but in that experiment, the radiation was simulated — it was caused by something hitting the event horizon and creating the pairs. These new results are the first observation of quantum Hawking radiation, which means that the pairs were created all on their own, out of nothing.