*The hottest debate in science right now: How to Build a Black Hole* https://www.symmetrymagazine.org/article/gravitys-waterfall <https://disq.us/url?url=https%3A%2F%2Fwww.symmetrymagazine.org%2Farticle%2Fgravitys-waterfall%3AfQwpYVNa6oYazKVIJPl3EAosaAc&cuid=2168707>
Gravity’s waterfall Physicists are using analog black holes to better understand gravity. Bose-Einstein condensates, or BECs, are typically ultracold gases like rubidium that are ruled by quantum effects odd enough to qualify them as another state of matter. Subtle quantum effects like Hawking radiation hidden by the noise present in normal fluids become apparent in BECs. Analog black holes can even use light as a fluid. The fluid is made of *quasiparticles called polaritons*, which are the collective state of a photon that couples to an electric field. Enough polaritons behave as a quantum fluid of light. So when the flow of polaritons goes faster than the speed of sound in the *polariton fluid*, just like Unruh’s waterfall, a horizon forms. Hawking radiation from this fluid of light still comes in the form of phonons. Also see https://www.quantamagazine.org/philosophers-debate-new-sonic-black-hole-discovery-20190625/ <https://disq.us/url?url=https%3A%2F%2Fwww.quantamagazine.org%2Fphilosophers-debate-new-sonic-black-hole-discovery-20190625%2F%3AzNMKi-FnLv0hsBE30e2sl-nAoHo&cuid=2168707> Philosophers Debate New ‘Sonic Black Hole’ Discovery Opinions differ about what recent measurements of a sound-trapping fluid reveal about light-trapping black holes.
