Back in 1974, Stephen Hawking had a "wild" prediction about black holes: rather than being totally black as the scientific community assumed, black holes evaporate over time and emit tiny amounts of radiation in the process, known as "Hawking radiation."
At the time, such an idea was completely unheard of — black holes were named as such because their gravitational force is so powerful that not even light can escape once it passes beyond the theoretical point of no return, the event horizon. Therefore, the belief that anything could escape once it reaches that point was regarded as lunacy — even if someone like Hawking was the one behind it.
Fast-forward to 2016, and now, Jeff Steinhauer, a physicist at Technion University in Israel, has published a paper in Nature Physics that suggests Hawking might have been right about black holes after all.
Acoustic Black Hole
To test whether Hawking's prediction panned out, Steinhauer created an analog black hole using Bose-Einstein condensates — exotic forms of ultra-cold quantum state matter where a bunch of atoms behave like a single atom.
Upon applying a second laser beam, it created a step that the atoms could flow over (similarly to a waterfall). Once they poured over that step, they accelerated, reaching supersonic speeds in the process.
As such, an acoustic black hole was born. Rather than the typical black hole that exists in space, this one deals with sound; specifically, sound waves inside the supersonic region can't escape because the condensate is flowing faster than the phonons (particles of sound) could travel.
Hawking Radiation
Of course, creating an acoustic black hole was merely a means to an end, as the objective was to see whether or not Hawking radiation was the real deal.
In 2014, Steinhauer conducted an experiment where he observed this radiation, but the radiation in that experiment was simulated — it was caused when something hit the event horizon and created the pairs.
This time around, however, the radiation was organic.
When pairs of phonons were created near the analog black hole, Steinhauer observed one particle falling in and the other escaping, which he argues is analogous to a photon escaping a real black hole — exactly what Hawking predicted all those years ago. What's more, they were even entangled, meaning that, when one phonon fell into the black hole, the one on the outside still retained all the information of that particle.
The end result now has two major implications: first off, this serves as a key factor in resolving the black hole information paradox, and one day devising a unified theory that combines quantum mechanics and general relativity. Second, it could earn Hawking a Nobel Prize more than 40 years after he made his first prediction.
Of course, this all depends on whether the result holds up, and Steinhauer believes it will.
"We've verified Hawking's calculation, and we've even seen that particles really are entangled," Steinhauer said. "I hope that this will give insight to physicists who think about real black holes."
