Black holes are still one of the mostmysterious objects in the universe. Once in their existence, few believed. And the fact that they exist in reality was described only in various physical models. The question is how to study what is located at a distance of millions of light years from our planet? Perhaps the answer to it will be able to give "sound black hole", which also helps to solve one of the paradoxes that have arisen during the research of Stephen Hawking. But what is a “sound black hole”? Let's figure it out.

First we need to plunge into history. Back in 1974, Stephen Hawking suggested that the black hole is not really black. Its black color is due to the fact that the gravity in the area of the event horizon is so strong that even the rays of light cannot overcome this effect. At the same time, Hawking assumed that the space-time structure on the event horizon would experience “quantum oscillations”. That is, at this moment, pairs of particles and antiparticles can be freed from the effects of gravity and appear on both sides of the event horizon.

This process was called Hawking Radiation. Due to the "quantum oscillations", particle-antiparticle couples arising from the black hole vacuum appear near the black hole event horizon and one of them "falls" inside the black hole, and the other "flies away". From the law of conservation of energy, it follows that a particle “fallen” beyond the event horizon must have negative energy, while a “flown away” must have positive energy. In other words, black holes lose energy when they are emitted. They slowly evaporate and shrink, eventually disappearing completely.

What is the paradox of black holes

The problem is that, according to Hawking’s calculations,black hole radiation will be random. This means that a volatile black hole destroys information, and quantum physics is based on the premise that information is never lost. This is the main paradox concluded in the study of the nature of black holes.

Also interesting: **“The first ever true photograph of a black hole” **

What is a “Sound Black Hole”?

Many years ago the theoretical physicist Bill Unruhargued that Hawking’s ideas about the horizons of black hole events should also apply to “sound horizons”. The sound horizon is, roughly speaking, an analogue of the event horizon, applied to sound waves with the only difference that the speed of light is used as a unit of speed for black holes, and the speed of sound for sound black holes.

In 2016, Jeff Steinhauer from Technion(Israel Institute of Technology) in the city of Haifa, Israel, in one of the experiments recreated the conditions for the emergence of the very "sound horizon", accelerating the liquid from the rubidium-87 atoms to supersonic speed. In the same year, an analogue of Hawking Radiation was discovered. Quantum units of sound, called phonons, appeared in pairs, and one phonon was directed along the flow of a moving fluid, while the other went upstream and ran away.

Now, three years later, an improvedthe apparatus allowed "to check Hawking's predictions." In their new work, Steinhauer and three of his employees discovered that their sound radiation carries no information.

“The discovery gives us hints on informationparadox. The thermal form of the spectrum suggests that Hawking radiation does not carry any information. Therefore, we must look for information elsewhere to resolve it. ”

Comparison of "sound" and "space" black holes

The key question is whetherconsider the space-time on the horizon of a black hole event as continuous. The new data confirm that in the case of a fluid, the flow of which, as is well known, is continuous, the paradox still persists, as the energy of the “sound black hole”, decreasing, leads to loss of information.

But there is a big hitch: a condition that is feasible for liquids may not work for spacetime, which may not necessarily have a continuous course in the region of the black hole event horizon. The presence of “interrupted” time flow in the event horizon area could explain the paradox associated with information loss, because in this case the pairs of particles produced by Hawking Radiation do not disappear without a trace, but simply “go to another level” of space-time.

So if you manage to model“Intermittent” flow in the framework of experiments with the “sound black hole”, we will be able to resolve the paradox associated with the disappearance of information arising in the region of the horizon of black hole events.

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