Scientists have taken another step towards proving the existence of Hawking radiation — fluxes of photons and other elementary particles that may emit black holes.
Following the general theory of relativity, the existence of black holes implies a simple fact: as soon as any object falls beyond the horizon of events, there is no return to the heart of a black hole. The gravitational force of these areas is so great that even light – the fastest phenomenon in the Universe – cannot develop the speed necessary to overcome attraction. Consequently, black holes do not generate electromagnetic radiation either. However, in 1974, young Stephen Hawking suggested that some kind of radiation did exist. Sounds paradoxical? It’s all about quantum mechanics.
This theoretical radiation is called Hawking radiation. Roughly – very roughly – it can be said that it appears as radiation as a result of the temperature of the black hole itself, which is inversely proportional to its mass. If it can be detected, it will mean that black holes scatter, albeit extremely slowly. However, according to mathematical calculations, this radiation is too weak for modern instruments to register.
What can be done? Try to recreate a black hole imitation in the lab. Do not worry, it will not cause space to collapse: scientists can simulate such phenomena using fluid and sound waves inside special tanks, from Bose-Einstein condensates or from light inside an optical fiber. The physicist Ulf Leonhardt explains in the pages of the journal Physics World that “Hawking radiation is much more common than we thought. It probably occurs whenever an event horizon is created — be it astrophysics or light in optical materials, fluid waves, or even ultracold atoms. ”
Obviously, on our planet it is impossible to create the same powerful gravity as inside black holes (and thanks for that). At the same time, mathematical measurements are similar to the mathematics that describes black holes in the general theory of relativity. As a final experimental method, a team of researchers chose a fiber optic system developed by Leonhardt several years ago.
How it works
Inside the optical fiber there are microscopic patterns that play the role of a kind of channel. When the light enters the fiber, it slows down slightly. To create an analogue of the event horizon, two very fast laser pulses of different colors are sent across the fiber. The first one interferes with the second, as a result of which the effect of the event horizon appears, which is observed as a change in the refractive index of the fiber.
By doing this, the team used additional light radiation, which led to an increase in the intensity of radiation with a negative frequency. Simply put, “negative” light scooped energy right from the event horizons — a sign that says Hawking’s successful radiation simulation.
Proved or still not?
Despite the fact that the result was successful, the final part of the study is the radiation of not the stimulated, but the spontaneous radiation of Hawking. Forced – as in the case of this experiment – requires an external electromagnetic effect, while Hawking radiation emanating from a black hole will be spontaneous, that is, without stimulation from the outside.
Another important circumstance is that it is impossible to exactly recreate conditions near the event horizon in a laboratory environment. For example, in this case one cannot be 100% sure that the radiation was not created as a result of the experiment itself, although scientists are sure of the opposite.
In any case, the team has another mystery – it turned out that the result obtained does not coincide with what the researchers expected. “On paper, our calculations show that Hawking radiation should be stronger than what we saw in the end,” Leonhardt said.