Scientists from the University of Glasgow have received confirmation of the reliability of one theory, expressed more than fifty years ago, according to which a very technologically advanced extraterrestrial civilization can use black holes as an almost inexhaustible source of energy.
Even the possibility of testing this theory was for a long time beyond the capabilities of our current technologies, but scientists nevertheless managed to do this using sound waves in their experiments.
The idea of using a black hole as a source of energy is reminiscent of an episode of the 1970s Doctor Who series. But, back in 1969, the British physicist Roger Penrose, studying the properties of the then theoretical black holes, found that black holes can be useful for civilizations that have reached a certain level of technological development. Penrose put forward the theory that if you take an object and place it in the region of the upper boundary of the black hole event horizon, it will stay there for a while, moving in a circle, gradually decreasing, acquiring "negative energy" and accelerating to a speed close to the speed of light. The special conditions of the space-time continuum in that region favor the fact that this object will receive kinetic energy, literally drawing it from the vacuum.
Then, if this object splits into two objects, one of which sinks into the abyss of the black hole, and the second is pulled out and lifted, this will compensate for the negative energy acquired by the object, borrowing it from the rotation of the black hole. Of course, the implementation of this, not to mention the possibility of being in the immediate vicinity of a black hole, will require a level of development of civilization technologies that is not even visible on the horizon of our earthly technologies.
In 1971, Soviet physicist Yakov Borisovich Zeldovich invented an experiment with "twisted" light, which could confirm Roger Penrose's theory. Twisted light is a specially formed beam of light that is twisted along its wavefront to a point at the center of the beam. The result is a spiral shape of a beam of light with an empty core in the center of the beam, and if such a beam is aimed at a metal cylinder rotating at a certain speed, the beam reflected from it would acquire additional energy, borrowing it from the energy of rotation of the cylinder due to some phenomena associated with the effect Doppler. However, such an experiment would require the cylinder to rotate at more than a billion revolutions per second, which is still unattainable today.
Installation for obtaining twisted sound waves.
The question with Roger Penrose's theory remained open for 50 years, while a group of scientists from the School of Physics and Astronomy of the University of Glasgow, using a very unconventional approach, tried to use twisted sound waves instead of twisted light, the frequency of which is much lower than the frequency of light waves. And this made it possible to conduct an experiment at the current level of technology development.
To create twisted sound waves, scientists used a variety of emitters arranged in a ring. The resulting wave was aimed at a rotating absorber, a disc made of construction foam. Microphones mounted behind the disc measured the frequency and amplitude of a sound wave passing through a rapidly rotating disc, the parameters of which were supposed to fit within the framework of the theories of Penrose and Zeldovich.
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In this experiment, the constantly accelerating rotation of the disk first reduced the amplitude of the sound to an almost inaudible threshold, but later the amplitude of the transmitted sound rose to its original level, and then to a level 30 percent higher than that emitted by the speakers.
"The rotational Doppler effect is similar to the usual linear, but its effect is limited to a circular space, and therefore it is the twisted sound waves that change their parameters by a significant amount," the researchers write, "And if the surface rotates fast enough, then very strange things, they can change their frequency from positive to negative and "steal", at the same time, a certain amount of energy from the rotating surface."
“What we got during our experiment is extraordinary from the point of view of physics. First, the frequency of sound waves is reduced to almost zero due to the Doppler effect. But when the speed of rotation increases even more, the sound appears again, while the frequency of rotation of the sound waves changes from positive to negative, the sound waves receive additional energy from the rotating disk and become louder than they were before. And all this fully fits into the theoretical calculations of Yakov Zeldovich, set forth by him in 1971”.