Acoustic black hole
See also: Black hole (homonymy)
Many assumptions were put forth on the propagation of the luminous rays in the neighborhoods of the black holes, the such emission of increasingly energy photons in order to check a constant radiation. But the field of very high energies is unknown because of the limit of the scale of Planck from which the current physical laws lose their validity.
Starting from work of William Unruh in 1981, physicists circumvented the problem. Unruh had shown the existence of an analogy between the propagation of the sound Onde S in a fluid moving and that of the light in the space time curve. This analogy could according to him solve the problem of very high energies at the origin of the radiation of Hawking.
The sound waves are defined like ordered fluctuations implying a very great number of molecules at distances much larger than the intermolecular distances. They are characterized like the light waves by a wavelength, a frequency and a propagation velocity. In a fluid cooled at a temperature so low that the displacement of the molecules becomes negligible, the sound waves behave as if they consisted of particles: the Phonon S. Unruh showed that when the fluid runs out in a nonuniform way, the phonons travel in a acoustic geometry curve. This one characterizes the trajectories of the phonons like the photons in the geometry of the space time.
“To manufacture” a black hole in a laboratory, one uses a conduit of Laval in which the fluid is subjected in a circular motion. We obtain a rate of the flow, which exceeds the speed of sound in a fluid after the throttling of the conduit. In the supersonic part, the waves which are propagated with counter-current are involved towards the downstream, like the light waves in the internal part of the black holes. The photons are trapped, they cannot leave the black hole. The zone of throttling plays the same part as the Horizon of the events of the black hole: it separates the rays which go up upstream and those which fall into the black hole. In the subsonic zone, the waves which go up the current redden because they lose energy while moving away from the horizon.
We thus find the principal properties observed in the surrounding of a black hole. Nevertheless, between the trajectories of the phonons and the photons very close to the horizon, it appears differences. While moving away from the acoustic black hole, the particles adopt the same trajectory. Thus a remote observer will not be able to determine the microscopic conditions of the production of the phonons close to throttling. One can think that there are the same effects for the black holes.
Studies would show that it would be necessary to regard the space time as a granulated medium. Indeed in such a medium, the difference in trajectory very close to the horizon could disappear. It would be a reversal of situation, because Einstein had denied the concept of a fluid in which the universe would bathe.
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