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Wednesday, October 1, 2014

Hawking Radiation tested experimentally in laboratory.

The spontaneous creation of photon with lasers that emulated the event horizon of a black hole was observed.

Event horizons of astrophysical black holes and gravitational analogues have been predicted to excite the quantum vacuum and give rise to the emission of quanta, known as Hawking radiation. They experimentally create such a gravitational analogue using ultrashort laser pulse filaments and our measurements demonstrate a spontaneous emission of photons that confirms theoretical predictions.

Further confirmation of this radiation is produced by the pairs of matter-antimatter particles to break free one of them, theoretically, in the event horizon of the hypothetical black holes or perhaps better named "dark holes", since a team theorists have mathematically shown that Hawking radiation would prevent the creation of black holes, and these being only a theoretical conclusion of general relativity (see previous post).

Furthermore, many observations suggest the existence of so called black holes so far, but all are indirect. Obviously a black hole can not be directly observed, only indirect effects on the surrounding stellar space. So, as happens with so-called dark matter and dark energy, which we have plenty of evidence, but also all indirect.

Thus, the proposal to call black holes, "dark holes".

With this new verification of the Hawking radiation in the laboratory for the first time, although there are already some hints that exists in the vicinity of the event horizon of the "dark holes", mathematical proof of the impossibility of existence of black holes is reinforced. But still there are a lot of indirect evidence accumulated in multiple observations of the formation of other types of black holes, such as supermassive, which do not come from ordinary stellar cycle described in the paper of the theorists, which postulate no existence of black holes.

Obviously it is not the same observing the presumed mechanism of Hawking radiation in lab with lasers, which it predicted in the famous 1974 paper by Hawking for black holes. But it is still an experimental test, which although is an empirical model, it could provide new evidence on how the radiation mechanism is formed and then study in the vicinity of the known and already observed event horizons and / or design experiments that can find that key of the radiation mechanism in the "dark holes".

About Hawking's radiation, observations and RIP mechanism:

In 1974 Hawking predicted that the space-time curvature at the event horizon of a black hole is sufficient to excite photons out of the vacuum and induce a contin- uous flux, referred to as Hawking radiation. In a simplified description of the process, vacuum fluctuation pairs close to the horizon are split so that the inner pho- ton falls in and the outside photon escapes away from the black hole. As the outgoing photon cannot return to the vacuum, it necessarily becomes a real entity, gain- ing energy at the expense of the black hole. It was soon realized that the essential ingredient of Hawking radiation was not the astrophysical black hole itself but rather the space-time curvature associated to the event horizon.

There are a wealth of physical systems that may exhibit event horizons ranging from flowing water or Bose-Einstein-Condensates to a moving refractive index perturbation (RIP) in a dielectric medium. In a few words, referring to the case of optical pulses in a dielectric medium proposed by Philbin et al. a laser pulse with large intensity, I, propagating in a nonlinear Kerr medium will excite a RIP given by δn = n2I where n2 is the so-called nonlinear Kerr index. Light experiences an increase in the local refractive index as it approaches the RIP and is thus slowed down. By choosing appropriate conditions (frequency of the light and velocity of the RIP) it is possible to bring the light waves to a standstill in the reference frame comoving with the RIP, thus forming a so-called white hole event horizon, i.e. a point beyond which light is unable to penetrate. A similar mechanism may be observed with water waves or with any kind of waves in a flowing medium, so that the formation of an analogue event horizon is a rather universal phenomenon that may be studied in accessible laboratory conditions. What remains to be established, is whether Hawking radiation is actually emitted in the presence of an event horizon of any kind, be it analogue or astrophysical.