SciAm: Hawking radiation

[Doum]

Artificial Event Horizon Emits Laboratory Analogue to Theoretical Black Hole Radiation

http://www.scientificamerican.com/artic ... -radiation

"A laboratory experiment may have offered the first glimpses of a long-predicted quantum effect known as Hawking radiation

By John Matson | October 1, 2010 "

The relatively faint emission has never been detected from a real black hole, so researchers have sought a number of laboratory proxies to demonstrate the general principles of the phenomenon. Now a group of Italian researchers reports what may be the first demonstration of a quantum-mechanical Hawking radiation analogue. In a paper set to be published in Physical Review Letters, the team reports observing photons trickling out from transient event horizons in a piece of glass.

As that perturbation travels through the glass, it forms a moving blockade for light trying to pass. "If you have a light pulse that's approaching the perturbation from behind, that is trying to catch up to it, it will feel an increase in refractive index that will slow it down," Faccio says. "Imagine yourself sitting on top of this perturbation, and you will see this light wave approaching you until it stops." In other words, the laser-induced perturbation acts as a boundary beyond which light cannot pass—a sort of moving event horizon. If a pair of photons is produced close enough to the event horizon, they will become separated and will be unable to return to the vacuum from whence they came. In a true black hole, the separation would be more pronounced; one of the particles would be lost for good to the black hole...

The researchers recorded photons streaking outward from the event horizon, about one photon per 100 laser pulses, with the traits predicted of Hawking radiation. The photon emission was unpolarized, for instance, and appeared in the right wavelengths. After taking steps to rule out possible contamination from more mundane mechanisms, such as fluorescence, the group concluded that the photons appeared to be spontaneously produced from the same physics underlying Hawking radiation...

But others are not as certain. "I still need to be convinced that what they are seeing is the analogue of what Hawking found for black holes...

The direction of emission is "a major point of ongoing discussion," Faccio says, noting that the position of the photon detector was chosen to minimize contamination from the laser. "I sort of prefer to think of it the other way around—we have a spectrum of photons that agrees exactly with theoretical predictions for the event horizon. Now we need to properly understand in detail why they're generated...

"In our big piece of glass we have no way of saying where the other photon will end up," Faccio notes. But Leonhardt's group, which is investigating the same phenomenon in optical fibers rather than blocks of glass, might be able to detect both photons from a separated pair and show their common origin. "Once he does that, I think it will close all the discussions," Faccio says. "That will be an undeniable proof that this idea is correct."

[bystander]

First Observation of Hawking Radiation
Technology Review | the physics arXiv blog | 27 Sept 2010

Hawking predicted it in 1974. Now physicists say they've seen it for the first time.

For some time now, astronomers have been scanning the heavens looking for signs of Hawking radiation. So far, they've come up with zilch.

Today, it looks as if they've been beaten to the punch by a group of physicists who say they've created Hawking radiation in their lab. These guys reckon they can produce Hawking radiation in a repeatable unambiguous way, finally confirming Hawking's prediction. Here's how they did it. ...

Hawking radiation from ultrashort laser pulse filaments - F Belgiorno et al

• arXiv.org > gr-qc > arXiv:1009.4634 > 23 Sep 2010