Slashdot Mirror
Hawking Radiation Claimed Created In a Lab
eldavojohn writes "In 1974, a young newcomer to the Royal Society named Stephen Hawking predicted that black holes emit Hawking Radiation. Researchers have been looking for it in space ever since. A new paper up for publication claims to have beaten searchers by observing it in a lab. Doing it wasn't easy. They say they brought light to a standstill by drastically increasing the refractive index of the material it was being fired at, creating a 'white hole.' This horizon, beyond which light cannot penetrate (event horizon), is the same between white and black holes, which caused the team to suspect they observed Hawking Radiation when light of a different uniform wavelength than the input laser was emitted. But, before you rejoice, the Tech Review article notes, 'Of course, the big question is whether the emitted light is generated by some other mechanism such as Cerenkov radiation, scattering or, in particular, fluorescence which is the hardest to rule out.'"
OK, either you're a troll and I'm wasting my time (most likely) or you're misunderstanding something. What Hawking admitted wasn't that the radiation didnt' exist but that the radiation did not in fact violate the principle of conservation of information. Previously Hawking had believed that it must violate said principle because there was no understood way for there to be a connection between the information about the matter that had fallen in and gone past the event horizon and the radiation that would be emitted. This was challenged by another physicist, whose name escapes me since I can't look it up at the moment, who reasoned (along with a more definite proof of course) that the information gets left at the event horizon also. This is because of the fact that from the perspective of anyone outside the event horizon any matter or energy falling in will never actually reach the event horizon it'll just appear to be slowing down further and further until it for all intents and purposes stops. This allows the virtual particles making up hawking radiation to be influenced by the information left at the event horizon without there being a need to have communication between the singularity at the center and the event horizon.
[citation needed]
As far as I know Hawking Radiation and black hole evaporation have not been ruled out. The effect is just so small that there is no experimental evidence of it.
Actually, you'd better hope black holes evaporate or the black holes the LHC might create may destroy the earth! I for one use a tin foil hat just to be safe.
Popular visualizations and even the notion of "virtual particles" do not allow very accurate reasoning with regards to Hawking radiation. In particular, the "promotion process" from "virtual" to "real" is just a crutch for proving something to all orders in perturbation theory. Shortly after Hawking-Bekenstein, Bill Unruh proved that simply being in a uniformly accelerated reference frame creates a perception of thermal background radiation coming from the background -- at a temperature equivalent to the pseudo-event horizon of the acceleration for the duration of the acceleration. You see, while if you move at a constant rate any photon will catch you just as quickly as if you were standing still (basic special relativity) if instead you accelerate forever, you asymptotically approach the speed of light, but there are photons far enough behind you that will never catch you. How far behind they need to be depends on how fast you are accelerating. So, every acceleration corresponds to a pseudo event horizon. As soon as one stops accelerating the photons can catch up to you. Unruh's result does *not* depend on the permanence of the horizon, but works for temporary accelerations. So, the horizon does not need to be "permanent" for the "promotion" to occur. A better way to think about Hawking radiation is any gravitation field (any curved space, that is) decaying via thermal radiation, or space itself providing some "resistance to acceleration" or intrinsic acceleration-only viscosity where the energy taken away from the acceleration is converted to thermal radiation. The image of a virtual pair around an event horizon is not, ultimately, how the result holds or is proven or even what the process is "about". It's more like an "inspiration to a derivation" than something to be taken so literally.