Hawking Radiation Claimed Created In a Lab 129
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.'"
Re:what bs are you posting (Score:5, Informative)
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.
Re:what bs are you posting (Score:5, Informative)
[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.
Re:Double emission? (Score:5, Informative)
Re:what bs are you posting (Score:1, Informative)
The model that predicts Hawking radiation is the only model that would let them produce miniature black holes in the first place.
Sing it with me: "you can't have one... without the other!"
Re:I don't understand... (Score:3, Informative)
As I mentioned above, one does not need a black hole for this -- all curved space should release thermal energy, though the rate is usually immeasurably small. Google Unruh effect and read about it in relation to the Sokolov-Ternov effect which has been observed since the 1970s. There is not perfect interpretational consensus about all this, though.
Re:I don't understand... (Score:1, Informative)
What you are missing is the laws of thermodynamics, where the universe ends up trying to "balance the books" in terms of mass and energy. Steven Hawking proposed this concept based upon the laws of thermodynamics in a broad sense, where mass and energy are always conserved.
In this case you can think of the particle falling into the event horizon from the virtual pairs as a sort of "negative mass". I know that isn't completely accurate from a pure physics perspective, but it is sufficient for mere mortals like you or I. The mass and energy to create these particles didn't come from the universe as a whole, but rather are random fluctuations that always happen in the universe on a rare occasion and generally can be ignored except in special circumstances. A black hole event horizon is such an extreme situation that such events do matter.
Perhaps another way to look at it is that on a quantum level the black hole event horizon isn't absolutely perfect and there are some "ripples" and "bumps" on the event horizon. These random bumps are where the radiation is formed and indeed it is a small hunk of the mass of the black hole that is leaving. Again, this isn't a really good explanation in terms of a formal scientific explanation, but it does get the job done for mere mortals.
Keep in mind that for most large mass black holes, the amount of radiation produced by these things from Hawking radiation is astonishingly small. For something that has the mass of our Sun, it would be measured as having a temperature that is colder than the background radiation caused by the Big Bang. In other words, simply by sitting there it is collecting more energy (hence mass) from the universe as a whole from the residual radiation of the Big Bang than it emits.
The cool thing about the LHC and some of the research that think they'll be able to create black holes in a laboratory is that these are going to be tiny, low mass black holes if they ever are created. In this case the radiation levels are going to be incredibly high and the lifetimes of these black holes are going to be very short. Short as in just a small fraction of a second or so. The large black holes like the one at the center of our galaxy are going to be hanging around for trillions of years or more... certainly longer than anything we would recognized as this universe is going to exist.
Re:what bs are you posting (Score:5, Informative)
'BTW, on a more serious note: a quick google search of "hawking radiation disproved" [google.com] doesn't seem to come up with much serious material.'
Well, you generally shouldn't come up with a lot of material for or against this theory; you need a black hole to really test it.
We all understand what Hawking radiation is, right? Its the run-off of actual particles created when a virtual particle pair "pops" into existence near the event horizon of a black hole; normally the two annihilate each other but in this case one of the two gets sucked into the black hole, the other shoots off into spacetime. This also gives the hole a little negative mass, leading to the other huge implication in this theory; black holes can evaporate.
Re:what bs are you posting (Score:5, Informative)
Probably not hawking radiation. (Score:5, Informative)
It sounds like the light they see is monochromatic. Hawking radiation would be blackbody radiation. Unless they have a reason why this blackbody would only have one mode and an incredibly high effective temperature. I'm guessing that they've found an uninteresting fluorescence feature.
Technology review's arXiv blog is so difficult to get any details out of. It's hard to figure out what these people have done. "frequency of 1055 nm"? I guess I'll have to go to the full article.
Re:I don't understand... (Score:2, Informative)
So, to answer (1), yes -- just an analogy. (2) would be correct if the answer to (1) were "no", but it isn't. :-)
As I've referred to above, "capture" and "escape" of "virtual" particles is all a bunch of highly specific visualization related to a black hole or event horizon, but the actual result pertains to all accelerating reference frames and all spacetime curvature. Though Hawking himself might disagree with me, I find it pedagogically misleading to "explain" the possibility of this thermal radition in terms of processes only happening at a literal even horizon.
This is actually an interesting case of the strong principle of equivalence -- that gravity is locally indistinguishable from an accelerating frame of reference for all physical processes. (The weak principle of equiv is only about graviational forces, but the quantum vacuum is broader physics than that.) Specifically, you can derive Unruh radiation from quantum vacuum transformations *or* you get the same numerical temperature as starting from the idea that an accerelating reference frame "event horizon" is the same as a gravitational event horizon. I derived that latter in high school in the mid 80s, actually, to prove to myself that strong P of E held in this case. It's a relatively easy exercise in hyperbolic functions and basic calculus to compute the asymptotic trajectory of uniformly accelerating frame and back out the effective accerelation event horizon. Plug that in to Hawking's formula for a black hole and you get Unruh's result for acceleration. (They really call it Fulling-Davies-Unruh since it was done three times independently after the Hawking-Bekenstein results.)
I would agree with another responder here that not mentioning the thermal character of the radiation and words suggesting its monochromicity makes this particular result a little dubious, but I have not read the arXive article.
Re:Probably not hawking radiation. (Score:2, Informative)
Re:what bs are you posting (Score:4, Informative)
While I too am not a physicist, my understanding is that, while normal particles are falling into the black hole, it is increasing its mass faster than it is losing it. However, for black holes that do not have an accretion disk or other inflow of matter, Hawking radiation would cause a slow but net decrease in mass of the black hole.
Re:Double emission? (Score:2, Informative)
In the case of black holes, the radiation of stellar or galactic mass singularities is absolutely miniscule. Evaporation is only a "noticeable" process for very tiny black holes with the mass of an asteriod packed into the space of a proton.
As for what you can or cannot picture, that is your issue. I am just letting you know the basic phenomenon is much more broad and actually much more fundamental than a black hole event horizon membrane. The membrane and virtual pairs may begin (but not end) arguments and derivations or motivate theoretical preferences for resolving various issues, but it is misleading to call that imagined scenario the essence of the process. Physics teaching often suffers from "historical bias". Because some physicist first imagined things a particular way or convinced his peers a particular way, this is often the path used to motivate things to a popular audience. The truth is that after some thought and generalization it may be much less sensitive to the original motivating visual picture.
Re:what bs are you posting (Score:3, Informative)
Re:what bs are you posting (Score:3, Informative)
No, this is incorrect. All it requires is for one very speculative piece of physics to be true: large extra dimensions [wikipedia.org].
If the only modification to the standard model is large extra dimensions, then it's just like any other particle physics experiment, where decay rates are closely related to formation rates. The black holes decay essentially instantaneously. That is why theories with large extra dimensions are not immediately falsified by the lack of geological evidence, or by the fact that we don't observe white dwarfs and neutron stars being destroyed by cosmic ray impacts.
To be *worried* about black hole production at the LHC, i.e., to think that it might be dangerous, is a whole different matter. Your criticisms above are all valid criticisms if someone is saying that the black holes might be produced and not immediately evaporate. That requires some very strange nonstandard physics. Here are some papers on the topic: http://arxiv.org/abs/hep-ph/0402168 [arxiv.org] http://arxiv.org/abs/0808.4087 [arxiv.org]