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Optical Black Holes in the Lab
spaceorb writes "According to researchers ... it may be possible to create black holes by creating a vortex of fluid that swirls at velocities comparable to the speed of light. Follow the above link for the theoretical discussion or here for the story on unisci.com." These are optical analogues of black holes, not really gravity wells, but they may advance our understanding of the real thing.
The actual speed of the photons is not reduced going through a medium. (this is the part of relativity) What is reduced is the apparent speed to an opserver (an important distinction). This is due to collisions with particles and fields that misdirect the photon along a much longer path through the object. (I know this is a very elementry explaination, but I fear going deeper)
What this vortex will do is make that path of misdirect infinitly long (ie a cirle like). Therefor the photon will never make it back out.
This is 'simular' to the idea of refraction in optical cable, the material is such that the light is always refracted back within itself (if it enters at a certain angle). what the vortex does is make a circular optical cable with prefect refraction trapping all light within itself. (I know this is an over simplification)
Gork the Enchanter
And copper acts as a waveguide for EM waves. Thats why he said 'light' as it doesnt necessarily mean visable light.
-Yarn - Rio Karma: Excellent
If only :)
I expect you could make a 'sonic black hole' using the same idea as this one, but the trouble is that this method doesnt seem to SUCK the light in like a gravitational black hole does. It has to hit part of the vortex to be captured.
-Yarn - Rio Karma: Excellent
"You wont"
"doh!"
-Yarn - Rio Karma: Excellent
Gotta be:
"A tornado, for example, attracts with ease substantial ``test particles'' such as cars"
:-)
dylan_-
--
Igor Presnyakov stole my hat
Physics is...not my strong suit. I don't claim it to be so, I'm not an expert in this field, I'm an outside observer that just has a few questions...
For one, exactly how do they propose to keep the water in liquid form?
Water remains liquid only at certain temperature/pressure ratios. Creating a vortex rather quickly creates large pressure differentials(almost by definition), and dumping light into something that isn't going to be able to spit it back out is going to increase temperature. How is the entire mass going to be kept in that one relatively small range that keeps the material liquid? Granted, an excessively smooth container might allow superheating of the fluid(water cannot boil unless there are microscopic ledges upon which bubbles may form, apparently), but having this fluid in contact with *any* other substance is going to create seriously ugly amounts of heat by way of friction.
Even supposing one could accelerate such a material to near-luminal speeds, at minimum a Zero-G environment and a vacuum would be required.
But that's one heck of a supposition! Assuming a massive objects could be spun at such extreme rates is...generous. Am I wrong, here?
I must also ask where the concept of absorption has gone. For a while there, I was imagining they were describing a merger between fiber optic cable and a roach motel--light got in, then was forced to spin round and round the vortex forever. But who said that the water would become instantly clear? As it spun around, wouldn't more and more of it be converted to heat until there was no light left? I'm not slowing down light if I move it through a fiber optic cable that's a kilometer long but on a spool only a foot thick. The light still moved a kilometer, even if (from my "perspective") it only moved a foot. But fiber optic cable is very transparent; water isn't nearly as such--particularly water that bubbles and is highly agitated.
And how would light enter the system if the outside walls of the vortex were so particularly
chaotic? This part, I'm really missing.
Something just seems...wrong here. Someone care to clue me in?
Yours Truly,
Dan Kaminsky
DoxPara Research
http://www.doxpara.com
Its not a black hole. It is an optical black hole which just means that light gets stuck in this vortex. It will no more emit hawking radiation than a mirrored room (which hence traps light). This vortex is not gravitational does NOT slow time or any such thing.
Marriage is the "pseudo-ethics" that cloaks the messy truth of sexuality in the raiment of propriety -- it's "Don't Ask,
> Next, it only takes an infinite amount of time
> for a particle to cross the event horizon from
> the outside perspective of an observer who is
> not falling into the hole. To the particle or an
> astronaut falling into the horizon, the trip is
> quite short. Therefore, to say that black holes
> only exist asymptotically is incorrect.
Two frames of reference:
From the perspective of the outside observer, what occurs is as described, the infalling object (albeit ripped apart tidally) slows and asymptotically approaches the event horizon, which over a very long but finite time shrinks until it vanishes.
From the perspective of the infalling observer, (which has been torn into subatomic particles and radiation by the tidal forces), it seems to cross the event horizon without delay -- except that there is no event horizon any more. During the short trip, the black hole has evaporated, and all the particles which had at one time or another been gravitationally captured outside the event horizon will be now "emitted" where the hole has just ceased to exist (but billions of years later from the perspective of outside observers).
Peace and love, y'all
It will be interesting to see whether they can actually create an "optical black hole", or just asymptotically approach one. Assuming that Hawking is correct, and that black holes emit a quantum radiation which reduces their mass as one-half of a particle/antiparticle pair escape, evaporating in a finite time, and considering the time dilation which requires an infinite time for a particle to actually cross the event horizon, then black holes only exist asymptotically. That is, trapped particles move inward as the event horizon shrinks, and cross it only as it evaporates.
Peace and love, y'all
Conservation may or may not work inside a sigularity or it may be transmitted to another point in this usniverse or another one. Since (luckily) we don't have any close singularities we haven't been able to study what happens inside them. It's very possible these photons are slowed down to an almost absolute stand-still (like in a Bose-Einstein condensate) and are actually accepted into the singularity as more mass. The energy of the photon increasing the energy of the singularity but the increased mass of the singularity counterbalances the energy inserted into the singularity. That would make it theoretically possible for conservation to work within a singularity. Singularities don't suck in light like a vacuum, they warp space-time and bend the path of the light into infinite vortexes. Light whose path isn't bent 100% would be sent off in on a tangent of the event horizon if it didn't smack through the matter swirling in the event horizon.
I'm a loner Dottie, a Rebel.
A black hole (in the sense of a gravitational black hole) actually destroys the photons etc.
No, that is not possible; conservation of energy expressly forbids such a thing from happening. In this case, as in all others, the energy is simply converted to some other form.
As for a brick being the same thing, that is also incorrect. The difference is that even the brick reflects light, otherwise you would be unable to see it. A black hole, however, not only does not reflect any light at all, it actually "sucks in" light that strays too close. In the case of the "fluidic black hole", presumably any light that strays too close to the vortex will similarly be sucked in.
Cheers,
Tim
It's official. Most of you are morons.
I think it's more along the lines of this...
;)
Light is *not* a constant speed, it is only a constant for a given energy density of space.
When light travels through air, or water, it slows down (albeit not by much).
I Think the theory goes that if you make it pass through a gas with a very high density.. it slows down even more.. and a BEC (Bose-Einstein Condensate) I believe can be used to create a gas or other transparent material with a very high energy density (BEC, if I recall, is basically a whole bunch of atomic nuclei stuck together acting like one large atom.. something like that).
If this density is high enough, and the material is trasparent, in theory the speed of light throug the material could be slowed extremely.
You are right, though.. they will make a whirlpool spinning at near light speed because they have slowed the speed of light
Bricks do not produce Hawking Radiation. It's that quantum effect that makes this experiment exciting and unusual.
Hawking radiation originates in the background of virtual particles in the universe -- particles that appear spontaneously from nothing along with their antiparticles, then collide and exterminate themselves. This background energy is a vital part of our models of the universe.
Stephen Hawking theorized that near a black hole some these virtual particles would be sucked into the black hole while their antiparticles would remain free. Thus, some virtual particles become permanent and real particles, and the black hole effectively radiates them into space. Conservation of mass states that the black hole must then be shrinking slowly in size...but that's not important here, with the laboratory optical black hole.
The optical black hole will have the same effect as a real one; virtual particles will be trapped within it, and their antiparticles will fly free. (Note that the trapped particles may be either matter or antimatter -- the radiated particles will be the opposite of the ones trapped.) Scientists will then be able to measure this Hawking Radiation and test some very central theories of cosmology and quantum physics.
Theoretically (and there's a point at which the theory is so remote, it's only fantasy...but here goes), an optical black hole *might* be configured to collect the radiated antiparticles as a bose condensate themselves. Then the optical black hole serves a purpose -- it's an antimatter generator. But that's really, really far beyond what they're trying to do now.
...
Remus Shepherd
Yes, I am a physicist. Yes, I do play one on Usenet.
Genocide Man -- Life is funny. Death is funnier. Mass murder can be hilarious.
This is not quite correct. The speed of light in a dielectric depends on the index of refraction, n, of the medium; n is in turn a function of the magnetic permeability, mu, and dielectric constant, epsilon of the material. At the root of it all mu and epsilon are functions of the molecular and electronic structure of the medium, as well as the frequency of the light itself. Thus, two materials with similar densities but very different dielectric constants will have very different indices of refraction, and hence light will propogate within them at different speeds. What's more, even for a single material, n (and hence the speed of light) will in general vary with wavelength. This is called "dispersion", and it is responsible for such diverse phenomena as rainbows, prisms, and smearing of pulses from pulsars.
The important thing to remember is that only the speed of light in vacuo functions as an absolute "speed limit". Particles can and do exceed the speeds of light in dielectric media, causing them to emit Cerenkov radiation in the process.
-r
-r
Imagine you have a lump of some material. The electrons circling the atoms or molecules of the material have some characteristic structure that depends on the elements involved, how the electrons are shared in any molecular bonds in the material, and how the atoms or molecules are arranged in the bulk material (proximity of other atoms or molecules distorts the energy levels for orbiting electrons). This latter factor, by the way, is the difference between coal and diamond.
Now, along comes an electromagnetic wave, which is really just an electric field oscillating with a magnetic field. The electrons in the material are going to feel a force due to the E field (in this naive treatment we'll ignore the magnetic field). What's more, that force will want to drive the electrons to oscillate, but those oscillations will be resisted by forces that depend on the factors I mentioned above. The punchline is that the more the electrons are free to respond to the electric field's driving force, the more energy they will dissipate, the more the incoming light will be attenuated, and hence the more opaque the material will appear. Conversely, if the electrons are not free to respond, the light is not attenuated (much) and the material appears transparent. As you might expect, for any given material the response of the electrons varies greatly with frequency (just like the case of mechanical resonators). This gives rise to all sorts of phenomena, which you can find described in any good optics text.
Now, in the case of conductors (like metals) the electrons are very free to move around (that's what gives them their conductivity), and hence you would expect them to quickly dissipate any electromagnetic waves incident on them, and that is generally the case. Typically the ``skin depth'' for metals is about 1/6 of a wavelength. However, as you go to higher frequency, things get complicated again, because the conductivity has a wavelength dependence. Generally that dependence takes the form of a strong drop off in conductivity above some characteristic frequency. Evidently, this characteristic frequency is well above visible light frequencies for naturally occurring metals.
Another poster mentioned that DARPA is working on transparent metals. Presumably, then, their line of attack is to try to find some alloy with a crystalline structure that makes that alloy's characteristic frequency lower than visible light frequencies. If and when they succeed, it will be interesting to see what that does to the metal's other characteristics like malleability and ductility.
Hope that helps (and I hope I didn't post it too late for you to get back around to reading it at some point).
-r
What's more, from the standpoint of General Relativity these constructs don't look anything like a black hole. The stress-energy tensor (the relativistic analog of mass density) is virtually unchanged by the modest rotational flows light traps made from Bose-Einstein condensate would require, meaning that these constructs should have exactly the gravitational properties you would expect of a static body of liquid in the laboratory (i.e. none to speak of). That means no space-time curvature, no ergosphere or frame dragging, no gravitational redshift, and no time dilation. For example, if they directed a stream of muons through these things they should find the muons' decay lifetime basically unchanged from what it would be if they sent the muons through the same liquid while it wasn't rotating.
I believe the authors make an important mistake when they say "... a moving dielectric medium acts on light as an effective gravitational field." That is clearly not true because this putative "gravitational field" does not obey the equivalence principle; viz. it accelerates light but not matter. The mistake is comparable to saying, "A charged pith ball in an accelerating train car will experience an `effective electric field' which will tend to accelerate it." and proceeding to compute the electromagnetic properties of this moving field. The analogy falls flat because the acceleration is not caused by an electric field, and so it can't be expected to act like one when you study its influence on anything else in the train car. Similarly, although you can compute a gravitational field that would trap light in the same way as these constructs, that doesn't mean that there is actually a gravitational field present, nor does it mean that other effects that would be present for the gravitational field you calculated will actually show up in your apparatus.
None of that means that this isn't interesting research, of course, but as far as I can tell the connection to black holes and astrophysics is nonexistent.
-r
Oh come on "-1, troll," it is so obviouly a joke.
Any culture that cannot laugh at itself does not deserve to exist.
People with high karma get automatic +1's to any comment they do not specifically designate "No Score +1 Bonus." That's why there is no reason specified for his score.
My guess is that if the black hole you dropped into the earth were big enough to have a net gain in mass as time progressed (ie it is not evaporating faster than it eats), then you would not get "a century or so." Since the growth of the hole would most likely be fit by y=x^x or some other god-awful function, we'd either be completely safe, or quickly dead.
On the other hand, I am basing this on almost no information. Can anyone point us to a well thought out mathematical model of this?
You are right, if the sun turned into a black hole, Earth would go on happily orbiting because the gravitational effects out here would not change. [Perhaps the added spin of the sun would make a bit of a difference, but I don't know what is conserved in this case]
However, there is a large difference between a 1g block of steel and a 1g black hole if you are trying to keep it sitting on a table [or in any other non-vacuum]. The steel and the hole will have the same gravitational effect if you are 2cm away from the center of each, but anything very close to the hole WILL get sucked in, because the gravity DOES make the escape velocity rise to above the speed of light as you move towards it. If you "set" your 1g black hole down on the table, it would not and could not be supported and would fall straight thru any matter in its way until it got to the center of the earth. As it went and once it was there, it most definitly continue to suck matter in. Perhaps the rate of suck would be very small at first, since particles have to get real close in order to be trapped, but the more that it eats, the more it sucks.
On the other hand: A 1g black hole would evaporate (read: explode) very quickly due to hawking radiation.
And: They are not making black holes anyway, that is just an analogy, RTFArticle.
Good point about it not stopping at the center. I never thought of that, and I think a whole lot of science fiction writers miss it as well.
At some point I will do the math for [1g black hole versus density of particles it will encounter] and [time it takes to explode due to hawking radiation], but right now I am too overworked already.
Read the article! They're NOT making a black hole, it's just an optics experiment. They want to study the effect of light in a moving medium, where the speed of light in that medium is very slow. They won't even have to "stir" it that fast. The worst that could happen is that, as more photons pile up at the "event horizon", where they will eventually just be absorbed by the medium and converted to heat, it will raise the temperature of the bose-einstein condensate enough to undergo a phase change (back to regular old cold rubidium atoms, I suppose). There may be a dim flash of light during the phase change... just a guess.
The whole experiment is about as dangerous as playing with a laser pointer.
-CausticPuppy "Of all the people I know, you're certainly one of them." -Somebody I don't know
Optical Black Holes reference:
U. Leonhard and P. Piwnicki, Physical Review Letters, 84, 822-825(2000).
This is the actual reference to the paper proposing optical black holes. It has been published in what is arguably the most respected physics journal(not some speculative rag). Many of you are asking about a material in which the speed of light is very slow. Such a material was demonstrated last year:
L. V. Hau, S. E. Harris, Z. Dutton, and C. H. Behroozi, Nature(London) 397, 594(1999).
In this paper Hau et. al. demonstrated that light traveling through a Bose Einstein Condensate is slowed to a mere 17 m/s. This is slower than most bicycles ride(as illustrated by the cover of that weeks nature). To find out what Bose Einstein Condensate is you can refer to:
Anderson, M. H., Ensher, J. R., Matthews, M. R., Wieman, C. E. & Cornell, E. A. Observation of Bose-Einstein condensation in a dilute atomic vapor. Science 269, 198-201 (1995).
Now go to your local University Physics Library and look a few of these things up before advertising your ignorance and pronouncing that this is bullshit just cause you read some bullshit article on real science
Of course, users of modern universes will gleefully point out that, in theirs, light rarely actually swaps -- it pages using an LRU algorithm.
Practice random senselessness and act kind of beautiful.
Then it sounds like this experiment, modified, could result in the instantaneous destruction of the universe:
First, get the light within the artificial vortex to slow down.
Then, place the device containing the experiment within a good-quality vaccuum, like an Electrolux (or an old VAX).
At that point, the light within the experimental device has a problem -- it's supposed to go the speed of light 'cause it's in a vaccuum, but it's supposed to go slower because it's going through some other materials.
The result of this contradiction might be the immediate destruction of the entire universe, followed by some quick behind-the-scenes fixing of microcode bugs and a reboot. (This sort of crash is known by the heavenly hackers as a "BSOD", or "Black Suck of Death".)
(Or, we might just learn which if these "laws" is wrong!)
Practice random senselessness and act kind of beautiful.
::raises hand:: How exactly do you make light go slower? I thought it was the one thing that was always constant, no matter what. But then again, I never did do very well in Physics. :)
How exactly do you make light go slower?
One method of making light go slower is to use a window. Light travles at approx 200,000 km/s in glass, compared with almost 300,000 km/s in air.
The speed of light is not constant. The speed of light in a vacuum is constant. The speed of light in a Bose-Einstien Condensate (which is what these folks are planning to use) is far far slower than the speed of light in glass or in air or in a vacuum.
It seems that everything you talk about relating to black holes is a paradox, it tookme a few seconds to work this out (because they expect you to know what *they* are talking about):
:)
;)
Here goes: They use the word 'comparable' when it may have been better to use 'relative'.
The gist of it is you can't accelerate matter up to the speed of light; therefore you slow the light down instead. So you don't need a whirlpool which spins at hundreds of thousands of miles
per hour
It would be interesting to see if some of Steven Hawkings theory is correct, and if you haven't read the 'brief history of time' go out and buy now! (but not from amazon.com) its worth it just to have on the coffee table when friends are round
(friend:"ooh, whats that book about" you:"well....")
Maybe you all understood better than I, just thought I would post this incase anyone was left scratching their head.....
Ripping an new rectum in the fabric of spacetime.
Actually, no we aren't. Not in the important sense of a gravitational singularity. This is merely something that simulates some aspects of a black hole, namely that light goes in and doesn't come out. Theory suggests that this violates preservation of information, meaning that there must be some other force at work countering it. That's the radiation part. To examine this would be an interesting insight into a realm we don't know much about.
But this is not a dangerous experiment in any way. Your armageddon scenario fails because there isn't any actual singularity in the picture.
-- Eythain
PS Besides, the 30 minutes calculation for a real balck hole is way off, or rather, that would depend entirely on the mass of the black hole in question. A natural black hole from a collapsed neutron star would squish us before we even got close, whereas a quantum black hole we could concievably make would probably be so small it would evaporate, or even if it wasn't, it would not significantly affect the Earth (I mean, it's not likely we can make a black hole a significant fraction the mass of Earth, where would that mass come from?) while growing. Since a singularity this small is basically point sized (even the event horizon), it would be severely limited in how quickly it could swallow matter. So relax, we'd certainly have a century or so to evacuate, even in the worst case scenario.
A good book on that horror scenario would be Earth, by David Brin.
"The idea is to use a medium where light is only going something like a few meters per second..."
A medium? That sounds more like sorcery than science. Is it done with crystals?
I think that if science can invent air brakes (presumably to help us brake wind), then why not invent light brakes to slow their light down? This is different than brake lights which are just an indicator (usually of the speed of traffic, not light).
Also, if they slow the light down, wouldn't it only be an optical brown hole? And since it's not a real black hole (or brown), but only an optical one, what's to prevent people from checking it out and saying, "I just don't see it"?
--
As a matter of fact, I am a lawyer. But I play an actor on TV.
What a load of bunkum. There's a world of difference (yuk yuk yuk) between an optically inescapable region and a gravitationally inescapable one.
Else I just made a black hole by lighting a cylume stick inside a brick, or putting a flashlight in a draw an closing it. Or drawing the blinds.
Rotating fluid faster than the speed of light within it is like putting a brick on the table and saying that it's going faster than the speed of light within it. Or sitting stock still in a vacuum and saying you're going faster than the speed of sound.