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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
"You wont"
"doh!"
-Yarn - Rio Karma: Excellent
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.
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As another poster indicated, they are using a Bose-Einstein condensate, not water. I believe that a Bose Einstein condensate was used in the last year to slow the speed of light passing through it to some ridiculously low value, like 38 miles per hour. If this were the speed of light in a particular medium, then it wouldn't take too much to make the medium go faster than that.
I am skeptical that these "optical black holes" will trap particles as well as they trap light. Particles have no problem traveling faster than the speed of light within the dielectric, so long as they do not exceed the speed of light in vacuo. Thus, particles should be able to escape these things, even if light cannot. In other words, these beasts have no true event horizon, and so any analogy to astrophysical black holes is suspect.
Robert Link
Also a physicist. Gave up on Usenet a long time ago.
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
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
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.
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.