First Acoustic Black Hole Created

KentuckyFC writes "One of the many curious properties of Bose Einstein Condensates (BECs) is that the flow of sound through them is governed by the same equations that describe how light is bent by a gravitational field. Now, a group of Israeli physicists have exploited this idea to create an acoustic black hole in a BEC. The team created a supersonic flow of atoms within the BEC, a flow that prevents any phonon caught in it from making headway. The region where the flow changes from subsonic to supersonic is an event horizon, because any phonon unlucky enough to stray into the supersonic region can never escape. The real prize is not the acoustic black hole itself but what it makes possible: the first observation of Hawking radiation. Quantum mechanics predicts that pairs of phonons with opposite momentum ought to be constantly springing in and out of existence in a BEC. Were one of the pair to stray across the event horizon into the supersonic region, it could never escape. However, the other would be free to go on its way. This stream of phononic radiation away from an acoustic black hole would be the first observation of Hawking radiation. The team hasn't gotten that far yet, but it can't be long now before either they or their numerous competitors make this leap."

Comments

And the news is where?

[Opportunist]

I got a shot Bose amp here, and any sound you put in turns into silence. Voila, accustic black hole.

I'd sell this baby for cheap, too!

Re:And the news is where?

[goombah99]

I'm giving my Bosewave radio new respect and standing a couple steps away from it just in case.

Re:And the news is where?

[Anonymous Coward]

I'd sell this baby for cheap, too!

Wow, this research is paying off already! Finally someone is selling a BOSE for what it's worth.

Re:And the news is where?

[grub]

Bosewave radio

Hey how are those things? They seem a bit pricey, are they really worth it?

.

Re:And the news is where?

[Anonymous Coward]

I'd mod you off-topic but since this is /. I think it's interesting.

Re:And the news is where?

[Anonymous Coward]

What happens when they shut the thing off - do you suddenly hear all the sound that got gobbled up??

Re:And the news is where?

[rock_climbing_guy]

I saw one on display at a mall. The sound quality was fairly good to my ear, but the price was astronomical. I'd never pay full price for one.

Re:And the news is where?

[grub]

Yeah, it is off topic but I have karma to burn and want to know.

Most people in the real world may say "It sounds good" and leave it at that.
A /.er may post links to logarithmic scaled charts with frequency responses, graphs with acoustical data, YouTube videos of someone installing Linux on it, etc. then end it off with "It sounds good"
:)

Re:And the news is where?

[Opportunist]

Hmm... I can only judge it by my shot Bose amp, and no, it doesn't make a sound when you switch it off. Actually, it seems to be permanently on, because even when I flip the switch you still don't hear anything.

OMG, I hope I didn't break the sound universe.

Re:And the news is where?

[m50d]

Terrible. They rely entirely on marketing and placebo effect; actual sound quality is if anything worse than your ordinary off-the-shelf.

Re:And the news is where?

[Hurricane78]

I think "Bose" is just the American way to write "Böse", which is German for "evil". Fits pretty well, doesn't it? *puts on double-layered tinfoil overall*

Re:And the news is where?

[Anonymous Coward]

Really? You can install Linux on a Bose Wave radio?! ;)

Re:And the news is where?

[saskboy]

And speaking of black holes, I had one for lunch. I put a meat patty and a veggie patty into the same burger. The Meat and the Anti-Meat annihilated each other and I was left with a Black Hole Burger.

Re:And the news is where?

[Red Flayer]

Fits pretty well, doesn't it? *puts on double-layered tinfoil overall*

And how, pray tell, will a tinfoil overall protect you from Evil Sound?

Perhaps you should consider tinfoil earmuffs instead. Or maybe a tinfoil hat with earflaps.

Re:And the news is where?

[jd]

That's just what They want you to believe. If they can't get rid of your tinfoil hat, get you to pay them for all the extras until it's too heavy to wear. THEN They get you.

Re:And the news is where?

[Hurricane78]

Simple. There's a vacuum between the two layers. That's why there are two.
The rest is for EM radiation.

We're still working on the weak and the strong force, and on gravity.

Re:And the news is where?

[Hurricane78]

Oh, and when I said overall, I meant over ALL. Basically a thin space suit. Without a window. So not only can you not be rickrolled. You can also not be goatse'd.

Buy now. Only 499.00 Internets.

Re:And the news is where?

[Tubal-Cain]

The mind-control signals travel through several million miles of vaccuum before entering Earth's atmosphere. What's a few more millimeters? Also, tinfoil actually amplifies the signals to the point of driving the wearers mad, so nobody believes them about the aliens. Of course, it's not really aliens on Cruithne, it's actually a secret government facility tha*&(#)$@#&) ***NO CARRIER***

Re:And the news is where?

[Anonymous Coward]

You get first post and it's not even a Goatse troll....geez.

Re:And the news is where?

[Keeper Of Keys]

Earmuffs made out of Bose Einstein Condensate? Fluffy ones, of course.

Re:And the news is where?

[physburn]

This is so cool. First of all I want this stuff for cavity insulation in my flat. Then I can play music all night without next door complaining. Having said that the BEC stuff might be either very loud or very hot, depend on the frequency spectrum it emits, BEC loudspeakers might be possible by varing the heat input to the supersonic regions. However since the apparatus only hold a tiny ammount of rubidium atom, in a magnetic trap. It might be long time before its practice.

I guess this proves...

[thewiz]

that in space, no one can hear you scre...

Re:I guess this proves...

[Abreu]

Actually, I have another reference to make...

So, does this mean that the octirion bells in Unseen University clock tower emit Hawking Radiation?

at last, the dream is realized!

[Tumbleweed]

"In one ear and out the other."

Re:at last, the dream is realized!

[damien_kane]

"In one ear and out the other."

Except that, in this case, it went in one ear and got stuck.

Consumer applications

[oneirophrenos]

I can't wait for the noise-cancelling headphones using this technology.

Re:Consumer applications

[Anonymous Coward]

That would be the coolest headphones I've ever seen.

Sort of Hawking Radiation

[Colonel Korn]

That's somewhere in between a metaphor for Hawking Radiation and the real thing. It's not true HR, but it would be a nice demonstration if they were to get it to work, especially if they could show some sort of analog to black hole "evaporation," which is the main implication of HR. I suppose that should naturally happen as the separation of the pairs sucks energy from the BEC and slows the fluid inside, shrinking the event-horizon-analogue.

Also, let's get properly flowing BEC layers in our noise canceling headphones!

Re:Sort of Hawking Radiation

[InsertWittyNameHere]

Ok, so the Bose Noise Canceling headphones create these so called "Acoustic Blackholes" in the ears of the headphones to eliminate noise. But wont the radiation cause brain cancer or something??

This will never sell!

Re:Sort of Hawking Radiation

[DriedClexler]

That's somewhere in between a metaphor for Hawking Radiation and the real thing.

Not a physicist, but here's how I think the metaphor between the experiment and the real thing is supposed to work:

Speed of light: maximum speed information can travel through a vacuum ("the void")
Speed of sound: maximum speed information can travel through a medium composed of atoms ("substance")

(When aircraft go supersonic, the air they run into is incapable of "preparing" to be hit, in a manner of speaking...)

We can't create stuff that goes faster than the speed of light, but we can create stuff that goes faster than the speed of sound. And just as you can't go fast enough to come back through an event horizon, information can't propagate fast enough in the experiment to go back across the subsonic/supersonic boundary. This shows us what it looks like to be in a situation like that of a black hole.

By the way, there's a similar, cheaper experiment you can do: pop a hole in a pressurized container. The gas cannot escape it (at the outlet) faster than the local speed of sound, which is obtained whenever the ratio of pressure inside to pressure outside exceeds a critical value. One gas dynamics professor said I can think of it like this: "even though a higher pressure ratio creates a greater pressure potential difference, the gas inside the tank cannot 'learn' of the greater difference because that would require information to go *into* the tank, *against* the gas that is escaping at the speed of sound"

Kind of like in the setup described in the article...

Re:Sort of Hawking Radiation

[bsy_at_play]

heisenberg: uncertainty in energy times uncertainty in time has a lower bound. what is the energy of the phonons? given the small time that heisenberg allows the virtual phonon pairs to exist, how far can the phonons travel? without actually working out the numbers, my seat of the pants guess is that the number of virtual phonon pairs for which one member crosses the acoustic event horizon will be vanishingly small.

Re:Sort of Hawking Radiation

[Anonymous Coward]

Except that in the term "Hawking radiation" they're referring to the motion of particles being radiated outwards, not radioactivity.

Re:Sort of Hawking Radiation

[SleepingWaterBear]

That's somewhere in between a metaphor for Hawking Radiation and the real thing.

This isn't really a metaphor exactly. If the equations governing two systems are the same, then we expect the behavior to be the same, and we can describe them in the same terms. Phonons themselves are a good example of this: a phonon is hardly the sort of thing that you would intuitively think of as a particle, but because the equations governing phonons are the same as those governing quantum mechanical particles, physicists describe phonons as particles. Subatomic particles themselves bear very little resemblance to the 'billiard ball' particles that most people imagine. I think that it would be better to say that Hawking radiation is just an effect predicted for systems obeying certain equations, and in that sense, both the acoustic and traditional black holes exhibit completely real Hawking Radiation.

It is true that getting 'acoustic Hawking radiation' wouldn't constitute absolute proof that Black Holes do the same thing - our model may be wrong. What it will do do is provide proof that, assuming our model is correct, Hawking radiation is real, and there isn't some unanticipated effect which invalidates the theory.

Re:Sort of Hawking Radiation

[Colonel Korn]

That's somewhere in between a metaphor for Hawking Radiation and the real thing.

This isn't really a metaphor exactly. If the equations governing two systems are the same, then we expect the behavior to be the same, and we can describe them in the same terms. Phonons themselves are a good example of this: a phonon is hardly the sort of thing that you would intuitively think of as a particle, but because the equations governing phonons are the same as those governing quantum mechanical particles, physicists describe phonons as particles. Subatomic particles themselves bear very little resemblance to the 'billiard ball' particles that most people imagine. I think that it would be better to say that Hawking radiation is just an effect predicted for systems obeying certain equations, and in that sense, both the acoustic and traditional black holes exhibit completely real Hawking Radiation.

It is true that getting 'acoustic Hawking radiation' wouldn't constitute absolute proof that Black Holes do the same thing - our model may be wrong. What it will do do is provide proof that, assuming our model is correct, Hawking radiation is real, and there isn't some unanticipated effect which invalidates the theory.

I take your point, and you may easily have more expertise than I do (non-specialist grad quantum mechanics classes and a couple undergrad astro classes along with some casual enthusiasm for the subject). My understanding of Hawking radiation is that the split virtual pair explanation isn't physically accurate, but that tunneling of particles through the event horizon is the more physically valid explanation.

1) I'm not aware of an analogous effect that will work for phonons. Tunneling itself is on the wrong lengthscale.

2) Since the virtual particle pair splitting explanation also satisfies the radiation equations, maybe this difference doesn't have much significance. Were someone to convince me of this, I'd fully agree with you.

Re:Sort of Hawking Radiation

[blincoln]

We can't create stuff that goes faster than the speed of light, but we can create stuff that goes faster than the speed of sound.

We can't create stuff that goes faster than the speed of light in a vacuum. We create things that travel faster than the speed of light in other media all the time. The blue Cherenkov Radiation glow in fission reactors is caused by particles exceeding the speed of light in water, and creating a light shockwave analogous to the sound shockwave that e.g. supersonic aircraft produce.

/nitpick

Re:Sort of Hawking Radiation

[clone53421]

One gas dynamics professor said I can think of it like this: "even though a higher pressure ratio creates a greater pressure potential difference, the gas inside the tank cannot 'learn' of the greater difference because that would require information to go *into* the tank, *against* the gas that is escaping at the speed of sound"

I really don't like that explanation... it makes it seem like the pressure differential is "known" to the gas inside the cylinder via some sort of acoustically-transmitted information. My initial reaction was "HUH" and my secondary reaction was "ok, I don't buy that."

After a little work on Google, I discovered that the effect really exists, but I think this link describes it better (emphasis mine):

However, once the downstream pressure reaches or is less than the critical pressure, the compressible mass flow rate does not increase even though the downstream pressure is decreased further.

This specific phenomenon is called as "choked flow", and the energy difference between the choked exit and ambient conditions is dissipated by shock wave and/or turbulence.

Also, choked flow does not occur for thin-plate orifices, which wouldn't make sense relative to the explanation as given by that prof. If the flow was really being limited by the non-propagation of information against a gas flowing at the speed of sound, the thickness of the plate shouldn't matter.

Re:Sort of Hawking Radiation

[Hurricane78]

If you yell a lot at your black sound hole, until it cries, and "evaporates", does it create something that resembles a Disaster Area recording from 30 miles away, in an atomic bunker?

Re:Sort of Hawking Radiation

[Hurricane78]

That's one of the coolest bits of not very useful knowledge I've seen a long time. (Although I should have known this, and mostly did.)

Re:Sort of Hawking Radiation

[SleepingWaterBear]

1) I'm not aware of an analogous effect that will work for phonons. Tunneling itself is on the wrong lengthscale.

2) Since the virtual particle pair splitting explanation also satisfies the radiation equations, maybe this difference doesn't have much significance. Were someone to convince me of this, I'd fully agree with you.

Well, I'll admit that my knowledge of Phonons is actually fairly limited, so I'm trusting the article in it's claim that the equations governing the two systems are the same. If not then the article is being very misleading, and I'd have to change my stance! My own personal opinion about quantum mechanics though is that the equations themselves represent the fundamental thing, and the particular interpretation you place on them is just a convenience.

So both the 'split virtual pair' explanation and the tunneling explanation are really just approximations that give us something to visualize. Particles themselves don't really exist as independent physical entities in a truly meaningful sense, they're just manifestations of modes in the system's wavefunction, and so both the ideas of 'virtual pairs' and of tunneling are somewhat misleading. We can pretend that quantum mechanical particles are like billiard balls, except with special properties like the ability to randomly appear in pairs, or to tunnel through potential barriers, and that'll get us a long way, but there will be places where the analogy breaks down. From the wave function point of view, virtual particles are no stranger than nodes and anti-nodes appearing in a string when you shake it.

The real metaphor here is the idea of the particle. It's a fairly good metaphor, but the equations of quantum mechanics aren't the equations of classical mechanics, and at some point the metaphor stops being relevant.

Re:Sort of Hawking Radiation

[lgw]

Arguably, light travels faster in a Casimir cavity than in a vacuum. Really, there's no reason to suppose that "emtpy space" represents the medium through which light flows the fastest, merely that it's somewhere close.

Re:Sort of Hawking Radiation

[shma]

We can't create stuff that goes faster than the speed of light, but we can create stuff that goes faster than the speed of sound. And just as you can't go fast enough to come back through an event horizon, information can't propagate fast enough in the experiment to go back across the subsonic/supersonic boundary. This shows us what it looks like to be in a situation like that of a black hole.

That's exactly right. What they have done is create an acoustic event horizon. It doesn't hold all the same properties as a real black hole, but as Korn says, there is a chance that you can see Hawking Radiation and possibly BH evaporation from this experiment. There has already been a paper suggesting that you can see Hawking radiation by looking at the density correlation functions of the BEC.

Re:Sort of Hawking Radiation

[ardle]

it would be a nice demonstration if they were to get it to work

One thing that would demonstrate is that the mathematics is valid. It's a bit like like trying to run a Java program on different JVMs ;-)

Re:Sort of Hawking Radiation

[amRadioHed]

Really, there's no reason to suppose that "emtpy space" represents the medium through which light flows the fastest

There kind of is. When light travels through a medium it is slowed down due to interactions with particles. The less it interacts with particles the faster the light travels. The photon's themselves don't ever actually change speed. How do you suppose that a substance could cause the light to travel faster than the speed of the photons themselves?

Re:Sort of Hawking Radiation

[rjmnz]

By the way, there's a similar, cheaper experiment you can do: pop a hole in a pressurized container. The gas cannot escape it (at the outlet) faster than the local speed of sound, which is obtained whenever the ratio of pressure inside to pressure outside exceeds a critical value. One gas dynamics professor said I can think of it like this: "even though a higher pressure ratio creates a greater pressure potential difference, the gas inside the tank cannot 'learn' of the greater difference because that would require information to go *into* the tank, *against* the gas that is escaping at the speed of sound"

Kind of like in the setup described in the article...

This is because at the fundamental level, sound is propagated by particle collisions. The speed of sound (in a gas) is determined by particle velocity which is linked to temperature and particle mass. Sound cannot move faster than the fastest particle (in a gas). Pressure is irrelevant.
Sound in liquids and solids is another matter entirely.

Re:Sort of Hawking Radiation

[Anonymous Coward]

sure it will matter.

If the information can travel through the wall of the container, rather than through the orfice, it ruins the choked flow.

I've no idea what i'm taking about by the way.

Re:Sort of Hawking Radiation

[node 3]

We can't create stuff that goes faster than the speed of light in a vacuum.

That's what "the speed of light" means. People almost never mean "the speed of light in water" (or some other non-vacuum medium) when they just say "the speed of light" unless they've previously established the context earlier.

Re:Sort of Hawking Radiation

[node 3]

I really don't like that explanation... it makes it seem like the pressure differential is "known" to the gas inside the cylinder via some sort of acoustically-transmitted information. My initial reaction was "HUH" and my secondary reaction was "ok, I don't buy that."

That's almost what he's saying. He's not saying there is acoustically-transmitted information, but that there is physically transmitted information.

Imagine you are inside the container. If you measure how much air is leaving the container, you have access to all the information required to know the pressure of the outside. At a certain point, the pressure of the outside has no further effect on the flow, so inside of the container, no further information about the outside is possible. You only know that the pressure is equal to or less than some specific amount. So while the external pressure is changing, no information about that fact is making its way into the container!

So the physical/mechanical transfer of information cannot exceed the speed of sound in this system, and if the air is leaving at the speed of sound, trying to go backwards at the speed of sound results in a net speed of zero. It's not that the container "knows" something in a "it comprehends the ideas of", but "knows" in that it contains within it that specific piece of information. It's used similar to how your computer "knows" what you are typing on the keyboard, but not that it "understands" what you are typing. And to extend the analogy a bit further, if your keyboard buffer fills, it can no longer "know" what you are typing, as that information is coming in faster than the computer (specifically the keyboard controller) is capable of processing it.

Re:Sort of Hawking Radiation

[drerwk]

The GP's point in referring to a Casimir cavity is that space is not empty. That there is a Casimir effect proves that there is a lower density of particles in the Casimir cavity than in normal vacuum. So if you are correct in your claim;

The less it interacts with particles the faster the light travels.

then light should travel faster in a Casimir cavity then in vacuum. Though, I would bet that it still does not allow you to send a signal faster than with light in vacuum.

Re:Sort of Hawking Radiation

[amRadioHed]

The casimir cavity is a vacuum.

Re:Sort of Hawking Radiation

[hasdikarlsam]

No, the casimir cavity has less energy than a vacuum. Negative, as it were.

That is not to say that photons would move faster in a casimir cavity. I have no idea whether they would, but it would be easy to calculate - does the permeability of the vacuum differ from that of a casimir cavity?

Re:Sort of Hawking Radiation

[hasdikarlsam]

It would also be an important point that we just believe the equations to be the same.

If "hawking radiation" shows up in this experiment, that does in no way prove it would for black holes. Or the other way around. Or in the details, for that matter.

Re:Sort of Hawking Radiation

[khanyisa]

We create things that travel faster than the speed of light in other media all the time. The blue Cherenkov Radiation glow in fission reactors is caused by particles exceeding the speed of light in water, and creating a light shockwave analogous to the sound shockwave that e.g. supersonic aircraft produce.

When you say "we", I'm presuming you're referring to all those of us who have fission reactors giving off Cherenkov Radiation glow in our back sheds...

Re:Sort of Hawking Radiation

[clone53421]

The acoustic properties of solids are generally pretty good. Again, I don't see the thickness of the plate really playing much of a role in determining whether or not information can "get inside" the tank.

Re:Sort of Hawking Radiation

[clone53421]

So while the external pressure is changing, no information about that fact is making its way into the container!

True enough, but why not? That's really the whole question.

So the physical/mechanical transfer of information cannot exceed the speed of sound in this system,

Why not? Why is the speed of sound the limiting factor?

if the air is leaving at the speed of sound, trying to go backwards at the speed of sound results in a net speed of zero.

I return to the thin-plate scenario: a thin plate should still obey your rules. Air is escaping at the speed of sound. If the flow of information is asymptotically limited by the speed of sound, the velocity shouldn't increase beyond that, no matter how thin the plate is. It does.

Re:Sort of Hawking Radiation

[Colonel Korn]

That's another great post. I think I'm comfortable with basic quantum mechanics until someone like you comes along and reminds me of a lot of things I know but that aren't intuitive.

"My own personal opinion about quantum mechanics though is that the equations themselves represent the fundamental thing, and the particular interpretation you place on them is just a convenience."

I thoroughly agree, and I'll try to remember that next time I try to get high and mighty with what are, at the very best, guesses.

Re:Sort of Hawking Radiation

[drerwk]

Are you aware that there are particles in any vacuum and that they are the supposed source of Hawking radiation?

Re:Sort of Hawking Radiation

[amRadioHed]

Yes, I am. Even ignoring virtual particles a perfect vacuum is just a theoretical construct, there is no such thing in reality. Some vacuums are better than others but none are completely particle free.

Re:Sort of Hawking Radiation

[node 3]

True enough, but why not? That's really the whole question.

That really wasn't your initial question. That question was whether there's some sort of information going into the container in the first place.

Why not? Why is the speed of sound the limiting factor?

Because that's essentially the definition of the speed of sound. It's the speed at which pressure waves propagate through a medium.

I return to the thin-plate scenario: a thin plate should still obey your rules. Air is escaping at the speed of sound. If the flow of information is asymptotically limited by the speed of sound, the velocity shouldn't increase beyond that, no matter how thin the plate is. It does.

The thin-plate orifice is an interesting side note note that you've elevated to a red herring. Clearly one system works one way, and the other works a different way. Finding a different scenario doesn't change the way the first one works.

Re:Sort of Hawking Radiation

[mshurpik]

My understanding of Hawking radiation is that the split virtual pair explanation isn't physically accurate, but that tunneling of particles through the event horizon is the more physically valid explanation.

Wikipedia's understanding is that nobody has any idea what it is.

Originally, I read in his book that a virtual pair would split, and the anti-particle would fall into the black hole, reducing its mass. He never said why with equal probability, regular particles wouldn't also fall in, though.

So then you get to quantum tunneling, which is the theory that any object can pass through any barrier with some probability. Over enough time, enough mass should tunnel through the event horizon to cause evaporation. However, I have noticed that the universe is pretty good at creating probabilities that are effectively zero.

Finally you have the Unruh effect, which is that an accelerating observer (like matter falling into the hole) should witness a sea of warm particles. If you think this is vague, well, everyone agrees it is.

What it comes down to, is that Hawking Radiation is based on the conclusion that a black hole is a perfect black body radiator. Forgive me for being skeptical that an object ruthlessly accumulating matter, that is unnaturally cold (black holes are near 0 Kelvin, below the vacuum average of 2.7k)...an object which very well may violate our common perceptions of entropy and thermodynamics radiates energy perfectly like a car on a hot afternoon?

Point being, Hawking's "perfect black body" is one hell of a leap of intuition. Or quantum field theory, according to him.

Re:Sort of Hawking Radiation

[clone53421]

The thin-plate orifice is an interesting side note note that you've elevated to a red herring. Clearly one system works one way, and the other works a different way. Finding a different scenario doesn't change the way the first one works.

It's not a red herring. What about the plate thickness makes it significantly different from the thick-plate scenario, and why does that influence the way the system behaves?

As far as I can tell, there's nothing "different" about the scenario in terms of the limitation of pressure. If you have a zone where gas is traveling at the speed of sound, I see no reason why a short vs. a long such region should make a difference. If pressure differential cannot be transmitted through the zone, the length of the zone could go to zero and this property shouldn't change.

Re:Sort of Hawking Radiation

[drerwk]

I decided that it will not change the speed of light in the Casimir cavity: The cavity by it's nature prevents light of wavelength bigger than the cavity from propagating anyway. Light with wavelength small enough to be unaffected will see particles also small enough to be unaffected. Hence, any light that can propagate in the cavity will not see the cavity, no any effect of the cavity.

Re:Sort of Hawking Radiation

[node 3]

It's not a red herring. What about the plate thickness makes it significantly different from the thick-plate scenario, and why does that influence the way the system behaves?

It's a red herring with regards to the initial scenario. This is a different scenario with different parameters. That you don't know what part about the difference is significant (nor do I) does not change the facts about the other scenario.

All you've shown is that different shapes react to pressure differently.

The OP basically stated that "speed limit X exists for scenario A". Then you came in and stated "I don't think speed limit X exists, for example, what about scenario B?" He never said it existed for scenario B, just scenario A.

Re:Sort of Hawking Radiation

[DriedClexler]

*is the OP*

I must confess, you have me stumped. I had forgotten about the supersonic thin-plate orifice flow, and to be honest, I don't know how far the information theoretic analysis I gave of gas leaving a tank carries over to that. (And FWIW, it looks like node turned my point into a circular argument.) It's also been a while since i took gas dynamics, and remember very little of the vena contracta problems.

In the article on orifice plate, though, it looks like a fundamentally different situation, that of pipe flow. My point referred to flow out of a tank, and the reason I gave for it choking at the speed of sound was basically a sort of "you can't get there from here" argument. That is, *initially* supersonic flow could stay supersonic through the hole, because it's already supersonic. But if it starts out *stagnant* in a tank, it can't *accelerate* to supersonic flow because:

1) The inside gas must "know" the pressure ratio is supercritical.
2) This "knowledge", in the form of a compression wave, cannot travel faster than the maximum compression wave speed, which maximizes its net velocity at zero and chokes the flow of information back into the tank.

However, if I'm wrong, and the vena contracta setup applies to tanks as well, or accelerates flow in pipes where the flow starts out subsonic, then the explanation I would give, as to why that shape permits information to flow back across the subsonic/supersonic gap, would be:

"The outlet speed refers to the cross-section-area-averaged speed; not every particle in the cross section must be supersonic, or even going to the right in the diagram. The vena contracta shape forces the gas flow to the center of the hole, where it exceeds the speed of sound. It can 'learn' of the lower downstream pressure because the gas flow at the outer edge of the hole is *not* supersonic, and so information can propagate back upstream along that outer edge. However, it requires a special orifice shape to get the cross-sectional speed variation to do this; otherwise, like if you just stab a random hole in a tank, the speed will be very nearly uniform across the cross section."

But I'll admit, "you got me". :-/

Re:Sort of Hawking Radiation

[badkarmadayaccount]

Please turn in your geek card on the way out.

Re:Sort of Hawking Radiation

[lgw]

My point was that "speed of light in a vacuum" is ambiguous. The "speed of light in an imagined perfect vacuum" may represent an interesting speed limit. The "speed of light in the space between the stars" does not. In fact, the perfect vacuum may not be realizable in the real universe.

Or, of course, the notion that information can't travel faster than the speed of light is simply wrong, much like 19th century notions of conservation of mass and energy were simply wrong.

From the tone of the description

[G3ckoG33k]

From the enthusiastic tone of the description, this sounds like Nobel Prize material.

Yet, I cannot judge it well enough.

Re:From the tone of the description

[Impy the Impiuos Imp]

From the description, this Hawking radiation sounds like the ability to close the deal. Occasionally, a human is born too close to an event horizon, and their ability to close the deal splits into a brief virtual pair. One goes into the black hole, and the other goes flying off. But the human is left without any ability to close the deal.

Re:From the tone of the description

[ShieldW0lf]

Here, I'll fix it.

The real prize is not the acoustic black hole itself but what it might makes possible: the first observation of something analogous to Hawking radiation. The Theory of Quantum mechanics predicts that pairs of phonons with opposite momentum ought to be constantly springing in and out of existence in a BEC. Theoretically, were one of the pair to stray across the event horizon into the supersonic region, it could never escape. However, the other would be free to go on its way. This stream of phononic radiation away from an acoustic black hole would be the first observation of anything even vaguely resembling Hawking radiation. The team hasn't actually achieved any of this though. It can't be long now before they or their numerous competitors make this leap. Unless their hypothesis is totally wrong, which is entirely possible. But that doesn't sound particularly impressive, so we'll just forget about that bit...

Re:From the tone of the description

[clone53421]

That's because the dronons were captured in the black hole, while the excitons weren't. What you've just experienced is the first known observation of Hawkings elation.

how about

[Anonymous Coward]

sound bomb ? sound propulsion ? just gather sound in an acoustic black hole then release it ... could be for an interesting application ( if ever B-E can get bigger )

Doppler Shift?

[Anonymous Coward]

I think it would be interesting to see a 3D graph of the magnitude of a 'chirp' sent across the "black hole" and compare it with doppler shift equations, and then overlay that with a graph of purposed light behaviors about a black hole. Experimental proof vs mathematical?

86 says

[Anonymous Coward]

Let's use the cone of silence, chief!

Phonon ey?

[Snowblindeye]

I knew light was quantized, but I had seriously never heard of Phonons, or that sound can be quantized as well.

Well, apparently it can: Phonon

Re:Phonon ey?

[Chris Mattern]

Everything is quantized if you're looking at it at a small enough scale.

Re:Phonon ey?

[getuid()]

"Phonos" are basically "crystal oscillations". Enter the concept of "reciprocal space": it's basically the Fourier transform of the real 3D space, and is very commonly used in solid state physics.

Now as you probably know, a clean frequency (i.e. a sinus wave) in the time domain results to a single peak in the Fourier-Transform (i.e. in the frequency domain). And similar for phonons: a clean crystal oscillation (i.e. a single-frequency sound wave propagating through a medium) in 3D space results in the equivalent of a single, localized "particle" in reciprocal space: a phonon.

Re:Phonon ey?

[phantomfive]

Yeah, it kind of ruins that whole debate about 'is light a particle or a wave', doesn't it? Even a sound wave is just a bunch of particles. Wish I had thought of that earlier.....

Re:Phonon ey?

[Brandybuck]

In other words, phonons do not exist objectively, but are mathematical constructs.

Re:Phonon ey?

[SquirrelsUnite]

Ah, but the concept of objective existence doesn't exist objectively - it's just a philosophical construct.

Re:Phonon ey?

[adavies42]

[citation required]

last i heard, there was no conclusion on space and/or time.

Re:Phonon ey?

[Falconhell]

See Hitch hikers guide then, quote;

Space is big, really big, big than the biggest thing ever. You may think its a long way down the street to the the shop but thats just peanuts compared to space!

Re:Phonon ey?

[Brandybuck]

Be careful at the next zebra crossing...

Re:Phonon ey?

[badkarmadayaccount]

Plank length and time.

Re:So...Bose sucks?

[Captain Splendid]

Nah, Bose doesn't suck so much as you can get similar quality gear for a better price. It's swanky audio gear for people who don't know anything about audio gear.

Not Hawking Radiation

[Big_Breaker]

There is an analogy there in the macro physics but that doesn't mean the small scale stuff like QM will be mirrored.

You can model gravity in the orbital mechanics sense with a marble and vertical cone that tapers at 1/square(height). That doesn't mean it will do anything relativistic or quantum mechanical.

Re:Not Hawking Radiation

[Manchot]

No, phonons are indeed quantum mechanical. (A phonon is essentially the joint wavefunction describing many different nuclei in a solid.) The main difference that I see between this setup and a black hole is in the "vacuum" from which particles are created. In a solid, phonons are typically created by a myriad of scattering events. Two electrons could scatter off each other, an electron could scatter off a nucleus, a photon of visible light could make dozens of phonons, etc. Near a black hole, though, virtual pairs need to be created spontaneously from the vacuum. So, the upshot is that while the general mechanism is the same in both cases, I would guess that phonons in a BEC are created far more frequently than virtual pairs near a black hole.

Re:Not Hawking Radiation

[The Master Control P]

Bose-Einstein condensation is an exclusively quantum mechanical phenomenon; What do you mean the quantum effects may not be mirrored?

maybe we can use this to...

[pha7boy]

I would hope we can use it to defend our civilization from both outside and inside attack. Maybe put a few of them in orbit that would suck in the drudgery of the reality shows and entertainment-news talking heads so that no outside civilization will feel the need to demolish the planet to build a hyperspace bypass. Plus, we won't have to listen/watch this crap anymore. A world without Fox/CNN/MSNBC... wow. I can only hope.

Re:maybe we can use this to...

[lgw]

Yes, when will humanity invent this mysterious technology that allows us to avoid reality TV and cable news? This device, known to SciFi writers as the "off switch" may forever be the stuff of fiction.

I buy it

[oldhack]

I need one of these for one of my neighbors. Does it swallow people and dogs, too? Cuz that'd be really good.

Not the first Acoustic Black Hole

[GameGod0]

Black holes in a Bathtub by E. Berti (2005):
www.iop.org/EJ/article/1742-6596/8/1/013/jpconf5_8_013.pdf

The argument basically goes that when you unplug your bathtub, there's a certain point at which waves generated past the "event horizon" near the hole never escape the hole. It's an interesting read, but I was under the impression that this is basically the same thing, albeit not an effect that arises from quantum field theory.

Re:Not the first Acoustic Black Hole

[valinor89]

So, every time I unplug my bathub there is a possibility to create a Black Hole? Why do we want the LHC when we have bathtubs? Are you sure the LHC isn't just a bathtub? Conspiracy teory, anyone?

Re:Not the first Acoustic Black Hole

[lennier]

Little known science fact: the LHC *is* a bathtub, and the Compact Muon Solenoid is merely a frontage for a giant yellow rubber duck.

This will all be explored in Dan Brown's upcoming novel.

Re:Not the first Acoustic Black Hole

[Anonymous Coward]

The bathtub analogy is a classical one, while the BEC is a quantum one. In the former case, sound waves exhibit only classical effects, while in the latter also quantum effects.

DONT DO IT SCIENTISTS!

[nausea_malvarma]

You'll create a BLACK HOLE that ENGULFS THE EARTH! Just like the LHC!

Re:DONT DO IT SCIENTISTS!

[Ukab the Great]

Or even worse, the Earth will continue to exist and be entirely populated by mimes.

Re:DONT DO IT SCIENTISTS!

[bugs2squash]

I wish I could mod you up for that - I just can't think of a worse fate.

Re:DONT DO IT SCIENTISTS!

[berashith]

Time to arm the motherless penguins with loaves of pumpernickel.

Re:DONT DO IT SCIENTISTS!

[Anonymous Coward]

In the land of the mime, the whispering man is king.

Re:DONT DO IT SCIENTISTS!

[dissy]

You'll create a BLACK HOLE that ENGULFS THE EARTH! Just like the LHC!

So *THAT'S* what happened! I've been wondering why my clothes felt tighter these past few weeks...

bah

[grub]

Motorhead could kill any wimpy acoustical black hole.

Re:bah

[Red Flayer]

Motorhead could kill any wimpy acoustical black hole.

Undoubtably Lemmy could kill an acoustical black hole.

But Soundgarden already did (or at least traveled through one). Unfortunately, the singer's voice was permanently damaged by the experience, and so when he sings "Black Hole Sound" we hear "Black Hole Sun" instead.

Or something.

Not that Lemmy doesn't have more talent in his superfluous third nipple than Soundgarden has, but he probably just hasn't bothered with an acoustic black hole yet.

Re:So...Bose sucks?

[bFusion]

It's like Monster Cables for speakers.

Acoustic Black Hole

[ronfuller]

now we know how they made the "cone of silence" http://en.wikipedia.org/wiki/Cone_of_Silence

What does it sound like?

[Lord Lode]

It must be "The Sound".

Dudley?

[AdamWill]

Hmm, wonder if it might be Dudley Bose? (c'mon, I can't be the only Hamilton fan around. sucky audio equipment is not the only type of Bose!)

Re:Dudley?

[Anonymous Coward]

. . . sucky audio equipment is not the only type of Bose!

I couldn't agree more - some of the audio equipment they make is sucky but, it isn't the only type. The other type they make is excellent quality audio equipment, which is the majority of their product line.

Yeah, Bose may not be the best, but they're still better than most so, stop acting like a fucking pretentious poser.

btw - what is Didley Bose?

Weaponize it and use it against car stereos.

[jeffb (2.718)]

This could be even better than the "bass-seeking missile" that I've wanted to deploy for years.

Re:Weaponize it and use it against car stereos.

[Anonymous Coward]

Yes, everybody knows a black hole generator is a terrifying weapon. It does take its space from the heavy cruiser, though. I personally prefer tachyon beams and the like myself, lots of them. The Death Ray, however, it's just a waste of space.

Re:Weaponize it and use it against car stereos.

[Anonymous Coward]

I'd be more interested in using it as a fish finder. *BOOM* the bass!

Re:Weaponize it and use it against car stereos.

[spydum]

I tried to process this statement a few times trying to comprehend why you were shooting fish with missles. Guess I'll learn to read the subject..

Re:Weaponize it and use it against car stereos.

[noidentity]

I think the RIAA might be very interested in this, as they could finally prevent everyone from ever hearing music again.

Re:Weaponize it and use it against car stereos.

[StikyPad]

I'm bassuming there's an unintended 'B' in that sentence..

Re:Weaponize it and use it against car stereos.

[T Murphy]

In the meantime you can do what I do. When an overly loud car pulls up next to you, blast the news at them.

Re:Weaponize it and use it against car stereos.

[MetalPhalanx]

My father (who happens to be almost deaf) has a unique approach to this that has seen good results through the years... He keeps a couple of CDs of music with him that are frankly just awful. When someone is being obnoxious with their music, he switches away from whatever he was normally listening to, takes his hearing aids out, selects the song(s) he think will cause the recipient the most auditory distress, and then cranks his music until his seat rattles... leaving it turned up until they're out of hearing range or they take the hint and lower their volume.

I wish I could contact him, he's drawn up a very amusing correlation between the type of music that the intended recipient is listening to and the music that will cause them the most distress. Oddly enough, it's not always the most diametrically opposed style that is the worst, sometimes it's a very similar style that is just badly done. Last I checked, his list included several songs from the backstreet boys, aqua, a couple of even shittier dance tracks, and several bad death metal bands (he takes the CDs I get from local metal shows and rips the worst sounding ones). There are others but I can't remember them.

Re:Weaponize it and use it against car stereos.

[Anonymous Coward]

For a minute there, I couldn't figure out what you had against fish...

Re:So...Bose sucks?

[Fuzi719]

or its like iPhone for a cellphone. :-) Popularity depends on the gullibility of the buyer.

Acoustic Black Hole?

[Anonymous Coward]

Doesn't this describe every song that James Taylor has published?

I had an acoustic black hole before...

[damn_registrars]

... back in the 90s, but then the local top40 station started playing boy bands nonstop and my black hole was, itself, pulled into the resulting immense vacuum.

Re:So...Bose sucks?

[bFusion]

At least noticing someone using an iPhone offers you the benefit of knowing what type of person s/he is in advance. :)

"First Acoustic Black Hole Created" Really?

[Anonymous Coward]

I thought it was Nirvana Unplugged.

I dont get it

[Anonymous Coward]

The more i see and read off these quantum and string Theories the more i think Bullshit

Re:I dont get it

[Anonymous Coward]

Does your mommy know you're using her computer without asking again, child?

New shield to be deployed soon...

[Salamalecs]

... against phonon torpedoes ?

Is it me or does this story scream Spinal Tap?

[revjtanton]

"Nigel Tufnel: The numbers all go to eleven. Look, right across the board, eleven, eleven, eleven and...
Marty DiBergi: Oh, I see. And most amps go up to ten?
Nigel Tufnel: Exactly.
Marty DiBergi: Does that mean it's louder? Is it any louder?
Nigel Tufnel: Well, it's one louder, isn't it? It's not ten. You see, most blokes, you know, will be playing at ten. You're on ten here, all the way up, all the way up, all the way up, you're on ten on your guitar. Where can you go from there? Where?
Marty DiBergi: I don't know.
Nigel Tufnel: Nowhere. Exactly. What we do is, if we need that extra push over the cliff, you know what we do?
Marty DiBergi: Put it up to eleven.
Nigel Tufnel: Eleven. Exactly. One louder.
Marty DiBergi: Why don't you just make ten louder and make ten be the top number and make that a little louder?
Nigel Tufnel: [pause] These go to eleven."
"Nigel Tufnel: It's like, how much more black could this be? and the answer is none. None more black. "

Re:Is it me or does this story scream Spinal Tap?

[PGOER]

Correct me if I'm wrong, but aren't BEC's near abosolute zero superfluids? These consist of small amounts of molecules super cooled with lazers and magnetic traps? How do you measure the sound comming off of them, you need a lazer just to see them? What if we got a really big speaker and an amp that goes to eleven, I'm sure we could impart enough energy to desroy the black hole.

Re:Is it me or does this story scream Spinal Tap?

[revjtanton]

hahahaha! YES!

Re:Is it me or does this story scream Spinal Tap?

[PGOER]

I actually replaced the volume pot in my Fender amp, it now turns approximately 2 points past 10, so it now goes to 12. "Me: Nigel, your amp that goes to eleven, wasn't loud enough to destroy the acoustic black hole, so we had to build one that went to 12, exactly one louder than eleven."

Re:Is it me or does this story scream Spinal Tap?

[revjtanton]

You sir are a genius! If these "scientists" try and display this one day to the public or for a nobel prize panel you should show up with the power of rock and destroy their evil!

Re:Is it me or does this story scream Spinal Tap?

[PGOER]

Now, this is sounding like Yahoo Serious - Young Einstien (real Stupid Funny movie) Were talking splittling beer atoms to power the worlds first electric guitar, and lets not forget the oversized speaker from Back to the Future. Let me tell you there is NO WAY that an accoustic black hole can withstand a 8' speaker, fed from an amp that goes to eleven, and powered by beer atom fission! We're talking, fucking, muscle.

Re:Is it me or does this story scream Spinal Tap?

[Anonymous Coward]

That's great, you could seriously hear a similarly braindead argument in audiophile shops.

Great

[segfault7375]

Sweet, now I just have to trick my wife into standing in it.. ah peace

Re:Great

[Anonymous Coward]

You are tricking us that you have a wife...

Re:Great

[Anonymous Coward]

Seems to me that you'd have to listen to half the things she said rather than the quarter that you do now.

Finally ... it's Cone of silence!

[Dragged Down by the]

Sorry about that, Chief.

Re:So...Bose sucks?

[FusionFox]

In the same way that finding somebody that judges a person based on what cellphone they use is a nice way to know what type of person they are in advance?

Re:So...Bose sucks?

[bFusion]

Yeah, but that remains hidden until I open my mouth. :)

Acoustic black hole...

[soconn]

Isn't that the name of the new Britney Spears album?

Re:Acoustic black hole...

[Anonymous Coward]

No. Britney Spears is a naturally formed acoustic black hole.

Phonon != Photon!

[Hurricane78]

How do you infer from the effects of phonons, that the same happens to photons? If they had the same effects, this would mean that luminiferous aether would exist. Which as far as we know, is not true, and replaced by the theory of relativity. Or would it be the effect of a quantized space-time? And would those quantums then be some kind of particles?

Or is the analogy just wrong, except for some subsets? ^^

Re:Phonon != Photon!

[cathector]

i think the key is trusting the equations.
ftfs: One of the many curious properties of Bose Einstein Condensates (BECs) is that the flow of sound through them is governed by the same equations that describe how light is bent by a gravitational field.

but w/r/t the aether, i'm kind of intrigued recently by this guy who posits that the aether theory is in fact correct and that the mistake in the michaelson/morley era was assuming that matter was not itself a [standing] wave propogating though the aether.

he's a bit wingnutty but he has a charming kiwi style.

Not so fast...

[fahrbot-bot]

The first Acoustic Black Hole was actually created back in 1981.

Black hole?

[clone53421]

If it traps sound instead of light, shouldn't it be called a silent hole instead?

This gives me an idea!

[caywen]

Ooh, this gives me a great idea on how to attack the Vatican! Much simpler than stealing antimatter from the LHC.

silence is golden

[flahwho]

now if i could only put my wife, kids and boss in it

Pardon my ignorance, but...

[Locke2005]

WTF is a Phonon?

Re:Pardon my ignorance, but...

[vonhammer]

This gives you the best explanation: http://lmgtfy.com/?q=phonon

Re:So...Bose sucks?

[gstoddart]

Nah, Bose doesn't suck so much as you can get similar quality gear for a better price. It's swanky audio gear for people who don't know anything about audio gear.

Depends on which end of the spectrum you're at.

At the entry-level end, if you're just talking about speakers in a system, it's just a matter of choice. My four matched Bose 201's and VC-10 centre channel cost neither more nor less than other speakers that were available at the time. To my ear, they sound just fine, and I'd know people whose Bose speakers had lasted decades without any problems. To date (~ 10 yrs), they've performed well and can handle what my Yamaha amp throws at them.

At the high-end, however, you're absolutely correct -- it's marketed at people who don't want to know much about stereos. They just want to plug it in and never think about it. Those package systems they sell just have less wiring and take up less space than a full component system.

The reality is, most people don't have super-discriminating ears, and are therefore not really capable of telling much difference between any speakers.

Cheers

Re:So...Bose sucks?

[Anonymous Coward]

2nd'd. You can spot an iPhaggot from 30 yards away, the camp twats with their white headphone's.

Re:86 says..

[Paracelcus]

Huh?

NO

[Anonymous Coward]

Pics or it didn't happen.

what would happen...

[Fuzzums]

we all know photon pairs are connected. an observation on changes the state of the other. (quantum entanglement) but what happens if one of a pair of photons enters a black hole and the other remains outside?

does quantum entanglement still exist fo these photons? does the photon still exist inside the black hole or does it disintegrate or change state? if so: what would happen to the other photon outside?

i call whatever will happen the Fuzzums effect ;)

Silent Hole

[Samah]

Given that this is designed to trap phonons and not photons, should it not be called a "Silent Hole"? (No I didn't RTFA)

Re:So...Bose sucks?

[dangitman]

The reality is, most people don't have super-discriminating ears, and are therefore not really capable of telling much difference between any speakers.

You don't need super-discriminating ears to know that Bose systems sound like shit. It's perfectly obvious. Bose doesn't even do well against inexpensive systems, let alone ones in the Bose price-range.

Dear Scientists...

[EEGeek]

Can you put this acoustic black hole around my girlfriend so I don't have to listen to her bitch at me anymore?

Re:Dear Scientists...

[TravisO]

I sure hope you already had yourself on mute when you said that, because if she heard you there will be hell to pay.

Re:So...Bose sucks?

[Falconhell]

Quite so, Bose is the most overated manufacturer in its field.

Back when I was doing live sound, we occasionally had to use 802 speakers. Quite a combination, crap sound and hopelessly inefficient!

Efficiecy was the biggest issue though, they were nearly 10db less efficient than the usual speakers.

Oh and we have had to replace the surrounds on a lot of the bose rane too, including 402 etc, so I wouldnt be that excited about reliability.

Re:So...Bose sucks?

[gstoddart]

You don't need super-discriminating ears to know that Bose systems sound like shit. It's perfectly obvious.

You know, sound is entirely subjective. Bose figures that to much of the listening public, a shift to the mid range is more pleasing to the ear. ("No highs, no lows, must be Bose" I believe is how it gets phrased.)

They've been in business for over 40 years. Clearly, a measurable percentage of people who aren't you, disagree with you.

Frankly, this isn't really any different that the whinging between Linux and Windows fanboi's around here. It really all does boil down to personal opinion and experience.

In the end, do you really give a shit that I think my speakers sound fine and you feel they could only sound like crap?

Cheers

From the trombone section:

[Ripit]

The violas and second violins that sit in front of me want to know when a portable model is coming out. Thanks.

Re:So...Bose sucks?

[dangitman]

They've been in business for over 40 years. Clearly, a measurable percentage of people who aren't you, disagree with you.

Bose used to make some decent products, but not anymore. Current buyers are simply victims of duplicitous marketing (lies, in other words).

In the end, do you really give a shit that I think my speakers sound fine and you feel they could only sound like crap?

I don't care about your tastes, personally. What I do care about is a company that is a bunch of lying parasites. I believe in honest business, and think that liars and scammers should be out of business, not making ridiculous profits based on ignorance.

So, your choice in speakers matters only insofar as you are enabling the scum.

Re:So...Bose sucks?

[Keeper Of Keys]

I don't have any experience of Bose speakers, but I have a pair of their noise cancelling headphones and used to own a pair of their earbuds - both of which were gifts, I hasten to add. Much as I love music, I am not a hi-fi buff and wouldn't spend £250 on headphones. Still, there have been innumerable occasions when I have heard details in familiar songs I had never noticed before in hundreds of plays. The headphones (QuietComfort 3s) are a little bass-heavy, if anything, but the buds sounded to me absolutely perfect (they were quite tough but eventually did the same thing as every pair of earbuds I've ever owned - bar the ones I shut in the car door - and perished at the point where the 3.5mm plug joined on to the wire).

Been done before.

[Anonymous Coward]

And we laughed at Maxwell Smart

Obsolete technology, I have a mute button

[TravisO]

on my TV remote for past few decades!