Because of the scale of the experimental setup, it is quite obvious that no gravitational effects are involved. Hence, there is no possibility for this experiment to recreate phenomena at the intersection of quantum mechanics and general relativity. What the Steinbauer does is he replicates a particular model of the black hole. If his setup works, fine, but it doesn't prove a single thing about how black holes behave - because he did not create one.
It tells us how horizons behave. The production of Hawking radiation in a gravitational black hole relies (and relies only) on the presence of a horizon. In an acoustic hole, we've got a horizon for phonons, rather than for photons, but it's still a horizon. The actual structure of the geometry in the simplest cases is Schwarzschild, but one can play some interesting games to get a more complicated setup which is more usable - and in any event, it also exhibits a horizon. Therefore, while the effective fiel
The production of Hawking radiation in a gravitational black hole relies (and relies only) on the presence of a horizon.
Does it? Because from what I've understood, it's caused by virtual particles getting sufficient energy from interaction with a field to become real particles, and even horizon is simply the boundary above which particles so produced can escape. If so, then any strong enough field should produce Hawking radiation - for example, a strong enough electric field would produce a stream of elect
by Anonymous Coward writes:
on Monday October 13, 2014 @03:57PM (#48133843)
Yes, actually. There's a lovely introduction to acoustic holes, acoustic geometries and acoustic Hawking radiation by Visser (http://uk.arxiv.org/abs/gr-qc/9712010) where he summarises this fairly well:
"In particular, perhaps the most important lesson to be learned is this: Hawking radiation from event horizons is a purely kinematic effect that occurs in any Lorentzian geometry with an event horizon and is independent of any dynamical equations imposed on the Lorentzian geometry. On the other hand, the classical laws of black hole mechanics [40] are intrinsically results of the dynamical equations (Einstein equations) that have no analog in the acoustic model. Thus Hawking radiation persists even in the absence of the laws of black hole mechanics and, in particular, the existence or otherwise of Hawking radiation is now seen to be divorced from the issue of the existence or otherwise of the laws of black hole thermodynamics. Hawking radiation is a purely kinematical effect that will be there regardless of whether or not it makes any sense to assign an entropy to the event horizon — and attempts at deriving black hole entropy from the Hawking radiation phenomenon are thereby seen to require specific dynamical assumptions about the (at least approximate) applicability of the Einstein equations."
(Entertainingly given the story we're commenting on, Visser also comments "it is clear that experimental verification of this acoustic Hawking effect will be rather difficult. (Though, as Unruh has pointed out [1], this is certainly technologically easier than building [general relativistic] micro-black holes in the laboratory.)")
An interesting related problem one can set is to work in Rindler spacetime. This is just normal Minkowski spacetime (ie flat, Euclidean spacetime plus a time coordinate), but observed from observers uniformly accelerated away from a point. Rindler spacetime then slices Euclidean spacetime in four; no Rindler observer can pass from one of the quadrants to another, in a manner that resembles -- not necessarily that closely, but resembles -- Schwarzschild spacetime. (See these diagrams: Rindler spacetime, https://people.math.osu.edu/ge... [osu.edu] and Schwarzschild spacetime, http://i.stack.imgur.com/bYrq7... [imgur.com] ). Now Rindler spacetime is really just Euclidean spacetime written from the point of view of accelerating observers. Due to the close link in GR between acceleration and gravity -- the weak equivalence principle states that locally one cannot distinguish between the two -- it's probably not a surprise to learn that if one calculates the vacuum in Rindler coordinates, there is Hawking radiation! (This is "Unruh radiation" -- Bill Unruh has done a lot of work in the last few decades on this kind of topic, including some of the earliest papers on acoustic, or dumb, holes.)
Mimicking a theory, not a phenomenon (Score:5, Insightful)
Re: (Score:5, Informative)
It tells us how horizons behave. The production of Hawking radiation in a gravitational black hole relies (and relies only) on the presence of a horizon. In an acoustic hole, we've got a horizon for phonons, rather than for photons, but it's still a horizon. The actual structure of the geometry in the simplest cases is Schwarzschild, but one can play some interesting games to get a more complicated setup which is more usable - and in any event, it also exhibits a horizon. Therefore, while the effective fiel
Re: (Score:2)
Does it? Because from what I've understood, it's caused by virtual particles getting sufficient energy from interaction with a field to become real particles, and even horizon is simply the boundary above which particles so produced can escape. If so, then any strong enough field should produce Hawking radiation - for example, a strong enough electric field would produce a stream of elect
Re:Mimicking a theory, not a phenomenon (Score:0)
Yes, actually. There's a lovely introduction to acoustic holes, acoustic geometries and acoustic Hawking radiation by Visser (http://uk.arxiv.org/abs/gr-qc/9712010) where he summarises this fairly well:
"In particular, perhaps the most important lesson to be learned is this: Hawking radiation from event horizons is a purely kinematic effect that occurs in any Lorentzian geometry with an event horizon and is independent of any dynamical equations imposed on the Lorentzian geometry. On the other hand, the classical laws of black hole mechanics [40] are intrinsically results of the dynamical equations (Einstein equations) that have no analog in the acoustic model. Thus Hawking radiation persists even in the absence of the laws of black hole mechanics and, in particular, the existence or otherwise of Hawking radiation is now seen to be divorced from the issue of the existence or otherwise of the laws of black hole thermodynamics. Hawking radiation is a purely kinematical effect that will be there regardless of whether or not it makes any sense to assign an entropy to the event horizon — and attempts at deriving black hole entropy from the Hawking radiation phenomenon are thereby seen to require specific dynamical assumptions about the (at least approximate) applicability of the Einstein equations."
(Entertainingly given the story we're commenting on, Visser also comments "it is clear that experimental verification of this acoustic Hawking effect will be rather difficult. (Though, as Unruh has pointed out [1], this is certainly technologically easier than building [general relativistic] micro-black holes in the laboratory.)")
An interesting related problem one can set is to work in Rindler spacetime. This is just normal Minkowski spacetime (ie flat, Euclidean spacetime plus a time coordinate), but observed from observers uniformly accelerated away from a point. Rindler spacetime then slices Euclidean spacetime in four; no Rindler observer can pass from one of the quadrants to another, in a manner that resembles -- not necessarily that closely, but resembles -- Schwarzschild spacetime. (See these diagrams: Rindler spacetime, https://people.math.osu.edu/ge... [osu.edu] and Schwarzschild spacetime, http://i.stack.imgur.com/bYrq7... [imgur.com] ). Now Rindler spacetime is really just Euclidean spacetime written from the point of view of accelerating observers. Due to the close link in GR between acceleration and gravity -- the weak equivalence principle states that locally one cannot distinguish between the two -- it's probably not a surprise to learn that if one calculates the vacuum in Rindler coordinates, there is Hawking radiation! (This is "Unruh radiation" -- Bill Unruh has done a lot of work in the last few decades on this kind of topic, including some of the earliest papers on acoustic, or dumb, holes.)