Sound can leap across a vacuum after all
I saw this retweeted by Jennifer, but sorry — No, it can’t.
When a sound wave reaches the edge of one crystal, the electric field associated with it can stretch across the gap and deform the crystal on the other side, creating sound waves in that second crystal (Physical Review Letters, vol 105, p 125501). “It is as if the sound waves don’t even recognise the vacuum – they just go through,” says Prunnila.
This is the kind of writing that really, really annoys me. Redefining terms in order to sensationalize the material. Sound doesn’t jump across the vacuum barrier — an electric field does, and that’s perfectly cromulent. The electric field causes the piezoelectric transducer on the other side to vibrate and recreate the sound. Neat. But if this counts as sound going through a vacuum, then transmissions using a satellite has to count, too. We’ve been doing this for more than 50 years.
Seems like the original article was addressing the possibility for phonon tunneling through a gap. That would be sound traversing a vacuum. You probably shouldn’t be so dismissive of the fact that the mechanism is explained in terms of electric fields, phonons themselves after all are just the result of strong correlation between the atomic motions. The force being the electric field the whole time.
And it should be pointed out that this is distinct from far field transmission. Evanescent fields are those kooky short range exponentially decaying fields that you can illicit to explain the Casmir force.
Now to be fair, the new scientist article is still horribly written, but I took away from my glance at the article that it was a discussion of phonon tunneling. Which probably shouldn’t be all that more surprising than any other quantum tunneling result.
As an undergrad I actually worked on an experiment for Advanced-LIGO, trying to employ a phenomenon similar to this as a possible cooling mechanism for the mirrors. This idea isn’t particularly new. Goes back at least as far as Polder and van Hove. Phys. Rev B. (1971): Theory of radiative heat transfer between closely spaced bodies: http://prb.aps.org/abstract/PRB/v4/i10/p3303_1 . Seems like the paper just works though a particular mechanism in detail.
i tried posting on Rhett’s Wired site about that new piece of equipment– am having trouble commenting/logging in with new account.
anyhoo, saw you posted and here is my two cents worth:
(feel free to rip off or add to my answer so you look cool over on the other site…)
🙂
the scale is in cm and inches, and the zeroes seem to line up. so i immediately think of some sort of pressure scale for a mercury gauge of some sort. manometer?
the clip confuses me, unless it is used to clip a hose going to what ever you’re measuring pressure of. doesn’t look like an electrical contact. plus, it should be mounted vertically. the rounded groove/slot up the middle looks perfect for placing a glass tube into, which holds the mercury.
Tom,
To be fair, the article they link to does seem to be a discussion of phonon tunneling. You shouldn’t be too quick to dismiss it just because the proposed mechanism is in terms of electric fields. Phonons themselves after all are just the result of strongly correlated electric interactions of the ions. And this transmission should be distinguished from far field radiation. The fields responsible here are those kooky short range evanescent (exponentially decaying) electric fields which can be solicited to explain the Casmir force.
So, the scientific article really is about phonon tunneling, which really shouldn’t be all that more surprising than any other kind of quantum tunneling. And to be fair to you, the new scientist article is still horribly written.
This actually isn’t a new idea. I did some undergrad research on this. Looking to this kind of scheme as a possible cooling technique for the mirrors for Advanced LIGO. The idea of heat tunneling goes back at least as far as Polder and van Hove (1971). Phys Rev B. Theory of Radiative Heat Transfer between Closely Spaced Bodies: http://prb.aps.org/abstract/PRB/v4/i10/p3303_1
To offer another perspective, it can be viewed as a change in scale for sound. The collisions of air molecules are electromagnetic interactions. They still are, but now the particles and their separations are larger.
So in that sense, it’s not so much a vacuum, but a coarsening of the medium.
Virtuosi,
I suppose the well-known article by Polder and van Hove (1971) deals with near-field heat transfer by photons and the article, which is the basis of the New Scientist story, is dealing with near-field heat transfer by phonons.