phonons

Gary Morrison wrote
>> Or equivalently, the elasticity of the vibration of a string, a steel
>>string for example, is manifested at the sub/atomic level by the
>>distortions of crystaline lattices. Crystaline lattices are, once again,
>>generated by electron attraction and repulsion, which again is conveyed by
>>photons.
>>...... So sound is, at this otherwise not very interesting sub/atomic
level,
>>ultimately conveyed by photons. The invention of a new particle, the
>>phonon, seems to be no more than a pointless complication that side-steps
>>well-accepted physical models for no apparent reason.

Phonons are the quanta of the normal vibrational modes of a crystaline
lattice. If you were immersed in a crystaline lattice (didn't this happen
on Star Trek?) the displacement of ensembles of molecules (a lattice
wave) would correspond to sound, and if you were another molecule in that
lattice, your interaction with the phonon would quantized. Thus molecules
experience quantized 'musical pitches'. Just as relativistic effects are
only noticable at incredibly high velocities, quantization of frequency
is only noticable at very high frequency and/or small scale. Our ears,
capable of hearing, at best, a 66 cent pitch difference ;-), would never
be able to detect quantum effects. Phonons can be thought of as
particles of fixed energy and momentum that move with the
ensemble velocity of the lattice wave (they also work in
continuous media calculations). Using the idea of a particle with
these properties, one finds that phonons interact in
many ways like the particles we use to imagine thermodynamic physical
process, and thus are a convenient mathematical fiction, like photons,
electrons, etc. for describing measured phenomena.


John Starrett


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From: "Paul H. Erlich"
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>Classically, two spherically symmetric neutral atoms would experience no
>electrostatic forces even if separated by a very small distance.
>Electron repulsion would be exactly balanced by attraction to the other
>atom's nucleus.

There's a very straight-forward response to it relating to the inverse
square law and the relative placements of the nucleus and the electrons in
an atom. But as with you, I don't think it appropriate to discuss over the
list.

Thus far I have seen no compelling reason to examine sound at other than
the macroscopic level of classical mechanics, but I certainly won't rule
out the possibility that a study in earnest of quantum mechanics would
change my mind. At the moment though, I don't have time to study quantum
mechanics now, so I think I should exit the discussion.


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From: mr88cet@texas.net (Gary Morrison)
Subject: Re: New Year
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