# Does sound show wave-particle duality?

We know that light and electrons both show wave-particle duality. Or in other words we can say that they can be both seen as a wave and a particle. Can a similar theory be applicable for sound? Can sound also be explained as a particle as well as a wave?

• @user36790: Calm yourself, and learn that there are indeed phonons for some modes of excitations, mainly in solids and liquids, though. – ACuriousMind Aug 23 '15 at 12:58
• @user36790 Please be nice – Manishearth Aug 23 '15 at 13:00
• @ACuriousMind: I am indeed aware of that, sir; but they are not just normal excitations, right? They are only meant for condensed matter, not some sort of normal air. – user36790 Aug 23 '15 at 13:04
• This is a manifestation of quantum behavior in macro objects: youtube.com/watch?v=W9yWv5dqSKk. And here is a paper describing the experiment: hekla.ipgp.fr/IMG/pdf/Couder-Fort_PRL_2006.pdf. The question, though, is whether packets of sound-carrying medium could act as the oil droplets in the experiment. – Ernie Aug 23 '15 at 14:51
• I asked a related question here. – knzhou Aug 6 '18 at 10:04

The notion you should look up and learn about is the phonon. It is a quasiparticle that arises in the quantum description of acoustics in condensed matter. The description is simplest and clearest in regular lattices of atoms / quantum particles, so it doesn't work so well for sound in a gas. But phonons can be thought of as quantums of sound in solid lattices.

Basically, a lattice is modelled as a system of coupled quantum harmonic oscillators, whose Schrödinger equation is very like a classical model of point masses linked by ideal massless springs. The system has eigenmodes with natural frequencies $\omega_j$, and the energy level of $j^{th}$ eigenmode can change only by integer multiples of $\hbar\,\omega_j$, whilst its ground state has energy $\frac{1}{2}\,\hbar\,\omega_j$. The quantum of this energy change $\hbar\,\omega_j$ corresponds to the phonons of the acoustic eigenmode in question.

• At least now OP could understand what I was talking of; phonons are not in the ordinary sound waves in air; they are only meant for condensed matters.+1:D – user36790 Aug 23 '15 at 13:26

To plainly put what WetSavannaAnimal have said. Yes, sound waves can behave like a particle. When sound wave have enough energy to excite the particles that is use for traveling to their excited state, the sound wave becomes a Phonon.

Phonons act like particles that oscillates relative to each other and no longer function like a wave.

no, in the macroscopic world of ordinary mass, sound is adequately and completely understood as just the transmission of air (or other media) alternating densities caused by the vibration of the source. There are no particles being transmitted at all, just as a wave on the surface of a body of water does not imply movement of particles themselves propagating the wave. Sound is not composed of elementary particles.

• This isn't true. Well it's true for sound in air, but in condensed systems lattice vibrations are quantised and we get quasiparticles called phonons. – John Rennie Jul 9 '17 at 7:01