Photons and phonons are massless entities, if my understanding is correct. Unlike photons, phonons do not travel at the speed of light, being "excitations of a classical acoustic wave." Because aging is relative to speed, and the speed of light is the cosmic speed limit, do phonons, in fact, age? And if so, is this aging unrelated to decay, given the phonon's massless quality?
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This depends heavily on the context. In real materials, phonons will scatter off impurities, be influenced by the environment etc. So if you start a material with a single phonon in it, it will eventually decay.
However, if everything is idealized, we have perfectly harmonic potentials and no influence from the environment whatsoever, a single phonon will just remain in its state forever. This is very similar to a frictionless ideal pendulum, which, once set in motion, will just continue to make harmonic oscillations forever.
Phonons are fundamentally different from photons in the way that they need a medium to propagate in. And this medium will never be even near-perfect. Light, on the other hand, can for example just travel largely undisturbed through the vacuum of space, giving it conditions much closer to the idealized world.
noah
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