Scientists Watch as Heat Moves at the Speed of Sound

Re:Scientists Watch as Heat Moves at the Speed of Sound by renholder on Sunday March 24, 2019 @01:03PM (#19477391)

Asking because it's an interesting phenomenon and I don't know enough to understand the question I'm putting forth:

If conductive heat is radiated through quanta, phonons[0], why would it be limited to the speed of sound? Is there a limitation to waveforms in matter that limits the speed at which it travels or is it purely dependent on the energy "type"? (Thinking of light travelling in waveform, when I posit this, which is the reason the ridiculous ask.)

[0] - https://en.wikipedia.org/wiki/Phonon#Acoustic_and_optical_ph...

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Re:Scientists Watch as Heat Moves at the Speed of Sound by freethemullet on Sunday March 24, 2019 @02:17PM (#19477815)

Long wavelength phonons are the familiar sound waves. Smaller wavelength phonons have different group velocities due to dispersion.

The speed of second sound is not the same speed of first sound. The speed of second sound is essentially determined by a weighted contribution of the different of speeds of the different phonon modes that collectively participate to produce a temperature wave.

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