Moderator notice.
You have posted a reply to a thread.
The post you replied to has been dormant for SIX YEARS.
Look and see how old the post is before you reply - the dates are right there.
Resurrecting threads this old is a violation of board etiquette.
As this is your first offense of this kind I will give you a pass.
Now that you know better, please do not do this again.
And finally, your reply had no meaningful content at all. You simply agreed and ended your post with "lol".
That is technically two violations of board etiquette in one.
1. Resurrecting a dead thread
2. With a content-free non-post.
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Helium II is a superfluid, a quantum mechanical state of matter with strange properties .
The thermal conductivity of helium II is greater than that of any other known substance, a million times that of helium I and hundred of times that of copper. This is because heat conduction occurs via a quantum mechanism.
Second sound is a quantum mechanical phenomenon in which heat transfer occurs by wave-like motion, rather than by the usual mechanism of diffusion. Heat takes the place of pressure in normal sound waves. This leads to very high thermal conductivity. It's known as "second sound" because the wave motion of heat is similar to the propagation of sound in air.
Sound waves are fluctuations in the density of molecules in a substance; second sound waves are fluctuations in the density of phonons. Second sound can be observed in any system in which most phonon-phonon collisions conserve momentum. This occurs in superfluids and in dielectric crystals when Umklapp scattering is small.
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