Why does heat flow from hot to cold?

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[@GeoffryGifari]

But is there a thermodynamic law that says energy transfer *needs* to happen, equilibrium must be reached, and that dS is strictly larger than 0 as long as the temperatures of the two systems Tᴬ and Tᴮ are different? If two systems A and B are in contact and they have different temperatures Tᴬ and Tᴮ , why is it not physically possible for them to just.... stay that way?

[@JonathonRiddell]

It absolutely is possible. Some systems simplify lack transport, like localized systems. When we talk about thermodynamics and statistical mechanics we are implicitly assuming our dynamics behave in a sort of "expected" way that you would see if you dealt with well behaved gas or something like that. You can absolutely have systems that don't have dynamics that look like this.

[@GeoffryGifari]

@@JonathonRiddell i can imagine the implications if systems like that exist at a large enough scale. i wondered "if superconductors exist, what about superinsulators?" a material that at the right condition, temperature *difference* is preserved and heat flow completely stops

[@GeoffryGifari]

hmmm if i have a many-body system, and it morphs in space and time in whichever way the Hamiltonian allows, are there cases where we can't even define temperature? where the concept of temperature doesn't even make sense

[@JonathonRiddell]

Hey! Yes for sure. Temperature is more or less an equilibrium concept. We can imagine a situation where we push our system so far from equilibrium that we are away from the thermodynamic description. Then, we might find ourselves, depending on the Hamiltonian, in a system that won't go back to equilibrium. Or it could return to an equilibrium that doesn't look like thermodynamics :). See for example my Anderson localization video. You could also have quantum scars that cause this.

[@GeoffryGifari]

@@JonathonRiddell this sounds like frontier stuff... i definitely wasn't taught about all that. and about pushing systems far from equilibrium, is there a limit on how much we can do that? how far from equilibrium can a system be?

[@GeoffryGifari]

@@JonathonRiddell return to "equilibrium that doesn't look like thermodynamics" sounds so new and cool. i naively thought that whenever there is a many-body system, thermo can still be applied, seeing that even for black holes, quark-gluon plasma, and the early universe you can still have a thermodynamic description. turns out that even when thermo works for such extreme cases, exceptions can still be found

[@GeoffryGifari]

btw do you happen to have an explanation on the chemical potential μ? i know its related to particle number but its origin, relationship to inter-particle interaction and how it can be measured to me seems unclear

[@JonathonRiddell]

Yes! Next video in the series :)

[@theperfectionist1607]

Do you still use desktop Linux? If so which distribution of Linux?

[@JonathonRiddell]

My new work computer unfortunately came with Windows 11, but I'm allowed to install Linux if I want, so I'm currently thinking about which to use :). I've used Ubuntu, CentOS and Fedora, to be honest I liked Fedora a lot, and found Centos to be a bit annoying to use. Ubuntu is always a great option.

[@tensorfeld295]

Thank you! :)

[@tanchienhao]

Awesome lecture!

[@JonathonRiddell]

Thank you :)