Timeline for How is a macrostate specified in quantum statistics?
Current License: CC BY-SA 3.0
9 events
| when toggle format | what | by | license | comment | |
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| Jul 7, 2017 at 10:41 | vote | accept | SRS | ||
| Jul 7, 2017 at 10:26 | comment | added | joshphysics | For a given physical context (e.g. thermal isolation, thermal equilibrium with heat bath, etc.), the values of the macroscopic variables defining a macrostate determine a probability distribution over microstates. | |
| Jul 7, 2017 at 10:12 | answer | added | ACuriousMind♦ | timeline score: 1 | |
| Jul 7, 2017 at 9:57 | comment | added | SRS | @joshphysics Isn't a macrostate in the classical case described by macroscopic constraints? For example, $E,V,N$? Doesn't the specification of the macroscopic variables $E,V,N$ specify a macrostate? If yes, why do you say that the phase space density describes a macrostate? I'm confused. | |
| Jul 7, 2017 at 6:53 | comment | added | joshphysics | In both the classical and the quantum case, macrostates are described by probability distributions (formalized as phase space density in classical case, and density operator in quantum case) over the microstates of the system. The distribution that is appropriate in a given context can be obtained by maximizing the information entropy of the distribution subject to appropriate macroscopic constraints (e.g. fixing average energy for the canonical distribution). | |
| Jul 6, 2017 at 21:37 | comment | added | user154997 | I wrote an answer explaining the classical case a while ago (not trying to plug my stuff: there are other similar answers; just too lazy!). Now you just replace the integrals $\int d^3xd^3p$ by a trace and the phase space density with the density operator, and that's it. | |
| Jul 6, 2017 at 21:29 | comment | added | SRS | I have. But density operator $\hat{\rho}$ is the analog of classical phase space density $\rho(q,p,t)$. In classical statistical physics, macrostates are described by ensemble averages and not by $\rho(q,p,t)$. Isn't it? | |
| Jul 6, 2017 at 21:27 | comment | added | user154997 | You have heard of density operators, haven't you? | |
| Jul 6, 2017 at 21:12 | history | asked | SRS | CC BY-SA 3.0 |