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Physics · 术语表

什么是 Boltzmann entropy?

Definition 16.4 University Physics — Year 3 · 第 16 章 — The Microcanonical Ensemble

The statistical entropy of a macrostate is

S=kBln⁡Ω,kB=1.38×10−23 J/K.S = k_{\text{B}}\ln\Omega , \qquad k_{\text{B}} = 1.38 \times 10^{-23}\,\mathrm{J}/\mathrm{K} .

The logarithm makes entropy additive where multiplicities multiply: for independent systems Ω=Ω1Ω2\Omega = \Omega_1\Omega_2 and S=S1+S2S = S_1 + S_2; Boltzmann’s constant calibrates the count to the kelvin-and-joule units thermodynamics had already chosen. This SS, we will verify, is the entropy of the Year 1 volume’s second law — now with a microscopic meaning: entropy measures, in logarithmic currency, how many ways the macrostate can be realised.

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