Hi guys, I'm going through Reif's book on statistical mechanics and have a question on the parameter omega, the number of microstates accessible to a system. Let's imagine a big box, and divide it into two equal halves. Now place a gas with a macroscopic amount of molecules in the left half, and say that it has an energy between E and E + dE. There is an initial value here of omega characterized by the energy and the volume.(adsbygoogle = window.adsbygoogle || []).push({});

Now remove the division in the box. Reif would say that since the volume is now increased, the number of accessible states of the systeminstantlyincreases; however, the probability of the system of being in most of them is zero, at least instantly after the division is removed (after an amount of time this is not the case). He says: since the probabilities of being in most of the accessible states are zero, the system will tend to evolve so that the probabilities become equal (due to the fundamental postulate of statistical mechanics). But this means that when the division is removed, the inverse of the absolute temperature instantly increases, for it is the partial derivative of log(omega) with respect to energy.

Is it correct that the absolute temperature instantly increases? Here is an alternative: maybe the value omega stays the same instantly after the division is removed; it then increases more or less continuously, approaching a maximum, final, value. Then, since the definition of temperature uses a partial derivative, the value would not change instantly after the division is removed. Rather, it would just be the same.

Which view of the amount of microstates is correct? I want to be sure I understand this book and the author's message. Thanks.

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# Definition of the number of microstates accessible to a system

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