On 19.02.2012 17:21 John Clark said the following:
On Sun, Feb 19, 2012 at 5:32 AM, Evgenii Rudnyi<use...@rudnyi.ru>

If one well defines a thought experiment with the Maxwell's
demon, then
it is quite clear that such thing does not exist. Why then to spend
on it so much time?

Maxwell's demon is possible in classical physics and it was not clear

I am not sure I understand what do you mean. How Maxwell's demon is possible in classical physics? I personally would say that Maxwell's demon could work just within a brain of some crazy scientist.


that quantum mechanics made it impossible until 1929 when Leo Szilard
proved that to be the case. And understanding just why it can not
exist aids in understanding the relationship between energy
information entropy and reversibility. Maxwell's demon was the
starting point for Rolf Landauer's discovery in 1960 that erasing
information always requires energy and increases entropy because it's
thermodynamically irreversible.

The bottom line is that Maxwell's demon would work if it had
information on when to open and close its shutter, if it had that
information it could decrease the pressure on one side of a tank
filled with gas and increase it on the other without expending
appreciable energy and use that pressure difference to do work.
However the stumbling block is the information, it would take more
energy to obtain that information than you'd get from that work.
Actually by pure chance Maxwell's demon can work, but only very very
rarely and only for a very very short time.

John K Clark **

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