Maxwell's Demon & Walls
Kent W. Mayhew
In 1867 Maxwell presents his famous argument: As a consequence of kinetic theory of gases it was possible to transfer heat from cold to hot body without doing any work
this became known as:
Maxwell’s Demon (1):
1) A vessel is divided into two parts: Namely, Parts A and B wherein Part A is hotter than Part B
2) The two parts are separated by a partition with small hole and shutter
3) The shutter operates so that only fast molecules (Maxwell distribution) pass from Part B to Part A, and slow molecules pass from Part A to Part B
Certainly, the above violates the second law, however the fact that someone/something must measure the molecule’s velocities, make a determination and then operate the shutter, really renders Maxwell’s Demon into a situation influenced by external controls, or if you prefer an external input.
Even so, in the world of probabilities there remains a finite possibility that this occurs in nature. The reality is that this most likely would occur on a microscale, over a very small duration. Certainly for systems over a long duration, and on a macroscale, the result is that the net heat transfer is from hot to cold.
Importantly the above statistical based argument depends upon the validity of Maxwell’s distribution for gases, which is really part of kinetic theory for gases. In my book, as well as my paper “Latent Heat and Critical Temperature”(1), I discuss how walls influence what we know in thermodynamics. Specifically, without walls surrounding a gas then those gas molecules would not necessarily adhere to the kinetic theory. Of course the arguments in my book are more encompassing than those in my short paper.
The point becomes; if kinetic theory falters without walls, then so does Maxwell’s distribution. Moreover, traditional statistical thermodynamics is all based upon systems surrounded by walls. Certainly experiments need to be contained, hence walls are necessary, but we must begin to understand how a system’s walls influence our results.
The above is not to say that heat now can flow from cold to hot on a regular basis. Common sense dictates that heat flows from hot to cold, without the using the seconds law. However this is to say that traditional thermodynamic arguments such as Maxwell’s demon all need a rethink. As does all aspects of traditional thermodynamics!
Copyright Kent W. Mayhew
1) M.S. Longair . “Theoretical Concepts in Physics: An alternative View of Theoretical Reasoning in Physics” Cambridge University Press 2003