What Rocks Dream About: Not Maxwell's Demon

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Brian Johnson
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What Rocks Dream About: Not Maxwell's Demon

Postby Brian Johnson » Wed Oct 03, 2012 7:21 pm

I read only a few paragraphs of "What Rocks Dream About" in Vol. 17 No. 3 before encountering an unfortunate misunderstanding of basic thermodynamics. Mr. Sirola argues that it is impossible, even in principle, to evacuate all of the air from a room, citing Maxwell's Demon as the reason.

Maxwell's Demon is a thought experiment and apparent paradox in which a knowledgable being can violate the second law of thermodynamics, creating a temperature difference between two regions initially at equilibrium. The being does so by observing all of the gas molecules in the two regions, so that he can predict when and where every molecule will hit the wall between the two regions, and then opening and closing a small door so as to allow fast-moving molecules to travel from one region into the other (heating it up), and slow molecules to travel in the reverse direction (cooling off the first region).

Maxwell's Demon appears to be a paradox because such a being could theoretically create a temperature difference in a system which is initially at equilibrium. The resolution of the paradox, which took considerable theoretical work, is that the demon's act of observing all of the gas molecules, and opening and closing the door, necessarily involves an increase in entropy, and this increase is greater than the decrease in entropy obtained from the demon's actions.

Like any discussion surrounding the second law, Maxwell's Demon makes sense only in a closed system. If an external source of energy is supplied, nothing prevents one from pumping heat from one region to another -- doing so is an everyday occurrence for anyone who owns a refrigerator or air conditioner. Appealing to Maxwell's Demon when a source of external energy is available is akin to the creationist argument that life cannot evolve because "entropy always increases". This is true in closed systems, but the Earth is not a closed system; it's powered by the sun. Similarly, the room in Mr. Sirola's article is not a closed system if an external agent is doing work to change its state.

Indeed, not only is Mr. Sirola's argument invalid, the conclusion is also false. It is most certainly possible, in principle, to remove each and every molecule of air from a room. The second law of thermodynamics merely states that it's impossible to do so without an external source of energy. But with a source of energy to power an increasingly sophisticated series of vacuum pumps, it would be entirely possible -- in principle -- to remove every last molecule of gas from a chamber. Doing so now, with current technology, would not be possible in practice, but that speaks to the limits of technology, not to the limits imposed on us by fundamental physics. We might, for instance, imagine covering the walls of the chamber with nanomachines which can capture and deliver gas molecules to an exhaust port, one by one.

Brian Johnson
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Re: What Rocks Dream About: Not Maxwell's Demon

Postby JO 753 » Fri Oct 05, 2012 5:36 am

Wut if Maxwellz Demon iz inside the 2 regionz?
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Re: What Rocks Dream About: Not Maxwell's Demon

Postby Austin Harper » Fri Oct 05, 2012 1:40 pm

I suggest you read the rest of the article.
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Re: What Rocks Dream About: Not Maxwell's Demon

Postby Major Malfunction » Fri Oct 05, 2012 2:08 pm

And read The Nargun and the Stars.
This being was produced using the same process as other beings, and therefore, may contain traces of nuts.


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