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What about the size of the door (space) and how long has it to be opened (time)?

I think Maxwell's demon would have a problem with space, if the door is too wide (more than one particle size), then direct interaction between the two part is possible and would lead to lose isolation restriction, like there were no demon, (even no isolation wall). On the other hand, if the door is too narrow, then no particle can go into or it will let pass only those which are direct aimed, then Maxwell's demon would lose its freedom of choice because the narrow gate itself "choose" particles having a direction perpendicular to the wall, despite any module criterion (no temperature can be choosen) again it is like there were no demon.

Finally assuming that there were an exact size door being useful for the demon work, then time would be the problem, when the door is open too long, both side particles can cross or collide, like there were no demon!, and if the door is opened too little time, then it only could "select" fast particles from both sides,then it couldn't separate temperatures.

I've read very complex arguments against Maxwell's Demon, concerning information store but I think size and time constraint could be enough arguments to defeat Maxwell's Demon, Do you know any related work about size and time constraint ?


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The demon is assumed to be able to deal with these issues, and these question are of little consequence because limits on the performance of the system can be placed without knowing the answers to them. Enter stage left: information theory. – dmckee Jan 24 '12 at 3:25
Yes, information seems to be a deeper limit, and I think in the same way, but how to avoid "the chicken or the egg dilemma ", I mean, what is the justification, perhaps we have an equal strong limit in information and implementation, (like lack of data vs no existence of an algorithm) if you suppose inversely that the daemon magically has the information about every molecule How we are sure we could avoid implementation problems? and I don't mean technological problems, I mean an algorithmical, geometrical, logical imposibilty of a daemon even having the information. – HDE Jan 24 '12 at 20:59
Maxwell's demon has been implemented experimentally, and it actually works. Information is indeed the solution to the paradox. – Peter Shor Mar 4 '12 at 13:18

Let us imagine a baseball player that is also a Maxwell's demon, and perfectly elastic baseball balls, that are flying around randomly. When the demon sees a fast ball, he catches it with a baseball glove. Now the demon has already done what a demon is supposed to do: catch one or more fast molecules.

If the demon must collect many balls into a container, there is very little problem collecting a few balls into a large container. As the container fills up the demon must be smarter and quicker.

Oh yes, the demon could also just drop the ball. The glove heats up anyway. I mean the energy is collected in the molecules of the glove.

A demon whose temperature is 0 Kelvins does not need any energy at all. The warmer the demon the more energy its brain uses to compute. This is actually very simple!

here is a story about some kind of maxwells demon device

here is a game where one can be a maxwells demon

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How does this answer the question? – Peter Shor Jan 24 '12 at 17:44
OP asks about impossibility to catch fast molecules, I tell how it very clearly is possible. That was my related work. Is there some problem? – kartsa Jan 24 '12 at 18:02
But Maxwell's demon doesn't just have to catch fast molecules, it has to separate them from the cold ones without expending any energy. As you've pointed out, in your scenario energy is going into the glove that the demon has to then get rid of. It's not that I don't think you couldn't build a Maxwell's demon that works this way, but I don't think you've actually demonstrated that you can. – Peter Shor Jan 24 '12 at 19:15

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