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Entropy question

  1. Jan 13, 2009 #1

    1. Sir Arthur Eddington once said:

    "If someone points out to you that your pet theory of the universe is in disagreement with Maxwell's equations—then so much the worse for Maxwell's equations. If it is found to be contradicted by observation—well these experimentalists do bungle things sometimes. But if your theory is found to be against the second law of thermodynamics I can give you no hope; there is nothing for it but to collapse in deepest humiliation."

    (Is this is a "dogma" or a "curse"?)

    2. Maxwell's demon cannot violate the second law because we postulate that there are no supernatural critters, so it must increase entropy while acquiring information about the particles.

    3. A perpetual motion machine of the second kind is a machine which spontaneously converts thermal energy into mechanical work. When the thermal energy is equivalent to the work done, this does not violate the law of conservation of energy. However it does violate the more subtle second law of thermodynamics.

    4. Feymann ratchet is conceptually right but impractical.

    Despite my best efforts, I couldn't find an argument against the following gedanken experiment:

    1. Imagine a closed system with two regions separated by a wall and a shutter between these regions.

    2. The regions are filled with a monoatomic gas at approximate ambient temperature and pressure (slightely different from each other).

    3. The shutter opens and closes randomly depending on its own conformation and the brownian storm around -- The demon was exorcized here!

    4. The conformation is such that after a sufficient time the system self-thermalizes, hitting a Boltzmannian form with an entropy level less than that obtained if the shutter were left permanently open.

    5. If feasible, such a device could be used to recycle ambient heat since the regions now possess different pressures.

    6. Kinetic energy can be replaced by letting the gas absorb it from external ambient in a cyclic fashion.

    7. It is intuitive (at least to me) that this apparatus seems to violate second law -- Not in terms of time arrow reversal but rather in terms of multiplicity decrement.

    8. Does it have the flavor of a perpetual motion machine? Could it be it is a cloaked kind of Feynmann ratchet?

    9. The shutter structure should be something vaguely resembling a subway station ratchet (it opens to one side only):

    Code (Text):

                         / |      /
                        /  |     /
                       /   |    / Gate                
                      /    |   /                        Region 1
                     /     |  /                          
                    /      | /
    _______________/       |/               ___________________________
    ------------------------o              '---------------------------

                                                        Region 2
    - For instance, carbon molecules (12) could be used to make up the wall and shutter while Xenon (131), the gas phase.

    - The stop structure on the left of the gate is important to increase the chance of particles accumulate on one side.


    I know that a refutation might be obvious, but I can't figure it out. So I'd appreciate any comments. Thanks.
    Last edited: Jan 13, 2009
  2. jcsd
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