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Karl Popper on brownian motion and the 2. law of thermodynamics

  1. Feb 1, 2008 #1


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    I'm reading an old, maybe outdated, paper by Karl Popper about the 2. law of thermodynamics, brownian motion and perpetual motion.

    Popper writes:
    Before that, Popper has described Planck's law as:
    So, my question is: Is brownian motion considered to be a violation to the 2. law of thermodynamics today? To me, it sounds like Popper is doing a lot of hand waving; and not so much with content in it.

    Se the attachment for the full article.

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    Last edited: Feb 1, 2008
  2. jcsd
  3. Feb 4, 2008 #2

    Andy Resnick

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    No, Browian motion is not incompatable with entropy increase. Feynman invented a nice puzzle- a brownian ratchet which can appear to raise a macroscopic weight, driven by brownian motion. The resolution to this puzzle is interesting, and the groups trying to understand actin polymerization in terms of a Brownian ratchet would do well to read it.

    The Second law of thermodynamics is a law of thermodynamics, and thus is a macroscopic, time-independant formulation. It has been experimentally demonstrated that entropy can decrease spontaneously for short times in out-of-equilibrium systems, in accordance with the fluctuation-dissipation theorem.
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