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Best explanation for 1-way entropy?

  1. Jul 30, 2011 #1
    What is the best explanation for why entropy must increase BY LAW. I can see it as being a good general rule, but I don't quite see why it's law, especially when you consider a micro-state explanation of entropy. What is the best argument for the law of increasing entropy?
  2. jcsd
  3. Jul 30, 2011 #2


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    My thermo is a bit rough, but the entropy of a system always increasing actually means the system, with overwhelming probability, tends towards states of increased entropy. You CAN see a system go from higher entropy to lower entry, but the probability is vanishingly small.
  4. Jul 30, 2011 #3
    Statistically, what Peng said is right in a short time scale. When you consider a sufficiently huge amount of time (and this is very, very huge amount of time, many times the age of our universe), every equilibrium state would be accessed and the total entropy variation would be null.
  5. Jul 31, 2011 #4
    Thank you both for the reply! I was thinking along those lines, but I wasn't sure at all. Physics Forums is such a good tool for this kind of thing..
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