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Thermodynamics as probability rather than unbreakable law?

  1. Jun 15, 2011 #1
    Excuse me if this is a really ignorant question but I tried searching google but all I got was debunking thermodynamics/creation arguments. My physics lecturer the other day was saying that in third year statistical mechanics we will be shown how to derive a formula giving the probability for the second law of thermodynamics. He said the probability of it being broken was somewhere in range of it happening once in the age of the universe to the power of 100 or something. Does anyone know this exact probability? Also, why is the second law of thermodynamics given such a high esteem as a law. I saw a quote that I can't remember word for word but something like "If you theory opposes Maxwell's equations then all the worse for Maxwell but if it opposes the second law of thermodynamics then all you can do is bow in shame". Any insight would be appreciated.
    Thanks.
     
  2. jcsd
  3. Jun 15, 2011 #2

    BruceW

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    I'm not an expert on entropy, e.t.c. But I do know that:
    The most likely state is the one which can be made by the greatest number of different ways.
    For example, if you start off with two separated gases, then remove the partition between them, the most likely outcome is that they will mix. But there is an extremely small probability that they will stay separated.
    As another example, if you shuffle a pack of cards, they are most likely to end up in an order with no particular pattern. But there is a very small probability that they will end up in perfect suit and number order.
     
  4. Jun 15, 2011 #3

    BruceW

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    Clearly, the pack of cards in perfect order is far more likely to happen than the gases staying separate because there are a very large number of gas molecules.
    You could work out the exact probability by counting the number of different states which can lead to each possibility.
     
  5. Jun 15, 2011 #4

    Mute

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    The second law is indeed only statistical in nature. In particular, the Fluctuation theorem quantifies the probability that one will observe a fluctuation in entropy in the opposite direction that the second law predicts.
     
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