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I Does Laplace's demon know about entropy?

  1. Jan 12, 2017 #1
    Hi.

    I read this thread with great interest and have similar question:
    In a deterministic universe, does entropy exist for Laplace's demon? Since he knows the universe to it's microstate, does the term "macrostate" even make sense to him?

    And say there is a "half-demon" that only knows the position of each particle in the universe. Since this greatly reduces the number of possible microstates, he should ascribe the universe a lower entropy than we humans do. Does this mean the notion of entropy is purely subjective? If I measure the temperature of a gas in my lab and compute the entropy, I might get a smaller number than my colleague outside who doesn't now the exact temperature and therefore needs to take into account microstates of other temperatures as well. Is he wrong, or are we both right?

    I know that in information theory, entropy is highly subjective and can change drastically upon learning new information. I have experienced entropy in thermodynamics to be used much more objectively, but why?
     
  2. jcsd
  3. Jan 13, 2017 #2

    DrDu

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    Science Advisor

    As you mention infomation entropy, where does the demon store all the information he has about the universe? What would be the information entropy of that storage device?
     
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