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Thermodynamics unified with QM?

  1. Jan 8, 2007 #1
    has thermodyamics been unified with QM?

    i thought that thermodyanimcs arises because of things that happen on the quantum level.

    for instance, as time's arrow been unified with QM or SR or GR? What does ST or LQG say about time's arrow?
  2. jcsd
  3. Jan 8, 2007 #2


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    Er... back off a bit here.

    Classical thermodynamics is a statistical description of the interactions of many particles. So it is nothing more than EM interaction, but done over a gazillion particles. There is nothing to "unite" it with.

    One can do the same with invoking QM into thermodynamic (often done in solid state/condensed matter physics that deal with such huge numbers). Again, there is nothing to "unite" because it is well-known what the interactions are at the microscopic scale.

  4. Jan 8, 2007 #3
    Is there some explanation for time's arrow and entropy in QM, in SR, GR, ST, or LQG?

    Or are we just saying "entropy happens."

  5. Jan 8, 2007 #4
    I think you may be pining for http://en.wikipedia.org/wiki/Statistical_mechanics" [Broken]. AFAIRemember, the increase of entropy is explained as a movement from a low-probability state to a higher-probability state.

    So imagine a gas in a box, and think about the positions and momenta of all the particles at any given moment - this is a certain state, a point in a hugely-dimensional 'phase space', and the point wanders around exploring this phase space in a seemingly random walk. Within the phase space, there's a tiny volume corresponding to having all the particles in one half of the box, and a huge volume corresponding to having the particles evenly distributed throughout the entire box.

    So if the box starts off partitioned, with all of the gas in one half, and we then release the partition, the gas spreads out because that's the overwhelmingly most probable thing for it to do.

    hope that helps
    Last edited by a moderator: May 2, 2017
  6. Jan 8, 2007 #5

    But why is it the most probable thing for the gas to do?

    Why is it the most probable thing, for a drop of dye in a swimming pool to spread out?

    What is the underlying mechanism that causes this?
    Last edited by a moderator: May 2, 2017
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