Local entropy decrease

Discussion in 'General Science & Technology' started by John Connellan, Oct 25, 2015.

  1. John Connellan Valued Senior Member

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    Indeed, and what would be the mechanism of increased universal entropy in this case? I guess it would be the fact that the clouds/stars heat up right?
     
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  3. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    I would only be inclined to refer to that scenario as a decreas in local entropy, not universal. And yes, the decrease would be evidenced by the heating up of the gas/environment to the point that the planets could host life. The mechanism would be gravity and compression producing heat, both to produce the first round super stars which burn quickly and explode, and then the reformation of stars and planets with heavier nuclei as a second round of decreasing entropy. Maybe then the generation of life would in fact qualify as a decrease in entropy as well, I'm not sure.
     
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  5. John Connellan Valued Senior Member

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    No, I'm referring to the fact that any local decrease must be offset by an even larger universal increase in entropy.
     
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  7. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Oh, I misread that. Universal entropy in a finite expanding universe model like the Big Bang, would in total always increase, so you can make a case for total entropy increasing everywhere else faster as a result of the local decrease.
     
  8. John Connellan Valued Senior Member

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    Yes, but generally when entropy locally decreases somewhere due to some mechanism, that same mechanism always results in greater universal entropy. If a mechanism was found that only decreased entropy, you could scale it up and theoretically decrease the entropy of the entire universe and of course, that is not allowed

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  9. origin Heading towards oblivion Valued Senior Member

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    Entropy is complete?
     
  10. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Yes, the local mechanism works at the expence of increased universal entropy. As the hydrogen gas condenses under gravity, the heat it produces is recycled from the surrounding energy in space, and the mechanics are dependent on the particular cosmological model. In Big Bang Theory, the heat would be a product of the effect that the condensation would have on the geodesics of the particles being accumulated. Their geodesics would not produce heat until the various particles interrupted each other's geodesics, which is the perscription for the produciton of gravitational waves referred to as ripples in spacetime, as I understand it. Those ripples equate to energy waves and their effect on the particles they encounter would be a jerk or jostle of the particles, which might be the mechanism for the heat generated as the star forms, I would suppose.
     
  11. origin Heading towards oblivion Valued Senior Member

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    Yes.

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  12. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    It is a way of saying that there is a limit to the increase in entropy of a closed system. That limit is reached when thermal equilibrium is reached, and I have heard that point referred to as the completion of entropy.
     
  13. origin Heading towards oblivion Valued Senior Member

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    I have never heard it expressed that way. Entropy can only zero at absolute zero, so it usually only makes sense to talk about the change in entropy.
     
  14. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    That explains why you keep referring to the change, and not the progress (increase) toward the limit. Also, when you refer to absolute zero, I see that you are taking about the universe in total, and the examples, and my discussion have been about local decreases in subsystems within the universe.

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    Last edited: Oct 27, 2015
  15. brucep Valued Senior Member

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    The system entropy is maximum at thermal equilibrium. What you want to know 'is there a correlation between entropy and temperature and entropy and area?' Look at the formulas for the black hole thermodynamics. They'll answer your question. A simple guess would be as the coffee cools off the system entropy would be less than maximum as it cools off but is at maximum once that process is done.
     
    Last edited: Oct 27, 2015
  16. origin Heading towards oblivion Valued Senior Member

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    My reference to absolute zero was not in relation to the universe in total, it was in reference to local entropy.
     
  17. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Just to be sure we are still on the same page, absolute zero is zero K on the Kelvin scale, right? -273 Celsius.
     
  18. origin Heading towards oblivion Valued Senior Member

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    Yes, absolute zero is 0 degrees Kelvin or 0 degrees Rankine
     
  19. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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  20. exchemist Valued Senior Member

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    Good diagram. As this makes clear, the entropy of a material at absolute zero is zero and it goes up as heat is put into the system and the temperature rises (due, if memory serves me, to the increasing ability of the atoms or molecules to populate more states, i.e. W in Boltzmann's famous expression increases).

    However if one considers the distribution of a fixed amount of heat in a system, then the highest entropy distribution will be the one in which the heat is evenly distributed i.e. there are no hotter or colder spots. This again will maximise W.

    There can thus be dangers in applying the idea of the usefulness of energy, unless one keeps in mind that "usefulness" of heat depends on making it flow across a temperature gradient.
     
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  21. arfa brane call me arf Valued Senior Member

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    About gas clouds coalescing or clumping into stars. This increases thermodynamic entropy because star formation includes a lot of heat and radiation, gravitational entropy increases because gravitational equilibrium (the state with greatest entropy), is the closest packed state for a given amount of matter with mass.

    And then the gravitational energy is highest for a system of massive particles packed as closely as possible, or "at rest" relative to each other.
     

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