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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    Are there any examples of local entropy decrease in the universe which are not directly linked to life. If not, could we say that local entropy decrease is the ultimate definition of life?
     
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  3. origin Heading towards oblivion Valued Senior Member

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    There are no examples of processes, including life, that show a decrease in the entropy of the universe. Life increases the entropy of the universe.

    As far as local decreases in entropy, it happens all the time. For example when your cup of coffee cools off the entropy of the cup of coffee decreases. Or when a frost occurs the entropy of the water vapor decreases.
     
    Last edited: Oct 25, 2015
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  5. arfa brane call me arf Valued Senior Member

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    When you forget something, that's a local entropy drop in some part of your brain. The memory is there but connecting it back to your "aware" part is now harder, or more work.
     
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  7. exchemist Valued Senior Member

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    My favourite example is freezing of water. There is a local decrease of entropy in the freezing water, but this releases low temperature heat (Latent Heat of Fusion) to the environment, so the total entropy of the system increases.
     
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  8. John Connellan Valued Senior Member

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    Thanks guys, yes and I guess natural spontaneous growing of crystals in a salt solution would be another example.
     
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  9. origin Heading towards oblivion Valued Senior Member

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    Yes. The reason that life is not an example of negative entropy (in a closed system) is because it takes a tremendous amount of energy for a baby to develop. This energy comes from the mother and the mothers body is way less than 100% efficient in converting food to useful energy.
     
  10. exchemist Valued Senior Member

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    Yes, absolutely.

    Perhaps an example closer to "life" is the formation of a long polymer chain from its monomer(s). But in all cases, loss of degrees of freedom as the building blocks assemble makes entropy go down for the structure being assembled, though not of course for the total system. In living things, the metabolic processes that enable construction of the complex biochemistry release waste heat to the environment as they do so. (But that does not stop some creationists claiming that life somehow violates the 2nd Law of TD.

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

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    Can you elaborate on this. If the entropy of a system increases, the useful energy declines, right? So are you saying that the cup of coffee is more useful when it cools, maybe meaning you really can't use it when it is too hot and have to wait until it cools so you can drink it?
     
  12. origin Heading towards oblivion Valued Senior Member

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    The entropy change:
    \(\Delta S=nC_p ln\frac{T}{T_o}\)

    n is the moles of the material
    C is the heat capacity of the material
    To is the initial temperature
    T is the final temperature

    So the change in entropy from the initial to final temperature is negative.
     
  13. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    https://en.m.wikipedia.org/wiki/Introduction_to_entropy

    Entropy is calculated in two ways, the first is the entropy change (ΔS) to a system containing a sub-system which undergoes heat transfer to its surroundings (inside the system of interest). It is based on the macroscopic relationship between heat flow into the sub-system and the temperature at which it occurs summed over the boundary of that sub-system. The second calculates the absolute entropy (S) of a system based on the microscopic behaviour of its individual particles. This is based on the natural logarithm of the number of microstates possible in a particular macrostate (W or Ω) called the thermodynamic probability. Roughly the probability of the system being in that state. In this sense it effectively defines entropy independently from its effects due to changes which may involve heat, mechanical, electrical, chemical energies etc. but also includes logical states such as information.

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    Ice melting provides an example of entropy increasing.
     
  14. origin Heading towards oblivion Valued Senior Member

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    Yes, and the formation of ice is an example of a local decrease in the entropy of the H2O. Hot water has more entropy than cold water so when your coffee cools the entropy change is negative of the coffee. The overall effect of cooling coffee in a closed system is to increase the entropy of the system (because the heat is transferred to the system).

    Does that make sense to you?
     
  15. spidergoat pubic diorama Valued Senior Member

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    If you put a bunch of evenly sized balls into a container, they will self organize into a grid. I guess that's analogous to crystallization. Drying mud will crack into uniformly sized areas.
     
  16. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Yes, as the cup of coffee cools, the entropy of the system increases; as oppoesd to your statement
    ...


    That is the point I was making. I was considering absolte entropy of the system.
     
  17. origin Heading towards oblivion Valued Senior Member

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    I was trying to be careful and make sure that I was clear when I was talking about a closed or open system, apparently I wasn't clear. It looks like we are on the 'same page' now, though.
     
  18. brucep Valued Senior Member

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    The entropy of the system is maximum at thermal equilibrium.
     
  19. John Connellan Valued Senior Member

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    Just to be clear then, the entropy of the coffee itself decreases but the entropy of the cup increases and the entropy of the system as a whole increases, right?
     
  20. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    Yes, and that is when entroy is complete, as opposed to increasing.
     
  21. brucep Valued Senior Member

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    If you treat the cup and the coffee as a closed system. The entropy of the system is maximum when the coffee and cup are in thermal equilibrium. The following link is a discussion about the discovery of black hole thermodynamics and what it means.
    https://en.m.wikipedia.org/wiki/Black_hole_thermodynamics#Interpretation_of_the_laws
     
  22. John Connellan Valued Senior Member

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    I don't think anyone disputes that entropy increases over time and that the cup reaches thermal equilibrium over time. The question is: does the entropy of the coffee inside the cup actually locally decrease?
     
  23. quantum_wave Contemplating the "as yet" unknown Valued Senior Member

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    When hydrogen stars coalesce from clouds of hydrogen atoms, that seems like a decrease in entropy to me. The gas heats up, accumulates into dense stars, and eventually, through a process of supernovae producing new dust clouds with heavier nuclei, which condense into stars and solar systems that can host life, maybe life will be generated there, and evolve. Still, once the life hosting planet is in place, the generation of life wouldn't necessarily be a phrased a decrease in entropy, would it?
     

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