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Entropy question

  1. Dec 27, 2009 #1
    Hi guys, I'm having a discussion with a friend in regards to entropy. I approach the concept of entropy in relation as the tendency for a system to tilt towards the disorder and randomness. with that said,

    I state that a human(biological system) possesses less entropy then a rock due to enormous structural complexity and order required to operate, where as a rock can be structured in all random fashion.

    I also say that heavy elements within the periodic table becomes more complex and structurally more ordered due to increase in proton, nuetron and electrons, thus more structural complexity equates to decrease in entropy.

    Lastly any solid will have less entropy then liquid due to strict stable bonding thus reducing random probability of atoms moving about in the system

    can someone confirm these for me thanks
     
  2. jcsd
  3. Dec 27, 2009 #2
    You're partly right. The number of microstates available to the human body far exceeds those available to a simple piece of rock, hence the human body has greater entropy. For that same reason, liquids have greater entropy than solids, which is what you concluded for different reasons.
     
  4. Dec 28, 2009 #3
    Entropy is merely a human invention. The reality is closer to this:

    There are many states things can be in, and usually we only want a few. We call these 'complex' or 'ordered', because something about them lines up in the right way to do something for us. The trouble is, there are a lot more states that are not like this out there. We call those the same, and since things change, we see it as more likely to change towards randomness, because to us 111111111 is special, but 1010111011 is not, and to us it is 'the same' as 101010110101.
     
  5. Dec 28, 2009 #4

    ideasrule

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    It's certainly true that liquids have more entropy than their corresponding solids. The http://en.wikipedia.org/wiki/Entropy_of_fusion" [Broken] is a well-known concept in chemistry.
     
    Last edited by a moderator: May 4, 2017
  6. Dec 28, 2009 #5
    Similar to what Galap said, I say that entropy isn't directly the tendency for disorder, but rather the statement that we if don't know where something is we assume it to be in the state that has most realizations. In some circumstances this will be the most disordered state.

    I will take your human/rock example (we take a rock with the same number of atoms as the human).
    The important point is that in the rock there are a lot of possible way to swap atoms while leaving the object still be a rock. So if a bunch of loose atoms randomly come together to form a rock they don't have to take care of their exact position and so they have a huge number of options to assemble themselves into a rock.
    However, in the human body you better not swap the liver with the heart. And you better not swap atoms at random too often. So for the same number of (different) atoms to assemble a human body there are far less possibilities to join correctly so that we would still call the result a human body.

    Galap's example is similar. If we call one state "100% 1's" and another "50% 1's" then the first has only one realization and the second has a lot.

    Liquids have more entropy since the atoms don't have to care about the position. In a solid however there are some additional rules restricting the atoms when forming a valid solid. The atoms have to be at crystal positions.

    So to sum up, states with highest entropy have the highest number of allowed realizations. Actually all this (the second law of thermodynamics) assumes that the time evolution of the system is completely homogeneous in space and time which isn't always true! Just as in chaos theory, a real system might have attractors and thus tend towards a state of lower entropy. That is how life developed.

    Basically, the more constraints you pose on the positions of the constituents of the objects, the smaller the entropy.
     
    Last edited: Dec 28, 2009
  7. Dec 28, 2009 #6

    Mapes

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    A better comparison would be a human body vs. an equal quantity of water, proteins, calcium phosphate (bone), etc. You're discussing configurational entropy only, so you want to match the composition. Otherwise, human tissue will always have a higher entropy than rock simply because water has a higher molar entropy than a solid mineral.
     
  8. Dec 28, 2009 #7
    I say 11111 is special not to us, but to this universe, order and structural complexity has to correspond to a set of laws in this universe in order for it to be considered so, that set of laws is not created by us, but rather discovered nature of the world. thus absolute order and structural complexity exist outside of human intellect, otherwise life wouldn't exist.
     
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