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Idiot question

  1. Mar 25, 2008 #1
    Okay, I'm not an idiot, but can someone explain to me (in common layman's terms) what entropy is? And it's relation to life?
  2. jcsd
  3. Mar 25, 2008 #2
    It is the movement from order to disorder, in laymens terms. It has no bearing on life as scientifically it is only valid in closed systems, if it were valid it would show that life is a sort of reverse entropy, from disorder to order, and its commonly touted by creationists as evidence that evolution is flawed as it does not fit in with the laws of thermodynamics. This is of course a scientifically flawed claim, but that doesn't seem to stop it being used for propaganda purposes.


    Last edited: Mar 25, 2008
  4. Mar 25, 2008 #3
    Still confused. Are there more layier laymens terms we can use?
  5. Mar 25, 2008 #4
    Not really does this help?

    Wiki also.

    If not could you outline exactly where you are stuck? I'm not sure what level you are at so I can't really give it any more simply than: in a system that is closed the "objects" in such a system will lose energy and thus become more disordered by the processes in such a medium. A closed system means there are no energy sources from outside the system, eg the sun to the Earth, where Earth is the system.
    Last edited: Mar 25, 2008
  6. Mar 25, 2008 #5


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    You leave the binder of your manuscript on the counter. You've numbered all the pages to keep them in order.

    Your rival sneaks in and rearranges one or two pages.

    When you return, you can tell very easily that some pages are out of order. In fact, any change in the page order is immediately obvious. In fact, every change, even the smallest change, is uniquely distinguishable from every other change. Your book has very low entropy.

    Your rival sneaks in again but this time thoroughly shuffles all your pages.

    In this new state, no page is next to its neighbour. At this, point whether small changes are made to page order or large changes are made to page order, it doesn't really matter. One change is indistinguishable from another. Your book has high entropy.

    When the universe ages and dies, everything will be distributed somewhat evenly. Moving molecules around, say switching two molecules - even switching countless billions of molecules - will make virtually no difference. Entropy will be near maximum.
  7. Mar 25, 2008 #6
    So life is in a sense, simply highly organized molecules that happen to create energy in order to sustain said organization? Like a perfect storm or something?
  8. Mar 25, 2008 #7
    Given that they don't reflect entropy, they are exactly what can happen when the papers are organised by an external person; despite people throwing them into disorder, sooner or later no matter how much disorder there is, if there is more of an outside influence that creates order, the papers will become more ordered.

    Nice analogy DaveC. :smile:
    Last edited: Mar 25, 2008
  9. Mar 25, 2008 #8


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    Please, credit where credit is due. Brian Greene is a brilliant, brilliant writer.
  10. Mar 26, 2008 #9
    Indeed apologies to Brian Greene, an inspired description.
  11. Mar 26, 2008 #10
    Entropy is another word for confusion--- but with a quantitative slant.

    So in fact you do already understand it; you could say that your state of mind when you are confused is one with high entropy! Entropy is an abstract descriptive term invented by physicists long ago to measure how confused simple systems can get. It is an abstract concept rather than a "thing", such as a dog or a star. When applied to the state of a gas, entropy is simple to define. When applied to the Universe it turns out that there are problems.
  12. Apr 7, 2008 #11
    Entropy ~ number of ways in which a system can arrange itself.

    (Actually it's just related to this quantity... entropy = k*log(ways) ...)

    Picture a "way" as a particular arrangement of positions and momenta for all the gas particles in a box of gas.

    Gas confined to half a box ~ fewer ways.
    Gas expanding to fill the whole box ~ more ways.

    Therefore: 2nd law says gas expands. Whoosh.
  13. Apr 7, 2008 #12


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    The trouble is, that's an ambiguous and rather vague definition. Suggesting it is synonymous with 'confused' is unhelpful.
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