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I Non-reversibility of '2nd Law' processes

  1. Oct 18, 2016 #1


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    [Moderator's note: this thread is spun off from another thread in order to separate discussion on different topics. The quote below is from the original thread and is what is being responded to by kith. Kith's original post has been edited slightly for clarity.]

    Here's a hint: f you drop an egg from a certain height, where does its (gravitational) potential energy go?
    Last edited by a moderator: Oct 20, 2016
  2. jcsd
  3. Oct 19, 2016 #2
    A good, clarifying hint for me -- thanks! A lot of what I'm doing now is trying to clarify what my questions actually are, so I greatly appreciate the patience of wiser heads and any hints that come my way.

    As to the grav. pot. energy, some is dissipated as atmospheric heat, some warms the floor a bit, some goes to break material bonds of shell and disrupt whatever accounts for the viscosity of the contents (adhesion?), some goes to splatter bits of egg everywhere, and so on.

    But (as it turns out) I was thinking more about structure or organization than about energy as such. The statistical or probabilistic interpretation of the 2nd law works for gases and thermal states, but I have seen people extend a probability-based interpretation of the 2nd to things like broken eggs and spilled wine, as if this sort of 'entropy-increasing' event is only statistically, not absolutely irreversible --i.e. that a self-reassembling egg is not impossible, only really^100^100^100... unlikely, as if, IF we could watch enough eggs, we'd eventually see one put itself back together again. Does any physicist really think that? Given not only the dissipation of energy but also the loss of structure, the breaking of molecule-to-molecule bonds of whatever types are involved in shell membrane and contents, and the dirt and mites, etc., now mixed with the egg, the probability of a kind of spontaneous reassembling of the egg (even given a source of energy) seems not just very^very low, but zero.

    Is that kind of irreversibility even a 2nd law issue? I guess I am used to seeing 'irreversibility'('time's arrow') explained in terms of the 2nd law -- not just heat flows and mixing of molecules in a fluid (Maxwell's Demon etc.) but also in terms of the improbability of highly organized systems and structures. (Here's an example from a random science blog: "For everyday (macroscopic) situations, the probability that the second law will be violated is practically zero." -- does not distinguish thermal issues from structural ones)

    Is there some other principle than 2nd law also at work to make the egg smash non-reversible? I know there's a difference between (improbable) a gas mixture resorting itself, and (never happen) a mountain uneroding, but I'm not sure what besides 2nd law effects is making for irreversibility. Or maybe the probability-statistical interp. of 2nd law is off the mark? Guess I need to take those to a gen. phys or other forum :D.

    And yeah, not QM - but half of my original question is about non-reversibility and entropy anyway, and probably belongs over in 2nd law or thermal systems or something anyway... Thanks again !!
    Last edited: Oct 19, 2016
  4. Oct 20, 2016 #3


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    As you noted, the "loss of structure" has to do with molecular bonds being broken. What about new molecular bonds being formed? If you suspect a probability of zero, you should be able to give an argument why new molecular bonds can't be formed.

    [Moderator's note: suggestion about moving thread removed since that has been done.]
    Last edited by a moderator: Oct 20, 2016
  5. Oct 20, 2016 #4
    @kith, Try Googling Poincare Recurrance Time.
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