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SLOT second law of thermodynamics

  1. Jun 15, 2011 #1
    I don't get how this ever came to be a law, since it seems so obviously false. Entropy in a closed system can only increase. If I close the doors in my room (so that it's a closed system) and spend one hour cleaning, then I have obviously decreased the entropy. It seems so obvious to me that SLOT should read: entropy in a closed system will only increase if there is no intelligent agent in the closed system. I can't figure out why that clause: "unless there is an intelligent agent in the closed system" was never added on to the law.
     
  2. jcsd
  3. Jun 15, 2011 #2
    So you think you are "[URL [Broken] demon[/URL]?

    You eat supper, which was supplied energy ultimately by the sun. You cleaned the room which you then need another room in the house to go dump the entropic waste you created. At least that part that you did not breath out, which would eventually suffocate you if you stayed in an enclosed room long enough.

    Being intelligent only allows you to trade more entropy over there for less over here, but the entropy created always exceeds the entropy removed. That is what life is, a way for nature to increase the efficiency of entropy in a system with an external energy source to keep the systems energy unbalanced, i.e., the sun.
     
    Last edited by a moderator: May 5, 2017
  4. Jun 15, 2011 #3
    I can clean up a room without creating any waste. I can just put things where they are supposed to be. In any case, it seems like the definition of entropy is highly subjective, if so, it has no place in science, and should not in any way be called a law.
     
  5. Jun 15, 2011 #4

    Drakkith

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    Look up what a scientific law is.

    This is incorrect. It is not a closed system. And even if it was a closed system the answer by My Wan explained it correctly.

    The waste he refers to is from your metabolism, not from your room.
     
  6. Jun 15, 2011 #5

    Dale

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    Not unless you can stop breathing and stop all of your cellular metabolism.

    After cleaning you are probably hungry and thirsty, and since the room is sealed it is starting to feel stuffy so you want to open the window. All of that is due entropy increasing. The room's entropy may have decreased a little, but your body's entropy increased a lot.
     
  7. Jun 15, 2011 #6
    Then why must you eat? You basically just claimed you can clean up a room without using any energy to do so.

    This not only makes you a Maxwell's demon but is also a claim that you are a perpetual motion machine. Not so.
     
  8. Jun 15, 2011 #7
    The only thing subjective about is is a lack of knowledge of where the energy comes from and where it goes. Only not everybody lacks such information about the energy sources and drains, making it not so subjective as you indicated. We can count this energy flow down to minute quantities and tell you how exactly how much food and what kinds that room cleaning cost.
     
  9. Jun 16, 2011 #8
    Referring to the OP, the argument doesn't make sense. You can't just focus on the clean room and measure that entropy and call it good. That's like saying that an air conditioner decreases entropy because it removes the heat from a room and since the room is a "closed" system, the SLOT doesn't hold (plus, the air conditioner isn't intelligent).

    I think this link sums up this whole argument:
    http://xkcd.com/675/
     
  10. Jun 16, 2011 #9
    the entropy of the room decreased but what about your entropy . you are also the part of system dont u
     
  11. Jun 16, 2011 #10

    atyy

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    It's a very interesting question - how can Maxwell's demon be exorcised?

    Nowadays, I hear that Landauer's principle has done it in. Thermodynamics only applies to systems with very large numbers of particles. So a demon with a finite amount of memory must eventually erase some memory, in order to keep on cleaning his room. In erasing the memory, the demon will cause entropy to increase.

    Interestingly, "[URL [Broken][/URL] lists controversy about how far the principle can be generalized. These articles by http://arxiv.org/abs/quant-ph/0203017" [Broken] look like good reads.
     
    Last edited by a moderator: May 5, 2017
  12. Jun 16, 2011 #11
    Yes, I find the limits of the second law interesting myself. I keep seeing the distinction between the state of a system and knowledge of the state of a system conflated in complex ways, especially when entropy is involved but sometimes in other situations.

    Consider the limits imposed by the 3rd law alone. This implies a minimum entropy such that at some point entropy does not decrease in total, rather some subsystem increases entropy to the gain of another. Maximal entropy would then be defined as a state where the losses and gains have a Poisson distribution.

    In terms of computer registers suppose instead of running out of registers the particular register that is overwritten by a new piece of information becomes unpredictable, but correlated with the new piece of information. Throws a bit of a loop into J. Bub's acquisition cost in the linked paper, because acquisition and erasure become consonant. So if you start with a blank state it can gain information up to the point when information acquisition and erasure balance out. Then to gain information above that it must be acquired through obtaining it from lucky encounters with a second system of slightly lower entropy.

    So long as there is some minimal entropy under which the total entropy can be reduced no further, there is one class of algorithm that allows the entropy of subsystems to decrease fractally. But does not give any one system any special advantaged information to locally reduce its own entropy. In biology this is evolution. In physics it is defined in the large number hypothesis. Consider Big Bang nucleosynthesis which entails super hot conditions for rapid production. Yet, given an enormous enough period of time the same thing could in principle occur at lower average temperatures. Requiring only very localized highly unusual events to produce the hot events needed. I am not making an argument against the Big Bang but essentially it is the same process resulting in particle productions that indefinitely lock in low entropy subsystems once they occur.

    Except by shear weight of numbers the opportunities to further decrease entropy at the individual system level is no better than what is defined by the usual thermodynamic laws. But with enough subsystems and a minimum entropy there will be lottery winners so long as a finite band-gap, Planck > 0, exist for those lottery winning subsystems to hang onto their gains.

    When we talk about information and what energy we can reliably derive from a low entropy source this game with the large number hypothesis becomes worthless. Because we cannot wait on a confluence of conditions to gain once out of countless events. The failures eat our gains. So we, as individual systems, can only talk about the usefulness of entropy in terms of information we have about a system, and not the information contained in that system. Our physically laws is also geared around available information in such a way that the actual information contained in that system cannot even be ascribed an ontological reality. This can often make entropy look like a moving target whenever we switch from one method of coding information to another.

    That is how I conceptualize the situation anyway, where entropy is always perfectly valid in terms of defining what I, or any particular system, can obtain to decrease local entropy, while doing so increases the total efficiency of entropy production to bring the lottery winners back into thermal equilibrium. It grows in a similar manner as a food web in ecology. However, I have seen pet theories roughly based on this kind of thinking that was patently absurd. I see it as merely a product of the large number hypothesis, finite fundamental band-gaps (Planck) or limits on the total entropy, and increases in the efficiency of returning the system to equilibrium at all scales.
     
    Last edited by a moderator: May 5, 2017
  13. Jun 16, 2011 #12

    ZapperZ

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    Who are you again to decide such a thing?

    Your idea of the second law is VERY primitive! The second law is much more than just "disorder". It has a very deep statistical meaning in terms of phase space states that are available, a concept that you haven't fully grasp.

    Furthermore, in your example, as has been pointed out, the amount of energy you expanded CREATES a higher level of entropy!

    Before you try to falsify something, it is imperative that you truly learn what IT is. If not, you come off looking rather foolish.

    Zz.
     
  14. Jun 16, 2011 #13
    In general, I would like to say that to accept/reject existing theories is something that everybody has to do for themelves, and only after having studied it with a critical attitude. What you have written here comes across to me as denying that idea.

    I agreed with the rest of your post though.
     
  15. Jun 16, 2011 #14

    A little? A lot? It is clear that entropy cannot be measured so why is this even a physical law? Sure, it's true that my body's entropy increase and the room's entropy decreased but there is no way to measure these different quantities of entropy, so this is not science. This is just a general rule of thumb.
     
  16. Jun 16, 2011 #15

    If entropy is not subjective then come up with way to measure the entropy of 100 books lying in no order on the floor and a way to measure the entropy of 100 books ordered alphabetically on a shelf. Stated another way, you can't come up with an objective system to measure 10K airplane parts lying disorganized on a factory floor versus all those 10K airplane parts assembled into an airplane.

    SLOT has no meaning, because it uses a word, entropy, that cannot be defined.

    If I say

    All x = y

    And I cannot define when something is x and when something is not x, then I have discovered nothing.
     
  17. Jun 16, 2011 #16
    I can't tell who you refers to, so I won't comment.
     
  18. Jun 16, 2011 #17

    Drakkith

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    It refers to zapperz, like the quote in the post says.
     
  19. Jun 16, 2011 #18

    Dale

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    Of course it can be measured. If it couldn't be measured then we would have no way to determine if it were increasing or not.

    What would possibly make you think that it couldn't be measured? The rest of your post is just wrong due to this misunderstanding.
     
  20. Jun 17, 2011 #19
    Answering this would cost me too much entropy. So, since you cannot tell me whether you can pick up 'that' rock or not you must not be able to pick up rocks, or measure how heavy they are?
     
  21. Jun 17, 2011 #20

    ZapperZ

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    Who says you can't? In fact, I can show you estimates of the entropy of the EARTH!

    1. http://arxiv.org/abs/1003.3937
    2. D. Styer, Am. J. Phys. v.76, 1031 (2008).
    3. http://arxiv.org/abs/0903.4603

    Calculating the mess in your room is nothing when compared to these!

    Entropy is very well defined within statistical mechanics. Where did you get the idea that it isn't? What do you think

    dS = dQ/T

    is?

    Zz.
     
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