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No this is completely and utterly wrong. Entropy is not a function of knowledge. Two people with varying and different levels of knowledge of a system does not

No this is completely and utterly wrong. Entropy is not a function of knowledge. Two people with varying and different levels of knowledge of a system does not mean the system has two different entropy values. Even if I knew the exact position of all atoms in a cup of water, the temperature of that water does not change due to that knowledge. Entropy does rely on what your picked configuration of macro states and microstates. Temperature is an arbitrary choice of macrostate.

jbay808 4y ago
> Even if I knew the exact position of all atoms in a cup of water, the temperature of that water does not change due to that knowledge. It actually does! You would disagree with the other person about the temperature of that water. But I agree that this is admittedly not obvious at first.
- deltaonefour 4y ago
  No it does not. The thermometer does not change based off of my knowledge or opinion.
  - jbay808 4y ago
    A thermometer doesn't measure temperature any better than a meterstick measures length. And we all know what Einstein had to say about the relativity of metersticks. To paraphrase from the paper I linked in another reply to you, a thermometer is just a heat bath equipped with a pointer which reads its average energy, whose scale is calibrated to give the temperature T, defined by 1/T = dS/d<E>. You can read the thermometer if you like, but if you know the exact microstate of the water to begin with, the thermometer reading will tell you much less than you already knew about the water. And precise knowledge of the water's microstate will (theoretically) allow you to extract much more work from that water than you would be able to with only the thermometer reading.
    - deltaonefour 4y ago
      But entropy does not change with this knowledge.
      - jbay808 4y ago
        You seem pretty convinced. Let me see if you're talking about the same pedantic distinction that oh_my_goodness was. A: "an urn containing either a white ball or a black ball". B: "I notice that the ball in the urn A is white". I would say that initially the entropy of our ball-urn system is 1 bit, and that with observation B, we have reduced the entropy of our ball-urn system to 0 bits. But if you are going to take the view that even knowing the ball in this particular urn is actually white doesn't change the fact that the entropy of <<"an urn containing either a white ball or a black ball">> is 1 bit and not 0, and that that's the entropy that we're discussing, then I won't argue about it any further. Except for the obligatory xkcd: https://xkcd.com/221/ https://xkcd.com/221/
        deltaonefour 4y ago
        No I'm not saying that. The entropy of the system was always 0 bits. Knowledge is irrelevant. If the urn actually contained nothing and would materialize a black or a white ball randomly then this can occur with or without your knowledge. When the ball materializes and nothing more can be done THEN the entropy has changed. Because there's no more possible microstates. You not having knowledge about microstates DOES NOT change available microstates. You seem to think that if you don't know about something, anything goes. You're really arguing abstract philosophy. Did a tree in the forest fall if no one was around to see it? Yes it did dude. Your knowledge of it has nothing to do with whether it fell. Same with entropy. And if you deny the fact that a tree in the forest never fell, then you're the one going off onto a pedantic tangent.
        deleted 4y ago
        [deleted]
        kgwgk 4y ago
kgwgk 4y ago
> Even if I knew the exact position of all atoms in a cup of water, the temperature of that water does not change due to that knowledge. If you knew the exact position of all atoms in a cup of water you wouldn't assign any temperature to it. Not a thermodynamic temperature at least.
- deltaonefour 4y ago
  The number of microstates does not change, even if you KNOW the the cup of water is in a specific microstate. The boltzman equation is based on total accessible microstates.
  - kgwgk 4y ago
    "accessible" means something only given a set of constraints. Like the temperature, if you keep the temperature of the water fixed. And the number of molecules if instead of a cup you have a close container to prevent it from evaporating. Then what you have is water at some temperature that you control. And you could have the water at a different temperature with exactly the same microstate. Or imagine gas at some fixed temperature within a cylinder with one movable wall. If you knew the location of every molecule of the gas it wouldn't make sense to talk about its pressure - you could compress it (reducing the number of accessible microstates) without doing any work. Edit: In summary, thermodynamics loses its meaning if you know the microstate and can act on that knowledge.
    - deltaonefour 4y ago
      >it wouldn't make sense to talk about its pressure - If I have a pressure gauge that reads the same thing regardless of my knowledge how is pressure meaningless? The tool that reads pressure gives me an accurate pressure number regardless of what I know or don't know. This number is correct. Your argument is basically saying that the pressure gauge becomes wrong once you have more knowledge of the system. No it doesn't. The pressure gauge is still giving you a number defined as "pressure." The gas in that cylinder is at a specific microstate within the macrostate defined as pressure.

jbay808 4y ago

> Even if I knew the exact position of all atoms in a cup of water, the temperature of that water does not change due to that knowledge. It actually does! You would disagree with the other person about the temperature of that water. But I agree that this is admittedly not obvious at first.

deltaonefour 4y ago
No it does not. The thermometer does not change based off of my knowledge or opinion.
- jbay808 4y ago
  A thermometer doesn't measure temperature any better than a meterstick measures length. And we all know what Einstein had to say about the relativity of metersticks. To paraphrase from the paper I linked in another reply to you, a thermometer is just a heat bath equipped with a pointer which reads its average energy, whose scale is calibrated to give the temperature T, defined by 1/T = dS/d<E>. You can read the thermometer if you like, but if you know the exact microstate of the water to begin with, the thermometer reading will tell you much less than you already knew about the water. And precise knowledge of the water's microstate will (theoretically) allow you to extract much more work from that water than you would be able to with only the thermometer reading.
  - deltaonefour 4y ago
    But entropy does not change with this knowledge.
    - jbay808 4y ago
      You seem pretty convinced. Let me see if you're talking about the same pedantic distinction that oh_my_goodness was. A: "an urn containing either a white ball or a black ball". B: "I notice that the ball in the urn A is white". I would say that initially the entropy of our ball-urn system is 1 bit, and that with observation B, we have reduced the entropy of our ball-urn system to 0 bits. But if you are going to take the view that even knowing the ball in this particular urn is actually white doesn't change the fact that the entropy of <<"an urn containing either a white ball or a black ball">> is 1 bit and not 0, and that that's the entropy that we're discussing, then I won't argue about it any further. Except for the obligatory xkcd: https://xkcd.com/221/ https://xkcd.com/221/
      - deltaonefour 4y ago
        No I'm not saying that. The entropy of the system was always 0 bits. Knowledge is irrelevant. If the urn actually contained nothing and would materialize a black or a white ball randomly then this can occur with or without your knowledge. When the ball materializes and nothing more can be done THEN the entropy has changed. Because there's no more possible microstates. You not having knowledge about microstates DOES NOT change available microstates. You seem to think that if you don't know about something, anything goes. You're really arguing abstract philosophy. Did a tree in the forest fall if no one was around to see it? Yes it did dude. Your knowledge of it has nothing to do with whether it fell. Same with entropy. And if you deny the fact that a tree in the forest never fell, then you're the one going off onto a pedantic tangent.
        deleted 4y ago
        [deleted]
        kgwgk 4y ago

kgwgk 4y ago

> Even if I knew the exact position of all atoms in a cup of water, the temperature of that water does not change due to that knowledge. If you knew the exact position of all atoms in a cup of water you wouldn't assign any temperature to it. Not a thermodynamic temperature at least.

deltaonefour 4y ago
The number of microstates does not change, even if you KNOW the the cup of water is in a specific microstate. The boltzman equation is based on total accessible microstates.
- kgwgk 4y ago
  "accessible" means something only given a set of constraints. Like the temperature, if you keep the temperature of the water fixed. And the number of molecules if instead of a cup you have a close container to prevent it from evaporating. Then what you have is water at some temperature that you control. And you could have the water at a different temperature with exactly the same microstate. Or imagine gas at some fixed temperature within a cylinder with one movable wall. If you knew the location of every molecule of the gas it wouldn't make sense to talk about its pressure - you could compress it (reducing the number of accessible microstates) without doing any work. Edit: In summary, thermodynamics loses its meaning if you know the microstate and can act on that knowledge.
  - deltaonefour 4y ago
    >it wouldn't make sense to talk about its pressure - If I have a pressure gauge that reads the same thing regardless of my knowledge how is pressure meaningless? The tool that reads pressure gives me an accurate pressure number regardless of what I know or don't know. This number is correct. Your argument is basically saying that the pressure gauge becomes wrong once you have more knowledge of the system. No it doesn't. The pressure gauge is still giving you a number defined as "pressure." The gas in that cylinder is at a specific microstate within the macrostate defined as pressure.