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> As physicists have worked to unite seemingly disparate fields over the past century, they have cast entropy in a new light — turning the microscope back on th

by kqr 2y ago

> As physicists have worked to unite seemingly disparate fields over the past century, they have cast entropy in a new light — turning the microscope back on the seer and shifting the notion of disorder to one of ignorance. Entropy is seen not as a property intrinsic to a system but as one that’s relative to an observer who interacts with that system. Maybe I have the benefit of giant shoulders, but this seems like a fairly mundane observation. High-entropy states are those macrostates which have many corresponding microstates. The classification of several microstates into the same macrostate, is this not a distinctly observer-centred function? I.e. if I consider 5 or 6 to be essentially the same outcome of the die, then that will be a more probable (higher-entropy) outcome. But that's just due to my classification, not inherent to the system!

niemandhier 2y ago
In physics the requirement for a valid changing the frame of reference is, that the laws of physics transform according to the transformation. Every observer should discover the same fundamental laws when performing experiments and using the scientific method. To stay in your analogy, saying 5 and 6 are the same would only work if the rules of the game you play could transform in such a way that an observer making a distinction between the two would arrive at the correctly transformed rules in his frame of reference. Given that we have things like neutron stars, black holes and other objects that are at the same time objects of quantum physics and general relativity, the statement feels pretty fundamental to me, to a degree even that I wonder if it might be phrased to strongly.
- bubblyworld 2y ago
  I think you may have misunderstood the OP's point - the entropy you calculate for a system depends on how you factor the system into micro and macro states. This doesn't really have anything to do with changes of reference frame - in practice it's more about limitations on the kinds of measurements you can make of the system. (you can't measure the individual states of all the particles in a body of gas, for instance, so you factor it into macrostate variables like pressure/temperature/volume and such)
  - lizzas 2y ago
    Can we take the anthropic out of this? I reckon it'll make things easier. Instead of me knowing, do other physical objects get affected. I might get anemsia and forget what the dots on a dice mean and say they are all the same: all dotty! Imagine each hydrogen atom has a hidden guid but this is undetectable and has no effect on anything else. This is a secret from the rest of physics! I guess!!! (Armchair pondering!) that that guid cannot be taken into account for entropy changes. At least from any practical standpoint. You could imagine each atom having a guid and come up with a scheme to hash the atom based on where it came from ... but is that info really there and if so does it affect anything physically beyond that atoms current state (as defined by stuff that affects other stuff).
    - bubblyworld 2y ago
      What anthropic do you mean? I'm describing properties of models, not people. Physics (probably) doesn't care what you "know". On the guid idea - fundamental particles are indistinguishable from one another in quantum mechanics, so they don't have anything like a guid even in principle. There is no experiment you could perform on an electron to determine whether it had been swapped out for a "different" one, for instance. Maybe I'm missing your point though?
      - lizzas 2y ago
        Sorry ... I am replying mostly to the dice idea which wasn't you. Yes correct about the guid idea. My point is the discussion is easier to follow if grounded in reality (as best modelled since that is all we have plus some evidence stored in the same "SSD"!)
        bubblyworld 2y ago
        Oh I see. But on your guid thing, people often describe entropy in terms of the set of micro states of your system (the actually physical states in your model) and the macro states (sets of microstates that are described by a collection of high-level state variables like pressure/temperature). Physically indistinguishable stuff would have the same micro state, so yeah, they wouldn't affect entropy calculations at all, no matter what macro states you picked. But I disagree a bit about grounding things in reality - some concepts are quite abstract and having clean examples can be helpful, before you start applying them to the mess that is our universe!
guerrilla 2y ago
> mundane observation What makes an observation mundane? I think what you said is insightful and demonstrates intelligence. I don't think it's at all obvious to the masses of students that have poured over introductory physics textbooks. In fact, it seems to me that often entropy is taught poorly and that very few people understood it well but that we are beginning to correct that. I point to the heaps of popsci magazines, documentaries and YouTube videos failing to do anything but confuse the public as additional evidence.
- LudwigNagasena 2y ago
  Maybe if you opened only introductory physics textbooks then it’s not mundane; but If you opened introductory information theory textbooks, statistical textbooks, introductions to Bayesian probability theory, articles about MaxEnt thermodynamics including articles by E.T. Jaynes, then it’s a quite mundane observation.
  - guerrilla 2y ago
    So, what you're saying is, not very mundane at all and, in fact, that it's specialized knowledge requiring advanced education. ;)
  - deleted 2y ago
    [deleted]
  - mitthrowaway2 2y ago
    Jaynes definitely made the case for this a long time ago, and in my opinion he's correct, but I think that view is still not mainstream; or even if mainstream, certainly not dominant. So I think we should welcome other people who reach it on their own journey, even if they aren't the first to arrive there.
kergonath 2y ago
> Maybe I have the benefit of giant shoulders, but this seems like a fairly mundane observation. It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. > High-entropy states are those macrostates which have many corresponding microstates. That is how you deduce entropy form a given model. But entropy is also something that we can get from experimental measurements. In this case, the experimental setup does not care about microstates and macrostates, it just has properties like enthalpy, heat capacity and temperature. We can build models after the fact and say that e.g. the entropy of a given gas matches that predicted by our model for ideal gases, or that the entropy of a given solid matches what we know about vibrational entropy. That’s how we say that e.g. hydrogen atoms are indistinguishable. It’s not that they become indistinguishable because we decide so. It’s because we can calculate entropy in both cases and reality does not match the model with distinguishable atoms. > The classification of several microstates into the same macrostate, is this not a distinctly observer-centred function? It seems that way if we consider only our neat models, but it fails to explain why experimental measurements of the entropy of a given materials are consistent and independent of whatever model the people doing the experiment were operating on. Fundamentally, entropy depends on the probability distribution, not the observer.
- LudwigNagasena 2y ago
  > It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. Articles about MaxEnt thermodynamics by E.T. Jaynes where he talks about the “anthropomorphic” nature of entropy date back to 1960s. How is that not right in physics?
  - kergonath 2y ago
    By the look of it, it is another misguided attempt to apply information theory concepts to thermodynamics. Entropy as information is seductive because that way we think we can understand it better, and it looks like it works. But we need to be careful because even though we can get useful insights from it (like Hawking radiation) it’s easy to reach unphysical conclusions. > How is that not right in physics? Why would it be right? Was it used to make predictions that were subsequently verified?

by kqr 2y ago

niemandhier 2y ago

In physics the requirement for a valid changing the frame of reference is, that the laws of physics transform according to the transformation. Every observer should discover the same fundamental laws when performing experiments and using the scientific method. To stay in your analogy, saying 5 and 6 are the same would only work if the rules of the game you play could transform in such a way that an observer making a distinction between the two would arrive at the correctly transformed rules in his frame of reference. Given that we have things like neutron stars, black holes and other objects that are at the same time objects of quantum physics and general relativity, the statement feels pretty fundamental to me, to a degree even that I wonder if it might be phrased to strongly.

bubblyworld 2y ago
I think you may have misunderstood the OP's point - the entropy you calculate for a system depends on how you factor the system into micro and macro states. This doesn't really have anything to do with changes of reference frame - in practice it's more about limitations on the kinds of measurements you can make of the system. (you can't measure the individual states of all the particles in a body of gas, for instance, so you factor it into macrostate variables like pressure/temperature/volume and such)
- lizzas 2y ago
  Can we take the anthropic out of this? I reckon it'll make things easier. Instead of me knowing, do other physical objects get affected. I might get anemsia and forget what the dots on a dice mean and say they are all the same: all dotty! Imagine each hydrogen atom has a hidden guid but this is undetectable and has no effect on anything else. This is a secret from the rest of physics! I guess!!! (Armchair pondering!) that that guid cannot be taken into account for entropy changes. At least from any practical standpoint. You could imagine each atom having a guid and come up with a scheme to hash the atom based on where it came from ... but is that info really there and if so does it affect anything physically beyond that atoms current state (as defined by stuff that affects other stuff).
  - bubblyworld 2y ago
    What anthropic do you mean? I'm describing properties of models, not people. Physics (probably) doesn't care what you "know". On the guid idea - fundamental particles are indistinguishable from one another in quantum mechanics, so they don't have anything like a guid even in principle. There is no experiment you could perform on an electron to determine whether it had been swapped out for a "different" one, for instance. Maybe I'm missing your point though?
    - lizzas 2y ago
      Sorry ... I am replying mostly to the dice idea which wasn't you. Yes correct about the guid idea. My point is the discussion is easier to follow if grounded in reality (as best modelled since that is all we have plus some evidence stored in the same "SSD"!)
      - bubblyworld 2y ago
        Oh I see. But on your guid thing, people often describe entropy in terms of the set of micro states of your system (the actually physical states in your model) and the macro states (sets of microstates that are described by a collection of high-level state variables like pressure/temperature). Physically indistinguishable stuff would have the same micro state, so yeah, they wouldn't affect entropy calculations at all, no matter what macro states you picked. But I disagree a bit about grounding things in reality - some concepts are quite abstract and having clean examples can be helpful, before you start applying them to the mess that is our universe!

guerrilla 2y ago

> mundane observation What makes an observation mundane? I think what you said is insightful and demonstrates intelligence. I don't think it's at all obvious to the masses of students that have poured over introductory physics textbooks. In fact, it seems to me that often entropy is taught poorly and that very few people understood it well but that we are beginning to correct that. I point to the heaps of popsci magazines, documentaries and YouTube videos failing to do anything but confuse the public as additional evidence.

LudwigNagasena 2y ago
Maybe if you opened only introductory physics textbooks then it’s not mundane; but If you opened introductory information theory textbooks, statistical textbooks, introductions to Bayesian probability theory, articles about MaxEnt thermodynamics including articles by E.T. Jaynes, then it’s a quite mundane observation.
- guerrilla 2y ago
  So, what you're saying is, not very mundane at all and, in fact, that it's specialized knowledge requiring advanced education. ;)
- deleted 2y ago
  [deleted]
- mitthrowaway2 2y ago
  Jaynes definitely made the case for this a long time ago, and in my opinion he's correct, but I think that view is still not mainstream; or even if mainstream, certainly not dominant. So I think we should welcome other people who reach it on their own journey, even if they aren't the first to arrive there.

kergonath 2y ago

> Maybe I have the benefit of giant shoulders, but this seems like a fairly mundane observation. It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. > High-entropy states are those macrostates which have many corresponding microstates. That is how you deduce entropy form a given model. But entropy is also something that we can get from experimental measurements. In this case, the experimental setup does not care about microstates and macrostates, it just has properties like enthalpy, heat capacity and temperature. We can build models after the fact and say that e.g. the entropy of a given gas matches that predicted by our model for ideal gases, or that the entropy of a given solid matches what we know about vibrational entropy. That’s how we say that e.g. hydrogen atoms are indistinguishable. It’s not that they become indistinguishable because we decide so. It’s because we can calculate entropy in both cases and reality does not match the model with distinguishable atoms. > The classification of several microstates into the same macrostate, is this not a distinctly observer-centred function? It seems that way if we consider only our neat models, but it fails to explain why experimental measurements of the entropy of a given materials are consistent and independent of whatever model the people doing the experiment were operating on. Fundamentally, entropy depends on the probability distribution, not the observer.

LudwigNagasena 2y ago
> It is not mundane, and it is also not right, at least for entropy in Physics and Thermodynamics. Articles about MaxEnt thermodynamics by E.T. Jaynes where he talks about the “anthropomorphic” nature of entropy date back to 1960s. How is that not right in physics?
- kergonath 2y ago
  By the look of it, it is another misguided attempt to apply information theory concepts to thermodynamics. Entropy as information is seductive because that way we think we can understand it better, and it looks like it works. But we need to be careful because even though we can get useful insights from it (like Hawking radiation) it’s easy to reach unphysical conclusions. > How is that not right in physics? Why would it be right? Was it used to make predictions that were subsequently verified?