4 ms·

I don't really have the necessary background in physics so maybe that's it but this article just doesn't seem to get the point across very well. > Two advances

I don't really have the necessary background in physics so maybe that's it but this article just doesn't seem to get the point across very well. > Two advances would be crucial to solving Maxwell’s demon. At this point in the article there had been a description of what Maxwell's demon is as: "Imagine that this nonexistent thing does X and has this outcome", however it's utterly unclear what the question is that needs to be solved. Whether such a system can exist? Whether two rooms with more order would violate some law and why? No idea. Can't I have two insulated rooms if some magical creature teleported certain particles magically from one room to the next? I saw other comments about the pointlessness of the thought experiment, but that's not my gripe. But there must be an explanation of why it really matters and what is to be "solved" here when the word "solve" is used. I have the same problem with other thought experiments or rather their dumbed down description, e.g. Schrödinger's cat. They focus too much on the quirky scenario and superficial outcome ("oh, that would mean ...") but not on what specific questions it raised in the end and what the exact follow-ups were. And most importantly they leave out very crucial details. For instance, I think one important piece to Maxwell's demon (from Wikipedia) is that the demon doesn't do "work".

zackees 5y ago
Maxwell’s demon lives on today as two sheets of graphene and two diodes. The vibrating sheets (due to virtual particles) causes oscillating electrical currents which are captured by the diodes and stored as charge. https://www.studyfinds.org/graphene-power-circuit-clean-energy/ https://www.studyfinds.org/graphene-power-circuit-clean-ener... The article mentions that Physics is safe. Yet this simple experiment shows that maxwell’s demon disproves the law of increasing entropy.
aidenn0 5y ago
The resolution of Maxwell's demon would involve proving that there is no way to implement such a device in an energy-positive manner. People generally suspect this is the case, but nobody can say why it must be the case.
- Nursie 5y ago
  Thanks for that concise explanation. My immediate thought was "the demon will be doing work to open and close its door, so the overall entropy is likely to be rising, only local order is increased" I guess the problem is around establishing that that has to be true, for any given demon.
  - scatters 5y ago
    The work to open and close the door can be reduced to an arbitrarily small level, so that doesn't resolve the paradox. The solution is that the demon has to collect and then destroy the information relating to its decision whether to open or close the door. It is the cost of destroying this information that balances out the entropy decrease in the system.
    - Nursie 5y ago
      Yeah we've just gone past my level of understanding :) I should probably learn about the information theory aspects here, they seem quite ... derived.
      - jfengel 5y ago
        Another way to put it: the decision to open the door requires some minimum unit of energy. That energy is itself at maximum entropy: there's no way to regain it for useful work. The total effect of this is that you can't beat entropy in the long term. That's often expressed in terms of deleting the information, which really does amount to the same thing viewed through a different lens. Looked at that way, the demon would be regaining the (organized) energy it would need to make the next decision. That requires energy input. I find the "deletion" view kinda confusing, but it does work. It's all a matter of where you want to set your zero points.
      - crdrost 5y ago
        That's okay, speaking as a physicist the connections between entropy and information are not at all obvious at first glance and you have to “get used to them.” For example, Maxwell's demon makes more sense if you phrase the second law as “there is no physical process which can move heat long-term from a colder temperature to a hotter temperature, without some extra input of energy.” So this says that refrigerators can work, but they only work by consuming power. There is no “spontaneous” flow the other way. Given that statement of the second law, you can very well imagine Maxwell saying, “well if a tiny fluctuation can transfer heat from cold to hot temperature, why can't I just look at these fluctuations and filter out the ones that I don’t want, and then I have a long-term process?” And it is not obvious that every mechanism for filtering is going to require energy input. Feynman gave a better example: a ratchet. A ratchet allows motion one way but not the other. Connect it to a wall between two gases, now the statistical fluctuations where the cold side happens to be pushing more on the wall can move the wall one way, and then the hot side cannot move it back because of the ratchet. You kind of have to peek inside the ratchet and see these springs and bits of metal interlocking, to see how the problem is resolved. The “entropy of erasure” argument is huge because it gives a very different language for all of this, one where these ratchets and filters are viewed as information processors like computers, and run into fundamental bounds on information processing which require the input of energy. So yes, it is several steps of derivation on (the above definition of the 2nd law doesn't even mention entropy!) and is more abstract, which is necessary to be more universal. But if you're not trying to be universal, you can see the ratchet with its asymmetrical cog and the pawl and the spring holding them together, and I just tell you that at nonzero temperature the spring & pawl must be randomly jittery and you can start to realize, “oh, ratchets can only work if they are refrigerated to get that energy out of the spring, once the random jitter is about the size of the cog’s notches, fuggedaboutit!”... Entropy of erasure says basically that this is going to be a universal problem.
dumpsterdiver 5y ago
> however it's utterly unclear what the question is that needs to be solved What Maxwell’s gate appears to imagine is a perpetual motion machine, which if possible would obviously be very important for our survival as a species. Remember, once the universe suffers heat death, obviously we’ll be gone too. As we reach nearer and nearer to the heat death of the universe it will become more important to utilize heat energy efficiently. The original term “demon” was intended as “daemon”, a tireless godlike worker, and not a malicious demon, but I find it more clear to instead envision a membrane (hence my use of the term “gate” instead of demon, which I think is a poor name for the thought experiment because it’s distracting) that allows heat to travel in only one direction, essentially providing free air conditioning by not allowing that heat energy to dissipate into thermal equilibrium. This may seem like a silly and minor thing (free air conditioning, what’s the big deal, right?) - it’s a big deal because assuming that an alien race survives far enough into the future and are orbiting the last star in the universe, that heat will be the only thing letting them power their starship, and the air conditioning will be the only thing keeping them from being fried to a crisp.
- zackees 5y ago
  Today maxwell’s demon can be represented as a diode and the flying particles can be represented as two sheets of graphene. The oscillating electrical shield produced by brownion motion can be captured by the diodes and stored as charge in a battery. This has already been implemented and we show we can extract energy from it. Maxwell’s demon has not be “disproven”, it’s been proven.

zackees 5y ago

Maxwell’s demon lives on today as two sheets of graphene and two diodes. The vibrating sheets (due to virtual particles) causes oscillating electrical currents which are captured by the diodes and stored as charge. https://www.studyfinds.org/graphene-power-circuit-clean-energy/ https://www.studyfinds.org/graphene-power-circuit-clean-ener... The article mentions that Physics is safe. Yet this simple experiment shows that maxwell’s demon disproves the law of increasing entropy.

aidenn0 5y ago

The resolution of Maxwell's demon would involve proving that there is no way to implement such a device in an energy-positive manner. People generally suspect this is the case, but nobody can say why it must be the case.

Nursie 5y ago
Thanks for that concise explanation. My immediate thought was "the demon will be doing work to open and close its door, so the overall entropy is likely to be rising, only local order is increased" I guess the problem is around establishing that that has to be true, for any given demon.
- scatters 5y ago
  The work to open and close the door can be reduced to an arbitrarily small level, so that doesn't resolve the paradox. The solution is that the demon has to collect and then destroy the information relating to its decision whether to open or close the door. It is the cost of destroying this information that balances out the entropy decrease in the system.
  - Nursie 5y ago
    Yeah we've just gone past my level of understanding :) I should probably learn about the information theory aspects here, they seem quite ... derived.
    - jfengel 5y ago
      Another way to put it: the decision to open the door requires some minimum unit of energy. That energy is itself at maximum entropy: there's no way to regain it for useful work. The total effect of this is that you can't beat entropy in the long term. That's often expressed in terms of deleting the information, which really does amount to the same thing viewed through a different lens. Looked at that way, the demon would be regaining the (organized) energy it would need to make the next decision. That requires energy input. I find the "deletion" view kinda confusing, but it does work. It's all a matter of where you want to set your zero points.
    - crdrost 5y ago
      That's okay, speaking as a physicist the connections between entropy and information are not at all obvious at first glance and you have to “get used to them.” For example, Maxwell's demon makes more sense if you phrase the second law as “there is no physical process which can move heat long-term from a colder temperature to a hotter temperature, without some extra input of energy.” So this says that refrigerators can work, but they only work by consuming power. There is no “spontaneous” flow the other way. Given that statement of the second law, you can very well imagine Maxwell saying, “well if a tiny fluctuation can transfer heat from cold to hot temperature, why can't I just look at these fluctuations and filter out the ones that I don’t want, and then I have a long-term process?” And it is not obvious that every mechanism for filtering is going to require energy input. Feynman gave a better example: a ratchet. A ratchet allows motion one way but not the other. Connect it to a wall between two gases, now the statistical fluctuations where the cold side happens to be pushing more on the wall can move the wall one way, and then the hot side cannot move it back because of the ratchet. You kind of have to peek inside the ratchet and see these springs and bits of metal interlocking, to see how the problem is resolved. The “entropy of erasure” argument is huge because it gives a very different language for all of this, one where these ratchets and filters are viewed as information processors like computers, and run into fundamental bounds on information processing which require the input of energy. So yes, it is several steps of derivation on (the above definition of the 2nd law doesn't even mention entropy!) and is more abstract, which is necessary to be more universal. But if you're not trying to be universal, you can see the ratchet with its asymmetrical cog and the pawl and the spring holding them together, and I just tell you that at nonzero temperature the spring & pawl must be randomly jittery and you can start to realize, “oh, ratchets can only work if they are refrigerated to get that energy out of the spring, once the random jitter is about the size of the cog’s notches, fuggedaboutit!”... Entropy of erasure says basically that this is going to be a universal problem.

dumpsterdiver 5y ago

> however it's utterly unclear what the question is that needs to be solved What Maxwell’s gate appears to imagine is a perpetual motion machine, which if possible would obviously be very important for our survival as a species. Remember, once the universe suffers heat death, obviously we’ll be gone too. As we reach nearer and nearer to the heat death of the universe it will become more important to utilize heat energy efficiently. The original term “demon” was intended as “daemon”, a tireless godlike worker, and not a malicious demon, but I find it more clear to instead envision a membrane (hence my use of the term “gate” instead of demon, which I think is a poor name for the thought experiment because it’s distracting) that allows heat to travel in only one direction, essentially providing free air conditioning by not allowing that heat energy to dissipate into thermal equilibrium. This may seem like a silly and minor thing (free air conditioning, what’s the big deal, right?) - it’s a big deal because assuming that an alien race survives far enough into the future and are orbiting the last star in the universe, that heat will be the only thing letting them power their starship, and the air conditioning will be the only thing keeping them from being fried to a crisp.

zackees 5y ago
Today maxwell’s demon can be represented as a diode and the flying particles can be represented as two sheets of graphene. The oscillating electrical shield produced by brownion motion can be captured by the diodes and stored as charge in a battery. This has already been implemented and we show we can extract energy from it. Maxwell’s demon has not be “disproven”, it’s been proven.