17 ms·

Argonne researchers posit way to locally circumvent Second Law of Thermodynamics

131 points by diggernet 10y ago

mabbo 10y ago
Someone smarter than me: why is this totally bullshit and will never work?
- jrpt 10y ago
  The second law of thermodynamics just follows from statistics and a large number of interacting particles. It's not actually inviolable as the article says. There are whole books written about far-from-equilibrium thermodynamics, and the fluctuation theorem quantifies the probability of entropy increasing https://en.wikipedia.org/wiki/Fluctuation_theorem https://en.wikipedia.org/wiki/Fluctuation_theorem
  - platz 10y ago
    Right, the second law simply is a result of selecting a result from a probability distribution that increases entropy, but drawing from tails of the distribution aren't impossible, only highly improbable.
- shoegumfoot 10y ago
  Haven't read the paper, but it sounds like they just rediscovered the microcannonical ensemble (but for quantum mechanics). Probably works, probably hard to do anything interesting with it in the near to medium term.
- deleted 10y ago
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- yk 10y ago
  Decreasing entropy locally is usually called a fridge, and I am currently betting my dinner that it is not bullshit. (I don't have the slightest idea what the article is actually talking about.)
digi_owl 10y ago
Could have sworn that one of the tricky things about that law was that while it may appear that you are decreasing entropy locally, you are just increasing it somewhere else, thus entropy still increased in aggregate.
- hammock 10y ago
  Why do you have to swear? We (lifeforms) are living, breathing examples of that concept.
  - btilly 10y ago
    Ironically someone downvoted you for this comment. I guess that they didn't understand how exactly true your statement is. In essence the entire biosphere is a giant heat engine, mainly fed off of the flow of energy from the Sun to Earth to outer space, and in some extreme environments fed by the radiation of heat out from the core of the Earth. Shut off those flows of energy, and the second law would shortly catch up to us and we'd all perish.
    - maxerickson 10y ago
      Shut off the flow of energy and the cold would catch up to us a long time before the second law of thermodynamics. (our frozen, desiccated corpses would probably retain their organization longer under such conditions)
      - hammock 10y ago
        Do nothing, and entropy still will catch up to us. Maybe. In the form of our environment collapsing, or the sun exploding, or something else. Even take a single human. Dust (to person) to dust. Ashes (to civilization) to ashes.
      - btilly 10y ago
        Becoming cold requires a flow of energy outwards. If you put a perfectly reflective energy shield above our atmosphere and about 2 miles down, we would not get cold. We would just wind up all dead at a uniform temperature.
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powera 10y ago
"The authors are planning to work closely with a team of experimentalists to design a proof-of-concept system, they said." - Pardon if I'm mistaken, but this seems like a fancy way of saying they have no evidence at all so far.
- lucideer 10y ago
  Like many theories... Peter Higgs et al had to wait ~50 years for evidence.
- Filligree 10y ago
  Quantum Mechanics is pretty damn solid. I expect they'll find their evidence, and figuring out that something is possible in QM is more than good enough reason to try it. If that turns out to be false then QM will have been disproven, which is even bigger news!
lucideer 10y ago
> "Although the violation is only on the local scale, the implications are far-reaching," Vinokur said. "This provides us a platform for the practical realization of a quantum Maxwell's demon, which could make possible a local quantum perpetual motion machine." > For example, he said, the principle could be designed into a "refrigerator" which could be cooled remotely — that is, the energy expended to cool it could take place anywhere. Perhaps there's another definition, but as far as I'm aware, a PPM has net negative/zero energy input from anywhere, be it local or remote. That said, apart from hyperbolic misapplication of terminology (not a PPM, no circumventing Second Law), this does sound like interesting research.
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azurelogic 10y ago
Countdown to a sci-fi movie where this idea is only half understood and the "proof of concept" device opens a portal to hell, where we meet the real Maxwell's demon... Now that I've typed this, I want to see it happen.
- pizza 10y ago
  Use a recurrent neural network to generate said script!
- theandrewbailey 10y ago
  If so, one can't get into or out of hell unless you're going this fast.
  - pbnjay 10y ago
    88mph of course...
- cableshaft 10y ago
  Wasn't that the plotline in the most recent Doom game?
  - eli_gottlieb 10y ago
    Several Doom games, and also Half-Life. Ripping a hole into Hell for travel purposes has been done in Doom, the movie Event Horizon, and the tabletop gaming franchise Warhammer 40K. Which goes to show what a terrible idea this all is ;-).
    - TeMPOraL 10y ago
      Also done in an excellent though unfinished series of books, The Salvation War[0]. Albeit travel was only a side effect of the real goal there. [0] - http://www.tboverse.us/HPCAFORUM/phpBB3/viewforum.php?f=29 http://www.tboverse.us/HPCAFORUM/phpBB3/viewforum.php?f=29 - full text of Armageddon and Pantheocide available there; the author decided to abandon the series because someone stole his work to destroy his ability to publish it.
api 10y ago
I recall having an idea at least a bit similar to this years ago when I was heavily studying evolutionary informatics. Some particularly avant garde types in that field have posited that the universe rather than having two constituents -- matter and energy -- has three primary first-order constituents. The third is information. Information is not merely an epiphenomena of matter and energy but a primary "thing." If that is the case then there should be an E=mc^2 type equation that relates matter to information and energy to information and all three should be interconvertible. It would then further follow that energy can be converted into information and vice versa in the same way that matter can. I then imagined a Dyson swarm of solar power satellites that produce a data stream encoding the energy they collect. This stream can be subscribed to and decoded to reconstitute this energy remotely. To globally conserve energy there would have to be a two-way aspect to this -- I imagined the receiver of energy transmitting "challenges" to the swarm that are then "solved" to yield energy stored in the form of the solution. The receiver then receives these solutions and executes them to generate what in effect would look like local perpetual motion. (But in reality energy is still being conserved.) It would look like a cryptographic hashcash-style challenge-response system with proof of work, but the energy input of the POW function can be reversibly extracted elsewhere. If such a thing were possible and sufficiently efficient and could function in the presence of high latency, this could power a starship among many other things. If it were latency-tolerant it might also be a way to store energy. Save your laptop's power to its hard drive. It reminds me a little bit of the "telematter stream" propulsion system from Peter Watts' Blindsight.
- eli_gottlieb 10y ago
  >Some particularly avant garde types in that field have posited that the universe rather than having two constituents -- matter and energy -- has three primary first-order constituents. The third is information. Information is not merely an epiphenomena of matter and energy but a primary "thing." Is that really so avant-garde? It seems a bit weird to claim that thermodynamics and the arrow of time are epiphenomena when we can measure the relevant quantities experimentally. The more avant-garde thing seems to be the kinds of papers where they claim space-time or gravity are somehow emergent from entropy/information. >If that is the case then there should be an E=mc^2 type equation that relates matter to information and energy to information and all three should be interconvertible. Uhh, why? Even the more exotic physics-of-information work seems to end up equating entropy with space-time or something like that: mass-energy would bend space-time-entropy, but wouldn't be convertible into it. Admittedly, this is all way above my head.
colanderman 10y ago
From the publication itself: > Note that in the discussed example the reservoir acts as some quantum analogue of the classical Maxwell demon. Namely, having been prepared in a special state, the reservoir is able to decrease the entropy of the system without the energy exchange with it, and can be referred to as a ‘quantum Maxwell demon’ […] In what was discussed above, an electron interaction with the quantum spin does not induce any correlations between the electron and the spin and, therefore, no classical correlations are present. Hence an important distinction between how do quantum and classical Maxwell’s demons operate. So, it sounds like the "refrigerator-at-a-distance" (and thus energy transmission, when combined with a heat engine) actually (1) is more of a battery, and (2) doesn't interact with classical systems. Is my reading correct?
- btilly 10y ago
  I don't think so. There is no energy transmission involved at all. I suspect that there is some entropy transmission, but I didn't see an analysis of that, and the amount is negligible compared to what is already in the quantum mechanical system. Of much greater surprise to me was the claim that an isolated quantum mechanical system neither gains nor loses entropy. I'm almost as astonished at this as I am at the fact that there are no chaotic quantum mechanical systems because quantum mechanical systems evolve linearly, while chaotic ones evolve exponentially. If the latter astonishes you, I recommend reading https://michaelberryphysics.files.wordpress.com/2013/07/berry337.pdf https://michaelberryphysics.files.wordpress.com/2013/07/berr....
  - pdonis 10y ago
    > Of much greater surprise to me was the claim that an isolated quantum mechanical system neither gains nor loses entropy. Why is this surprising? It's a simple consequence of unitarity.
    - btilly 10y ago
      It surprises me because the universe is an isolated quantum mechanical system that certainly appears to be gaining entropy.
ivan_gammel 10y ago
The best thing with local and short-term effects is that eventually someone finds the way to extend the space and time boundaries a bit, then a bit more and then we are talking about astronomical scale. Can be a nice story plot for a sci-fi book, in which science finds the way to defer the rise of enthropy to some almost infinitely distant moment in future (that end of time, we've always being expecting) and move the boundaries of locality to the observable universe. What a world that would be.
ThePhysicist 10y ago
The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consisting of two compartments that are separated by a wall, where one of the compartments contains N particles. The system has low entropy because all the particles are on one side of it. Now, if you remove the barrier between the two compartments, particles will distribute evenly on both sides, increasing the entropy of the system. If we assume that the position of the particles is random, the probability of finding all of them on one side of the system is (1/2)^N, which quickly converges to zero for most macroscopic systems, which often contain > 10^23 particles.
- beagle3 10y ago
  The second law of thermodynamics is as fundamental as the uncertainty principle: The former is a result from markov chains and information theory, the latter is a result from fourier analysis of conjugate variables. What would you consider a "fundamental physical law"?
  - greydius 10y ago
    Nature is under no obligation to comply with mathematical analysis.
    - Balgair 10y ago
      Especially as the subject is quantum physics and thermodynamics, this is a very interesting viewpoint. Though I agree with you in principle, many centuries of inquiry about our universe by some of the most intelligent humans to date seems to say that mathematical formulations and ideas are the best (if not only, as with QM) way to think about our universe. No other way has really been as incredibly useful in terms of prediction as a mathematical one. I think you do have a point, but I will continue to take the so-called Copenhagen Interpretation of QM: Shut Up and Calculate.
mrcactu5 10y ago
I don't see what the big deal is. Let's try the ideal gas. For starters temperature ∝ Kinetic energy We have two rooms. One were molecules all travel at speed A and other room molecules travel at speed B and we open a small window. Eventually, over a long period of time the temerature in both rooms will settle at a temperature between that of B and of A. Let's try to formule this mathematically. This is something like the mean value theorem in calculus that f'(C)(B-A) = f(B) - f(A) for some intermediate value C. And here are function f(C) is the equilibrium temperature. In statistical mechanics we imagine we could count the number of particles -- 10^23 or 10^25 -- something very large. And some fraction M travel at speed A and N-M of them travel at speed B. And we count the probabilities of various mixtures occurring. Feynman Lectures on Computation is a great book https://www.amazon.com/Feynman-Lectures-Computation-Richard-P/dp/0738202967 https://www.amazon.com/Feynman-Lectures-Computation-Richard-...
keithlfrost 10y ago
arxiv preprint of original paper here: https://arxiv.org/abs/1407.4437 https://arxiv.org/abs/1407.4437
IBCNU 10y ago
Is not the 2nd Law of Thermodynamics always circumvented on Earth? We absorb more energy in the form of light from the sun than we emit.
- snowwrestler 10y ago
  We're currently absorbing very slightly more energy that we emit. We call it global warming. Other than that, output balances input. The atmosphere is a heat reservoir, but just like a water reservoir behind a dam, that doesn't mean it's ever-rising. Energy flows in one side and out the other, but between the two there is room for life.
- btilly 10y ago
  The second law is not violated because the Earth is not a closed system. Also to a very good approximation, we emit what we absorb. When averaged over a long period, that approximation gets better. (It has been somewhat worse over the last century though.)
timnic 10y ago
There is a free PDF on the nature site, but the paper is also available on arxiv (https://arxiv.org/abs/1407.4437 https://arxiv.org/abs/1407.4437), the first version on the arxiv dates back to 2014. It's strange, but I find the arxiv version much more readable in terms of typesetting than the polished version in nature. Also there are additional appendices in the arxiv version.
GregBuchholz 10y ago
This article seems a little light on details, and the original paper (not behind a paywall!) is quite dense, but some of my favorite paper's on Maxwell's demon are: http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.pdf http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.... http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.pdf http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.... ...and to ease into things, an article by one of the authors: "The Simplest Exorcism of Maxwell's Demon -- No Information Needed" https://web.archive.org/web/20140309110028/http://www.pitt.edu/~jdnorton/Goodies/exorcism_phase_vol/exorcism_phase_vol.html https://web.archive.org/web/20140309110028/http://www.pitt.e...
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highfestiva 10y ago
I just knew it! Soon it won't be that local after all. ;)
maxwellion 10y ago
> if a small theoretical being sat at the door between the hot and cold rooms and only let through particles traveling at a certain speed. This theoretical imp is called "Maxwell's demon." Maxwell's demon is considered a slight of hand because it requires energy to perform its task. But if a passive energy-free equivalent can be found with a novel quantum substrate then any liquid could be separated into hot and cold pools. I am highly sceptical of such a claim. The difference in temperature between these hypothetical pools would likely be too small to create any useful energy. See also: https://en.wikipedia.org/wiki/Exergy https://en.wikipedia.org/wiki/Exergy https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator
mirekrusin 10y ago
I wonder if we're going to read titles like "Global warming solved? We're going to send heat to Mars?".
crpatino 10y ago
You lost me at "locally". Of course if you take a closed system A and make it a subsistem of some bigger closed system B you are going to be able to diminish entropy at A by increasing entropy even further at (B + !A). My grandmother's freezer was doing this 50 years ago, and I am pretty sure the engineers who designed it did not think their work was fundamental research in any way or form.
ihaveahadron 10y ago
There aren't any laws of physics dumasses. They are laws at and before the time of DISCOVERY. Then new shit gets discovered and those laws don't apply any more. People are just STUUUUUUUUUPID.
gandolfinmyhead 10y ago
Maxwell's demon is probably laughing his head off.
pjdorrell 10y ago
By "locally" I think they mean something like "entropy will decrease within what looks like a closed system, and it might not be immediately obvious where else in the universe the corresponding increase in entropy is occurring". So not actually "free energy", but perhaps it could be used to stage a convincing demo to potential investors.
lubesGordi 10y ago
So this article does the Maxwell Demon some injustice. There is a key point about the demon that when he is 'sorting' the particles into two bulbs or rooms, that the gate he is working on is frictionless. In this way, you can can see that there is no energy entering the system, yet the entropy is decreasing. Now, this is where things get interesting to me (please correct me if I'm wrong here). What the demon is adding is information to the system. It decreases entropy. Natural selection is a sort of maxwell demon in it's selection process. I have a theory though that it all evens out. The more complex/evolved the organism, the more entropy the organisms generate themselves.
- trentlott 10y ago
  I think that was Schrodinger's argument in "What is Life": nature seeks to maximise entropy, and life does a very good job of it.
  - eli_gottlieb 10y ago
    That theory has gotten a bit more elaborated these days: http://rsif.royalsocietypublishing.org/content/10/86/20130475 http://rsif.royalsocietypublishing.org/content/10/86/2013047...
- swiley 10y ago
  I thought the idea with Maxwell's daemon was that detecting the particles heated it up which made the particle detector less accurate.
- taneq 10y ago
  > There is a key point about the demon that when he is 'sorting' the particles into two bulbs or rooms, that the gate he is working on is frictionless. Exactly. Maxwell's Demon is a magical construct. In reality, any active device that sorts molecules into high and low energy bins would take power to run, and would generate more heat (or other entropy) than it removed by doing the sorting.
  - lubesGordi 10y ago
jbmorgado 10y ago
This doesn't actually violate the law. This just goes on to prove it. The reduce the entropy locally but in the process of doing so, increase it globally. It strictly follows the 2nd law of thermodynamics.
al2o3cr 10y ago
A quick read of the paper shows it's mostly focused on systems with discrete levels; IIRC there's already plenty of thermodynamic weirdness in those, like "negative temperature" states in the Ising model and so forth. They touch on a continuous system in the final section, but that also includes a system with a finite upper bound to its energy (phonons). Wonder if that's related to the potential for 2nd Law violations.
maverick_iceman 10y ago
Original article[1]. [1] http://www.nature.com/articles/srep32815 http://www.nature.com/articles/srep32815
effie 10y ago
It seems as though the authors are confusing Boltzmann's H-theorem and its cousins expressed in more complicated formalisms with the Second law of thermodynamics. That's a very common misconception, often resulting in announces of apparently great discoveries, while the sober account would be more akin to "we derived a theorem where this special expression, similar to Boltzmann's H-function, does not behave as one would expect based on the H-theorem, which in turn is proven to be valid only for a simplified model of ideal gas in special condition." Not so interesting. Second law is an experimental law that concerns macroscopic systems. So far, this law was not shown to be violated based on any broadly accepted theory.

131 points by diggernet 10y ago

mabbo 10y ago

Someone smarter than me: why is this totally bullshit and will never work?

jrpt 10y ago
The second law of thermodynamics just follows from statistics and a large number of interacting particles. It's not actually inviolable as the article says. There are whole books written about far-from-equilibrium thermodynamics, and the fluctuation theorem quantifies the probability of entropy increasing https://en.wikipedia.org/wiki/Fluctuation_theorem https://en.wikipedia.org/wiki/Fluctuation_theorem
- platz 10y ago
  Right, the second law simply is a result of selecting a result from a probability distribution that increases entropy, but drawing from tails of the distribution aren't impossible, only highly improbable.
shoegumfoot 10y ago
Haven't read the paper, but it sounds like they just rediscovered the microcannonical ensemble (but for quantum mechanics). Probably works, probably hard to do anything interesting with it in the near to medium term.
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yk 10y ago
Decreasing entropy locally is usually called a fridge, and I am currently betting my dinner that it is not bullshit. (I don't have the slightest idea what the article is actually talking about.)

digi_owl 10y ago

Could have sworn that one of the tricky things about that law was that while it may appear that you are decreasing entropy locally, you are just increasing it somewhere else, thus entropy still increased in aggregate.

hammock 10y ago
Why do you have to swear? We (lifeforms) are living, breathing examples of that concept.
- btilly 10y ago
  Ironically someone downvoted you for this comment. I guess that they didn't understand how exactly true your statement is. In essence the entire biosphere is a giant heat engine, mainly fed off of the flow of energy from the Sun to Earth to outer space, and in some extreme environments fed by the radiation of heat out from the core of the Earth. Shut off those flows of energy, and the second law would shortly catch up to us and we'd all perish.
  - maxerickson 10y ago
    Shut off the flow of energy and the cold would catch up to us a long time before the second law of thermodynamics. (our frozen, desiccated corpses would probably retain their organization longer under such conditions)
    - hammock 10y ago
      Do nothing, and entropy still will catch up to us. Maybe. In the form of our environment collapsing, or the sun exploding, or something else. Even take a single human. Dust (to person) to dust. Ashes (to civilization) to ashes.
    - btilly 10y ago
      Becoming cold requires a flow of energy outwards. If you put a perfectly reflective energy shield above our atmosphere and about 2 miles down, we would not get cold. We would just wind up all dead at a uniform temperature.

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powera 10y ago

"The authors are planning to work closely with a team of experimentalists to design a proof-of-concept system, they said." - Pardon if I'm mistaken, but this seems like a fancy way of saying they have no evidence at all so far.

lucideer 10y ago
Like many theories... Peter Higgs et al had to wait ~50 years for evidence.
Filligree 10y ago
Quantum Mechanics is pretty damn solid. I expect they'll find their evidence, and figuring out that something is possible in QM is more than good enough reason to try it. If that turns out to be false then QM will have been disproven, which is even bigger news!

lucideer 10y ago

> "Although the violation is only on the local scale, the implications are far-reaching," Vinokur said. "This provides us a platform for the practical realization of a quantum Maxwell's demon, which could make possible a local quantum perpetual motion machine." > For example, he said, the principle could be designed into a "refrigerator" which could be cooled remotely — that is, the energy expended to cool it could take place anywhere. Perhaps there's another definition, but as far as I'm aware, a PPM has net negative/zero energy input from anywhere, be it local or remote. That said, apart from hyperbolic misapplication of terminology (not a PPM, no circumventing Second Law), this does sound like interesting research.

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azurelogic 10y ago

Countdown to a sci-fi movie where this idea is only half understood and the "proof of concept" device opens a portal to hell, where we meet the real Maxwell's demon... Now that I've typed this, I want to see it happen.

pizza 10y ago
Use a recurrent neural network to generate said script!
theandrewbailey 10y ago
If so, one can't get into or out of hell unless you're going this fast.
- pbnjay 10y ago
  88mph of course...
cableshaft 10y ago
Wasn't that the plotline in the most recent Doom game?
- eli_gottlieb 10y ago
  Several Doom games, and also Half-Life. Ripping a hole into Hell for travel purposes has been done in Doom, the movie Event Horizon, and the tabletop gaming franchise Warhammer 40K. Which goes to show what a terrible idea this all is ;-).
  - TeMPOraL 10y ago
    Also done in an excellent though unfinished series of books, The Salvation War[0]. Albeit travel was only a side effect of the real goal there. [0] - http://www.tboverse.us/HPCAFORUM/phpBB3/viewforum.php?f=29 http://www.tboverse.us/HPCAFORUM/phpBB3/viewforum.php?f=29 - full text of Armageddon and Pantheocide available there; the author decided to abandon the series because someone stole his work to destroy his ability to publish it.

api 10y ago

I recall having an idea at least a bit similar to this years ago when I was heavily studying evolutionary informatics. Some particularly avant garde types in that field have posited that the universe rather than having two constituents -- matter and energy -- has three primary first-order constituents. The third is information. Information is not merely an epiphenomena of matter and energy but a primary "thing." If that is the case then there should be an E=mc^2 type equation that relates matter to information and energy to information and all three should be interconvertible. It would then further follow that energy can be converted into information and vice versa in the same way that matter can. I then imagined a Dyson swarm of solar power satellites that produce a data stream encoding the energy they collect. This stream can be subscribed to and decoded to reconstitute this energy remotely. To globally conserve energy there would have to be a two-way aspect to this -- I imagined the receiver of energy transmitting "challenges" to the swarm that are then "solved" to yield energy stored in the form of the solution. The receiver then receives these solutions and executes them to generate what in effect would look like local perpetual motion. (But in reality energy is still being conserved.) It would look like a cryptographic hashcash-style challenge-response system with proof of work, but the energy input of the POW function can be reversibly extracted elsewhere. If such a thing were possible and sufficiently efficient and could function in the presence of high latency, this could power a starship among many other things. If it were latency-tolerant it might also be a way to store energy. Save your laptop's power to its hard drive. It reminds me a little bit of the "telematter stream" propulsion system from Peter Watts' Blindsight.

eli_gottlieb 10y ago
>Some particularly avant garde types in that field have posited that the universe rather than having two constituents -- matter and energy -- has three primary first-order constituents. The third is information. Information is not merely an epiphenomena of matter and energy but a primary "thing." Is that really so avant-garde? It seems a bit weird to claim that thermodynamics and the arrow of time are epiphenomena when we can measure the relevant quantities experimentally. The more avant-garde thing seems to be the kinds of papers where they claim space-time or gravity are somehow emergent from entropy/information. >If that is the case then there should be an E=mc^2 type equation that relates matter to information and energy to information and all three should be interconvertible. Uhh, why? Even the more exotic physics-of-information work seems to end up equating entropy with space-time or something like that: mass-energy would bend space-time-entropy, but wouldn't be convertible into it. Admittedly, this is all way above my head.

colanderman 10y ago

From the publication itself: > Note that in the discussed example the reservoir acts as some quantum analogue of the classical Maxwell demon. Namely, having been prepared in a special state, the reservoir is able to decrease the entropy of the system without the energy exchange with it, and can be referred to as a ‘quantum Maxwell demon’ […] In what was discussed above, an electron interaction with the quantum spin does not induce any correlations between the electron and the spin and, therefore, no classical correlations are present. Hence an important distinction between how do quantum and classical Maxwell’s demons operate. So, it sounds like the "refrigerator-at-a-distance" (and thus energy transmission, when combined with a heat engine) actually (1) is more of a battery, and (2) doesn't interact with classical systems. Is my reading correct?

btilly 10y ago
I don't think so. There is no energy transmission involved at all. I suspect that there is some entropy transmission, but I didn't see an analysis of that, and the amount is negligible compared to what is already in the quantum mechanical system. Of much greater surprise to me was the claim that an isolated quantum mechanical system neither gains nor loses entropy. I'm almost as astonished at this as I am at the fact that there are no chaotic quantum mechanical systems because quantum mechanical systems evolve linearly, while chaotic ones evolve exponentially. If the latter astonishes you, I recommend reading https://michaelberryphysics.files.wordpress.com/2013/07/berry337.pdf https://michaelberryphysics.files.wordpress.com/2013/07/berr....
- pdonis 10y ago
  > Of much greater surprise to me was the claim that an isolated quantum mechanical system neither gains nor loses entropy. Why is this surprising? It's a simple consequence of unitarity.
  - btilly 10y ago
    It surprises me because the universe is an isolated quantum mechanical system that certainly appears to be gaining entropy.

ivan_gammel 10y ago

The best thing with local and short-term effects is that eventually someone finds the way to extend the space and time boundaries a bit, then a bit more and then we are talking about astronomical scale. Can be a nice story plot for a sci-fi book, in which science finds the way to defer the rise of enthropy to some almost infinitely distant moment in future (that end of time, we've always being expecting) and move the boundaries of locality to the observable universe. What a world that would be.

ThePhysicist 10y ago

The second law of thermodynamics isn't really a fundamental physical law, but rather a promise based on statistics that says "disorder will increase or stay constant in a closed physical system". That said, it's entirely possible for entropy to spontaneously decrease in a closed system, the probability of this happening is just astronomically small for typical macroscopic systems. Example: If you have a system consisting of two compartments that are separated by a wall, where one of the compartments contains N particles. The system has low entropy because all the particles are on one side of it. Now, if you remove the barrier between the two compartments, particles will distribute evenly on both sides, increasing the entropy of the system. If we assume that the position of the particles is random, the probability of finding all of them on one side of the system is (1/2)^N, which quickly converges to zero for most macroscopic systems, which often contain > 10^23 particles.

beagle3 10y ago
The second law of thermodynamics is as fundamental as the uncertainty principle: The former is a result from markov chains and information theory, the latter is a result from fourier analysis of conjugate variables. What would you consider a "fundamental physical law"?
- greydius 10y ago
  Nature is under no obligation to comply with mathematical analysis.
  - Balgair 10y ago
    Especially as the subject is quantum physics and thermodynamics, this is a very interesting viewpoint. Though I agree with you in principle, many centuries of inquiry about our universe by some of the most intelligent humans to date seems to say that mathematical formulations and ideas are the best (if not only, as with QM) way to think about our universe. No other way has really been as incredibly useful in terms of prediction as a mathematical one. I think you do have a point, but I will continue to take the so-called Copenhagen Interpretation of QM: Shut Up and Calculate.

mrcactu5 10y ago

I don't see what the big deal is. Let's try the ideal gas. For starters temperature ∝ Kinetic energy We have two rooms. One were molecules all travel at speed A and other room molecules travel at speed B and we open a small window. Eventually, over a long period of time the temerature in both rooms will settle at a temperature between that of B and of A. Let's try to formule this mathematically. This is something like the mean value theorem in calculus that f'(C)(B-A) = f(B) - f(A) for some intermediate value C. And here are function f(C) is the equilibrium temperature. In statistical mechanics we imagine we could count the number of particles -- 10^23 or 10^25 -- something very large. And some fraction M travel at speed A and N-M of them travel at speed B. And we count the probabilities of various mixtures occurring. Feynman Lectures on Computation is a great book https://www.amazon.com/Feynman-Lectures-Computation-Richard-P/dp/0738202967 https://www.amazon.com/Feynman-Lectures-Computation-Richard-...

keithlfrost 10y ago

arxiv preprint of original paper here: https://arxiv.org/abs/1407.4437 https://arxiv.org/abs/1407.4437

IBCNU 10y ago

Is not the 2nd Law of Thermodynamics always circumvented on Earth? We absorb more energy in the form of light from the sun than we emit.

snowwrestler 10y ago
We're currently absorbing very slightly more energy that we emit. We call it global warming. Other than that, output balances input. The atmosphere is a heat reservoir, but just like a water reservoir behind a dam, that doesn't mean it's ever-rising. Energy flows in one side and out the other, but between the two there is room for life.
btilly 10y ago
The second law is not violated because the Earth is not a closed system. Also to a very good approximation, we emit what we absorb. When averaged over a long period, that approximation gets better. (It has been somewhat worse over the last century though.)

timnic 10y ago

There is a free PDF on the nature site, but the paper is also available on arxiv (https://arxiv.org/abs/1407.4437 https://arxiv.org/abs/1407.4437), the first version on the arxiv dates back to 2014. It's strange, but I find the arxiv version much more readable in terms of typesetting than the polished version in nature. Also there are additional appendices in the arxiv version.

GregBuchholz 10y ago

This article seems a little light on details, and the original paper (not behind a paywall!) is quite dense, but some of my favorite paper's on Maxwell's demon are: http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.pdf http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist1.... http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.pdf http://www2.pitt.edu/~jdnorton/papers/ExorcistXIV/Exorcist2.... ...and to ease into things, an article by one of the authors: "The Simplest Exorcism of Maxwell's Demon -- No Information Needed" https://web.archive.org/web/20140309110028/http://www.pitt.edu/~jdnorton/Goodies/exorcism_phase_vol/exorcism_phase_vol.html https://web.archive.org/web/20140309110028/http://www.pitt.e...

deleted 10y ago

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highfestiva 10y ago

I just knew it! Soon it won't be that local after all. ;)

maxwellion 10y ago

> if a small theoretical being sat at the door between the hot and cold rooms and only let through particles traveling at a certain speed. This theoretical imp is called "Maxwell's demon." Maxwell's demon is considered a slight of hand because it requires energy to perform its task. But if a passive energy-free equivalent can be found with a novel quantum substrate then any liquid could be separated into hot and cold pools. I am highly sceptical of such a claim. The difference in temperature between these hypothetical pools would likely be too small to create any useful energy. See also: https://en.wikipedia.org/wiki/Exergy https://en.wikipedia.org/wiki/Exergy https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator

mirekrusin 10y ago

I wonder if we're going to read titles like "Global warming solved? We're going to send heat to Mars?".

crpatino 10y ago

You lost me at "locally". Of course if you take a closed system A and make it a subsistem of some bigger closed system B you are going to be able to diminish entropy at A by increasing entropy even further at (B + !A). My grandmother's freezer was doing this 50 years ago, and I am pretty sure the engineers who designed it did not think their work was fundamental research in any way or form.

ihaveahadron 10y ago

There aren't any laws of physics dumasses. They are laws at and before the time of DISCOVERY. Then new shit gets discovered and those laws don't apply any more. People are just STUUUUUUUUUPID.

gandolfinmyhead 10y ago

Maxwell's demon is probably laughing his head off.

pjdorrell 10y ago

By "locally" I think they mean something like "entropy will decrease within what looks like a closed system, and it might not be immediately obvious where else in the universe the corresponding increase in entropy is occurring". So not actually "free energy", but perhaps it could be used to stage a convincing demo to potential investors.

lubesGordi 10y ago

So this article does the Maxwell Demon some injustice. There is a key point about the demon that when he is 'sorting' the particles into two bulbs or rooms, that the gate he is working on is frictionless. In this way, you can can see that there is no energy entering the system, yet the entropy is decreasing. Now, this is where things get interesting to me (please correct me if I'm wrong here). What the demon is adding is information to the system. It decreases entropy. Natural selection is a sort of maxwell demon in it's selection process. I have a theory though that it all evens out. The more complex/evolved the organism, the more entropy the organisms generate themselves.

trentlott 10y ago
I think that was Schrodinger's argument in "What is Life": nature seeks to maximise entropy, and life does a very good job of it.
- eli_gottlieb 10y ago
  That theory has gotten a bit more elaborated these days: http://rsif.royalsocietypublishing.org/content/10/86/20130475 http://rsif.royalsocietypublishing.org/content/10/86/2013047...
swiley 10y ago
I thought the idea with Maxwell's daemon was that detecting the particles heated it up which made the particle detector less accurate.
taneq 10y ago
> There is a key point about the demon that when he is 'sorting' the particles into two bulbs or rooms, that the gate he is working on is frictionless. Exactly. Maxwell's Demon is a magical construct. In reality, any active device that sorts molecules into high and low energy bins would take power to run, and would generate more heat (or other entropy) than it removed by doing the sorting.
- lubesGordi 10y ago

jbmorgado 10y ago

This doesn't actually violate the law. This just goes on to prove it. The reduce the entropy locally but in the process of doing so, increase it globally. It strictly follows the 2nd law of thermodynamics.

al2o3cr 10y ago

A quick read of the paper shows it's mostly focused on systems with discrete levels; IIRC there's already plenty of thermodynamic weirdness in those, like "negative temperature" states in the Ising model and so forth. They touch on a continuous system in the final section, but that also includes a system with a finite upper bound to its energy (phonons). Wonder if that's related to the potential for 2nd Law violations.

maverick_iceman 10y ago

Original article[1]. [1] http://www.nature.com/articles/srep32815 http://www.nature.com/articles/srep32815

effie 10y ago

It seems as though the authors are confusing Boltzmann's H-theorem and its cousins expressed in more complicated formalisms with the Second law of thermodynamics. That's a very common misconception, often resulting in announces of apparently great discoveries, while the sober account would be more akin to "we derived a theorem where this special expression, similar to Boltzmann's H-function, does not behave as one would expect based on the H-theorem, which in turn is proven to be valid only for a simplified model of ideal gas in special condition." Not so interesting. Second law is an experimental law that concerns macroscopic systems. So far, this law was not shown to be violated based on any broadly accepted theory.