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Imagine a container, with balls of diameter 1x and 10x, moving randomly in all directions. These balls are mixed, so it is a low order system.

Now this container is connected to another container via a slightly modified Tesla valve which has the passage of width 8x. So this passage allows only the balls of diameter 1x and filters the 10x balls. The image below is a section of the Tesla valve, many such can be connected in series to increase the efficiency.

enter image description here

In the allowed direction, the probability of a ball making it through the valve is high. But the probability of a ball travelling in opposite direction is very small, as it has to take the correct path all the time, and even if it takes a single wrong path, it will end up moving in the opposite direction.

Now after a period of time one container has mostly 10x balls and another container has only 1x balls. It is as if though they are sorted automatically, hence a higher order system came out of a lower order system.

Does this work? Is second law of thermodynamics not work in this scenario? What's happening here?

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  • $\begingroup$ A vending machine sorts the coins by size/denomination automatically and passively. It does not violate any law. Also, your thermodynamical system still has particles moving randomly and your energy is conserved. You only separated the constitutional elements. You don't even need to go to such lengths to describe things that already exists: for example an osmotic barrier which lets water through, but no heavier ions. $\endgroup$
    – José Andrade
    Commented Dec 29, 2022 at 15:03
  • $\begingroup$ @JoséAndrade well in that case, what's the big fuss about Maxwell's demon? $\endgroup$
    – INAR
    Commented Dec 29, 2022 at 16:01
  • $\begingroup$ well, Maxwell demon is not about other physical properties. Its about how energy is distributed in a sense. In your experiment you will still have thermal equilibrium over your whole system. Why is the entropy lower if you would connect the two boxes? At first you have a single box with a mix of balls. Afterwards you apply a filter (image a coffee filter that filters particles but not water) and now on the other box you have only the smaller balls. Why is the entropy of the whole system lower? $\endgroup$
    – José Andrade
    Commented Dec 29, 2022 at 17:32

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Maxwell's demon highlights the importance of information and ignorance in thermodynamics. By "information" I mean the type of knowledge that is accessible to the observer and by "ignorance" the type of knowledge that remains inaccessible. In the statistical mechanical view of a molecular system the information available to us is macroscopic: the volume of the container, the number of molecules it contains and its energy. On the other hand we are ignorant regarding all microscopic details: where each molecule is and how fast it is moving. Maxwell's demon demonstrates the implications of the fact that some information is unavailable to us: if we could gain access to it we would be able to do things that we otherwise can't.

To get back to the original question, sorting that is based on macroscopic properties (i.e., on knowledge that is accessible to the sorter) is possible and violates no laws (I sort my socks after laundry each time). What is impossible is to sort things based on properties that we cannot observe. When we put it this way there is nothing controversial about Maxwell's demon.

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What you really need is a massive set of TINY tesla valves. That way, the random motions of the particles in the fluid (heat) get converted directly into flow. This because the tiny waves of particles that result from ambient heat in the backwards direction get scattered, but not in the forwards direction. I imagine that the fluid coming out would have to be cold because heat powered the motion, but that's the whole idea anyhow, get the energy into a more usable, organized state.

I also imagine that this isn't possible for some other reason, but I'm not qualified enough to know what it is off the top of my head.

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