Is this another Maxwell's demon?

In summary: A thought experiment that asks a question about a possible mechanism for a Maxwell demon.In summary, the experiment suggests that it is possible to create a Maxwell demon using only non-moving parts. This is done by using a Tesla valve to create a diode-like effect.
  • #1
pkv
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A though experiment:

We have two gas chambers at the same temperature and pressure, separated by a wall punctuated by very small pores. Let's say small enough to allow the pass of only a few gas molecules at a time (so, no complex interactions between gas molecules inside the pore).

These pores are designed to allow molecules passing from one chamber to the other easy, and hard or very hard in reverse.

This design (for the pore) comes to mind:

Non-imaging optics CEC
Nonimaging.png


Another one could be a version of a Tesla valve, although I am not so sure of it's validity for single molecules.

valve.png
The question is: would pressure/temperature in both chambers remain stable, or would the gas slowly migrate to the "easy pass" chamber, raising it's pressure?
If the second option happens, the systems seems to me akin to the Maxwell demon, as it violates the second law.
Such a system would allow to extract mechanical energy from the gases without a cold reservoir, until it's kinetic energy is exhausted, so I guess it's impossible.

Where is the catch?
 
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  • #2
All that matters is the size of the hole between chambers. Any baffling you put in the chambers is irrelevant.
 
  • #3
Yep, that was correct.
I simulated a gas and different connections between chambers and eventually the gas density always equilibrates...
I used this program as base, and added code for vector walls.

https://www.falstad.com/gas/
Simple passage
passage.png


Using a CEC
cec.png


Using a Tesla valve
tesla.png


...didn't see any noticeable difference in any scenario.

An interesting thing I noticed (for any configuration, like the simple passage), for low quantities of particles (<100) you can't get temporal density irregularities, sometimes quite high (like 20 particles in one side, 30 in the other).

That makes me think you can define a different type of Maxwell demon, one which only needs to count how many particles pass in each direction in the passage, and close it just once whenever the densities are different enough.

That would cause different densities in both chambers, but not necessarily different temperatures I guess. In that case, it wouldn't violate 2n law, right?
 
  • #4
pkv said:
Using a Tesla valve
The name "Tesla" seems to grab my attention whenever I see it and it so often is associated with apparent 'Magic'. That valve is only an extension (surely) of the same effect that allows an aerodynamically shaped car body to move forward at a given speed than it can move backwards (with the same mpg). Fluid flow is not perfectly reversible so that 'party trick' valve is not particularly remarkable.
Am I over-sensitive to that guy or did he really promise much more than has been actually achieved in his name?
 
  • #5
I was trying to answer the question about if it's possible to build a Maxwell demon only using non-moving parts. A kind of diode device that allows particles to pass on on direction but not in the other, without having any information about such particles (unlike Maxwell's demon).

The only check valve I know using only non-moving parts is the Tesla valve (which is being used in microfluidics). I don't think it's magic, but I was obviously misunderstanding its working principles.

I guess a Tesla valve acts as a diode only with a coherent and dense stream of particles.
 
  • #6
A bit off topic but ...

sophiecentaur said:
Am I over-sensitive to that guy or did he really promise much more than has been actually achieved in his name?

Yes and no. Tesla was a true genius, and a prolific inventor. The 3 phase induction motor, the Tesla turbine, and the Tesla Valve are examples of his contributions. He had more than 300 patents

https://en.wikipedia.org/wiki/List_of_Nikola_Tesla_patents
But later in life he became erratic, kooky or worse. His infamously bad idea was wireless power transmission. That made him a cult hero and a scientist's devil forevermore.

Both descriptions of the man are true making him a true enigma.
 
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  • #7
anorlunda said:
He had more than 300 patents
There's nothing about a patent to say a device is of any use or that it will actually work.
anorlunda said:
a prolific inventor.
. . . and successful self-publicist, I think.
anorlunda said:
erratic, kooky or worse
He obviously filled a need at that time. I guess that one can't judge him in isolation. But there is a serious lack of numerical evidence to support his ideas. His fans tend to ignore this and they 'all' quote his Wireless Power Transmission idea as if it actually worked. I wonder how he would have fared if he were alive these days.
anorlunda said:
a true enigma.
Hmm. That term can be interpreted in an over appreciated way. But I guess he was relatively harmless and not many were killed as a result of his efforts.
 
  • #8
pkv said:
That makes me think you can define a different type of Maxwell demon, one which only needs to count how many particles pass in each direction in the passage, and close it just once whenever the densities are different enough.

In order to count molecules, the demon must be able to see them. He is in a container in equilibrium at constant temperature, where the radiation must be that of a blackbody. As it is impossible to see anything in the interior of a black body (the demon has the same temperature), he needs photons with energy above the thermal background to locate the molecules. Gaining information by this way is thermodynamically costly, so that the second law of thermodynamics cannot be violated on the whole as has been proved by L. Brillouin.

L. Brillouin in “Maxwell's Demon Cannot Operate: Information and Entropy. I” (Journal of Applied Physics 22, 334 (1951)):

In an enclosure at constant temperature, the radiation is that of a ``blackbody,'' and the demon cannot see the molecules. Hence, he cannot operate the trap door and is unable to violate the second principle. If we introduce a source of light, the demon can see the molecules, but the over‐all balance of entropy is positive.
 
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  • #9
A quantum version of Maxwell's demon has recently been realized, and the famous information theoretical work by Landauer and Szilard has been confirmed (the entropy of a qubit is ##k_{\text{B}} \ln 2##:

https://www.pnas.org/content/114/29/7561
 
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Related to Is this another Maxwell's demon?

1. What is Maxwell's demon?

Maxwell's demon is a thought experiment proposed by physicist James Clerk Maxwell in 1867. It involves a hypothetical creature that can sort and separate molecules based on their energy levels, seemingly violating the second law of thermodynamics.

2. How does Maxwell's demon relate to the second law of thermodynamics?

The second law of thermodynamics states that the total entropy (disorder) of a closed system will always increase over time. Maxwell's demon appears to violate this law by creating order and decreasing entropy within the system.

3. Is Maxwell's demon a real creature?

No, Maxwell's demon is a thought experiment and does not exist in reality. It is used to illustrate and explore the concepts of thermodynamics and entropy.

4. Are there any real-world applications of Maxwell's demon?

While Maxwell's demon itself is not real, the principles behind it have been applied in various technologies, such as information storage and computing. These applications rely on the manipulation of energy levels and the separation of particles, similar to what Maxwell's demon does in the thought experiment.

5. Does the existence of Maxwell's demon disprove the second law of thermodynamics?

No, the existence of Maxwell's demon does not disprove the second law of thermodynamics. While it may seem to violate the law, it is a thought experiment that does not take into account all of the factors and limitations of a real system. The second law of thermodynamics has been extensively tested and has been shown to hold true in all observed cases.

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