Maxwell's demon and the second law of thermodynamics

[Endy0816]

Here's a link to the paper, doesn't sound like it violates the second law though.

 

 

Erasing the memory of Maxwell’s demon in this way implies that work can be extracted from a single thermal reservoir at a cost of angular momentum and an increase in total entropy.

http://rspa.royalsocietypublishing.org/content/467/2130/1770

[Moreno]

Here's a link to the paper, doesn't sound like it violates the second law though.

 

http://rspa.royalsocietypublishing.org/content/467/2130/1770

 

So, basically he proposes to harness energy of electron's angular momentum? Could you explain it?

Edited February 23, 2017 by Moreno

[Moreno]

Let to do a curious thought experiment. Modern physics do not set a theoretical limit on how small elementary particles can be with exception of Planck length (1.6 x 10^-35 m). 

What if there can be a small elementary particles (as small to protons as protons to tennis balls) and these extremely small elementary particles are capable to form matter indistinguishable in physical and chemical properties from the common matter known to us. And there exist a tiny conscious creatures made of these tiny elementary particles and each such creature is the size of a common molecule.

If these tiny creatures would got in our World somehow, would they be able to gain use of thermal fluctuation in our world associated with Brownian motion an harness energy of fluctuations for some useful purposes (in one word to construct a perpetuum mobile of 2 kind)?

[Carrock]

30 minutes ago, Moreno said:

Let to do a curious thought experiment. Modern physics do not set a theoretical limit on how small elementary particles can be with exception of Planck length (1.6 x 10^-35 m). 

What if there can be a small elementary particles (as small to protons as protons to tennis balls) and these extremely small elementary particles are capable to form matter indistinguishable in physical and chemical properties from the common matter known to us. And there exist a tiny conscious creatures made of these tiny elementary particles and each such creature is the size of a common molecule.

If these tiny creatures would got in our World somehow, would they be able to gain use of thermal fluctuation in our world associated with Brownian motion an harness energy of fluctuations for some useful purposes (in one word to construct a perpetuum mobile of 2 kind)?

What would these creatures live on?

i.e. they presumably have to violate the second law themselves.

[Moreno]

1 hour ago, Carrock said:

What would these creatures live on?

i.e. they presumably have to violate the second law themselves.

Sorry, can you develop your questions? Why would they?

[Carrock]

18 hours ago, Moreno said:

Sorry, can you develop your questions? Why would they?

Only a rhetorical question.

 

Consciousness as we know it depends on brains which inter alia are sophisticated heat engines producing a net increase of entropy. Actions by such creatures would also increase entropy at least as much as the reduction of entropy by their actions.

If they are not limited like that, you may may as well say they run on magic or call them 'Maxwell's demons.'

Such demons are an interesting concept, and if they existed could be used in a second order perpetual motion machine.

You may find  https://en.wikipedia.org/wiki/Maxwell's_demon  interesting.

 

 

[Moreno]

2 minutes ago, Carrock said:

Only a rhetorical question.

 

Consciousness as we know it depends on brains which inter alia are sophisticated heat engines producing a net increase of entropy. Actions by such creatures would also increase entropy at least as much as the reduction of entropy by their actions.

If they are not limited like that, you may may as well say they run on magic or call them 'Maxwell's demons.'

Such demons are an interesting concept, and if they existed could be used in a second order perpetual motion machine.

You may find  https://en.wikipedia.org/wiki/Maxwell's_demon  interesting.

 

 

Well, my question was kind of: "The thermal fluctuations which surround as (Brownian motion) are extremely small in comparison to our own size and therefore can be hardly useful. But what about extremely tiny conscious creatures from a parallel universe? Would they be able to get any useful energy from these fluctuation which are very small by our dimensions, but significant by their scale? Can extremely small amounts of useful energy (by our scale) be obtained  from Brownian motion or not at all?".

Another example: "Humans create a tunnel in a parallel universe in which atoms and molecules are huge by our size. Each molecule may be the size of human. The energy of thermal photons these giant molecules absorb and radiate is also huge. Would humans be able to harness any useful energy from Brownian motion in this parallel universe?".

 

[Carrock]

16 minutes ago, Moreno said:

"Humans create a tunnel in a parallel universe in which atoms and molecules are huge by our size. Each molecule may be the size of human. The energy of thermal photons these giant molecules absorb and radiate is also huge. Would humans be able to harness any useful energy from Brownian motion in this parallel universe?"

The energy doesn't scale up.

A football is a reasonable approximation to a giant gas molecule. It doesn't get moved around by random variations in air molecules' K.E. like a grain of pollen as observed in Brownian motion.

There's lots of apparently plausible perpetual motion machines around; this is as far as I'm going with this one.

 

 

[Moreno]

There is also an interesting questions rase regarding our universe heat death. Some people claim that irreversible increase in entropy doesn't apply to our universe because it is infinite and therefore can't be regarded as a thermodynamically closed system. This statement however looks a bit speculative to me because it doesn't explain how entropy reversal is happening in our universe and order increases due to the fact (assumed) it is infinite. Even if it is infinite it doesn't mean we cannot apply such notion as an "average energy density per space" and deny that energy density is prone to equalization practically everywhere in observed universe (which is something like 13 billions of light years). So, the concept of infinite universe doesn't explain why we aren't in the state of the heat death already if we assume that the first or the second law of thermodynamics are never violated.

Edited December 5, 2017 by Moreno

[Carrock]

17 hours ago, Moreno said:

There is also an interesting questions rase regarding our universe heat death. Some people claim that irreversible increase in entropy doesn't apply to our universe because it is infinite and therefore can't be regarded as a thermodynamically closed system. This statement however looks a bit speculative to me because it doesn't explain how entropy reversal is happening in our universe and order increases due to the fact (assumed) it is infinite. Even if it is infinite it doesn't mean we cannot apply such notion as an "average energy density per space" and deny that energy density is prone to equalization practically everywhere in observed universe (which is something like 13 billions of light years). So, the concept of infinite universe doesn't explain why we aren't in the state of the heat death already if we assume that the first or the second law of thermodynamics are never violated.

I agree with that as far as it goes. Conservation of energy and increasing entropy to heat death however are not always applicable in general relativity and quantum mechanics.

---------------------------------------------------------

Statistically, very small regions undergo spontaneous reductions in entropy and there are also quantum fluctuations.

Inflation posits that suitable very small low (classical) entropy fluctuations inflate into very large (> observable universe) low entropy volumes. Some versions of eternal inflation posit that this continues for finite but unlimited time.

Other equally (im)plausible theories are available; a few have been falsified.

 

[Moreno]

It is assumed that classical Maxwell's demon suppose to work in cycles. So, it starts from equilibrium system, then make it non equilibrium by sorting fast and slow atoms, and reduces its entropy in this way, then system performs some useful work and when it does entropy increases and system returns to equilibrium state again. Then demon starts his work again... The common objection against it is that: "entropy of the system cannot spontaneously decrease". 

But let imagine that demon never decreases entropy and entropy constantly stays at the same level. And the system never comes to equilibrium. For example, let imagine we have a container separated by atomic membrane through which individual atoms can pass and demon can sort fast and slow atoms. Gas pressure in the part A of the container is initially 10 times higher than in the part B. Gas atoms are allowed to pass prom part A to part B through a rotating turbine and perform a useful work. But once one additional atom passes from part A to part B, the demon opens a membrane and allows a fast atom from container B return to container A. So, in this way pressure and temperature in each individual part of container never changes. Possibly, in this way we are going to obtain an ideally reversible process. 

 

[Bender]

16 hours ago, Moreno said:

It is assumed that classical Maxwell's demon suppose to work in cycles. So, it starts from equilibrium system, then make it non equilibrium by sorting fast and slow atoms, and reduces its entropy in this way, then system performs some useful work and when it does entropy increases and system returns to equilibrium state again. Then demon starts his work again... The common objection against it is that: "entropy of the system cannot spontaneously decrease". 

But let imagine that demon never decreases entropy and entropy constantly stays at the same level. And the system never comes to equilibrium. For example, let imagine we have a container separated by atomic membrane through which individual atoms can pass and demon can sort fast and slow atoms. Gas pressure in the part A of the container is initially 10 times higher than in the part B. Gas atoms are allowed to pass prom part A to part B through a rotating turbine and perform a useful work. But once one additional atom passes from part A to part B, the demon opens a membrane and allows a fast atom from container B return to container A. So, in this way pressure and temperature in each individual part of container never changes. Possibly, in this way we are going to obtain an ideally reversible process. 

 

But the average speed of the atoms decreases because some of them bounce off the turbine, slowing down.

[Moreno]

1 hour ago, Bender said:

But the average speed of the atoms decreases because some of them bounce off the turbine, slowing down.

Not necessarily, if the turbine is the part of the closed system. Then total heat energy that gas atoms transfer to turbine will be equal to total energy the turbine transfers back to the gas atoms. 

Edited March 10, 2018 by Moreno

[Bender]

Then what is the point of the turbine?

[Moreno]

1 hour ago, Bender said:

Then what is the point of the turbine?

To rotate and perform useful work. 

[Bender]

6 hours ago, Moreno said:

To rotate and perform useful work. 

But it's a closed system where the turbine transfers all its energy to the gas atoms (I suppose you mean gas molecules). How can it transfer energy outside the system (do work) if it has already transfered all its energy to the gas?

Suppose we each have 50 euro. I give you 50 euro and you give me 50 euro and then you give Jack 10 euro. Now our total has decreased to 90 instead of 100 euro.

[Moreno]

8 hours ago, Bender said:

But it's a closed system where the turbine transfers all its energy to the gas atoms (I suppose you mean gas molecules). How can it transfer energy outside the system (do work) if it has already transfered all its energy to the gas?

Suppose we each have 50 euro. I give you 50 euro and you give me 50 euro and then you give Jack 10 euro. Now our total has decreased to 90 instead of 100 euro.

Why do you think it suppose to transfer energy outside the system in order to do the work? Principally we can imaging that closed system is entire Earth, and we all live inside one part of container. And huge, huge turbine located within this closed system and powers all the power grids on Earth. Heat energy has nowhere to go outside the system, so it totally conserved within it.

[Bender]

I'll ignore the fact that the Earth is far from a closed system, and that it is quite unusual to talk about a closed system that includes everything. 

Instead, let's focus on the turbine. You say that all the energy transferred to the turbine is transferred back to the gas. How much energy is left in the turbine after it transfers all its energy?

In other words. If I give you all my money, how much money do I have left to give Jack?

[Moreno]

1 hour ago, Bender said:

I'll ignore the fact that the Earth is far from a closed system, and that it is quite unusual to talk about a closed system that includes everything. 

Instead, let's focus on the turbine. You say that all the energy transferred to the turbine is transferred back to the gas. How much energy is left in the turbine after it transfers all its energy?

In other words. If I give you all my money, how much money do I have left to give Jack?

To a larger extent Earth exist in thermodynamic equilibrium with Sun as it radiates as much energy into space as it receives from Sun. We may ignore here the space rays or similar phenomena.

But let imagine for simplicity that entire Earth is surrounded from space with shield completely restricting for any radiation to come in and out. And all Earth is divided in two containers separated by molecular membrane with a demon who allows fast or slow molecules to come from one container to another, sorting them at will. All humans may live in one of part of the container together with their factories, cars, houses and entire civilization. Let say another part of container is completely uninhabitable. The air pressure in inhabitable part of container is constant and is always 10 times higher than in uninhabitable part. Air is allowed to travel from one part of container to another part through a turbine and this huge turbine powers entire human civilization. Demon allows molecules return to high pressure container by opening molecular membranes when needed. In this way the constant air pressure is supported in both part of containers and entropy never changes. Entropy would diminish if pressure difference between both containers grow larger at some point, but this is not a case as demon constantly preserves the same amount of molecules in each particular part of container. As entropy of entire system never changes, I assume will neither change its ability to perform a useful work. So, factories, cars, computers, trains will keep going forever and ever. Entropy growth = amount of useful work diminishes. Entropy never change = no useful degradation.

Turbine is not going to transfer all the energy at any given point. Turbines work smoothly.

[Bender]

Where does the demon get its energy to perform the sorting?

1 hour ago, Moreno said:

Turbine is not going to transfer all the energy at any given point. Turbines work smoothly.

I simply used your terminology. Feel free to replace "energy" with "power" which is indeed more appropriate. 

[Moreno]

14 minutes ago, Bender said:

Where does the demon get its energy to perform the sorting?

I simply used your terminology. Feel free to replace "energy" with "power" which is indeed more appropriate. 

I think word "energy" may be appropriate here as well, if we are trying to describe heat exchange between gas molecules and those atoms/molecules the turbine made of at the atomic level.

20 minutes ago, Bender said:

Where does the demon get its energy to perform the sorting?

It may draw part of the turbine's energy.

[Bender]

Doesn't really matter. The key question is where the demon gets its energy. 

[Moreno]

2 hours ago, Bender said:

Doesn't really matter. The key question is where the demon gets its energy. 

I've already said. It may use some part of energy produced by the turbine.

[Bender]

But the second law of thermodynamics dictates that decreasing the entropy (increasing enthalpy ) of a system requires more energy than the decrease in entropy.

So you just demonstrated that to be able to violate the laws of thermodynamics, you need a demon which violates the laws of thermodynamics.  

[Moreno]

1 hour ago, Bender said:

But the second law of thermodynamics dictates that decreasing the entropy (increasing enthalpy ) of a system requires more energy than the decrease in entropy.

So you just demonstrated that to be able to violate the laws of thermodynamics, you need a demon which violates the laws of thermodynamics.  

But that's a point. The demon doesn't decrease entropy. It just prevents it grow, so basically keeps it at the same level.