Thought experiment about entropy

[Matthew99]

Dear community!

I've recently come across following intriguing thought experiment: Imagine a jar filled with water where infinitesimally small particles of iron dust are dissolved. The average particle diameter is small enough that they do not descend, therefore they are randomly distributed in the jar (high entropy). Now you take a magnet and hold it next to the jar - after some time has passed, the density of iron particles on the magnet side of the jar will be significantly higher than the density at the opposite side. Considering entropy, such a behavior should only be possible if the total amount of entropy increases or at least stays the same. However, this demixing/separation effect definitely has negative entropy, maybe not much but not zero. The only counteractive measure that would increase entropy I can think of is an increase in temperature. But if this is really the solution to this thought experiment, where would the energy necessary to heat up the system come from?

Thanks a lot for every input

[joigus]

It's a beautiful experiment, and it seems to me that it's quite doable. But keep in mind that, as long as your jar is not a closed system, it doesn't have to display entropy increase. Same reason why the gas in a refrigerator can be made to cool by expanding adiabatically --not getting or giving heat from/to the outside--, but exchanging work. In this way, the universe as a whole would see its entropy increase, but parts of it --the jar's interior-- would see their entropy decrease.

Why don't you try it? Some people here could give you advice. A Dewar flask, a magnet, and a thermometer could do the trick.

Edited January 9, 2021 by joigus

[studiot]

1 hour ago, Matthew99 said:

Dear community!

I've recently come across following intriguing thought experiment: Imagine a jar filled with water where infinitesimally small particles of iron dust are dissolved. The average particle diameter is small enough that they do not descend, therefore they are randomly distributed in the jar (high entropy). Now you take a magnet and hold it next to the jar - after some time has passed, the density of iron particles on the magnet side of the jar will be significantly higher than the density at the opposite side. Considering entropy, such a behavior should only be possible if the total amount of entropy increases or at least stays the same. However, this demixing/separation effect definitely has negative entropy, maybe not much but not zero. The only counteractive measure that would increase entropy I can think of is an increase in temperature. But if this is really the solution to this thought experiment, where would the energy necessary to heat up the system come from?

Thanks a lot for every input

 

33 minutes ago, joigus said:

It's a beautiful experiment, and it seems to me that it's quite doable. But keep in mind that, as long as your jar is not a closed system, it doesn't have to display entropy increase. Same reason why the gas in a refrigerator can be made to cool by expanding adiabatically --not getting or giving heat from/to the outside--, but exchanging work. In this way, the universe as a whole would see its entropy increase, but parts of it --the jar's interior-- would see their entropy decrease.

Why don't you try it? Some people here could give you advice. A Dewar flask, a magnet, and a thermometer could do the trick.

 

Not all all sure about either the question or the answer.

Iron particles are not soluble in water.
They may be suspended which is a different thing.

Since there is no solvation, there is no heat of solution to replace when you de-suspend them.
In fact the particles move to a lower energy state because of the introduced magnetic field.

But the jar containing the supension is definitely a closed system.

[joigus]

5 minutes ago, studiot said:

 

 

Not all all sure about either the question or the answer.

Iron particles are not soluble in water.
They may be suspended which is a different thing.

Since there is no solvation, there is no heat of solution to replace when you de-suspend them.
In fact the particles move to a lower energy state because of the introduced magnetic field.

But the jar containing the supension is definitely a closed system.

You're right. I was in doubt about that too.

Maybe a ferromagnetic salt could play the role of the "iron particles"? You could package permanent magnetic dipoles, while having the particles be soluble in water... Just a thought.

https://en.wikipedia.org/wiki/Ferrofluid

Edit: Ferromagnetic salt is probably not the proper term. Paramagnetic salt is more like it.

7 minutes ago, studiot said:

Since there is no solvation, there is no heat of solution to replace when you de-suspend them.

This checks with what I was thinking, although you know much more than I do about this. My impression was that it wouldn't release/absorb much heat.

Edited January 9, 2021 by joigus

[Matthew99]

Thank you very much for your answers! Indeed such an experiment would be very interesting but unfortunately I do not have any lab equipment at home & university labs are currently closed.

Quote

"Iron particles are not soluble in water.
They may be suspended which is a different thing"

You are right, my example probably isn't very appropriate. But as joigus mentioned, just think of some magnetic soluble substance / macro structure. Putting a magnet near the isolated jar, the entropy in the jar will decrease by the entropy of mixing (or maybe a bit less as even with the magnet on one side there will still be a few molecules in the other parts of the jar).

Quote

Not all all sure about either the question or the answer

Now, as total entropy cannot decrease in closed systems (as the mentioned perfectly isolated jar is), there should be an increase in temperature and my question is, where does the energy for this come from as the system itself is closed?

[John Cuthber]

56 minutes ago, studiot said:

But the jar containing the supension is definitely a closed system.

Yes, because the term is ambiguous; as wiki says.
A closed system is a physical system that does not allow transfer of matter in or out of the system, though, in different contexts, such as physics, chemistry or engineering, the transfer of energy is or is not allowed.

Moving a magnet near a magnetic material involves a transfer of energy

 

If I put a beaker of water on a magnetic stirrer, the water will get warm because work is done by the stir bar against the viscosity of the liquid.

[Matthew99]

Quote

Moving a magnet near a magnetic material involves a transfer of energy

You just brought me to an idea, thank you for your input. Would it be correct to say that the increase in thermal energy inside the jar comes from the decrease of potential energy as the distance between magnet and solution decreases?

[sethoflagos]

By applying an external magnetic field to the system, haven't you introduced new potential energy terms boosting the system total energy?

As the magnetic particles descend this new energy gradient to a new equilibrium position how is this energy going to be dissipated other than in the form of heat?

As a practical example, you might compare and contrast the removal of particulates from eg coal-fired power station flue gas by electrostatic precipitators. The pretty efficient separation of gas and solids suggests an entropy decrease, but on the other hand, electricity is consumed, and that's going to end up releasing heat somewhere or other. 

[Matthew99]

3 minutes ago, sethoflagos said:

By applying an external magnetic field to the system, haven't you introduced new potential energy terms boosting the system total energy?

As the magnetic particles descend this new energy gradient to a new equilibrium position how is this energy going to be dissipated other than in the form of heat?

As a practical example, you might compare and contrast the removal of particulates from eg coal-fired power station flue gas by electrostatic precipitators. The pretty efficient separation of gas and solids suggests an entropy decrease, but on the other hand, electricity is consumed, and that's going to end up releasing heat somewhere or other. 

You are absolutely right, thank you very much for your answer. This is the solution to my thought experiment. From my point of view a very astonishing reminder of how theoretical physics apply to such a simple practical experiment.

[JohnSSM]

IF one were to view entropy as disorder, or the tendency to become less ordered, then order is referred to as negentropy.  The presence of the magnet adds energy and order (magnetic field), so it adds negentropy.

"after some time has passed, the density of iron particles on the magnet side of the jar will be significantly higher than the density at the opposite side. Considering entropy, such a behavior should only be possible if the total amount of entropy increases or at least stays the same."

The magnet adds order, which the iron particles must follow, this would be a loss of entropy, not a gain.  The magnet adds order, and the randomness becomes ordered as the iron flakes migrate towards the magnet.  I dont understand why you believe randomness is order and magnetism is disorder.  It seems backwards to me, but I am new to understanding entropy.

[studiot]

4 hours ago, JohnSSM said:

IF one were to view entropy as disorder, or the tendency to become less ordered, then order is referred to as negentropy.  The presence of the magnet adds energy and order (magnetic field), so it adds negentropy.

"after some time has passed, the density of iron particles on the magnet side of the jar will be significantly higher than the density at the opposite side. Considering entropy, such a behavior should only be possible if the total amount of entropy increases or at least stays the same."

The magnet adds order, which the iron particles must follow, this would be a loss of entropy, not a gain.  The magnet adds order, and the randomness becomes ordered as the iron flakes migrate towards the magnet.  I dont understand why you believe randomness is order and magnetism is disorder.  It seems backwards to me, but I am new to understanding entropy.

 

This is not the way thermodynamic entropy works.

Considering your background information in your own thread about Free Energy, here is a suitable explanation of the link between 'order /disorder' and thermodynamic entropy.

 

Consider a system and the possible states it can find itself in.

Label the states a, b , c, d.........and so on.

For each state assign a probability of finding the system in this state upon random inspection. So we have P(a) = probability of state a and so on.

Inspect the system and find it in state x.

Now consider a change of state. That is the system from state x to some other ste, say y.

If P(x) < P(y)  Then we say there is an increase in entropy of the system for such a change. ie a change from state x to state y.

If P(x) > P(y)  Then we say there is a decrease of entropy of the system for such a change  ie a change from state x to state y.

If P(x) = P(y)  Then we say that the system is in equilibrium and there is no change to the entropy of the system.

Depending upon the nature of the system there are implications or consequences resulting from such a change.

Thermodynamics identifies entropy as connected with energy in the system.
So the change is linked to the energy structure of the system and by inference any energy transferred into or out of the system by the change.
This is true whether the theoretical approach is 'classical' or statistical. The states are energy states.
It is about material things.

But the same mathematical structure can appear in non material things like information technology
Here we are talking about 'bits' of information.
These could be marks on a piece of paper, the contents of a computer memory cell or the positions of beads on an abacus.
Energy is not involved at all.

In either system (or indeed in any other that follows the same mathematical structure) the probabilities are determined by the number of ways a state can occur.
This is how we define 'order and disorder'.

The fewer the number of ways a state can occur , the more ordered the system.
Note this leads to an inverse relationship between entropy and order.

 

[MigL]

This is no different than the case where the iron particles are suspended in water with no external magnetic field.

The iron particles stay in suspension because they are josteled about by the kinetic energy of the water molecules in the weak gravitational potential.
When you apply the external magnetic field of much greater potential, the iron particles now have much greater kinetic energy as they move towards the magnet, imparting some of their kinetic energy to the water molecules and heating it up.

[JohnSSM]

4 hours ago, studiot said:

 

This is not the way thermodynamic entropy works.

Considering your background information in your own thread about Free Energy, here is a suitable explanation of the link between 'order /disorder' and thermodynamic entropy.

 

Consider a system and the possible states it can find itself in.

Label the states a, b , c, d.........and so on.

For each state assign a probability of finding the system in this state upon random inspection. So we have P(a) = probability of state a and so on.

Inspect the system and find it in state x.

Now consider a change of state. That is the system from state x to some other ste, say y.

If P(x) < P(y)  Then we say there is an increase in entropy of the system for such a change. ie a change from state x to state y.

If P(x) > P(y)  Then we say there is a decrease of entropy of the system for such a change  ie a change from state x to state y.

If P(x) = P(y)  Then we say that the system is in equilibrium and there is no change to the entropy of the system.

Depending upon the nature of the system there are implications or consequences resulting from such a change.

Thermodynamics identifies entropy as connected with energy in the system.
So the change is linked to the energy structure of the system and by inference any energy transferred into or out of the system by the change.
This is true whether the theoretical approach is 'classical' or statistical. The states are energy states.
It is about material things.

But the same mathematical structure can appear in non material things like information technology
Here we are talking about 'bits' of information.
These could be marks on a piece of paper, the contents of a computer memory cell or the positions of beads on an abacus.
Energy is not involved at all.

In either system (or indeed in any other that follows the same mathematical structure) the probabilities are determined by the number of ways a state can occur.
This is how we define 'order and disorder'.

The fewer the number of ways a state can occur , the more ordered the system.
Note this leads to an inverse relationship between entropy and order.

 

I have read your reply and thought on it many times, re-reading it slowly in order to find the order.  I believe you do know what you are talking about.  But I still don't. Ha.  

I want to follow your instructions as best as I can.

The system I want to consider is the sun, and the amount of, size of and percentage of the sun, taken up by sunspots are the various states.  It should turn out to be a proportion of the amount of sunspots to non-sunspots.

I have no way to predict the probability of finding the sun in any of these states, and that is what Im trying to figure out.  SO I dont understand how I might be able to summarize them with the state itself. ie...P(a).  I have no idea of the probability of that state occurring, s I cant come up with a P that is valid in anyway.  And how do you multiple a certain state of the sun, when it comes to sunspot coverage, by the probability of that state happening, even if you do know the probability?  

Is this something that can be applied to figuring out possible random states of the sun?  And if those are terms that do not work with this understanding, what terms should i be using?  I assume, numbers, but in the physics, those numbers must represent some physical property or law. I truly appreciate the time you put into this explanation.  If you how I have interpreted your explanation, can you give me some "real world" applications of your explanation?  Right off the bat, I dont know what world to apply those terms.  

 

Also Studiot.   Doesnt thermodynamic entropy require a closed system?  When the magnet enters the picture, the system is no longer closed.  The energy of magnetism is now effecting the iron flakes, and it was not before.  Doesnt the magnet introduce, order, in the form of energy, that the iron must respond to?  If the iron flakes follow the order of magnetism, at least in magnetism's sake, it seems to have created order and taken away entropy, or added negentropy.

 

[JohnSSM]

Studiot, I think I did figure out thermodynamic entropy.  In one explanation I read, it came down to heat.  In simple terms, cold things have more order and less entropy, even when they appear to have more or less disorder to our own perceived standards of order.  A nice example.  A glass of crushed ice may appear to be more disordered, than a nice glass of evenly distributed water.  That is how I might perceive the disorder according to my subjective beliefs about order.  But, the truth of theromdynamic entropy is that water gains entropy as it heats up, and loses it as it cools and approaches order.  The result doesnt look ordered to me, and that is how powerful subjectivity is.  Now I fully see that cold objects have less probability within them, and less probability means more predictable order, entropy from heat which creates vibrations, creates more possibility for probability, and along with it entropy, and as it loses the vibrations that inspire its possibilities down to nothing, or absolute zero.  It then becomes totally cold, mostly motionless, with very few possibilities to add to its probability matrix.  Removing variables until order is achieved.  But entropy doesnt want that!  To entropy, variables are possibilities for more freedom.  To order, each variable creates another possibility to lose order.  They call this surprise in some realms.  I think it's a bad analogy.  ITs not just surprise, there is an inherent fear, in order to dislike entropy.  Of course, it isnt a fear in thermodynamics.  Entropy and order simply work against each other.  Entropy takes work, or energy or heat. So, when you want to add what you believe to be order to your lawn, during fall, you actually add entropy to the lawn to organize the leaves and take them away.  If you have the free energy to do so, it will take heat that you can count as calories.  This transfer of heat now puts your body is a state of more order, as you lose heat, but without more heat, you will lose your ability to organize leaves, so we eat to replace the heat.  Order can kill the body, which is why almost everything lives in a state of equilibrium.  Thermodynamcally, the most order for our bodies would be found at absolute zero.  IN terms of life, our best thermodynamic equilibrium seems to be 98.6 degrees.  And in this way, entropy can be relatively applied to solve any problem, or find any solution.  Like, how to get to the store quickest, without breaking laws or risking more entropy, because if I dont rush and find the fastest route, I am risking not being able to pick up my son.  If I am late to pick up my son, it creates more disorder in my life, and the apparent disorder may make him believe i cannot produce the probabilities to care for him in a timely fashion.  Our human selves seek to fight the entropy of disorder.  IF we don't spend that energy, our life sinks into disorder, which can create actual disorders of thinking, even in our son.  That all came together just now.  Thanks for the inspiration.  You heated me up just enough to make me put more energy into balancing mu own understanding. Its exactly what we need from each other.  Thank you!

 

[studiot]

8 hours ago, JohnSSM said:

I have read your reply and thought on it many times, re-reading it slowly in order to find the order.  I believe you do know what you are talking about.  But I still don't. Ha.  

I am sorry but my post didn't help. It was rather brief since you are taking someone else's thread off topic.

You really should start a thread of your own about sunspots, asking a clearly phrased question about what you want to calculate.

I note that sunspot occurrence is quite diffrent from comparing classic thermodynamics to psychological states as you seem to be trying to do in your free energy thread.

So please choose one topic and start a new thread about it.

8 hours ago, JohnSSM said:

Also Studiot.   Doesnt thermodynamic entropy require a closed system? 

 

No, entropy changes can be calculated for any system  - at least in principle thought it may be difficult in practice.

6 hours ago, JohnSSM said:

Studiot, I think I did figure out thermodynamic entropy.  In one explanation I read, it came down to heat.

Yes this was the original reason entropy concept was introduced and lead to what I call classical thermodynamics.
This is also the simplest and easiest to understand explanation.
I can post it if you wish, it has nothing directly to do with order or probability and was introduced for engineering calculation purposes in the age of steam engines.
 

Edited March 13, 2021 by studiot

[JohnSSM]

6 hours ago, studiot said:

I am sorry but my post didn't help. It was rather brief since you are taking someone else's thread off topic.

You really should start a thread of your own about sunspots, asking a clearly phrased question about what you want to calculate.

I note that sunspot occurrence is quite diffrent from comparing classic thermodynamics to psychological states as you seem to be trying to do in your free energy thread.

So please choose one topic and start a new thread about it.

 

No, entropy changes can be calculated for any system  - at least in principle thought it may be difficult in practice.

Yes this was the original reason entropy concept was introduced and lead to what I call classical thermodynamics.
This is also the simplest and easiest to understand explanation.
I can post it if you wish, it has nothing directly to do with order or probability and was introduced for engineering calculation purposes in the age of steam engines.
 

I have no interest in sunspots, but I cannot understand things with equations that use no reference.  And I have yet to see any real world references to those equations.  SO you can tell me to consider a topic with a large set of possibiltiies, then figure the probability for each one, and then multiply it by the event itself.  Thats essentially what you told me to do, but it doesnt work at all for sunspots.  So can you tell me what it does work for?  Can you create a real world example of a probability you are trying to know, then give me the A, B, C, D possible states it will be in, and then show me the results of multiplying them by the event itself?  I even got pretty far with calculus, and just have no idea what you might solve with the equations you presented.  Alas, im not sure I need to understand that, but a real world example helps folks like me.  

Your input actually helped me a lot. Inspiration is usually the responsible party...ha

[studiot]

You say

20 minutes ago, JohnSSM said:

I have no interest in sunspots,

after introducig them in an exchange of views about probability.

 

You then ask about heat and entropy to which I respond

7 hours ago, studiot said:

Yes this was the original reason entropy concept was introduced and lead to what I call classical thermodynamics.
This is also the simplest and easiest to understand explanation.
I can post it if you wish, it has nothing directly to do with order or probability and was introduced for engineering calculation purposes in the age of steam engines.

Nothing whatsoever to do with statistics and probability as you seem to have agreed to abandon it for the moment.

But you reply

23 minutes ago, JohnSSM said:

SO you can tell me to consider a topic with a large set of possibiltiies, then figure the probability for each one, and then multiply it by the event itself.  Thats essentially what you told me to do, but it doesnt work at all for sunspots.  So can you tell me what it does work for?  Can you create a real world example of a probability you are trying to know, then give me the A, B, C, D possible states it will be in, and then show me the results of multiplying them by the event itself?  I even got pretty far with calculus, and just have no idea what you might solve with the equations you presented.  Alas, im not sure I need to understand that, but a real world example helps folks like me.  

which is all about statistics and probability and nothing about the offered real world of engineering.

 

Please focus.

[JohnSSM]

Studiot.  I simply have to use real world examples to understand equations.  So I offered a totally real world example, and it didnt work at all, did it?  I am the student here.  I still have yet to hear you mention a real world example.  I have doubts that you can even think of one and present it at this point, but what does it matter?  I have the knowledge I need to move on.  Thanks!

[studiot]

44 minutes ago, JohnSSM said:

I have doubts that you can even think of one and present it at this point, but what does it matter?  I have the knowledge I need to move on.  Thanks!

 

Shrug.