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Author Topic:   Entropy in Layman's Terms
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


(1)
Message 1 of 51 (544059)
01-23-2010 3:33 AM


Dr Adequate says that the entropy cannot be expressed in layman's terms. As the author of a primer that I've posted here that derives the Second Law from first principles, I thought I'd take a crack at it.
There are many pithy sayings regarding the Second Law and entropy, but the problem with them is that they wind up being used in places where they make no sense. The reductions are accurate, but can only be understood within the concept of thermodynamics, not other areas. So if we're going to explain it in layman's terms, we have to start with making the point that entropy is a statement about energy. It isn't about "information" or "order" or "disorder."
In short, entropy is the energy in the system that cannot be used for work. Thermodynamics works by moving energy around from one place to another. But because this transfer is a physical process, this means that this energy will go into the physical transfer mechanism as well as to the delivery place. It's a bit like trying to carry water from one place to another: Some of it is always going to stick to the vessel. If I take a cup of water and pour it out, there will always be a few drops sticking to the cup. I can shake the cup and bang it, but there is always going to be something left over. That water that wets down the vessel is like entropy: It isn't being transferred from one place to another but is lost as you transfer all the rest of the water.
As you move the same energy around and around the system, you eventually come to a point where there isn't any energy left that can be used: It's all been bled away as entropy. But that assumes a completely closed system. If we had more water entering the system, we can afford to lose some of it sticking to the sides of the vessel.
This is why concepts of "information" or "disorder" make no sense in their regular senses: It isn't a question of "ordering" the energy. It's that it is no longer physically available to do any work. When we reduce the concept of the Second Law and entropy to the phrase, "The universe tends towards disorder," what we mean is that the energy distribution of the universe is tending toward a uniformity. You see, energy transfer depends upon variations in energy states. If everything is the same, then there can be no reaction.
Back to the water concept: If you have a cube of ice and a pot of boiling water, there will be energy flow between the two if we put them into a system: However, that energy flow only happens because of the disparity in their energy states. The heat flows from the boiling water into the ice and eventually, the water hits equilibrium. When everything hits the same temperature, no more energy flow takes place. All the heat is now unavailable to do any work because there isn't anywhere for it go. That doesn't mean there isn't any energy: It's just that there is no disparity between any two places in the system and thus, there can be no transfer of any energy of any kind.
Eventually, all the energy in the universe will be equally dispersed throughout the universe and no reactions of any significance can take place. That's what we mean when we say "disorder": There is no pattern to anything because everything is dispersed.
The better metaphors for entropy are the ones that I put through in my primer:
There are no perfect engines.
OR
There are no perfect refrigerators.
In the first sense, this has to do with the water example I gave above: Some of the water always sticks to the vessel. You cannot convert heat entirely into work. Some of the energy gets used on the engine itself, rather than being used to drive the engine. In the case of heat, that means some of the heat is used to heat the engine rather than being used to make work the engine facilitates. You can make the engine more efficient such that more energy is converted into work, but there will always be some heat lost to the engine itself and thus, there is no way to make it perfect.
In the second sense, this is a more practical idea: A refrigerator takes heat from a low-temperature area and moves it to a high-temperature area. But the only way it can do this is by doing some work to move it. Heat simply doesn't flow from low to high. When you put a piece of ice into boiling water, the ice doesn't become colder and dump the heat into the boiling water to make it hotter. Instead, the heat flow from hot to cold. And yet, a refrigerator is possible because of the work involved. You can make the refrigerator more efficient such that not as much work is required to move the heat, but there will always be some work required and thus, there is no way to make it perfect.
Entropy is simply energy unavailable to do work.

Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.

Replies to this message:
 Message 5 by Son Goku, posted 01-26-2010 3:28 PM Rrhain has not replied
 Message 9 by Fiver, posted 04-17-2010 3:38 PM Rrhain has not replied
 Message 11 by purpledawn, posted 04-23-2010 7:32 AM Rrhain has replied
 Message 18 by Buzsaw, posted 04-24-2010 8:32 AM Rrhain has replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 35 of 51 (557407)
04-25-2010 8:15 AM
Reply to: Message 11 by purpledawn
04-23-2010 7:32 AM


purpledawn responds to me:
quote:
quote:
There are no perfect refrigerators.
I didn't quite understand where the wasted energy is in this one unless it is still the heat wasted in the moving process.
A refrigerator, at its most basic level, is simply an engine that runs in reverse.
Now, an engine is something that takes energy and converts it into work. Thermodynamically, this means we have a thing that we call a "high-temperature reservoir," that is, the thing that has all the heat, and it delivers it to a mechanism that extracts some of that energy to turn it into work. The rest of it gets dumped to the "low-temperature reservoir." What is being dumped there is the lost energy, the entropy. It hasn't been converted into work and it cannot be used: The engine is hooked up to the high-temperature reservoir, not the low.
Now, the engine works specifically because the heat wants to flow from the high to the low. If the high and low reservoirs were at the same temperature, there would be no heat flow and thus no work could be extracted. What the engine does is extract some of that energy out of that natural flow and use it to do some work, whatever it cannot use being lost.
We can abstract all this to have a box that is the high-temperature reservoir, an arrow coming out of it to another box that is the engine, and two arrows coming out of the engine: One goes to that thing we call "work" and the other goes to a box that is the low-temperature reservoir. If we let the size of the arrows dictate how much energy is being transferred at each step, then the Second Law states that while we can reduce the size of the arrow going from the engine to the low-temperature reservoir (and in compensation, increase the size of the arrow going to the work bubble), we can never reduce it to nothing.
A refrigerator reverses all the arrows. In a refrigerator, we input work into the "engine" and in the process, it pulls some heat out of the low-temperature reservoir and transfers it to the high-temperature reservoir.
Now, suppose there were a perfect engine. That is, suppose there were an engine that could take all of the energy it takes from the high-temperature reservoir and convert it into work: The size of the arrow going out of the engine to the work bubble is the same size as that of the arrow coming in and the arrow going to the low-temperature box doesn't exist. Well, if that were the case, we could hook this engine up to a refrigerator. The work that this engine produces can be used to drive the refrigerator and the net result of this is that energy is flowing from the low-temperature reservoir to the high-temperature reservoir without any external work being required to run the thing...it's being run by the high-temperature reservoir which actually gets hotter and thus has more energy that it can give to the engine.
This is perpetual motion and impossible.
Thus, no perfect engines.
Now the flip side of this is the perfect refrigerator. There are two arrows going into the refrigerator: The energy arrow from the low-temperature reservoir and the work arrow. Those get combined and the result is to dump all that energy upon the high-temperature reservoir. We can increase the efficiency of this by requiring less work to drive the refrigerator. A perfect refrigerator would be to reduce that incoming arrow from the work to zero. We could then hook this up to the engine: The refrigerator takes energy from the low-temperature reservoir and dumps it to the high-temperature reservoir which then is used by the engine to extract work and thus, we get work for nothing.
Once again, this is perpetual motion and impossible.
Thus, no perfect refrigerators.
Does that help?

Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.

This message is a reply to:
 Message 11 by purpledawn, posted 04-23-2010 7:32 AM purpledawn has replied

Replies to this message:
 Message 42 by purpledawn, posted 04-25-2010 3:58 PM Rrhain has replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 36 of 51 (557409)
04-25-2010 9:00 AM
Reply to: Message 18 by Buzsaw
04-24-2010 8:32 AM


Buzsaw responds to me:
quote:
With ID, there is no energy in the system which cannot be managed so as to be used for work.
Which is a direct violation of the Second Law. All physical processes lose energy to entropy. While the processes may be extremely efficient such that this loss is very slow, it can never be eliminated and always takes a finite amount of time which is why your eternal universe is a violation of physics.
I'm still waiting for you to answer the question I asked of you the last time you tried to claim that everything we know about physics is wrong (Message 127):
What would happen if we hooked up your engine to a refrigerator? I wrote about this very specific example when discussing how one can derive the second law from scratch. It is a common example and is used in all three of my physics textbooks, which is why I also used it. You say that god expends work. That's fine. You say that god takes up energy back. That is fine, too.
You seem to think that this cycle can continue indefinitely, especially since you claim that universe is eternal. But this is a direct violation of the second law. Heat to work, work to heat, what does the second law tells about this?
Unless and until you can answer this question, I'm going to respectfully ask you that stay out of this thread because I don't want it derailed.

Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.

This message is a reply to:
 Message 18 by Buzsaw, posted 04-24-2010 8:32 AM Buzsaw has replied

Replies to this message:
 Message 37 by Buzsaw, posted 04-25-2010 10:55 AM Rrhain has not replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 43 of 51 (557468)
04-26-2010 2:34 AM
Reply to: Message 42 by purpledawn
04-25-2010 3:58 PM


purpledawn writes:
quote:
Heat that is not used for work is entropy?
In the sense of there being a process by which energy is flowing, yes. But, we must be careful to recognize that the products of a reaction can themselves be used in another reaction. That is, the heat from the hot water can be used to melt the ice, but depending on just how much heat was used in the process, the leftover warm water might be capable of being used in another reaction.
When we say it is "lost," we are referring to that one particular reaction. If you take a hot object and you put it in contact with a cold object, heat naturally flows between them until the two reach equilibrium. The engine allows us to extract some work from that flow. But once the system reaches equilibrium, no more work can be extracted because there is no more flow.
If, however, you introduce a third object into this system that is at a different temperature, then we can hook the engine up again and extract some work while the two reach equilibrium.
On a cosmological scale, eventually all energy gets bled away. Eventually, everything in the universe will be of the same uniform temperature. This is what we mean by the "heat death" of the universe. But we're a long way from that and while we're still in the middle of things, plenty of reactions can take place, chained together. And with a star shining down on us, continually dumping energy onto the planet, we don't really have any problem with entropy.
quote:
I understand the waste in machines. How does the waste manifest itself in things that are not manmade or influenced by man?
That's the glory of the Second Law: It doesn't matter what the engine is. Human-created engines are fairly obvious because they're big and we can directly see how energy comes in, stuff comes out, and the engine heats up. But there are other kinds of engines, too.
For example, photosynthesis. It's a chemical engine. Two photons strike a molecule of chlorophyll and excite the electrons in it to a higher energy state. Because those electrons are now at a higher energy state, the chlorophyll can now engage in a reaction that transfers those electrons to another chemical. That chemical then transfers the electrons to another, those to another, etc., until eventually the electrons get passed back to the molecule of chlorophyll and the process can start all over again. This is called "photophosphorylation." Here's how my biology textbook described it:
A person swings a sledgehammer, hitting a lever that throws a heavy ball into the air (like a"ring the bell" game). The ball lands on a ramp, rolling down it and dropping to a second ramp; from there it falls onto a wheel, causing the wheel to turn. When the ball falls from the wheel, it falls into another ramp, rolls down it, and finally falls back onto the lever where it started. If the turning wheel is used to do work (to run a machine), then we can see that the system transforms the original work of the person swinging the hammer into work done by the machine attached to the wheel. The energy of the falling sledgehammer is analogous to the photon in photophosphorylation, the lever to chlorophyll, the ball to an electron, the ramps to the electron carriers, and the turning of the wheel to the formation of ATP.
--Life: The Science of Biology, "Photosynthesis"
Each step of this process is its own reaction and thus has its own options to bleed energy out of the system, but that's fine so long as the energy of the original photons is enough. If the excited chlorophyll is energetic enough, there will be enough energy in the system such that even though we lose some to entropy, heating up the cell, there is enough energy to drive all the reactions and deliver the electrons back to the chlorophyll to be used again. That's why chlorophyll requires sunlight of a certain wavelength. Put your plants under red light, which doesn't have a lot of energy, and they won't survive for long. That's why grow lights tend toward the blue end of the spectrum: There's more energy in blue light which will activate the chlorophyll sufficiently.
Does that help?

Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.

This message is a reply to:
 Message 42 by purpledawn, posted 04-25-2010 3:58 PM purpledawn has replied

Replies to this message:
 Message 44 by purpledawn, posted 04-26-2010 5:44 AM Rrhain has replied
 Message 48 by Taq, posted 04-27-2010 11:57 AM Rrhain has not replied

  
Rrhain
Member
Posts: 6351
From: San Diego, CA, USA
Joined: 05-03-2003


Message 51 of 51 (558402)
05-01-2010 4:25 AM
Reply to: Message 44 by purpledawn
04-26-2010 5:44 AM


purpledawn writes:
quote:
So energy lost in one reaction is not necessarily unusable in another reaction.
Yes. But you must remember that we talk about a "system." That is, we assume that we have accounted for all players in the game: We have the pot of hot water, the ice cube, and some sort of "engine" that can do work as the heat flows from the hot water to the frozen water.
Eventually, all of those things will be the same temperature, there will be no more heat flow, and the engine grinds to a halt.
We call this system "closed."
Now, suppose we could add something to this system. Perhaps we heat some of the water so that it's even hotter or take some of the water and refreeze it. Then we can run the engine again, but notice that it required something outside the system to do this.
We call this system "open."
Note, a "closed" system can be quite complicated. For example, suppose the engine between the hot water and the ice cube is used to freeze some water. That'll certainly keep things going for a while but since we can never convert all the heat into work, eventually everything equalizes.
This is why the thermodynamic concept of entropy is dependent upon temperature. Mathematically, entropy is defined as energy ("Q") divided by temperature ("T"). Thus, the entropy of a reaction is related to the temperature at which the reaction takes place.
There's a connected concept: Enthalpy. It's sort of the opposite of entropy: Where entropy is the energy unavailable to do work, enthalpy is the energy that is available to do work. This is why some reactions result in a decrease of entropy. If the amount of energy used to run the reaction is sufficiently large such that the total energy of the system reduces, then we can reduce entropy, too. Remember that example I gave above where we use an engine to create ice? That's an example of energy being used to reduce entropy.
You take some coal and burn it, producing heat. That heat is used to heat up water into steam. The steam is used to turn a turbine. The turbine generates electricity. The electricity is used to power a refrigerator. The refrigerator is used to make ice.
Now, the water going from liquid to solid is a decrease in entropy. But the amount of energy that was used and processed in this system is much more than the entropic decrease.
quote:
Why would a layperson need to understand entropy?
To a certain extent, they don't. There is the joy of simply being an educated person, but it isn't like the typical person needs to be able to make a thermodynamic calculation in their daily lives.
Around here, however, it's important because one of the common complaints made by creationists is that evolution somehow violates the Second Law. They can never explain how, but they are certain that it does. It's because they don't understand what entropy is.
There are multiple failures in their claim connected to their misconception of entropy. The first is their assumption that a "more complex" organism (and note that what makes it "more complex" is never defined) represents less entropy than a "more primitive" one (again, notice the lack of definition as to what the means.)
Why? Why would this necessarily be the case? If we assume the concept of going from a single cell to a multicellular organism is what we mean by "more complex," it would seem that entropy has actually increased: There are so many more reactions taking place that the biological functions have plenty of opportunities to bleed off energy as entropy.
But even so, why would a "more complex" process be a problem? If the new process is more efficient, isn't that a more favored reaction? It can make use of the available resources better, supporting more organisms than one that is wasteful. This doesn't stop entropy from happening. It just happens more slowly.
And on top of that, there's this thing called the sun. If you take a look at the way life on this planet works, tracing back the energy, you find that most life traces back their energy to the sun. Suppose that refrigerator example from above was powered by solar cells rather than coal. Well, we've got a ton of sunlight available: That refrigerator is going to be working for quite some time, generating a lot of ice. The reason why this works is because the huge thermodynamic reaction of the sun and its entropic increase far outweighs the puny entropic decrease that we have here on this planet.
The idea that evolution is a violation of physics is laughable and shows a fundamental misunderstanding of both biology and physics.

Rrhain

Thank you for your submission to Science. Your paper was reviewed by a jury of seventh graders so that they could look for balance and to allow them to make up their own minds. We are sorry to say that they found your paper "bogus," specifically describing the section on the laboratory work "boring." We regret that we will be unable to publish your work at this time.

Minds are like parachutes. Just because you've lost yours doesn't mean you can use mine.

This message is a reply to:
 Message 44 by purpledawn, posted 04-26-2010 5:44 AM purpledawn has not replied

  
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