SLOT second law of thermodynamics

[bobsmith76]

I don't get how this ever came to be a law, since it seems so obviously false. Entropy in a closed system can only increase. If I close the doors in my room (so that it's a closed system) and spend one hour cleaning, then I have obviously decreased the entropy. It seems so obvious to me that SLOT should read: entropy in a closed system will only increase if there is no intelligent agent in the closed system. I can't figure out why that clause: "unless there is an intelligent agent in the closed system" was never added on to the law.

 

[my_wan]

So you think you are "[URL demon[/URL]?

You eat supper, which was supplied energy ultimately by the sun. You cleaned the room which you then need another room in the house to go dump the entropic waste you created. At least that part that you did not breath out, which would eventually suffocate you if you stayed in an enclosed room long enough.

Being intelligent only allows you to trade more entropy over there for less over here, but the entropy created always exceeds the entropy removed. That is what life is, a way for nature to increase the efficiency of entropy in a system with an external energy source to keep the systems energy unbalanced, i.e., the sun.

 

[bobsmith76]

I can clean up a room without creating any waste. I can just put things where they are supposed to be. In any case, it seems like the definition of entropy is highly subjective, if so, it has no place in science, and should not in any way be called a law.

 

[Drakkith]

Look up what a scientific law is.

If I close the doors in my room (so that it's a closed system)

This is incorrect. It is not a closed system. And even if it was a closed system the answer by My Wan explained it correctly.

I can clean up a room without creating any waste.

The waste he refers to is from your metabolism, not from your room.

 

[Dale]

I can clean up a room without creating any waste.

Not unless you can stop breathing and stop all of your cellular metabolism.

After cleaning you are probably hungry and thirsty, and since the room is sealed it is starting to feel stuffy so you want to open the window. All of that is due entropy increasing. The room's entropy may have decreased a little, but your body's entropy increased a lot.

 

[my_wan]

I can clean up a room without creating any waste.

Then why must you eat? You basically just claimed you can clean up a room without using any energy to do so.

This not only makes you a Maxwell's demon but is also a claim that you are a perpetual motion machine. Not so.

 

[my_wan]

In any case, it seems like the definition of entropy is highly subjective, if so, it has no place in science, and should not in any way be called a law.

The only thing subjective about is is a lack of knowledge of where the energy comes from and where it goes. Only not everybody lacks such information about the energy sources and drains, making it not so subjective as you indicated. We can count this energy flow down to minute quantities and tell you how exactly how much food and what kinds that room cleaning cost.

 

[timthereaper]

Referring to the OP, the argument doesn't make sense. You can't just focus on the clean room and measure that entropy and call it good. That's like saying that an air conditioner decreases entropy because it removes the heat from a room and since the room is a "closed" system, the SLOT doesn't hold (plus, the air conditioner isn't intelligent).

I think this link sums up this whole argument:
http://xkcd.com/675/

 

[llaaxxmmaann]

I don't get how this ever came to be a law, since it seems so obviously false. Entropy in a closed system can only increase. If I close the doors in my room (so that it's a closed system) and spend one hour cleaning, then I have obviously decreased the entropy. It seems so obvious to me that SLOT should read: entropy in a closed system will only increase if there is no intelligent agent in the closed system. I can't figure out why that clause: "unless there is an intelligent agent in the closed system" was never added on to the law.

the entropy of the room decreased but what about your entropy . you are also the part of system don't u

 

[atyy]

So you think you are "[URL demon[/URL]?

It's a very interesting question - how can Maxwell's demon be exorcised?

Nowadays, I hear that Landauer's principle has done it in. Thermodynamics only applies to systems with very large numbers of particles. So a demon with a finite amount of memory must eventually erase some memory, in order to keep on cleaning his room. In erasing the memory, the demon will cause entropy to increase.

Interestingly, "[URL [/URL] lists controversy about how far the principle can be generalized. These articles by http://arxiv.org/abs/quant-ph/0203017" look like good reads.

 

[my_wan]

It's a very interesting question - how can Maxwell's demon be exorcised?

Nowadays, I hear that Landauer's principle has done it in. Thermodynamics only applies to systems with very large numbers of particles. So a demon with a finite amount of memory must eventually erase some memory, in order to keep on cleaning his room. In erasing the memory, the demon will cause entropy to increase.

Interestingly, "[URL [/URL] lists controversy about how far the principle can be generalized. These articles by http://arxiv.org/abs/quant-ph/0203017" look like good reads.

Yes, I find the limits of the second law interesting myself. I keep seeing the distinction between the state of a system and knowledge of the state of a system conflated in complex ways, especially when entropy is involved but sometimes in other situations.

Consider the limits imposed by the 3rd law alone. This implies a minimum entropy such that at some point entropy does not decrease in total, rather some subsystem increases entropy to the gain of another. Maximal entropy would then be defined as a state where the losses and gains have a Poisson distribution.

In terms of computer registers suppose instead of running out of registers the particular register that is overwritten by a new piece of information becomes unpredictable, but correlated with the new piece of information. Throws a bit of a loop into J. Bub's acquisition cost in the linked paper, because acquisition and erasure become consonant. So if you start with a blank state it can gain information up to the point when information acquisition and erasure balance out. Then to gain information above that it must be acquired through obtaining it from lucky encounters with a second system of slightly lower entropy.

So long as there is some minimal entropy under which the total entropy can be reduced no further, there is one class of algorithm that allows the entropy of subsystems to decrease fractally. But does not give anyone system any special advantaged information to locally reduce its own entropy. In biology this is evolution. In physics it is defined in the large number hypothesis. Consider Big Bang nucleosynthesis which entails super hot conditions for rapid production. Yet, given an enormous enough period of time the same thing could in principle occur at lower average temperatures. Requiring only very localized highly unusual events to produce the hot events needed. I am not making an argument against the Big Bang but essentially it is the same process resulting in particle productions that indefinitely lock in low entropy subsystems once they occur.

Except by shear weight of numbers the opportunities to further decrease entropy at the individual system level is no better than what is defined by the usual thermodynamic laws. But with enough subsystems and a minimum entropy there will be lottery winners so long as a finite band-gap, Planck > 0, exist for those lottery winning subsystems to hang onto their gains.

When we talk about information and what energy we can reliably derive from a low entropy source this game with the large number hypothesis becomes worthless. Because we cannot wait on a confluence of conditions to gain once out of countless events. The failures eat our gains. So we, as individual systems, can only talk about the usefulness of entropy in terms of information we have about a system, and not the information contained in that system. Our physically laws is also geared around available information in such a way that the actual information contained in that system cannot even be ascribed an ontological reality. This can often make entropy look like a moving target whenever we switch from one method of coding information to another.

That is how I conceptualize the situation anyway, where entropy is always perfectly valid in terms of defining what I, or any particular system, can obtain to decrease local entropy, while doing so increases the total efficiency of entropy production to bring the lottery winners back into thermal equilibrium. It grows in a similar manner as a food web in ecology. However, I have seen pet theories roughly based on this kind of thinking that was patently absurd. I see it as merely a product of the large number hypothesis, finite fundamental band-gaps (Planck) or limits on the total entropy, and increases in the efficiency of returning the system to equilibrium at all scales.

 

[ZapperZ]

I can clean up a room without creating any waste. I can just put things where they are supposed to be. In any case, it seems like the definition of entropy is highly subjective, if so, it has no place in science, and should not in any way be called a law.

Who are you again to decide such a thing?

Your idea of the second law is VERY primitive! The second law is much more than just "disorder". It has a very deep statistical meaning in terms of phase space states that are available, a concept that you haven't fully grasp.

Furthermore, in your example, as has been pointed out, the amount of energy you expanded CREATES a higher level of entropy!

Before you try to falsify something, it is imperative that you truly learn what IT is. If not, you come off looking rather foolish.

Zz.

 

[Sybren]

Who are you again to decide such a thing?

In general, I would like to say that to accept/reject existing theories is something that everybody has to do for themelves, and only after having studied it with a critical attitude. What you have written here comes across to me as denying that idea.

I agreed with the rest of your post though.

 

[bobsmith76]

The room's entropy may have decreased a little, but your body's entropy increased a lot.

A little? A lot? It is clear that entropy cannot be measured so why is this even a physical law? Sure, it's true that my body's entropy increase and the room's entropy decreased but there is no way to measure these different quantities of entropy, so this is not science. This is just a general rule of thumb.

 

[bobsmith76]

Who are you again to decide such a thing?

If entropy is not subjective then come up with way to measure the entropy of 100 books lying in no order on the floor and a way to measure the entropy of 100 books ordered alphabetically on a shelf. Stated another way, you can't come up with an objective system to measure 10K airplane parts lying disorganized on a factory floor versus all those 10K airplane parts assembled into an airplane.

SLOT has no meaning, because it uses a word, entropy, that cannot be defined.

If I say

All x = y

And I cannot define when something is x and when something is not x, then I have discovered nothing.

 

[bobsmith76]

In general, I would like to say that to accept/reject existing theories is something that everybody has to do for themelves, and only after having studied it with a critical attitude. What you have written here comes across to me as denying that idea.

I agreed with the rest of your post though.

I can't tell who you refers to, so I won't comment.

 

[Drakkith]

I can't tell who you refers to, so I won't comment.

It refers to zapperz, like the quote in the post says.

 

[Dale]

It is clear that entropy cannot be measured so why is this even a physical law?

Of course it can be measured. If it couldn't be measured then we would have no way to determine if it were increasing or not.

What would possibly make you think that it couldn't be measured? The rest of your post is just wrong due to this misunderstanding.

 

[my_wan]

A little? A lot? It is clear that entropy cannot be measured so why is this even a physical law? Sure, it's true that my body's entropy increase and the room's entropy decreased but there is no way to measure these different quantities of entropy, so this is not science. This is just a general rule of thumb.

Answering this would cost me too much entropy. So, since you cannot tell me whether you can pick up 'that' rock or not you must not be able to pick up rocks, or measure how heavy they are?

 

[ZapperZ]

If entropy is not subjective then come up with way to measure the entropy of 100 books lying in no order on the floor and a way to measure the entropy of 100 books ordered alphabetically on a shelf. Stated another way, you can't come up with an objective system to measure 10K airplane parts lying disorganized on a factory floor versus all those 10K airplane parts assembled into an airplane.

SLOT has no meaning, because it uses a word, entropy, that cannot be defined.

If I say

All x = y

And I cannot define when something is x and when something is not x, then I have discovered nothing.

Who says you can't? In fact, I can show you estimates of the entropy of the EARTH!

1. http://arxiv.org/abs/1003.3937
2. D. Styer, Am. J. Phys. v.76, 1031 (2008).
3. http://arxiv.org/abs/0903.4603

Calculating the mess in your room is nothing when compared to these!

Entropy is very well defined within statistical mechanics. Where did you get the idea that it isn't? What do you think

dS = dQ/T

is?

Zz.

 

[lalbatros]

A little? A lot? It is clear that entropy cannot be measured so why is this even a physical law? Sure, it's true that my body's entropy increase and the room's entropy decreased but there is no way to measure these different quantities of entropy, so this is not science. This is just a general rule of thumb.

People asking homework questions here are supposed to have made a fair atempt at solving their homework. Maybe a similar rule could be applied to people pretending to discuss anything here!

It is the most elementary background in thermodynamics that entropy can be measured.
When bobsmith76 will be exhausted he will die in his closed room.
Heat transfer from his cold body to the rest of the room will allow an evaluation of the entropy creation according to the Clausius equality: dS=dQ1/T1 + dQ2/T2 . This quantity will be positive because bobsmith76 was initially warmer (T1) than the room (T2): T1>T2 and dQ2=-dQ1>0.

Entropy is used daily in industry and engineering.
I just spent almost a full week studying part of this document:

http://pbadupws.nrc.gov/docs/ML0907/ML090770163.pdf

My interrest was in cement hydration are related topics.
Entropy or free energy is one of the main data considered in this document.
It was measured thousands times from thousands of chemical reactions and other transformations.
The aim is quite practical.

 

[Dale]

3. http://arxiv.org/abs/0903.4603

Thanks, I especially liked this one.

 

[bobsmith76]

Everyone keeps saying that entropy can be measured but no one as of yet has offered a measure of the difference in entropy of every single part on a airplane lying on the ground disorganized and every single part of an airplane assembled in the way it was intended by its designers to be assembled.

There's no way to determine objectively or with mathematics the entropy or lack thereof, of, say, the Washington Monument. There is no way to determine this mathematically because it requires an intelligent agent to decide what counts as proper or ordered and what doesn't. If I'm wrong, let's see some proof rather than just empty assertions.

How are we supposed to falsify SLOT if entropy can't be measured? Defining just exactly what is a closed space also seems to be rather fuzzy. If SLOT is such a hard law then set up a test whereby it can be falsified. I'll stand in my room for 10 minutes, closing all the doors and I will decrease the entropy in that room. But of course there is no way this experiment can be carried out because there is no hard and fast measure for defining how much entropy has decreased if I alphabetically arrange 300 books.

 

[ZapperZ]

You are here not to learn, but to exercise your ignorance. This thread is done.

Zz.

 

[Dale]

In an effort of helping the OP and other people learn, let's calculate the maximum possible reduction in entropy from the OP's cleaning a room example.

In order to make the entropy change as large as possible we will start with a very large room, 10 m x 10 m x 5 m. We will say that the room contains 10000 items which are all scattered throughout the room and must be put in their proper place. We will further say that there is only one proper place for each item and that if it is 1 micrometer away in any direction or 1 arcsecond misaligned on any axis then it is out of place. This means that the entropy reduction from messy to clean is:
\Delta S_{clean} = - k \; ln\left( \left( \frac{10 \;m}{10^{-6} \;m} \frac{10\;m}{10^{-6}\;m} \frac{5 \;m}{10^{-6}\;m} \left( \frac{360 \; 60 \; 60}{1} \right)^3 \right)^{10000} \right) = -1.2 \; 10^{-17}\; J/K

Now, assuming somebody with a very low basal metabolism rate of 50 W and a very warm room temperature of 309 K the rate of entropy gain by the room/person system is:
\frac{dS_{BMR}}{dt} = -\frac{50 \;W}{310 \;K} + \frac{50 \;W}{309 \;K} = .5 \;mW/K

Comparing this to the entropy change from cleaning the room, we find that as long as it takes more than about .02 ps to clean the room, the warm person adds more entropy to the room than is removed through cleaning. The second law of thermo is definitely safe from people cleaning their room.

 

[lalbatros]

Congratulations DaleSpam.

This is obviously related to the Avogadro number in the sense that the number of atoms involved in the metabolism is much larger that the number of pieces involved when clean a room. It is intuitively very clear.

However, bobsmith6 might still argue that the room cleaning entropy is not a real measurement.
The metabolism is measured with thermometers.
In contrast the cleaning of the room is evaluated theoretically.
And there is still the question of why the precision of the alignement needs to be considered for the cleaning process, when it is absent when measureing the metabolism.

That's where we can see that thermodynamics is by far the most difficult topic in the whole physics, not technically, but conceptually, in my opinion. It seems that the interpretation of thermodynamics is more demanding than the interpretation of quantum mechanics!

Similarly to the bobsmith6 problem, the thermodynamic data to be used in chemistry can be compiled by many many different methods. Thermodynamics is the theory that relates all these methods like calorimetry to equilibrium measurements. Today purely theoretical methods, like for room cleaning, are more and more feasible thanks to our computational means.

would it be conceivable to "measure" the cleaning entropy instead of calculating it?

 

[Dale]

there is still the question of why the precision of the alignement needs to be considered for the cleaning process, when it is absent when measureing the metabolism.

Alignment of what? In thermal energy transfer there isn't anything to align. For the room cleaning the alignment of items is just part of the definition of what it means for a room to be "clean".

would it be conceivable to "measure" the cleaning entropy instead of calculating it?

Conceivable, certainly, but not even close to possible with current technology. The amount of entropy changed by cleaning a room is so minuscule that it would be completely swallowed up in the noise of the entropy that we can measure. We can't even turn a measuring device on and off fast enough. It is completely negligible currently.

 

[my_wan]

And there is still the question of why the precision of the alignement needs to be considered for the cleaning process, when it is absent when measureing the metabolism.

This part is easy. It is not that state of the system itself that determines the entropy change it is the likelihood of a state relative to all possible states. Consider a well defined system rather than the junkyard type states generally used in qualitative descriptions. This will help show what some people are calling arbitrary and why it is when taken as singular states. This also illustrates why local reductions in entropy are not a violation in the second law.

Take a pool table with balls randomly distributed on it. Any particular arrangement of balls is just as likely as any other particular arrangement. Hence some would say that means called a racked set balls cannot be a lower entropy than balls randomly distributed around the table, but it is for the fallowing reason. If you take every possible configuration of balls, every one being just as likely as the other, then the number of possible configurations with about equal numbers of balls on both sides of the table greatly outnumber the possible configurations with all balls on one side of the table. The more balls the more unlikely. Hence states with all balls on one side of the table is extremely unlikely and have a lower entropy.

Hence when you poke a hole in your car tire the air leaks out not because there is a law of motion that says it must come out, it comes out because the physical law says that it is more likely to come out than go in. The more likely it is to come, with more balls per unit volume, the more energy we can use from it to do work, i.e., use it to reduce the entropy of another system. None of this changes the fact that the "particular" singular state of the air in a room with the air evenly distributed is any more or less likely that than a "particular" singular state of the air with all the air on one side of the room. Only the number of all possible states that are more or less even distributed far outnumber the the number of possible states with all air on one side. Hence we never see it, and if we do the probable change of state to follow is so likely that we can use that knowledge to do work for us.

So even energy is nothing more than playing a game of odds with what is most likely to happen and the result of using that food, gas, whatever creates higher entropy making the same gas not usable twice.

In the airplane in the junkyard example, the state of the airplane parts lying around is just as unlikely as and assembled plane. Yet the number of ways the parts can be lying around outnumber the ways it can all be assembled. Just like the air in the room example. If you wanted the air distributed in the room in a precise high entropy state, like it was a few seconds ago then even without any entropy change, then the entropy cost of getting it back to that prior state is even higher than just getting it all on one side of the room, since there are many ways it can be distributed on one side of the room and only one way to have it back to the way it was a few seconds ago. So the degree of accuracy you want in a state is important in defining the entropy cost of getting it into a certain state even if you are not wanting a new state that has less intrinsic entropy.

The room cleaning example is not even necessarily a lower entropy. Some of my messes are more usable with lower entropy for me than it would be if somebody came along and made it all nice and neat. Making it all nice and neat destroys the multidimensional relational associations in the mess giving it a higher entropy from my perspective. The media style descriptions of entropy just do not work very well.

 

[lalbatros]

Conceivable, certainly, but not even close to possible with current technology. The amount of entropy changed by cleaning a room is so minuscule that it would be completely swallowed up in the noise of the entropy that we can measure. We can't even turn a measuring device on and off fast enough. It is completely negligible currently.

You are right again DaleSpam.
I think you illustrate very well the main difficulty of thermodynamics: it is sometimes very abstract.
Here, it is abstract because the measurement cannot actually be done, and there is no hope at all to do it anytime.
Therefore, in the room cleaning problem, the entropy can be calculated by extending the principle beyond anything that is reasonably measurable.
It crosses the border between engineering and philosophy.

In other circumstances, the entropy can be measured, but by various indirect ways.
This doesn't make the physical reality of entropy much easier to grasp.
It remains rather abstract, unless you get really familiar with it by your work and by the applications.

For example, it is not so obvious to grasp why equilibrium measurement can lead to free energy data and from there to enthalpy, and why from such equilibrium data we could predict some reaction enthalpy. The relationships are often rather abstract.

I can really understand questions like those from bobsmith76.
(although they make me nervous)

 

[Dale]

I can really understand questions like those from bobsmith76.
(although they make me nervous)

The problem was that bobsmith76 wasn't asking questions. He was making assertions. First he was asserting that cleaning a room is a violation of the 2nd law, second that entropy was subjective, third he was asserting that it cannot be measured, and fourth that entropy cannot even be defined. None of which are correct.

Btw, you are certainly correct that thermodynamics is abstract, but as long as it is self-consistent and consistent with experiment then it is good science.