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Caloric Theory

Isn't the idea of heat being a physical substance called caloric a debunked theory? Is the current understanding of the 2nd law of thermodynamics still based on this obsolete theory? Should it be noted that mainstream science no longer considers caloric a valid model of thermodynamics?--Subversive Sound (talk) 16:07, 10 August 2009 (UTC)

Indeed, heat is not a physical substance, if by "substance" we mean collections of molecules. However, none of the laws of thermodynamics require considering heat a physical substance. David spector (talk) 22:17, 26 December 2009 (UTC)

No such thing as equilibrium under real conditions.

A few years ago I spent considerable time analyzing natural ambient temperature fluctuations on a macro scale by means of two thermistors and an appropriate amplifier. Each thermistors was ~ 1mm in length. Regardless of how well the system was insulated there were always thermal fluctuations. On a nanoscopic scale it is a violent world where particles are in random rapid motion. Regardless of sample duration, temperature in any closed system will vary from measurement to measurement. One interesting universal effect is 1/f noise (also referred to as Pink_noise, Occurrences) where the noise (in this case temperature fluctuations) is relative to the reciprocal of frequency. The 1/f noise alone prevents consistent measurements regardless of sample duration. Another interesting study in terms of 2LoT is the Universe where one region of space is cold while another is hot such as our Sun. One may suggest the Universe is not yet at equilibrium, but then such a question becomes meaningless when asked at what point in time would the Universe be at 100.0...0% equilibrium.--PaulLowrance (talk) 16:52, 12 July 2008 (UTC)

Please reserve this space for discussion of potential improvements to the article. General discussion of the topic itself is not appropriate. - Eldereft (cont.) 21:30, 12 July 2008 (UTC)
The obvious point is the article makes various references to equilibrium when such a state is impossible. The article should make that clear.--PaulLowrance (talk) 23:25, 12 July 2008 (UTC)
The article already says "the second law applies only to macroscopic systems with well-defined temperatures." That means that if you only view the "nanoscopic" as "reality", then thermodynamic equilibrium is not "real." It's just an oversimplified bulk generalization. However (fortunately, I think) human beings are larger than a millimeter shortly after conception, and we don't have the sensitivity of an amplified thermistor, so equilibrium makes a lot of sense to us out here in our larger world. It's a useful concept to us big people who read Wikipedia. Maybe you will be able to understand us someday, millimeter-man. Flying Jazz (talk) 13:36, 4 August 2008 (UTC)
I agree thermodynamic equilibrium is an oversimplified bulk generalization. On a scale of say the size of an apple objects appear to be stable as far as the human eye's concerned, but take for example Brownian motion on particles that the unaided human eye can barely detect such as a grain of pollen. Anyone with a good magnifying glass can see such particles jittering around on water at room temperatures, even inside the best isolated chambers. In fact it was such pollen that helped confirm the existence of the atom-- reference: Einstein's 1905 paper. Such Brownian motion that occurs at macro scales always exists due to the natural ambient thermal energy. My point is that thermodynamic equilibrium does not exist at any scale. The Universe is in constant change. Even the Earth's spin that causes daily temperature fluctuations between night and day will affect the best insulated systems to some degree, as it would require infinite insulation. It would nice if the wiki article included a section on how the mathematical thermodynamic equilibrium is an impossible state. --PaulLowrance (talk) 18:08, 8 August 2008 (UTC)
I agree with PaulLowrance. I know next to nothing about thermodynamics, but already reading his comments has confirmed some thoughts I had been formulating after reading the article. --203.55.211.33 (talk) 04:37, 7 January 2009 (UTC)

The Sun

The section concerning the sun is largely irrelevant to this article.67.163.246.108 (talk) 05:40, 15 July 2008 (UTC)

The example is cited fairly regularly in second law contexts (I think my thermodynamics course put it between solar flux received by Earth and before degenerate white dwarves). I believe that its purpose here is as a material demonstration that figuring out how the second law holds can be fairly subtle. - Eldereft (cont.) 10:28, 15 July 2008 (UTC)
In any case, the section does not describe how the second law holds. As it is written, it seems fairly irrelevant. I think this section should be deleted. Jacob2718 (talk) 14:20, 11 September 2008 (UTC)

Dubious

The figure of 1kW/m² of at the sun's surface is surely wrong. This is the approximate value of the sun's energy at the surface of the earth, not the sun. Jdpipe (talk) 05:12, 19 July 2008 (UTC)

Section on the Sun

I deleted the section discussing heat transport in the sun. At first glance, there are several situations where the second law appears not to hold (a refrigerator!) and I don't think this is the right place to discuss all of them. If the issue is historical i.e if this was historically proposed as a violation of the second law, maybe we can include that but only if the appropriate historical references are added. Jacob2718 (talk) 14:26, 11 September 2008 (UTC)

Entropy And Gravity

"In simple terms, the second law is an expression of the fact that over time, ignoring the effects of self-gravity, differences in temperature, pressure, and density tend to even out in a physical system that is isolated from the outside world. Entropy is a measure of how far along this evening-out process has progressed."

I have some queries concerning this statement : 1) What motivates the caveat whereby the effects of self-gravity must be ignored in order for the differences in temperature, pressure, and density to even out with time. I severely doubt that the author of this passage meant to imply this, but are we to take it that the effects of a self-gravitating system (where, hopefully, an example could be provided of such a self-gravitating system) somehow preserve the overall entropy of a system so that either the entropy of the system remains unchanged OR that the entropy may even be reversed?

Perhaps I should rephrase this question - how did the author envision that gravity interferes with the progression of entropy as per the Second Law of Thermodynamics? Surely, gravitation and self-gravitation should not be expected to alter whether the Second Law of Thermodynamics holds? If so, why include the phrase "ignoring the effects of self-gravity,"?

ConcernedScientist (talk) 11:17, 29 September 2008 (UTC)

Hmm, self-gravity will lead to differences in composition between non-miscible phases: Structure of the Earth is a good and well-known example. I don't like the phrase quoted, but I can't immediately see that its wrong. Physchim62 (talk) 11:34, 29 September 2008 (UTC)
The problem lies with the "simple terms", not with self-gravity. While the second law always holds true, the simplified formulation does not, as can be seen in many real (but maybe somewhat uncommon) systems. Take for example a crystal. The density is not uniformly distributed, but nevertheless a crystalline state can be the equilibrium state of a system. I propose to remove the reference to self-gravity and add some caveat in the form "Often (but not always) the second law can be seen as an expression of the fact [...]" Hweimer (talk) 12:46, 30 September 2008 (UTC)
I am a physicis (long time ago that I did thermodynamics in first year university though), but I wouldn't have the slightest clue about the self-gravity remark. Can there be at least a link to an article explaining it better, or move it to a section going into more detail. I wouldn't expect an opening remark to contain this kind of vague remarks to little known effects. —Preceding unsigned comment added by 85.18.14.0 (talk) 21:49, 2 October 2008 (UTC)
Consider a nebula, a vast cloud of cold dispersed gas in space. Assume that the system is in complete equilibrium, with gravity force which is holding the nebula together equal to gas pressure (thus, the gas doesn't expand or contract). If this system were isolated, it obviously has maximum entropy and nothing can happen in it anymore - but in reality, it's not isolated and even a slight shock wave (e.g. a nearby supernova exploding) can break the equilibrium, contract the gas and help gravity overcome gas pressure. The gas condenses and makes new stars, drastically reducing entropy of the system. Can someone explain me how this phenomenon corresponds with "second law of thermodynamics"? As I see it, either the law does not work, or there is no such thing as an "isolated system" in reality.
Dear unsigned, there is no such thing as an isolated system in nature, only in thought experiments and in real-world thermodynamic systems considered for finite time segments. If the Big bang is a true theory, then it is an example of this evolution from order to disorder, compact to expanded. The laws of thermodynamics have more to do with probability and order, and less with the functioning of the the real world, in which "isolation" of a system is always relative and partial. This is why the second law apparently fails in the case of a refrigerator (mentioned above). The entire universe, considered as an isolated thermodynamic system, obeys the laws of thermodynamics. David spector (talk) 22:41, 26 December 2009 (UTC)

This article misrepresents the second law

I have a question/possible need for a correction. The article says: “The second law of thermodynamics is an expression of the universal principle of entropy, stating that the entropy of an isolated system which is not in equilibrium will tend to increase over time, approaching a maximum value at equilibrium.” Isn’t entropy a measure of “disorder” or the distance from equilibrium? If yes, at equilibrium the value should be at the minimum value. I studied this many years ago, I prefer to ask instead of making the change myself. —Preceding unsigned comment added by Adartsug (talk • contribs) 20:14, 3 February 2010 (UTC)


"In a system, a process can occur only if it increases the total entropy of the universe."

The second law is a generlization, and a *tendency*. A process that does the above *can* occur. It is not the second law of thermodynamics. Putting these similar, but misleading quotations up will only lead the reader in the wrong direction. Comments? Fresheneesz (talk) 01:46, 5 October 2008 (UTC)

I don't see the problem. Just because a process can occur doesn't mean that it will occur in a given finite time period, but all processes which do occur lead to an increase in the entropy of the universe. Physchim62 (talk) 09:40, 5 October 2008 (UTC)
The problem is that processes that decrease the total entropy of the universe *can* spontaneously occur, and that is at odds with that sentence. Fresheneesz (talk) 10:11, 5 October 2008 (UTC)
Give me one example of a spontaneous decrease in the total entropy of the universe… Physchim62 (talk) 10:32, 5 October 2008 (UTC)
I'm not going to answer that because it is a statistical improbability. And that is the point. Entropy and the second law of thermodynamics are about the tendency toward more likely states of matter. Heat transfers to cold because of simple statistics - the hot particles are more likely to give more heat to nearby particles, than cold particles are. However, statistics (and the second law of thermodynamics) does not prohibit that statistically improbable things happen. In fact they happen all the time (in small amounts of course). Please read this explanation. Fresheneesz (talk) 06:37, 6 October 2008 (UTC)
The classic thought experiment is Maxwell's demon. In practice, any Maxwell's demon has to do work to separate the two systems so as to lower the entropy, so increasing the entropy elsewhere. As for the blog link you posted, firstly, evolution by natural selection does not require a decrease in entropy in any closed system (the systems described are neither closed nor decreasing in entropy). Secondly, if entropy did spontaneously fall in a closed system, we would never know about it: if we did, the system wouldn't be closed, and our act of measuring the supposedly lowered entropy in the system would increase the entropy of the surroundings! Physchim62 (talk) 08:23, 6 October 2008 (UTC)
Two examples. The first is equilibrium fluctuations of macroscopic quantities about their maximum entropy values. If from S = k ln W we infer S = k ln p + const., where p is the probability, we can invert that to give p ~ exp (S/k). Now consider the entropy function S(x) for some macroscopic variable x. The equilibrium value of x will be that which maximises S(x). Sufficiently close to this maximum, we can assume that S(x) will be quadratic, so p ~ exp (S(x)/k) will have a Gaussian bell shape. Hence x will typically not take the value which completely maximises S(x), but will fluctuate in a band of slightly lower entropy close to this value. For example, the local air pressure in part of a room will mostly be close to the average air pressure - this is the value of the local pressure which maximises the entropy. But there is a random chance that very slightly more molecules will be in that part of the room at a particular time - a pressure fluctuation, exploring a state of slightly lower entropy. Often, of course, the standard deviation of these fluctuations is very small (though calculable). But sometimes the fluctuations Δx can become really quite large compared to x, particularly at parameter values close to phase transitions -- see for example critical opalescence.
A second example is entropy fluctuations in non-equilibrium systems on their way to equilibrium. The system entropy will usually increase; but there is a calculable probability that due to a fluctuation it will actually fall, and the system will (temporarily) explore a further-from-equilibrium state. See fluctuation theorem for the formula. Such excursions away from entropy increase have actually been observed in sufficiently small mesoscopic systems - see eg G.M. Wang, E.M. Sevick, E. Mittag, D.J. Searles & Denis J. Evans (2002). "Experimental demonstration of violations of the Second Law of Thermodynamics for small systems and short time scales". Physical Review Letters 89: 050601/1–050601/4. doi:10.1103/PhysRevLett.89.050601. -- Jheald (talk) 09:45, 6 October 2008 (UTC)
Exactly Jheald. The point of my complaint is that entropy does not always fall, but because of statistical anomalies will not always decrease at the same rate and might even increase. It is a very nitpicky complaint, but one I think need to be addressed. If I'm correct in my thinking, the statistically improbable decreases in entropy will even more rarely cause equilibrium to be reached later in time. Fresheneesz (talk) 04:08, 7 October 2008 (UTC)
About 14 billion years ago, if the Big bang theory is correct, an apparent statistical anomaly occurred in which all matter and energy "happened" to be confined to a rather small space. Such a random massively-reduced state of entropy is therefore apparently possible. This state of the universe doesn't violate the second law if the universe is not an isolated system, if the laws of physics started from the singularity that apparently occurred about 14 billion years ago, or if the second law alternates with an anti-second law. But all of this is speculation that is outside of the scope of this article; it is also mostly an area where the WP policy of WP:OR would prevent inclusion in the article. Just as Newtonian mechanics fails in certain "regimes" (very short time intervals, velocities comparable to the speed of light, temperatures close to absolute zero, energies in small multiples of Quanta (see Planck constant), and size close to the Planck length) and must be extended, you can think of the laws of thermodynamics as applying only to regimes most familiar to us. Any extension of thermodynamics for regimes in which it fails is beyond the scope of this article. Anyone is free to speculate, but WP articles must describe verified information, not speculation. David spector (talk) 23:04, 26 December 2009 (UTC)
Consider our universe as 'one point that banged', but 'other points' were all around us, and each of them banged. Since all of our universe is traveling away from itself quite quickly, we may never visit 'another point that banged'. Therefore, we must consider the second law of thermodynamics as defined by the best sources on our world, and thereby improve Wikipedia. --Sponsion (talk) 15:35, 2 May 2010 (UTC)

Applications to living systems

It is stated that:

However it is incorrect to apply the second law of thermodynamics to any system that can subjectively be deemed "complex".

Is this correct, in general? I would for instance expect a closed system to behave according to the second law of thermodynamics, even if it is complex. -- Crowsnest (talk) 12:27, 24 October 2008 (UTC)

I don't believe that the second law breaks down if a system is "complex". As for application to living systems, please see the article Entropy and life. David spector (talk) 23:12, 26 December 2009 (UTC)
In it's simplest for the second law states "In a closed system, entropy approaches the maximum"
The important part here is "In a closed system". A perfectly closed system can not exist in nature, except as the universe as a whole, and possibly not even there. Kid Bugs (talk) 22:58, 5 January 2010 (UTC)

Entropy?

Let me state just two strange things that, to me, seem to be implied by the second law of thermodynamics:

If I run either my (1) refrigerator or my (2) air-conditioning for an extended period of time (BILLIONS of years), what would happen? Entropy? Or does the law enable me to keep running my fridge and AC forever? 97.103.81.29 (talk) 18:16, 2 November 2008 (UTC)

Anything you do will increase the total entropy of the universe. In this case you would get an astronomical electric bill and help accelerate the heat death of the universe! --Itub (talk) 09:24, 4 November 2008 (UTC)
One consequence of the Second Law is that you can't run a refrigerator or air conditioning without an external power source: if you ran them for billions of years, your external power source would run out. On a related note, I was living in Paris during the 2003 European heat wave, when temperatures reached 44 ºC (112 ºF)… at the time, French newspapers ran commentaries on the Second Law, reminding people that keeping the fridge door open was a very expensive way of making the room even hotter! Physchim62 (talk) 21:39, 4 November 2008 (UTC)


On An apparent paradox about the 2nd law of thermodynamics

The 2nd law of thermodynamics states, in certain way, that all physical laws' information tend to dispersion, to deaccumulation, and, in this sense, all physical laws tend to dissipation and minimization.

But, the 2nd law of thermodynamics, is also another physical law.

So, how can the 2nd law of thermodynamics "dissipate" and "minimize" itself? (in certain sense, 2nd law of thermodynamics states that physical laws are false)

(PS: btw, if there's a time arrow, then there's an arrow; and if there's an arrow, then there's order and information.) --Faustnh (talk) 14:47, 5 April 2009 (UTC)

At the heat death of the universe, it will no longer be possible to observe if the Second Law is true or not! Physchim62 (talk) 15:29, 5 April 2009 (UTC)
The second law does not state, "all physical laws' information tend to dispersion". It states that isolated physical systems tend to disorder. The second law does not apply to Newtonian mechanics, for example, a set of laws that describe everyday physical force and motion almost perfectly. It also does not apply to Brewster's Law or any other. It does not apply to itself. It applies only to isolated thermodynamic systems.

The laws of physics have all been verified through experimentation, observation, and the consistency of a large body of theoretical reasoning based on them. If you feel that a law of physics is incorrect, paradoxical, or has some other such flaw, you may simply not understand the particular law. In such a case, a WP article may need to be clarified to help remove the possibility of the misunderstanding.

My own opinion: just because some WP articles may be too advanced for a casual reader to understand is no justification to claim that such an article is incorrect. People reading WP are expected to be educated enough to understand the scope of any article. On the other hand, WP articles should be written as clearly and completely as possible within a reasonable amount of space. David spector (talk) 23:29, 26 December 2009 (UTC)

On another strange question about the 2nd law of thermodynamics

Hi, I'm considering another special question about this physical law:

If the Universe doesn't suffer losses, then how come the 2nd law can be fulfilled at universal scale? (The second law bases on radiation arrow of energy; what happens when this arrow meets the border of Universe? should it reverse somehow? And if the Universe is a borderless sphere, what implications should this have with respect to that arrow?) --Faustnh (talk) 22:23, 8 May 2009 (UTC)

See WP:TALK: this page is for discussing improvements to the article, based on verifiable sources, not your original research. If you want to blether or get all existential, follow the arrow elsewhere. . . dave souza, talk 23:48, 8 May 2009 (UTC)
I agree with Dave Souza's comment, but I would have expressed it far more politely and gently. Foustnh is clearly sincere and interested in a discussion exploring implications of the second law of thermodynamics. Unfortunately, WP, as Souza points out in an unnecessarily rude way, is an encyclopedia of information, not a discussion forum. David spector (talk) 23:33, 26 December 2009 (UTC)

Rigorous treatment based on statistical physics

The derivation of the equation dS = dQ/T for reversible processes should be derived in this article from first principles, as it is an essential part of the second law. I gave a derivation (similar to given in the book by F. Reif) here, but it obviously belongs to this article.

I mentioned in the previous section of the article in the fundamental relation that dS = dQ/T for a reversible process is part of the second law, but even this statement is not emphasized in this article.

So, I think this article needs an appendix in which the derivaton of dS = dQ/T can be moved to. And a new section is needed to explain how you get from the definition S = k Log(Omega) to the conclusion that the entropy of an isolated system can only increase. Count Iblis (talk) 03:16, 11 August 2009 (UTC)

I agree.. the heat expression is in fact a special case of the general Boltzman equation S = k Log W (W = thermodynamic probability, which should also be defined) and W is replaced with Wp (most probable microstate).
Vh mby (talk) 10:05, 31 May 2010 (UTC)

easier explanations

Is it possible to include an easier explanation of this subject (and related)? Especially for childs or people with no background in physics jargon. Are there already some introductory articles on the subject?

Dear unsigned, I agree that WP should include in each article explanations that can be more or less understood by everyone as well as compact explanations that use jargon, mathematics, and other such mechanisms that permit eloquent description in a small amount of text.
In this case, the portion of the article just after "In simple terms..." gives the intuitive heart of the second law.
Web searching (or reading books in a library) can almost always uncover easy-to-understand information on any subject. WP is not a place to receive a complete, well-balanced education. David spector (talk) 23:41, 26 December 2009 (UTC)
What a foolish thing to say. The point of reading an encyclopedia article is to learn about a topic that you don't already understand. This is simply a very bad article, which badly needs improvement. Certainly no one who isn't already well-grounded in thermodynamics can make sense of this mish-mash. Even the statements of the 2nd law are couched in weasel-words. "Generally"? "Tend to"? Sheesh! What exactly do you think the purpose of this article is then, if not to educate? Yappy2bhere (talk) 06:44, 31 December 2009 (UTC)
I'm afraid I must agree with Yappy2bhere, this article is a hopelessly overcomplicated mish-mash that needs a ground-up re-write.
From the very first paragraph it falls apart. That paragraph could have been stated simply as:
"In a closed system, entropy approaches the maximum"
After that, definitions of the terms "closed system", "entropy" and the maximum value of entropy would complete the needs for casual research. The remainder of the article could then happily wander into areas for the more serious researcher.
Furthermore, the section "Applications to living systems", intended to correct the common misrepresentation of the second law by creationists, is probably much more than is necessary. The easiest rebuttal to their argument is to point out that a key phrase in the second law is the first four words, "In a closed system", which creationists leave out of their argument as a deliberate lie of omission. It is clear that they do not leave that part out by accident, as they are not stupid, and doing so would flunk anyone from grade 10 physics. It's pretty hard to convince someone that something that they desperately want to believe is wrong. Kid Bugs (talk) 21:36, 3 January 2010 (UTC)

Miscellany

I've gone ahead and deleted the following miscellany. None of it serves to improve the article.

  • Flanders and Swann produced a setting of a statement of the Second Law of Thermodynamics to music, called "First and Second Law".
  • The economist Nicholas Georgescu-Roegen showed the significance of the Entropy Law in the field of economics (see his work The Entropy Law and the Economic Process (1971), Harvard University Press).
  • Creationist Duane Gish incorrectly used the Second Law of Thermodynamics to argue that evolution was impossible, although stand-up comedian Dave Gorman has pointed out that Gish misunderstood the definition of a closed system.
  • The Last Question, a science fiction short story by Isaac Asimov, is centered around the question of how to reverse the Second Law of Thermodynamics, or entropy.
  • One of acclaimed comic writer Alan Moore's short stories, chronicled in a collection called Wild Worlds, depicts indestructible and/or immortal characters facing down the unstoppable entropy at the end of the universe.

Chemeditor (talk) 19:32, 11 October 2009 (UTC)

IMO, these items deserve to be moved somewhere where they can be preserved and found. Although they are less WP:Notable (or important) to be included in WP, they do appear to be true and clearly relevant for some WP users. David spector (talk) 23:44, 26 December 2009 (UTC)

QM derivation

Worth mentioning?

--Dc987 (talk) 07:40, 8 December 2009 (UTC)

Yes, but then this article has already been criticized, so we need to then mention the criticism also... Count Iblis (talk) 15:10, 8 December 2009 (UTC)
Where can I find it? I've only seen a few comments on the blogs. --Dc987 (talk) 19:52, 8 December 2009 (UTC)
arXiv:0909.1726, arXiv:0911.2610, arXiv:0912.1947 Hweimer (talk) 15:12, 4 February 2010 (UTC)

Heat radiation

When we speak of heat traveling in the form of radiation it seems to me we are really talking about net heat. As I understand it, two bodies of different temperatures are both radiating heat. The net effect is for the cooler body to warm up and wamer body to cool down, but heat travels from the cooler body to the warmer body at the same time heat travels from the warmer to the cooler body. The net effect does not contradict the 2nd law but in the process, heat is traveling from cooler to hotter. Jojalozzo 13:58, 2 May 2010 (UTC)

If in a vacuum, you had a microscopic, hot body separated 1 millimeter from cooler heat lamps surrounding at all angles, may be possible that heat can flow from cold to hot, and the reason is while the heat flux density of the cooler lamps is by definition lower than that of the hotter body, the effective area of radiation reduces as the heat from the heat lamps concentrates toward the center. Therefore, if the lamps are not too cold, it is conceivable that the heat flux from the lamps may be concentrated at the microscopic body, resulting in a heat flux density higher than the hot body, thereby warming it up.Kmarinas86 (6sin8karma) 19:28, 2 May 2010 (UTC)
A macroscopic example is an array of reflectors set to point at a particular spot, such as the PS10 solar power tower, where it is evident that heat in the form of radiation is reflected by the cooler solar reflectors into a spot that is heated to 285 degrees centigrade.Kmarinas86 (6sin8karma) 19:37, 2 May 2010 (UTC)

Introduction

The rules for editing and writing encyclopedia entries require the knowledge to be verifiable (ie true as far as possible to determine) and stated with clarity. Which excludes philosophical speculation.. reference to the 'equal a priori probability postulate to the future' have no relevance to the introduction of this topic, is unclear and inadequately referenced. Vh mby (talk) 03:53, 31 May 2010 (UTC)

log vs. ln

Shouldn't the equations containing "log" be changed to "ln" so that they don't get confused with logarithm of base 10? Compare with, for example, the entropy article. /Natox (talk) 07:56, 4 June 2010 (UTC)

Proposed deletion

Under the definition proposed by Lord Kelvin, the statement:

"This also means that it is impossible to build solar panels that generate electricity solely from the infrared band of the electromagnetic spectrum without consideration of the temperature on the other side of the panel (as is the case with conventional solar panels that operate in the visible spectrum)."

Is unclear at best, and incorrect at worst. If the phrase it accurate, it needs supporting explanation to justify the claim. Infrared and visible light are the same thing, just at different frequencies. Why then would it be necessary to consider the other side of the panel in one case but not the other? Perhaps the statement assumes that the hypothetical solar panel works off the net IR radiation, in which the radiation from the panel must be subtracted from the incoming radiation.

I personally don't see the relevance of this statement and suggest it be deleted. 65.112.42.84 (talk) 20:34, 24 June 2010 (UTC)

Well, it certainly needs clarification, but there is a grain of truth in there somewhere. At a temperature of, say, 3000 K, black body radiation is well into the visible. So its like saying you cant have a solar panel at 3000 K that generates electricity from the visible without at least worrying about a temperature gradient. If there is no temperature gradient, then the solar panel will be acting like a black body in the visible, emitting as many visible photons as it absorbs, whatever the mechanism, and there won't be any net gain of energy. PAR (talk) 00:44, 25 June 2010 (UTC)

Nuclear Fusion contradicts Thermodynamics

In nuclear fusion, matter is converted into energy which means energy CAN be created and contradicts the second law. —Preceding unsigned comment added by 88.106.65.159 (talk) 11:51, 27 June 2010 (UTC)

I think you mean first law. And, no, energy is not created. --Michael C. Price talk 23:58, 28 September 2010 (UTC)

NinjaQuick (talk) 17:51, 28 September 2010 (UTC) Not really, Nuclear Fusion, in its current form (read in the form we can use) requires energy to push the balance towards the products, this reaction produces less energy than it takes in. As such, it can be said that energy is lost when it transforms several times through the process of fusion. The actual energy loss, of course, is to the effect of radiation and valence/nuclear bonding. The energy (and matter) is not destroyed or created, it simply changes.

Remember, the only way we can know about energy is when we see its impact on matter, there is no loss of mass in nuclear fusion, however, there is particle radiation that will result in a transfer of energy eventually.

All this to say, if there is an increase of energy there is an increase of measurable behavior delta in the matter observed, we cannot actually measure the energy, only its "shadow".

Actually there is a mass loss in nuclear fusion, the masses of the products are less than the mass of the reactants, but in relativity, the first law would be re-expressed as a law of conservation of mass/energy. PAR (talk) 02:13, 29 September 2010 (UTC)

"Matter is converted into energy". That's horrible nomenclature. Matter is a form of energy.Kmarinas86 (6sin8karma) 21:04, 29 September 2010 (UTC)

Its not so bad. Which is a better statement: "space is converted to time" when you change inertial systems, or "space is a form of time"?. I think the first statement is better, and "matter is converted into energy" is better than "matter is a form of energy". Just like space and time, the distinction between matter and kinetic or potential energy is clear for a given reference frame. Its when you change reference frames that one loses and the other gains. Even in the same reference frame when the change is due to say, a fusion reaction, the distinction is clear before and after. PAR (talk) 02:52, 30 September 2010 (UTC)
Energy cannot be created or destroyed. Only transformed. You miss the point of nomenclature. Good nomenclature has less to do with what words or phrases sound like and more to do with what they appear to mean. Statements like "matter is converted into energy" give the impression that any process involving the "release of energy from mass" violates the first law of thermodynamics. Mass can be considered as a form of internal energy, and it can be easily taken into account in thermodynamic systems.Kmarinas86 (6sin8karma) 04:59, 30 September 2010 (UTC)

Contradiciton within the article

Non -isolated systems section: Also, John Ross writes:[11] 

   Ordinarily the second law is stated for isolated systems, but the second law applies equally well to open systems.

Applications section: Furthermore, the second law is only true of closed systems.

It's a long article and I suspect these aren't the only things that don't match up. therefore I recommend a complete rewrite by an expert or whatever 131.151.90.125 (talk) 08:49, 28 July 2010 (UTC)

It would be most appropriate to see a mathematical example which would indicate the validity of this statement by John Ross.Kmarinas86 (6sin8karma) 00:07, 29 July 2010 (UTC)

Rewriting the article

This article is not only self-contradictory,but also poorly organized.I suggest to rewrite it into these parts(not the names of sections,just the content):

  1. Kelvin and Clausius form of the Theorem and their equivalence
  2. Carnot's theroem and Perpetual motion of the second kind
  3. Clausius' inequality
  4. Introduction and the well-definity of Entropy and the mathematical form of the Theorem
  5. Available useful work
  6. Several so-called "paradoxes" of the Theorem(like Maxwell's Demon,Gibbs paradox)
  7. Self-organisation and life
  8. Derivation by stastical mechanics
  9. Unresolved problems(time arrow,and the heat death of the universe)

I have no idea where to put the "History" section and perhaps an independent section containing all the common misinterpretations of the Theorem will be useful. --Netheril96 (talk) 13:54, 2 October 2010 (UTC)

Oh,I forget,another issue to address is the generalization when it comes to negative thermodynamical temperature.--Netheril96 (talk) 14:21, 2 October 2010 (UTC)

LaRouche

Perennial candidate for U.S. President Lyndon LaRouche has strong view on this topic:

  • Pobisk Kuznetsov.... and I agreed on many things, ... But, we disagreed on his defense of the so-called Second Law of Thermodynamics, which, for me, is bunk. [..] Now, the problem with this Second Law of Thermodynamics, is it's based on the assumption of a mathematical physics, not a physical chemistry. [..] In other words, that the Second Law of Thermodynamics is bunk: throw it away! [1]
  • The presumption concocted by such hoaxsters as Rudolf Clausius, Hermann Grassmann, Lord Kelvin, et al., which is known as the claimed principle of reductionist thermodynamics, the so-called principle of entropy (or, ‘second law’ of thermodynamics), was an ontological fraud from its inception. [2]
  • Among the most notable effects among what the work of Vernadsky has contributed to economic science, has been the crucial and systematic refutation of the hoax associated with the term "second law of thermodynamics." [3]

As these excerpts indicate, LaRouche views this so-called law with great skepticism, apparently believing in energy-flux density instead. Since LaRouche has followers, editors will occasionally drop in to add critical views.[4].   Will Beback  talk 

"apparently believing in energy-flux density instead." Obviously that is the case. You can take a bunch of mirrors and/or lenses to heat things above the temperature of the light source. It's just hard to engineer, but it is not impossible. Lenses and mirrors are obviously ways of increasing the "energy-flux density". It is also a way of sending heat energy from a colder object to a hotter object in an continuous and reliable manner. Such is impossible with systems relying only on conduction or convection however. The ability to concentrate heat this way must rely on the radiation form of heat that travels at the speed of light. As we know, light can be redirected at will using its properties of reflection and refraction. Also, recent attempts to treat the atom as a "hot" heat reservoir seem ad hoc and inappropriate to use for what is actually a quantum system whose ability to give off heat is selective in nature, and indeed, is the purview of quantum chemistry, not entropy.Kmarinas86 (Expert Sectioneer of Wikipedia) 19+9+14 + karma = 19+9+14 + talk = 86 14:04, 15 November 2010 (UTC)
Why are we discussing this? If it wasn't obvious before, it certainly is now - LaRouche is a crank, in thermodynamics as well as politics. --Michael C. Price talk 14:32, 15 November 2010 (UTC)
This was just meant as a "heads-up".   Will Beback  talk  19:41, 15 November 2010 (UTC)

"Proof"

This is a bit out of my area, but should it be a concern that having lost every instance of the word "proof" from the article last month, the lead now says "There is no formal proof for the second law."? --McGeddon (talk) 10:24, 9 November 2010 (UTC)

The second law is a basic law of physics, so how can you prove it? The sentence "There is no formal proof for the second law" is inappropriate, though.--Netheril96 (talk) 10:48, 9 November 2010 (UTC)
No proof? Rubbish. Classically there was no proof since the atomic behaviour was a black box. Quantum mechanically, though, the proof is trivial, and is sourced in the article. --Michael C. Price talk 12:40, 9 November 2010 (UTC)
Don't mix thermodynamics and statistical mechanics up. In thermodynamics the second law is a fundamental law, or axiom; while in statistical mechanics it is derived from the equal probability postulate. It is better not to mention whether it is provable or not in the article.--Netheril96 (talk) 13:04, 9 November 2010 (UTC)
The only meaningful distinction between thermodynamics and statistical mechanics here is that the former is classical, the latter quantal. So perhaps we should say that there is no proof classically, but that it can be proved from QM. --Michael C. Price talk 17:27, 9 November 2010 (UTC)
The current lead is OK.--Netheril96 (talk) 13:05, 9 November 2010 (UTC)
Actually I don't think the lead is okay. It states that the 2nd law relies on the assumption "that all accessible states of an isolated system are a priori equally likely" which is a bit vague (requires equilibrium?) and begs the question of why that is a reasonable assumption. A better proof/derivation is from unitarity, which the article already mentions. Any objections to mentioning that in the lead? --Michael C. Price talk 17:23, 9 November 2010 (UTC)
The term proof might mean different concepts in different fields and I think it is best to avoid the term when it comes to physical laws or axioms. For a physicist deriving thermodynamics from another theoretical framework, such as QM might constitute a proof since the same result has been obtained, but for a mathematician that might not be enough, as the new frame work might still have other basic axioms that should be proven first as well. Derivation from other frameworks seems better language. It would certainly be alright to mention the derivation from the principle of unitarity of probabilities, as the lead should be a summary of the article. But I think the section in the body should also be presented in more accessible detail, in particular, why the 2nd law actually follows specifically.
@Michael C. Price:If you expand the unitary section, it is OK to mention that in the lead.--Netheril96 (talk) 00:48, 10 November 2010 (UTC)
Slightly expanded the unitary section. --Michael C. Price talk 21:20, 19 November 2010 (UTC)
Seems to me that a heavy dose of caution, and some industrial-strength caveats, are in order regarding "proofs" of the Second Law.
In particular, consider Loschmidt's paradox: if one could ever prove that entropy increased going forwards in time, if one applied the same mathematics starting from boundary conditions specified at a particular point in time but trying to retrodict into the past where the system came from, one would see entropy getting larger the further into the past one went.
There are also some questions to consider as to what assumptions are being made to allow entropy to change at all -- where is the mixing behaviour being considered to come from? If one could project forward from perfect information with perfect accuracy, there would be no mixing at all, and no entropy change, just determinism. Arguably, the entropy increase arises from coarse graining of states -- ie from a choice made by the analyst as to how to describe the system, and what information will be systematically thrown away.
For more detail, see the careful discussion of the H theorem and its meaning (or not) in the Tolman's classic book on Statistical Mechanics; its echo in Kittel [5]; also PCW Davies, p. 43 et seq [6]. Jheald (talk) 00:15, 20 November 2010 (UTC)
FWIW I go with your entropy increase arises from coarse graining of states -- ie from a choice made by the analyst as to how to describe the system, and what information will be systematically thrown away. At a fundamental level (i.e. no coarse graining) there is no entropy increase, which is the resolution to Loschmidt's paradox - no entropy increase in either temporal direction. But once we start restricting our interest to macrostates, then the entropy increase sneaks in. So where does this leave the article? --Michael C. Price talk 01:22, 20 November 2010 (UTC)
Michael C. Price - I've been reading Everett's thesis - I think that coarse graining is not the source of the increase of entropy over time. Coarse graining only adds a constant to the entropy. According to Everett - and I agree - from an information-theoretic point of view, looking at a classical situation, a microstate is a point in a 6N dimensional space. If you have a probability density in this space, then you can calculate a "total entropy" in the usual way. It can be proven by Liouville's theorem that this entropy remains constant in time. Its easier to talk of "information" defined as the negative of the "entropy". So it can be shown that Liouville's theorem implies that the information is constant in time. This information can be separated into a sum of "correlation information", which is information from knowing correlations among particle velocities, and "independent information", which is information available assuming no correlation exists. If, for example, you start out with a probability distribution in which each position and velocity of every particle is independent of any other (i.e. the probability density is a product of individual probabilities for each particle), then the information is pure "independent information". As time goes by, this information decreases while correlation information increases. The resolution to Loschmidt's paradox - no entropy increase. When you decide to renounce knowledge of correlations in position and momentum resulting from collisions (stosszahlansatz), you are left with the decreasing "independent information" or, equivalently, increasing "independent entropy" which is thermodynamic entropy divided by the Boltzmann constant, to within an additive constant. PAR (talk) 03:58, 27 April 2011 (UTC)

Derivation from unitarity

An IP keeps reverting the derivation of the 2nd law in QM, claiming it is unsourced bullshit. I have expanded the reference to to make the sourcing more explicit. The quote in the reference now reads

Appendix I, pp 121 ff, in particular equation (4.4) at the top of page 127, and the statement on page 29 that "it is known that the [Shannon] entropy [...] is a monotone increasing function of the time."

Hopefully that is sufficient. -- cheers, Michael C. Price talk 10:44, 28 May 2011 (UTC)

The current text reads: "The time development operator in quantum theory is unitary, because the Hamiltonian is hermitian. Consequently the transition probability matrix is doubly stochastic, which implies the Second Law of Thermodynamics.[14][15] This derivation is quite general, based on the Shannon entropy, and does not require any assumptions beyond unitarity, which is universally accepted. It is a consequence of the irreversibility or singular nature of the general transition matrix."
I claim that this is both unresourced and BS. Specifically:
The first statement is correct. The first half of the second statement - "consequently the transition probability matrix is doubly stochastic" - is misleading, because in order to get the result the paper relies on the collapse postulate (to calculate the probabilities using the Born rule), which is itself not a consequence of the dynamics and is known to be in contradiction with it (aka the measurement problem - the many worlds interpretation, for which the quoted text is the locus classicus, is one of the attempts to get around this contradiction, but it is itself quite problematic). Hence it is not true that the derivation "does not require any assumptions beyond unitarity" (even if the unitary nature of the time development operator is used at one point). The last sentence - that the "singular nature of the general transition matrix" is responsible for the "derivation" is also completely opaque and if we take the standard meaning of "singular" matrix then is false. This whole section is misleading since it suggests that we are in a better position to "derive" the Second Law from QM (or QM+information theoretical approach to entropy) then in classical mechanics. We are not.
Regardless of the validity of the claims I contend that the quoted text itself does not make them. Sourcing is needed for:
  • the claim that unitarity is the only assumption needed to derive entropy increase
  • the claim that the doubly stochastic nature implies the Second Law of Thermodynamics.
Neither of these claims are made in the referenced text. In fact the text reiterates (on p 107) the by-then universally accepted claim that it is an "erroneous impression that the quantum formalism itself implies the existence of quantum-jumps (stochastic processes) independent of acts of observation." Without smuggling in collapse in one form or another the derivation can not be made. The way how the text smuggles in collapse is merely an interpretation of QM, there are other interpretations, like Bohmian mechanics, which do not rely on this assumption. This conjecture may have some value in the context of the Many World interpretation of QM but then it is needed to be appropriately sourced and merged under that heading. Inclusion under the Second Law article in this form is misleading. Cheers, Gyepi (talk) 14:38, 28 May 2011 (UTC)
It doesn't matter how the collapse (in one form or another) is smuggled in, the fact is that every interpretation smuggles it in one way or another, so this is not an interpretational issue - otherwise we would have the absurd situation where we could derive the 2nd law in some interpretation and not in others.
The derivation of double stochasticty from unitarity is trivial; tag that statement as requiring sourcing, if you must, but sources will be easy to find. -- cheers, Michael C. Price talk 17:05, 28 May 2011 (UTC)
This in untrue. Look up De Broglie–Bohm theory - there is absolutely no collapse in this interpretation (the theory is deterministic), and yet it is empirically equivalent with QM (or with Many Worlds interpretation). In that fraimwork this argumentation does not go through either. Again, a derivation which makes use of a contradiction which is then explained away by an interpretative move is not a derivation; it still faces the Lochsmidt's paradox.
Regardless of this debate (in which I'm trying to explain why the section is BS) I maintain that the section needs to be removed on grounds of not being sourced, or formulated in a way that is not misleading. Currently it is misleading and it is not sourced, there is no direct mentioning of these conclusions and their application to the Second Law even by the referenced author. I appeal to another editor to check the veracity of this claim. — Preceding unsigned comment added by Gyepi (talk • contribs) 17:33, 28 May 2011 (UTC)
Upon further reflection I might be wrong about the difference in derivability of the same statement between MW and Bohmian mechanics. I don't know how much does the derivation exploit the contradiction between dynamics and collapse, however I maintain that the interpretation of the results by the current wikipedia note is misleading even if this does not cause a problem. The reason is that the theorems referenced explicitely make use of the uniform measure. I.e. on page 29 referenced as the source by Michael C Price "This entropy is, however, simply the negative of the information relative to the uniform measure", Corollary 2 on p. 128 says that information relative to the uniform measure is decreasing in case of a doubly-stochastic matrix. Hence even if the derivation is not making use of a contradiction it is only valid given the fundamental postulate (=equal a priori probabilities). The current wikipedia entry juxtaposes the derivation in classical thermodynamics and statistical mechanics implying that in the second such postulate is not used. ("In classical thermodynamics, the second law is a basic postulate applicable to any system involving measurable heat transfer, while in statistical thermodynamics, the second law is a consequence of unitarity in quantum theory.") This is misleading and false.
Regardless of whether I'm identifying the source of the problem correctly I maintain that these statements can not be found in the original text. Given that they would be fairly important if they were true one would assume that they appear somewhere in the physics literature between 1956 and 2011 so finding another source should not be a problem. I wouldn't have high hopes for this; for instance many experts read Everett's thesis (since as I mentioned it is the locus classicus of MW interpretation), yet this achievement of Everett somehow seems to have skipped the attention of all these scholars since it is not even gestured at in articles written by experts (ie http://plato.stanford.edu/entries/qm-everett/ ). — Preceding unsigned comment added by Gyepi (talk • contribs) 18:55, 28 May 2011 (UTC)
I don't know whether the second law follows from unitary evolution or not. I do know that Loschmidt's paradox and classical statistical mechanics do not need quantum mechanics for their resolution, and I expect their resolution in QM is analogous. Not knowing enough about this, I would hope that this article will inform me of any controversy about this and provide me with enough references to allow me to investigate the controversy. I would hope that the article does not provide one single point of view because one school or the other "won" the argument. PAR (talk) 20:21, 28 May 2011 (UTC)
I agree here. Forgetting about Everett and Many Worlds specifically, just using common sense, you can see that the psysical state of a sysem has to contain correlations of a conspirational nature, otherwise the entropy cannot become smaller when evolving the system back in time. But these correlations can apparently be ignored when evolving the system forward in time. It is perhaps more interesting to include some modern treatments that consider the case of isolated systems. I have seen some articles were random matrix theory is invoked to derive thermodynamics (instead of ergodicity, which is typically irrelevant realistic situations). Count Iblis (talk) 20:49, 28 May 2011 (UTC)
Iblis, you can't evolve the system back in time with a non-invertible transition matrix. -- cheers, Michael C. Price talk 22:27, 28 May 2011 (UTC)
I see, but then the validity of invoking those transition matrices is an assumption that is not purely implied by unitarity alone. Count Iblis (talk) 00:03, 29 May 2011 (UTC)
There is no "resolution" of Loschmidt's paradox, classical or quantum, which would be widely accepted in the literature as such. There are resolution attempts, such as relying on the past hypothesis, which are seriously criticised. It is me who defends the generally accepted position here, namely that we don't have yet a non-postulate based derivation of the Second Law from either classical or quantum dynamics. (For the state of literature on these issues see e.g. http://plato.stanford.edu/entries/time-thermo or http://plato.stanford.edu/entries/statphys-statmech .) It is fine to mention a controversy in the literature, but this is not what the current page does, the current page makes it seem this is a settled issue, and does so by making claims which are not sourced (by making claims which are not made by the referred text, but which are interpretations of a wikipedia contributor). I don't know what is not clear about this point I'm making. The current text either needs to be changed significantly, or sourced appropriately, or removed. Gyepi (talk) 21:01, 28 May 2011 (UTC)
I don't know what is not clear about this point I'm making. What is clear is that you haven't understood a lot of your claims.
  1. You either don't understand DeBroglie-Bohm or see the significance of my rider about collapse "in some form or another". However this is all irrelevant; Everett's derivation of the 2nd law preceeds, and is independent of, his interpretational construction.
  2. You claim that Everett relies on assuming equal a priori probabilities; you have confused his "uniform measure" with the a priori probabilities; there is no connection.
  3. You have failed to explain why the quote "it is known that the [Shannon] entropy [...] is a monotone increasing function of the time." is not explicit enough.
-- cheers, Michael C. Price talk 22:27, 28 May 2011 (UTC)

Clausius-Mussoti etc.

To To 59.177.108.25 aka 120.56.176.59:

I think you are confusing the Clausius statement of the second law with the Clausius–Mossotti relation, which has to do with dielectrics. Please provide a reference if I am wrong, and check the spelling of the second name. Also, the Kelvin statement might be properly referred to as the Kelvin-Planck statement, I don't know. At any rate, your spelling of Planck is also incorrect. PAR (talk) 15:44, 7 October 2011 (UTC)

William Sidis's speculation is not mentioned

How come William Sidis's mental experiment,the one that comes to the conclusion that there are ( might be) regions in the universe where the second law of thermodynamics operates in reverse, is not mentioned? I could not find any article that refutes his claim. To be fair i have not found anything that might validate the conclusion either. Still it probably should be mentioned in the article even though his speculations have not been verified to this date ( from what i know...). — Preceding unsigned comment added by Olajon (talk • contribs) 11:25, 6 July 2012 (UTC)

Is there a reference (preferably online) that clearly explains his reasoning? PAR (talk) 12:28, 6 July 2012 (UTC)
http://www.sidis.net/ANIMContents.htm . Somewhere in chapter 4 he reaches a first conclusion regarding the 2LoT. Well, if by "reference" you mean a reputable 3rd party source,no. But Buckminster Fuller " (upon receiving a copy of The Animate and the Inanimate 65 years later, expressed in a letter to Scientific American his "...excitement and joy that Sidis did go on to fulfill his promise.") " and that is a good indicator that WJS's reasoning which is probably based on theories, postulates and observations of the time ( including theory of relativity and quantum mechanics which where available in 1920 when he finished the book and in 1925 when he decided to publish it) isn't all mumbo-jumbo and might deserve to be mentioned in the article. Hopefully some physicists ( astrophysicists actually) might further clarify whether there any observations that contradict his claims from the first half of the book. Olajon (talk) 19:52, 7 July 2012 (UTC)
I've looked at the reference, and it appears to me that he does not speak the language of statistical mechanics except in a very vague way. For example:

"Tracing thus from a given momentary condition of the universe, our forward and backward reasoning combined might be interpreted, if such reasoning could be trusted, to mean that the second law of thermodynamics holds good as a probability as to the future, but that its reversal holds true as to the past. Aside from this result being untrue in point of fact, it is self-contradictory, for any given moment of time is always future as to moments that precede it, and past as to moments that follow it. It follows, then, that there must be some fallacy in Clerk-Maxwell's reasoning, which, when extended, gives us the second law of thermodynamics in the general form."

This is, to me, an impenetrably vague statement. The article is basically in the same vein, without any mathematical development. I think, in order for this theory to be taken seriously, it has to have some discussion and support by peer-reviewed third parties. PAR (talk) 16:07, 8 July 2012 (UTC)
Mathematical development would probably make the book much larger. I agree that the particular paragraph you quote is kind of vague ( to me) but I thought it was just because i'm not a native speaker of english and i don't understand some of the constructs he uses. I also see that loschmidt also imagined and pointed the weirdness of the 2LoT when time is reversed before Sidis.

it has to have some discussion and support by peer-reviewed third parties

True but i think most are avoiding the book probably because of it's second part which discusess life and other topics.
The part in the book where the 2LoT is suggested to be an overwhelming probability rather than a law is also confirmed in the fluctuation theorem ( from what i understand)
What's left is the claim that there are regions where the 2LoT is reversed which has not been discussed by reputable sources.( As i said before,I sometimes feel this book is not viewed seriously because of the second part, not because of the lack of math development).I'm a little busy right now but once my workload gets lighter i will see at least what the physics-forums people think about this and maybe send some emails to some random picked universities's science departments.That hopefully will spur an interesting discussion.Or maybe some angry replies :)
In the end i still believe it would deserve a honorable mention maybe in a new chapter called Unproved claims pertaining to 2LoT if not in the controversies section .But maybe that is too much, as you say. Olajon (talk) 05:44, 10 July 2012 (UTC)
It looks that at very small scale the probabilities of 2LoT are a little different, since there are intervals smaller than 2 seconds when the 2LoT is not respected overall. http://www.newscientist.com/article/dn2572-second-law-of-thermodynamics-broken.html Olajon (talk) 06:03, 10 July 2012 (UTC)
The idea that the second law can be "broken" is not news. Even Boltzmann, the guy who developed the statistical mechanics description of the second law, knew it could be "broken". And using the word "broken" is arguable. You could say that the second law only strictly holds in thermodynamic limit - the limit of an infinite number of particles, and the fluctuation theorem describes the probabilies that a finite system will deviate from the predictions of the second law. The smaller the system, the larger the expected amount of deviation. You could say the second law is never broken, because there is no real system that it applies to, its a limiting case that never happens in the real world, and its value lies in the fact that larger systems obey it more closely than small systems. But there's more drama in setting up the second law as a straw man by pretending it applies to all systems, and then knocking down the straw man with "fascinating" experiments that prove that it is violated.
I cannot imagine a case where the second law is reversed. The statistical mechanics explanation of the second law is based on the idea that all possible microscopic configurations of a system are equally likely to occur over an infinite amount of time, and that most of the macroscopic states of a system are indistinguishible from each other. It follows that a macroscopically unlikely state (low entropy) will most probably evolve towards a macroscopically likely state (high entropy). If the second law is to be reversed, then one of these assumptions has to be suspended. Sidis' musings never delve this deep into the foundations of the second law, so I am really doubtful of the validity of his reasoning. PAR (talk) 02:47, 11 July 2012 (UTC)

My ha'penny worth

"...natural processes have a preferred direction of progress..." should be re-phrased without using the concept of preference. It is absurd to suggest that natural processes 'prefer' anything. Please try to work out exactly what you mean, and express it clearly. Perhaps 'spontaneous' might be what you have in mind ?

"This also means that it is impossible to build solar panels that generate electricity solely from the infrared band of the electromagnetic spectrum without consideration of the temperature on the other side of the panel (as is the case with conventional solar panels that operate in the visible spectrum)." It is not impossible in principle that photovoltaic cells working on the energy-gap principle could be made to work in the infra-red region. In fact, given the properties of silicon as a semiconductor one can predict that conventional photocells do in fact operate in the infrared. The point which should be made here is not the difference in wavelength involved, but alternative thermodynamic principles, namely the random nature of heat, and the 'ordered' nature of e-m radiation as energy forms. Replacing "the infrared band of the electromagnetic spectrum" by "heat" would be a gesture in the right direction. Conversion of e-m radiant energy to other forms is theoretically possible with 100% efficiency just as the conversion of mechanical energy is; this happens in wireless aerials. But the conversion of thermal energy to other forms is subject to the implications of the 2nd law, Carnot's law, etc; it is in fact the basic problem of thermodynamics. Perhaps rather than obscuring this important basic idea it might be worth elaborating it, and trying to say what it is about thermal energy which distinguishes it from other forms in this respect. This, it seems to me, is the key concept involved in the 2nd law, and in fact is what it is all about; it should at least be mentioned, preferably at the top of the page.

(This was last edited on 19 December 2012. It lacks a time of editing label and I think has therefore eluded the usual archiving process. Time to archive it, I think.Chjoaygame (talk) 06:54, 21 November 2015 (UTC))

Carathéodory statement

Is the Carathéodory statement different from a careful topological/differential-geometric statement (for a suitable manifold of states of thermodynamic equilibrium) that has the physical meaning just that temperature belongs to a 1-manifold, and that transfer of energy as heat is one-way, from hot to cold?Chjoaygame (talk) 07:19, 24 January 2013 (UTC)

Lead really needs to be simplified

The lead is extremely dense. As a non-scientist, I came to this page for a quick refresher of what the 2nd Law states. Instead, I had to sift though some fairly obtuse text to realize the simple answer I was looking for is it's about entropy. I am sure the information provided is more precise, and would be more useful to people in certain situations. But, for the average reader, would it be correct to say something along the lines of "The 2nd law generally states that, in a closed system, entropy tends to increase"? I acknowledge this involves a weasel word (i.e. generally states) but it's much easier to digest. And, if someone wanted more info, they could still find the additional specifics within the body of the article.

I should note again that I am not a scientist and haven't studied this since high school -- it's entirely possible my proposed definition is not entirely correct. But, perhaps we could modify it to make sure it's accurate, and yet still easy to understand. Thoughts? JoelWhy? talk 13:34, 6 June 2012 (UTC)

Agreed. The lead is awful. Even if you understand physics, its still a headache to read. For example instead of "The second law declares the impossibility of machines that generate usable energy from the abundant internal energy of nature by processes called perpetual motion of the second kind", we could just say ""The second law declares that perpetual motion machines are impossible". Kaldari (talk) 23:44, 5 July 2012 (UTC)

I modified lead section accordingly. Dan Gluck (talk) 21:47, 15 February 2013 (UTC)

"Accordingly" is not accurate. The 'modification' was not a simplification. It was a re-casting from a particular point of view.Chjoaygame (talk) 01:28, 17 February 2013 (UTC)
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