Talk:Second law of thermodynamics/Archive 11

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Archive 11

Strangely constructed first sentence

The first sentences is poorly constructed. The first phrase up to the "that is" makes sense but the second clause is incomprehensible as it stands. A simple correction would be to insert an "it is" before the "a system" and stylistically, "in other words" sounds better to me than "that is"

..."the total entropy of an isolated system of particles can never decrease over time, that is, a system in which neither energy nor matter can enter nor leave. — Preceding unsigned comment added by 2A02:C7F:C409:DA00:A91E:3E6A:6C23:3615 (talk) 17:58, 14 March 2018 (UTC)

Not sure why this doesn't break the Second Law

WP:NOTFORUM

I'll assume it doesn't, but I can't see why. Advice welcome, I've been scratching my head for a decade.

The molecules of a gas, have most of their energy as translation. As they move about, they are subject to gravity, losing speed as they rise, and gaining speed as they fall. Particle speed equates to temperature, so a column of gas, in a gravitational field, will be colder with height, as is observed in the atmosphere. There may well be adiabatic cooling as a pocket of gas rises and expands, caused by stirring ; but the principle suggests that cooling with altitude would occur, even if there were no other effects. That means an atmosphere of gas, around a planet, will maintain a permanent variation of temperature.

Power could be extracted continuously in many ways :

A very long thermo-couple would connect large metal plates at different altitudes

A vapour-filled balloon is bigger when hotter, so it has more net buoyancy ; and any thermal insulation would give a time lag. The balloon would rise until it chilled, then fall until it heated, cyclically.

A reservoir at one altitude, is hotter than one at a higher altitude. A U-tube which is fed from the top reservoir, and is insulated except where it dips in the lower reservoir would, once flow was started, have cold water in one arm, and hot water in the other. The water in the cold falling arm being denser, would support a taller rising column of water in the hot arm ; the excess of which would be ejected as a fountain. GeoffAvogadro (talk) 21:35, 6 July 2018 (UTC)

Earth is not an isolated system. The warm temperatures at lower altitudes are maintained by input of solar energy. So there is no violation of the laws of thermodynamics.--agr (talk) 21:53, 6 July 2018 (UTC)

An idea similar to your balloon example already exists: see drinking bird. Tigraan^{Click here to contact me} 17:18, 23 July 2018 (UTC)

Imagine the Earth were so far from the Sun, that there was no solar heating, and it had no internal radioactive decay ; would the atmosphere ( probably needing to be only Helium, to be a gas at 6 Kelvin ) be the same temperature on the surface, as at say 10 kilometres altitude ? If so, how would a molecule of air moving vertically, in the Earth's gravitational field, keep the same kinetic energy ( and hence velocity and hence temperature ), as it gained or lost the gravitational potential energy, of that 10 km of height ? Air molecules may well interact, sharing and equalising their kinetic energy ; but over any finite change of height, there must be an equal and opposite change of kinetic energy. If this were not true, a molecule of air which was moving upwards, would continue at the same speed, indefinitely, until it escaped to space ; and that would seem to break the even-more unbreakable First Law.GeoffAvogadro (talk) 19:42, 24 July 2018 (UTC)

@GeoffAvogadro: Ask such questions at Wikipedia:Reference_desk/Science. The talk page of articles is intended to discuss how to edit articles, not the topics they cover. Tigraan^{Click here to contact me} 07:13, 25 July 2018 (UTC)

Muse

Should mention that the album The Second Law by Muse be mentioned as being name after this? DemonDays64 (talk) 23:24, 26 September 2018 (UTC)

New term "Carnot limitation"

A new edit by Editor isentrop has introduced the term "Carnot limitation", as if it were commonly encountered. It is not familiar to me, and a quick hunt has not found it in some recognized reliable sources on thermodynamics in physics. Perhaps Editor isentrop has several reliable sources for it? They are needed for the edit to stand.Chjoaygame (talk) 16:30, 18 August 2019 (UTC)

It would be desirable to have several reliable sources for the two terms advanced by this further edit. If the terms are commonly encountered, such reliable sources should be easy to muster. The lead of a Wikipedia article is not a reliable source. The term 'Carnot's theorem' seems to me to be commonly encountered. It seems to me that "A principle that specifies limits on the maximum efficiency" would be better worded as 'A principle that specifies the maximum possible efficiency'; the phrase 'limits on' seems pleonastic, and to miss the point about possibility.Chjoaygame (talk) 19:27, 18 August 2019 (UTC)

Chjoaygame I will try to find which of my old textbooks I got the expression from. Most of my good thermo texts were published before ebooks so I can't commit any time to investigating this at the moment. I suppose we could delete it for now and I'll add it when I find the source. Thanks. - isentrop

I recommend the expression be deleted or removed from view until an adequate source can be cited. Dolphin (t) 11:46, 21 August 2019 (UTC)

A reliable source is given for 'the Carnot limit', but not yet for 'the Carnot rule'. The lead of a Wikipedia article is not a reliable source.Chjoaygame (talk) 12:13, 27 August 2019 (UTC)

undid promotion

I have undone an insertion, into the sources section, of the details of a book that is not a cited source. It seems that the insertion was a promotion.Chjoaygame (talk) 21:16, 15 October 2019 (UTC)

Reasons for undo of faulty good faith edit

I have undone this edit. It was made without adequate understanding of the topic and most of the many changes were deteriorative.Chjoaygame (talk) 19:21, 13 August 2020 (UTC)

reasons for undo of good faith edit

I have undone this good faith edit.

My reasons are several.

The edit has no reliable source. Doubtless, there are many who think the edit makes sense, including (if my memory is right), and undoubtedly and regrettably, the otherwise heroic Richard Feynman.

It is practically inconceivable that a reliable source could be found for such an edit. The second law of thermodynamics concerns processes for systems that start and in their own states of internal thermodynamic equilibrium, conditions necessary for the definition of thermodynamic entropy. I find it hard to imagine anything further from thermodynamic equilibrium than the big bang. Consequently, a source that tries to apply the entropy versions of the second law is thereby certifying its own unreliability. Versions that refer to processes involving the surroundings of the universe are practically self-contradictory.

It is perhaps regrettable the Clausius allowed himself to be carried away with enthusiasm so as to talk about "the universe" for his unreserved interpretation of the first two laws. One can make sense of what he wrote, though, by interpreting his words "the universe" to mean something such as 'universe of discourse', or 'logical universe', referring to things far less extensive than the kind of 'universe' referred to in talk of the big bang. Nevertheless, Clausius' original words have led some of their readers into what seem to be nearly delusions of grandeur for physicists.Chjoaygame (talk) 00:46, 28 November 2020 (UTC)

I have restored the content and added references. While your personal views are interesting and could be correct, Wikipedia should reflect the scientific consensus.Dan Gluck (talk) 01:22, 28 November 2020 (UTC)

Additionally, entropy is actually often defined for off-equilibrium processes. E.g. using Shannon's entropy. It is surprising and unscientific that you claim that any source (including by some notable physicists) that contradicts your opinion or understanding is by definition unacceptable.Dan Gluck (talk) 01:28, 28 November 2020 (UTC)

Thank you, Editor Dan Gluck, for your comment.

For the moment, I will limit my reply to saying that the context is the second law, which refers not to Shannon's function in general, but to thermodynamic entropy in particular. In this light, talk of "scientific consensus" is inadequate.Chjoaygame (talk) 01:45, 28 November 2020 (UTC)

Dear Editor Chjoaygame.

First, your assumption that the very early universe was far from thermal equilibrium is not correct. In fact, the universe was thermalised between the electroweak epoch and the recombination period, except for neutrinos and dark matter that decoupled earlier. This is something very basic in cosmology.

Second, entropy of a macrostate in general is defined as

k_{B}\cdot ln(\Omega )

, where

k_{B}

is Boltzmann's constant time and

\Omega

the number of microstates in the macrostate. This is in fact the number of bits needed to describe the macrostate (times the Boltzmann constant), hence it is easily generalized to information entropy.

The Second law of thermodynamics states that this quantity increases over time; it is valid also far from equilibrium, as long as the initial conditions include no correlations, and as long as you can define macrostates in some sense.Dan Gluck (talk) 14:00, 28 November 2020 (UTC)

Thank you, Editor Dan Gluck, for your reasons. I see practically no chance of our making progress in this.Chjoaygame (talk) 14:26, 28 November 2020 (UTC)

If you are interested in the subject, hep-ph/9304273 is a quite interesting paper about how early the universe could have thermalised.Dan Gluck (talk) 14:35, 28 November 2020 (UTC)

Thank you for your concern.Chjoaygame (talk) 15:19, 28 November 2020 (UTC)

undoing a good faith edit

I am undoing this good faith edit because it is faulty.

The bibliographic citation of the source is inadequate. No author. No date. No publisher. No ISBN.

The source does not say what the edit attributes to it.Chjoaygame (talk) 00:01, 3 November 2021 (UTC)

How is active transport possible since it contradicts the second law of thermodynamics?

— Preceding unsigned comment added by 2601:2c3:4201:d70:6c74:b5ed:f0c0:cc5f (talk) 01:50, 21 July 2021 (UTC)

What evidence do you have that it does contradicts the second law of thermodynamics? If you have any that is sound, it will be published in every newspaper in the world!! --Bduke (talk) 03:46, 21 July 2021 (UTC)

This section has no business here. A talk page is not for general discussion of arbitrary topics. The request to present evidence is inappropriate and should not be followed.Chjoaygame (talk) 10:26, 22 July 2021 (UTC)

I think this is a reasonable question which is relevant to the article from an admittedly confused reader. No, active transport doesn't really contradict the second law but I think we should go further and explain why, for the benefit of readers who are not experts in thermodynamics.

The point is that the second law can predict one spontaneous direction for an isolated system, and the opposite direction when sufficient external work is provided to the system by the environment. Active transport of a solute is movement from a region of lower concentration to a region of higher concentration, which is forbidden by the second law when the solute-solvent system is isolated. But in some biological systems as detailed in the article on active transport, the environment (ATP, electrochemical gradients, etc. etc.) provides external energy (work) which makes the process possible.

An analogous but simpler example is a refrigerator. If you take the electric plug out of the socket, the system is essentially isolated and the removal of heat from the inside would contradict the second law of thermodynamics. But if you put the plug back in, the electric supply does work on the inside and heat can be removed so that the refrigerator can get cold.

This is the qualitative idea. The quantitative second law predicts a minimum amount of work necessary to make a given process thermodynamically possible. Dirac66 (talk) 22:15, 1 August 2021 (UTC)

I have now added a qualitative section on Direction of spontaneous processes. I have distinguished isolated and non-isolated systems - the latter includes refrigerators, heat pumps, heat engines, and ... active transport. Sometimes useful ideas can be found in edits which are only partly correct. In this case let's say that I interpreted the original question as How is active transport possible since it apparently contradicts the second law of thermodynamics? So I tried to answer as I would answer one of my students who asked a similarly confused question, and explain what the questioner had not understood. Dirac66 (talk) 03:27, 16 November 2021 (UTC)

Introduction is faulty and unclear

The current introduction begins with the sentence: "The second law of thermodynamics is a physical law of thermodynamics about heat and loss in its conversion" This is redundant (the words "of thermodynamics" appear twice, separated by five words). Even worse, it is unclear ("loss" of what?). Worst of all, the wording makes it appear that heat energy is simply lost, rather than becoming unavailable to do work (which is what the second law affirms). I propose to replace this sentence with the following:

"The second law of thermodynamics expresses universal experience concerning certain phenomena having to do with heat and energy interconversions."

Then I suggest to write:

"One simple statement of the law is that heat always moves "downhill", that is, from hotter objects to colder objects, unless energy is supplied to reverse the direction of heat flow."

The current wording of the simple statement of the law: "Not all heat energy can be converted into work in a cyclic process" is only clear if you already know something about thermodynamics.

Comments? If editors agree, I will make this change in a few days.Ajrocke (talk) 19:38, 21 June 2022 (UTC)

I agree that your suggestion is a better introduction than the current wording. I would however retain the words "physical law", and write the first sentence as "The second law of thermodynamics is a physical law based on universal experience concerning certain phenomena having to do with heat and energy interconversions.

As for the current wording "Not all heat energy can be converted into work in a cyclic process" with 3 references, I think this should be retained but moved further down in the article. I'm not sure exactly where, but I agree that it is too technical for the introduction. Dirac66 (talk) 20:12, 21 June 2022 (UTC)