Talk:Irreversible process

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Is there any interest for a brief quotation of refereed papers on R. M. Santilli's studies of irreversibility via the Lie-admissible coverings of Lie's formulations? If so, I can provide a few references for consideration. Note that these studies occurred at the level of mechanics and are now under study at the level of thermodynamics as well. Cheers. Zkurko, November 26, 2013. — Preceding unsigned comment added by Zkurko (talk • contribs) 18:35, 27 November 2013 (UTC)Reply

I removed this:

==Absolute versus statistical reversibility==

Thermodynamics defines the statistical behaviour of large numbers of entities, whose exact behavior is given by more specific laws. Since the fundamental theoretical laws of physics are all time-reversible,^[1] however experimentally, probability of real reversibility is low, former presuppositions can be fulfilled and/or former state recovered only to higher or lower degree (see: uncertainty principle). The irreversibility of thermodynamics must be statistical in nature; that is, that it must be merely highly unlikely, but not impossible, that a system will lower in entropy.

This made no sense to me -- I can understand the topics, but not what is said about them. The second sentence has unclear grammar. The uncertainty principle is not the source of irreversibility in classical thermodynamics. "Higher or lower degree" says very little. "Must be" is unclear -- is it an imposed condition or a reluctant conclusion?

Is the author trying to define absolute irreversibility, then say that it doesn't describe what happens in thermodynamics, where we only have statistical irreversibility? This is a natural move, and the distinction would be welcome, but this treatment doesn't succeed at all. 84.227.250.98 (talk) 01:06, 14 April 2014 (UTC)Reply

I agree that this section should be removed for several reasons. The second sentence not only uses ambiguous grammar (theoretical laws?) but it is contradictory. The Second Law of Thermodynamics is certainly fundamental but is irreversible. The cite is also highly questionable; it is not clear that that is a quote by Albert at all and seems to be more of an introduction for him to speak at an event. 'Former presuppositions can be fulfilled'? I have no clue what that is suppose to refer to. 'Higher or lower degree'? Degree of what? The Uncertainty Principle does not belong in this article at all; even the Wikipedia article on Quantum thermodynamics doesn't mention the Uncertainty Principle.

The last sentence is a common misconception about entropy and irreversibility; it is not based in statistics. Absolute entropy has a statistical definition but the irreversible changes in entropy do not. The change is accompanied by increasing numbers of microstates but it isn't defined by statistics any more than a change in temperature is (another statistically defined state variable). 'Must be statistical'? According to whom? That statement certainly doesn't follow from the rest of this section or anything else in the article. The Second Law does in fact state that the process IS irreversible in a closed system. Recommend complete deletion of the section as inaccurate and not helpful. Hank Bayside (talk) 21:39, 14 January 2017 (UTC)Reply

The phrase "Intuitively, a process is reversible if there is no dissipation," from a general perspective, seems wrong. Since, simply a spontaneous heat flow between a finite temperature difference does not include dissipation. Yet, it is certainly not reversible. The spontaneous heat flow is irreversible, not because it represents dissipation, but because it violates a law of physics, the 2nd law. — Preceding unsigned comment added by 134.39.93.254 (talk) 00:33, 4 March 2022 (UTC)Reply

I think this statement is misleading. If, as seems likely, the laws of nature are something like the standard model of particle physics coupled with a theory of gravitation like general relativity, then all natural processes are reversible - ie one can theoretically reverse time and obtain a solution of the laws of nature that is the reverse of the one given. Now if "irreversible" means that we will never reach initial conditions that are exactly the same as a given one but for time direction being reversed, then all natural processes, complex or not, are irreversible. I understand that here we are talking of thermodynamic models of natural processes, and a thermodynamic notion irreversibility, but it should be stated clearly. Thermodynamics are only approximate models of nature, and it is this approximation, ie loss of information, that leads to the possibility of theoretical irreversibility - as opposed to practical irreversibility which holds in any theory of all physics, as indicated. Plm203 (talk) 04:29, 5 June 2025 (UTC)Reply

I would like to suggest that the diagram accompanying the "Irreversible adiabatic process" section may be potentially misleading for readers trying to understand the concept of free expansion (Joule expansion).

The image shows masses placed on top of the pistons throughout the process, which would indicate that the gas performs work against external pressure during expansion ($W = P_{ext} x \DeltaV$ > 0). However, the caption describes this as a Joule expansion, which by definition occurs when a gas expands into a vacuum with no external pressure opposing the expansion, resulting in W = 0.

The presence of masses in the diagram suggests a quasi-static expansion against constant external pressure, which is fundamentally different from free expansion. This could confuse readers about the thermodynamic nature of the process being illustrated.

Perhaps the diagram could be modified to show the expansion occurring without external masses, or a note could be added clarifying that the masses are removed during the initial expansion phase. DavideTorre (talk) 17:07, 22 July 2025 (UTC)Reply