Dear Colleagues,

“There’s as many formulations of the second law as there have been discussions of it.”

– Percy Bridgman, The Nature of Thermodynamics (1941).

This is because the Second Law of thermodynamics is ubiquitous and universal, among the most fundamental laws of nature. However, and furthermore, the true equivalency of the different formulations could be established and thus proven, rendering the Second Law to be universal and valid without exceptions: in closed and open systems, in equilibrium and non-equilibrium, in inanimate and animate systems—that is, in all space and time scales. Its causational simplicity is defining the forceful directionality and thus irreversibility of the spontaneous mass-energy flows in nature, from higher to lower potential towards mutual equilibrium. Spontaneity implies forced-directionality and in turn irreversibility. The Second law provides conditions and limits for process forcing, i.e., transfer of mass-energy direction and limit.

After editing the Special Issue, "Entropy and the Second Law of Thermodynamics" in 2013, and reviewing and reflecting on related publications and activities, including ever growing attempts to challenge the Second Law, it is evident that the further exploration of the Second law of thermodynamics is more than justified. The goals of this Special Issue are to put certain physical and philosophical concepts in perspective, to initiate further discussion and constructive criticism about these fundamental concepts, including some recent challenges, as well as to revisit and further comprehend the very fundamentals of the Second Law of thermodynamics.

The phenomenological Laws of Thermodynamics have much wider, including philosophical significance and implications, than their simple expressions based on the experimental observations – they are The Fundamental Laws of Nature: The Zeroth (equilibrium existentialism), the First (conservational transformationalism), the Second (forced, irreversible-directional transformationalism), and the Third (unattainability of 'emptiness'). These Laws are defining and unifying our comprehension of all existence and transformations in the universe.

The Second Law of thermodynamics is among the most fundamental principles of engineering, science and nature. Since its discovery more than one-and-a-half century ago, its status is generally considered supreme. It can and should be challenged, but cannot be violated.

Sadi Carnot’s ingenious reasoning of reversible processes and cycles (1824) laid foundations for the Second Law before the First Law of energy conservation was even known (Joule 1843) and long before Thermodynamic concepts were established in the 1850s. Einstein, whose early writings were related to the Second Law, remained convinced throughout his life that “Thermodynamics is the only universal physical theory that will never be refuted.” There are many puzzling issues surrounding the Second Law and other concepts in thermodynamics, including subtle definitions and ambiguous meaning of the very fundamental concepts.

The Second Law is often challenged in biology, life and social sciences, including evolution and information sciences, all with history rich in confusion. Creation and organization of artificial and natural (including life) structures, and thus ‘creation of local non-equilibrium’ is possible and is always happening in many processes while entropy is generated (never destroyed), using another functional structures (channeling, filtering, hardware/software templates, pumping, devices and tools, information knowledge-‘intelligent’ templates, DNAs, etc.). However, the mass-energy flows (transfers) within those structures will always and everywhere dissipate energy and generate entropy, according to the Second Law, i.e., on the expense of internal and/or surrounding/boundary systems' non-equilibrium. It may appear that the created non-equilibrium structures are self-organizing from nowhere, from within an equilibrium (thus violating the Second Law), due to the lack of proper observations and ‘accounting’ of all mass-energy flows, the latter maybe in ‘stealth’ form or undetected rate at our state of technology and comprehension, as the science history has taught us many times.

We welcome submissions addressing these fundamental issues, as well as those on more specific topics illustrating the broad impact of the Second Law of thermodynamics and the concepts of entropy (as system property), and entropy generation (as measure of process irreversibility).

Specific topics of interest include (but are not limited to):

• Carnot cycle and heat engine fundamentals and applications
• Reversibility and Irreversibility
• Thermodynamic temperature
• Entropy fundamentals and Clausius Equality and Inequality
• Non-equilibrium processes and ‘entropy generation’
• Work availability and Exergy
• Second Law of Thermodynamics – concept and fundamentals
• Equivalency of different Second Law statements
• Second Law and Statistical Thermodynamics
• Second Law and Quantum theory
• Perpetual motion of the second kind
• Maxwell’s Demon and other challenges

It is hoped that this Special Issue will inspire and motivate the scientists and practitioners to revisit important and critical issues related to the Second Law of Thermodynamics as one among the most if not the most relevant fundamental laws of nature.

Prof. Dr. Milivoje M. Kostic
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Entropy is an international peer-reviewed open access monthly journal published by MDPI.

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• Carnot cycle
• heat engine
• reversibility
• irreversibility
• thermodynamic temperature
• entropy
• entropy generation
• Clausius equality, 
• Clausius inequality
• non-equilibrium
• work availability
• exergy
• Second Law of thermodynamics
• equivalency of the Second Law statements
• statistical thermodynamics
• Second Law in quantum theory
• perpetual motion of the second kind
• Maxwell’s Demon