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Questions tagged [entropy]

An important extensive property of all systems in thermodynamics, statistical mechanics, and information theory, quantifying their disorder (randomness), i.e., our lack of information about them. It characterizes the degree to which the energy of the system is *not* available to do useful work.

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Proving that $c_V$ is positive

On my professor's lecture notes he claims that $c_V>0$. Intuitively, this would have been my guess as well but he mentions how you can prove this by constructing a setup: "Construct an isolated ...
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How does entropy exactly relate to the heat flow of a system

Entropy is this awesome concept with many faces. For a classical mechanics point of view, it would represent all the possible properties of a physical system, which is supposed to be unknown. For a ...
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Can the second law of thermodynamics be derived from Quantum randomness?

The second law of thermodynamics says that the entropy of an isolated system continuously increases. Can we say that this is due to Quantum mechanics, which continuously increases the information ...
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information theory and energy mass relationship (E=mc2) - just a hunch … [on hold]

I was walking on the street the other day and thought to myself, maybe E=mc2 can be derived from information theoretic principles. I did not do too much work on this, just want to brainstorm a bit. ...
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Can body of one temperature ever cause higher temperature in another body?

If you have one body that radiates heat at a constant rate and, forgive my simple assumption, thus constant temperature, and a body that may absorb this heat, may the temperature of second body ever ...
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What is the relationship of syntropy to dissipative structures? [on hold]

In considering the function of dissipative structures, which must either collapse or escape to a new order of being, do the forces of syntropy "pull" the dissipative structure toward the new order of ...
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Statistical mechanical perspective of entropy in this computer simulation

I've scoured the internet for a clear answer on entropy and I see contradictory answers everywhere so I'm going to refine my question here. Please read carefully as the question is not as it seems at ...
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Will Vacuum Energy persist at the Heat Death of the Universe?

By "vacuum energy" I mean the underlying background energy that exists in space throughout the entire Universe, codified in Heisenberg's energy–time uncertainty principle, a special case of zero-point ...
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Brouwer fixed point theorem

How does the Brouwer fixed point theorem (which provides a solution to the photo camera paradox of a causal loop) generalise to show that objects in closed time-like curves do not violate the second ...
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What so special about Q(heat) and not special for “X(any other energy transfer)” in non-heat engines?

I understand Bolzmann definition of entropy well enough, but I keep struggling to understand entropy $S$ and it's relation to heat and efficiency in classical (non statistical) thermodynamics. As ...
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Thermodynamics second law variational statement query

In thermodynamics as I understand entropy is a state function. A state function is a property whose value does not depend on the path taken to reach that specific value. In contrast, functions that ...
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Reversibility of compressed air sinking in water

Consider an apparatus in which air is trapped in a small insulated container with an open bottom, and weighted with weights so that the air is slightly above neutral buoyancy. This apparatus is ...
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60 views

Entropy generation

Does entropy generation fully define if the process is possible or not? For example if I have a piston cylinder device expands freely and isothermally from 200kpa to 10kpa - which is not possible ...
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Difference between adiabat and isentrope in Caratheodory's formulation?

In Caratheodory's formulation of thermodynamics, he mentions adiabatic accessibility as a total order $\overset{A}{\prec}$ on the state space of a thermodynamic system and proceeds to define entropy ...
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Can the entropy of mixing be negative? [on hold]

There is a general notion that the entropy of mixing should always be positive (or zero if we are mixing exactly the same stuff). However, I have a seeming counterexample at hand. Consider a box ...
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Entropy and observers

Struggling to understand the stance Bousso takes in his paper, The Entropic Landscape, https://arxiv.org/abs/1001.1155 Is he saying that because only by observing an increase in available state we ...
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Does chemical bonding decrease the entropy of the universe?

I have read in many credible texts ( including "a brief history of time" ) that nature always increases entropy, that is, the entropy in the universe increases. But I learnt that atoms and molecules ...
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Multiplicity of statistical weight of macrostates when combining systems in thermodynamics (Boltzmann entropy)

In my lecture notes, the Boltzmann entropy form was motivated as a valid form for entropy partly because it was extensive. However this hinges on the assumption that the statistical weight for a ...
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Introductory to statistical mechanics text query

In the text "Introduction to modern statistical mechanics" by Chandler the following is stated in the first chapter: Entropy obeys several other important properties as well. To derive them, ...
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Derivation of 2nd law of Thermodynamics from ergodicity assumption

In Wikipedia it is claimed that: Assumption of the ergodic hypothesis allows proof that certain types of perpetual motion machines of the second kind are impossible. Since perpetual motion ...
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Entropy generation in an endoreversible engine

An endoreversible engine is one that is internally reversible (i.e., a perfect Carnot engine) but the heat transfers occur across imperfect conductors (resistances), thus rendering the engine ...
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Is this a correct derivation of the second law or it is just nonsense?

In this article, the author makes the following argument. The difference between entropy and information is that entropy is the bits that you don't understand while information is the bits you do ...
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Kelvin–Planck statement and entropy derivation

I'm only starting to "feel" what phenomenological entropy (not statistical) mean. Well, they mean the same thing, but I never "felt" classical Entropy definition as I could "feel" and understand ...
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How is enthalpy change equal to work input/output in an isentropic process?

I'm an engineering student, and I'm fascinated by thermodynamics. I'm taking a module for heat engines, and I was recently looking at an example problem found in Thermodynamics: An Engineering ...
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Why is the total change of entropy of a reversible process equal to zero

Why is it that, in order to attain reversibility, the temperature difference between the system and the surroundings must be infinitesimally small, I understand that it has to be quasi-static, but why ...
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If universe is expanding shouldn't its 'disorderness' decrease?

I've came across Clausius Inequality which says that entropy of an isolated system always increases (in an irreversible process). Assuming universe to be an isolated system, a time will come when ...
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Bekenstein bound and black hole

I'm confused with this sentence from Wikipedia: "Upon exceeding the Bekenstein bound a storage medium would collapse into a black hole." Does that mean "the storage medium will become a black ...
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Entropy increase from chaos?

From a heuristic standpoint it makes sense that when a system goes from being periodic to chaotic, the occupied volume of the phase space increases (while not violating liouville theorem). Since the ...
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Entropy and reversibility

I'm very confused right now, I need to make sure of the following if they're correct or not: A reversible path is a path in which if if you return back to your initial state, there would be no change ...
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Why/When does thermal Entropy equal von Neumann Entropy?

I'm reading a paper that claims that for thermal states both entropies are equal up to the Boltzmann-Faktor. 'for states in thermal equilibrium, i.e. states of the form ... it is known that the ...
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Does Isobaric process imply quasi-static?

For a system that undergoes a process that takes place at atmospheric pressure, the work done by the gas can be expressed as $-P_{\rm atm}\mathrm{d}V$. Does this mean that the process is always ...
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Interactions between “particles” to prevent diffusion and to cause phase segregation

The free energy of particles reads, if we assume no internal energy : $\tilde f(c)= \frac{f(c)}{k_bT}=-c \, ln(c)-(1-c)\, ln(1-c)$, with $c$ the concentration. If we had a term $F(c)$ for the ...
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Does a heat engine inside of a refrigerator increase efficiency?

Consider a normal refrigeration cycle, except a heat engine runs off of the temperature difference between the evaporator and the condenser, as shown below. This heat engine powers the compressor, so ...
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How to arrive at the thermodynamic definition of entropy?

My question is, how do we say that, $$dS=\dfrac{dQ}{{T}} ~?$$ How do we relate heat and temperature to entropy? Why is the temperature in the denominator? Can we replace heat by work? How does ...
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Example of both energy being/not being a monotonically increasing function of entropy and vice versa?

In (https://theoreticalminimum.com/courses/statistical-mechanics/2013/spring) Dr. Susskind says we can assume that in most of the cases energy is a monotonically increasing function of entropy and ...
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Average entropy of a subsystem

In this paper by Don Page, https://arxiv.org/pdf/gr-qc/9305007.pdf, He conjectures average entropy of a substem of dimension m with Hilbert space dimension mn, $m \leq n$. to be : $ S_{mn} = \sum_{n+...
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Why am I a Bolzmann brain? [duplicate]

The Boltzmann brain hypothesis states that a big-bang-causing entropy fluctuation is larger than a brain-causing entropy fluctuation, therefore, you are much more likely to be a BB rather than a wet ...
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Does the definition of entropy rely on the Clausius equality?

I think there is a weird logical loop I keep running into with the second law of thermodynamics. One sequence is Clausius Equality: $\oint \frac{\delta Q}{T}=0$ for reversible processes. This means ...
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How to form a Toeplitz matrix for entropy extraction in a random number generator?

This question concerns Toeplitz randomness extraction within a quantum true random number generator. The relevant paper is:- Enhancing Extractable Quantum Entropy in Vacuum-Based Quantum Random ...
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Why don't all gasses have infinite entropy? [duplicate]

Entropy of an ideal gas is defined as the logarithm of the number of possible states the gas can have multiplied by Boltzmann's constant: $${\displaystyle S=k_{\mathrm {B} }\log \Omega .}$$ In ...
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Question about Isentropic flow

I'm reading a book "A Mathematical Introduction to Fluid Mechanics" by Alexandre J. Chorin that says that the flow is isentropic if $$ \nabla w = \frac{1}{\rho}\nabla p $$ where $w$ is an enthalpy, ...
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Explain the second principle of thermodynamics without the notion of entropy

I will teach some basic physics concepts to a group of university students not having to do with maths, physics, engineering and the like (mainly students of law, of political sciences and of similar ...
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Entropy of an expanding early universe. Why is it constant?

When one models the early universe it is most often assumed to be in thermal equilibrium i.e. the entropy is maximized and therefore constant $$dS=0$$ As far as I understand this can be explained as ...
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Mixing and Entropy in Dynamical Systems

I'm writting a short introductory report about chaos theory, and one of the conditions for a dynamical system to be chaotic seems to be the presence of topological mixing. Now, the document I'm using ...
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What would be the most practical way to implement a universal disassembler?

Let's say I wanted to create a "universal disassembler", which I define as a machine into which you can insert any (reasonably-sized) object into the input end, and the object is reduced to its ...
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If energy can't order itself, how did energy get ordered or made? [duplicate]

In the universe we see that hydrogen (bound up energy) is found in a highly concentrated ordered state in some places and it's highly dispersed in most other places. There is a natural progression ...
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Specific heat capacity is a function of temperature for ideal gases?

So far, I have the impression that temperature is the unit energy per unit entropy of a system. And entropy is some (logarithmically increasing) function of the average number of significantly ...
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Should all black holes have Bekenstein-Hawking entropy especially in string theory?

There are so many confusing descriptions of how Bekenstein-Hawking entropy binds black holes, and thus the question. I previously asked similar questions, but I realized questions were misleading and ...
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The entropy of lottery drawing machines

Suppose we have a fair lottery drawing machine where you have a container of numbered balls that is rotated many times such that interaction of the balls with themselves and the container produces a ...
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entropy transfer v. work transfer

Are there any work transfer mechanisms that cannot transfer entropy and if so why? What are the general theoretical limitations on entropy transfer from one system to another? By system I do not just ...