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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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Why is Sun's energy entropy low on Earth?

Warning i dont have physics background, having said that i was recently looking into sun's radiation energy entropy and i had couple of questions. So it is said that we can utilize the energy from the ...
Marinos Eftichiou's user avatar
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Isentropic or isenthalpic expansion for the remaining fluid in a previously pressurised tank? [closed]

Imagine a container filled with ammonia at 25 bar and 100 degC. Assume that an orifice is opened, so that fluid can flow through ...
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Definition of heat from stat phys [duplicate]

I don't really understand how to couple the idea of entropy as info with heat. Let's say that you have an isolated system. A cube with a a series of movable partitions parallel to a face of the curve. ...
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How can we calculate entropy produced by plastic deformation in this example?

Suppose we have a massless spring of spring constant $k$ attached to a mass $m$ at equilibrium position $x_{0}$ at temperature $T$. The mass may oscillate in one dimension only for simplicity. We ...
Maximal Ideal's user avatar
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Confusion regarding the equation $dS=\frac{\delta Q_{rev}}{T}$

In Reif's Fundamentals of Statistical and Thermal Physics he outlines a "proof" (sections 3.8 and 3.9) of the equation $dS=\frac{\delta Q}{T}$ for any quasi-static, infinitesimal process (i....
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Gravitational collapse - proof that energy dissipation is required?

As an undergraduate, I took a short course on astrophysics, where I encountered the Jeans mass. This is the critical mass for a spherical cloud of interstellar gas above which the cloud is predicted ...
Martin Vaughan's user avatar
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Gibbs Free Energy and Definitions of Entropy [duplicate]

When we speak about entropy, it's classically defined as $\delta S = \frac {\delta Q}{T}$ Where, I emphasize that it's the definition for only a change in entropy and not entropy itself (That's how I ...
BlackKnight23's user avatar
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Different Bekenstein bound equations – what’s the difference?

Can someone help me understand the difference between the Beckenstein bound equations that I’ve come across? They all appear to have different dimensions. I’ve been told that if you include the ...
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Why does entropy obey the superposition principle?

I was deriving the Boltzmann's entropy formula $${\displaystyle S=k_{\mathrm {B} }\ln \Omega}$$ We start with two prepositions: Let's consider two systems and we know the entropy of the first is $S_1$...
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Definition of entropy and microstates (Huang)

The definition of Boltzmann entropy given in Ref. 1 appears to be different from most sources I've seen up to this moment. Let me start from the latter: typically textbooks assume that in a given ...
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Does quantum entropy take into account the quantum uncertainties present in a system?

The von Neumann entropy of a mixed state is non-zero, and this makes sense as mixed states are just statistical descriptions of quantum systems, so there's some amount of classical uncertainty causing ...
Pratham Hullamballi's user avatar
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Feasibility of entropy at zero temperature

I remember a college lecturer of mine once gave me this equation of entropy during one of his lectures on thermodynamics: $$ \begin{align*} \Delta{S} = \frac{ d {Q} }{T} \\ \end{align*} $$ I found out ...
groaking's user avatar
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How much information is encoded in a ball on a field? [closed]

Consider a soccer ball placed on a planar field of finite dimension (just like a soccer field). How much information can be realistically encoded in the position of the ball on the field?
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At what size of matter does the second law of thermodynamics breakdown?

I'm in high school and I was studying some topics related to heat transfer. While studying, I was curious about why heat strictly flowed from a higher temperature (more energy) to a lower temperature (...
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High fidelity implies low entropy

I was reading the security proof of QKD by Lo-Chau. One of their main idea is to bound the entropy of the eavesdropper if the singlet states are of high fidelity. Here I summarized the first lemma: ...
JasonWS 's user avatar
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Is the 2nd law a reason for the irreversibility of natural processes or a consequence of it?

I have been introduced to chemical engineering thermodynamics due to my academic background. I had learnt about internal energy, entropy etc and applied the equations to various scenarios of practical ...
Explorer's user avatar
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Entropy change of an isolated system consisting of two thermally conductive blocks of equal isochoric heat capacity at different temperatures

A classic example considered in most introductory treatments of elementary thermodynamics consists of two thermally conductive (e.g., metal) blocks placed in thermal contact. In particular, I find ...
user104761's user avatar
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Why must solids in equilibrium become crystalline?

In Landau's Statistical Physics's analysis of solids, he begins with the remark that solids are caracterized by their atoms' small oscillations about equilibrium positions. However, he states that ...
Lourenco Entrudo's user avatar
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What exactly does the quantum mutual information measure? [duplicate]

Quantum mutual information (QMI) is often said to be the quantum mechanical analog of Shannon mutual information (MI). I realize they can be written with the same formula: $$S_x+S_y-S_{xy} \ ,$$ where ...
Mat's user avatar
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Unitary Evolution and the Second Law of Thermodynamics [duplicate]

Apologies for the long question. This problem has been mentioned multiple times on this platform, with no real resolution, in my opinion. So I'd like to gather all my thoughts below with hopes of ...
Sahand Tabatabaei's user avatar
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Is von Neumann entropy symmetric? [closed]

In a multiparty system, Shannon entropy is symmetric with respect to exchange of two parties. Is this also true for von Neumann entropy in case of a multiparty density matrix? If yes, is there any ...
asu's user avatar
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Is it physically possible for an ordered system to endure forever? [duplicate]

I am seeking to understand whether my theological views align with the current understanding of the second law of thermodynamics. As a physicalist, I believe that all ontological existents consist of ...
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Meixner and the Impossibility of Non-equilibirum Entropy [closed]

Meixner in a series of publications, see a short list below, starting from 1959 criticized and ultimately denied the possibility of defining the entropy concept in an irreversible process. His ...
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Entropy in irreversible adiabtic process

We know that, $$dS=\dfrac{\delta Q_{rev}}{T}$$ If you have an irreversible adiabatic process between two thermodynamic equilibrium end states of a system, there exists no possible reversible adiabatic ...
Shivansh Jain's user avatar
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Use of Clausius theorem to prove entropy inequality in Fermi's Thermodynamics

At the beginning of Section 13 (at the bottom half of page 54 through the top half of page 55) of Enrico Fermi's classic Thermodynamics, he sets out to prove the relation (using his notation) $$S(B) - ...
user104761's user avatar
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What causes the latent heat of solidification?

Every explanation that I read says: "When a crystal (solid state) forms from a liquid, heat is being produced." This seems rather weird, why would the production of something as ordered as ...
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Do neutrons have a higher entropy than protons?

Since free neutrons want to undergo beta decay into a proton while protons are relatively stable does that mean that neutrons have higher entropy than protons?
Oreoluwa Matilukuro's user avatar
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Is topological entanglement entropy independent on the state of the system? [closed]

I just read a paper by M. Levin and X.-G. Wen (https://arxiv.org/abs/cond-mat/0510613) where they present a general formula to evaluate the topological entanglement entropy $\gamma$. They also prove ...
Truth and Beauty and Hatred's user avatar
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1 answer
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What is the relationship between Clausius Inequality and 2nd Law?

I am confused about the application of the 2nd Law for reversible and irreversible processes and cycles. I want to know how the Clausius principle, the Kelvin-Planck statement, and the Clausius ...
Skaeler's user avatar
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Is it possible to say that entropy would affect the charge transportation?

I noticed there are a few papers from Dr. Karuppuchamy Navamani, for example: Generalization on Entropy-Ruled Charge and Energy Transport for Organic Solids and Biomolecular Aggregates Theoretical ...
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Generalized entropy of black holes

In the review paper 2006.06872 by Maldacena, in eq.(2.4) they wrote that the total entropy of a black hole and its environment also has a contribution from the quantum fields outside the horizon which ...
mathemania's user avatar
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What does life (photosynthesis) change for entropy? A thought experiment

The relationship between entropy and life is complex and has even "philosophical" ramifications. The following thought experiment seems simple enough to bring a clear answer, but I'm unsure ...
YAG's user avatar
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2 answers
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What is the difference between a reversible process and an equilibrium? [closed]

I am confused about the differences between a reversible process and an equilibrium when considering their energy aspect. Here is what I know so far. (1) Equilibrium and Reversibility Equilibrium ...
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How is free energy in thermodynamics related to free energy in information theory/neuroscience?

Background In thermodynamics, free energy refers to either Helmoltz ($U - TS$) or Gibbs ($H - TS$) free energy, the quantity that is minimised at equilibrium in a closed system maintained at constant [...
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On the definition of topological order

I am currently reading the "Quantum Information Meets Quantum Matter -- From Quantum Entanglement to Topological Phase in Many-Body Systems". I am trying to understand the proper definition ...
Truth and Beauty and Hatred's user avatar
1 vote
2 answers
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What happens if you factor in the energy required to switch between the reservoirs and insulating stand of the Carnot engine?

I'm reading about the Carnot cycle (as a non-physicist!) and much of the focus is on the idealisation around the infinite time needed due to the requirement of only infinitesimal differences in ...
Kathryn Nave's user avatar
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Entropy change in reversible vs irreversible cycles [duplicate]

Is the entropy change in a real heat engine cycle (irreversible) greater than, equal to, or less than the entropy change in an engine that uses the Carnot cycle (reversible)?
Albano Pietro's user avatar
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What is the appropriate 'Page Value' for entanglement entropy in a symmetry sector, say for example with a $U(1)$ symmetry?

Don Page derived the formula for the average entropy of a subsystem of a quantum system (assumed to be in a pure state), if the system is partitioned into two subsystems of dimensions $m$ and $n$, ...
Tanmay Bhore 's user avatar
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Does time arising from entropy agree with GR?

There's a theory that the direction of time arises from entropy and the correlations (interactions) between bodies. However, I don't see how this would incorporate the effects of General Relativity, ...
Flamethrower's user avatar
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1 answer
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Prove that the conditional von Neumann entropy satisfies $S(A|C)=-S(A|B)$ if computed on a pure $\rho_{ABC}$

Can someone show me how to prove this relation? If $\rho_{ABC}$ is a pure state, then $S(A|C)=-S(A|B)$ I already know that $S(A|B)=S(\rho_{AB})-S(\rho_{B})$ and that I should somehow use that $S(\...
Synonym's user avatar
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4 answers
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The second law of thermodynamics and the uniqueness of heat flow?

From wiki: A simple statement of the law is that heat always flows spontaneously from hotter to colder regions of matter (or 'downhill' in terms of the temperature gradient). I have a question: Isn'...
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A question regarding entropy change in a cyclic process

I was studying thermodynamics and my textbook said that for an irreversible process in a closed system,$$dS \geq \frac{\delta Q}{T}\tag{1}$$ which can also be written as, $$\Delta S = S_2-S_1 \geq \...
A. Srivastava's user avatar
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AdS$_3$ Geodesics' Length in ambient space as done in "Aspects of Holographic Entanglement Entropy"

I have been following the mentioned paper ("Aspects of Holographic Entanglement Entropy" hep-th/0605073 by Shinsei Ryu and Tadashi Takayanagi), trying to get into AdS/CFT. In section 6.2 ...
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Why is entropy defined in the way it is?

In thermodynamics course we were taught that in a reversible adiabatic process of an ideal gas the entropy change is zero. Now what I didn't get intuitively is that if the system is compressed ...
Ankit's user avatar
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3 votes
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Why is the number of microstates corresponding to a macrostate even finite for an ideal gas in a box? [duplicate]

I was looking at the Sackur-Tetrode equation which gives an exact formula for the entropy of an ideal gas. I tried to relate it to Boltzmann's famous $$S = k_B \ln(W)$$ where $S$ is the entropy and $W$...
Hadi Khan's user avatar
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Why does the entropy not decrease when inserting a partition into a macroscopic amount of different particles? [duplicate]

Here is a thought experiment. Imagine a box with 10^20 different particles, all different types of molecules, such that they are not indistinguishable according to QM. I insert a parition in the ...
Amit Levy's user avatar
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2 answers
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Does temperature difference alone equate to stored energy?

A heat engine uses a temperature difference in a hot side and a cold side to produce work. But when you run a heat engine, with a fixed amount of heat in the hot and cold sides until equilibrium is ...
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Partition function of $N$ distinguishable particles

Suppose there are $N$ distuinguishable particles. Each particle can have energy either $\epsilon_1$ or $\epsilon_2 $. $ n_1$ particles have energy $\epsilon_1 $and $n_2$ particles have $\epsilon_2$ i....
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Diffusion of van der waals gas

the problem is diffusion of non-ideal gas i think, in this situationm the change of internal energy, work, and heat during process is zero because this process is free expansion(diffusion) but, how ...
williwilli's user avatar
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4 answers
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Is the spontaneous flow of heat to thermal equilibrium an explicit law or is it implicitly assumed in thermodynamics?

This sounds like a really daft question, but I am trying to clarify details on foundations on thermodynamics to myself, which will involve asking really (seemingly) basic things. When you have two ...
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