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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Additional resources to Landau's approach to entropy

I extensively studied thermodynamics but was never really satisfied with how entropy is treated in this theory. Some time ago I started reading Landaus statistical physics. I find most of the book ...
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Does the Big Bang have the absolute lowest amount of entropy? [duplicate]

We know that the event of the Big Bang has low entropy (and we don't know why), but... do we know for certain (or through convincing mathematical evidence) that the event of the Big Bang indeed has ...
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Thinking of entropy in terms of energy? Thermodynamic Limitations & Entropy Generation in an Engine [closed]

I'm currently working on a report in which in discuss the thermodynamic limitations of an I.C.E. In this section is give rudimentary explanation of how the second law of thermodynamics apply to the ...
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Entropy and Competition

Is there any particular reason why entropy cannot be considered to be a measure of or proxy for the level of competition in a system? Take a system of competitive or cooperative agents (human, ...
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Time rate of thermodynamic potentials

In equilibrium thermodynamics we're concerned with the change in thermodynamic potentials between two equilibrium states (e.g. $\Delta U$, $\Delta G$, etc.), and we use these changes to make ...
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Calculating entropy in truncated Wigner

I'm trying to get some reasonable measure of the entropy of a system modelled by the truncated Wigner method. The Wigner function contains all the information about a density matrix. So, I figure it ...
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Calculate entropy of a sphere (?)

I saw these two videos (1 and 2) and in both of them Tony Padilla gives basically the same definition of maximum entropy in a region of space (a sphere). Now, searching the web I haven't found any ...
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Why is entropy maximal under $(U,V)$ constraint? Construction of maximal entropy at equilibrium from thermodynamic potential

Let us consider a system exchanging work via pressure force only. It is assumed to be at mechanical equilibrium with the environment. We can write down the differential of the thermodynamic potential ...
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Is entanglement a bulk property or surface property?

The degree to measure entanglement in a many-body system is entanglement entropy. There are different measures for entanglement entropy, for example, Von Neumann entanglement entropy and Renyi ...
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Uncertainty of wave function over time [duplicate]

If entropy is the amount of randomness in a certain system, and it has to increase, by the second law of thermodynamics, does that mean that the uncertainty of the state of a particle always increases ...
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Second law of thermodynamics less intuitive [closed]

The zeroth and first laws of thermodynamics seem like common sense but the second law is not very intuitive- how can someone think of ' the entropy of the universe is always increasing'? Shouldn't ...
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How can you (computationally) calculate the halfchain entanglement entropy of a spinchain?

I am simulating a (small) spinchain with exact diagonalization and dynamics. I would like to track the entanglement entropy of half the chain with the other part of the chain. I have the vectors of ...
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Generalised basis independent relationship between Von Neumann Entropy and Purity of a quantum state [duplicate]

I have been trying to find a generalized relationship between Von Neumann Entropy and Purity of a quantum state? In this post there is a discussion of a specific case for a qubit and a more general ...
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What do the phrases “connected therewith” and “direct contact” in Clausius's law mean?

I have questions about Clausius's law. The specific questions are: 【My Questions】 (1)What and what is connected in “connected therewith” in 【Quote 1】 below? (2) Give me some specific examples of "...
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Would entropy maximized at equilibrium if there were no irreversible processes?

I have read this question, but it does not answer my question: In a truly ideal isolated system (say an ideal gas), it is quite possible that there is no irreversible process such that the net ...
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How should I interpret this thermodynamic inequality?

I'm a little bit confused over the following inequality: $$ dS > \frac{\delta Q_{irrev}}{T} $$ An infinitesimal change in entropy is defined in this way: $$ dS = \frac{\delta Q_{rev}}{T} $$ ...
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Confused with Entropy and Clausius inequality

I am confused with a question in my thermodynamics class and would like to seek some clarification. The problem I was given: A reversible heat engine operates on a Carnot Cycle between a heat source ...
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Heating of Water, Reversible/irrevserible process

I'm hoping that someone can help me understand this problem. I am determining which of these processes are reversible and irreversible. If we had some beaker of water at room temperature which came in ...
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Is it possible to deduce the second law of thermodynamics from the first?

Considering the First law of thermodynamics as an axiom dU=dQ-pdV for any infinitesimal process, we should be able to prove that for any reversible(quasistatic) and cyclic transformation, there is at ...
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Quantum System with Only One Energy Level

Is it possible for a quantum system to have a maximum energy level. And, is it possible for that maximum energy to also be equal to the ground energy? Let's assuming such a system can exist. What ...
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Does the Casimir effect violate the Generalized Second Law of Thermodynamics?

In order to avoid violation of the Generalized Second Law of Thermodynamics by classical non-minimally coupled scalar fields, Ford et al demonstrated that the quantum inequalities prevent the negative ...
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Should entropy be always extensive?

My question came up from the discussion in class which is about whether we should treat a specific system distinguishable or indistinguishable. To figure out what will happen in these two ...
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Change in entropy of an iron bar [closed]

A small iron bar of mass $M = 1kg$ at temperature $1000 K$ is put in a lac at temperature $288 K$. Given that the thermic capacity of the iron bar is $440 J \cdot kg^{-1} \cdot K^{-1}$ I need to ...
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Thermodynamic entropy and energy required for measurement

In the framework of information entropy, one common question is how to develop a code that minimizes the cost of transmission of a message, given that each bit as a fixed unit price. If the ...
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Why does the minimum energy principle work?

The principle of minimum energy states that in a thermodynamic system the equilibrium state corresponds to the minimum energy state among a set of states of constant entropy. I believe I understand ...
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Is entropy conserved in an isolated system with two containers of gas separated by a diathermal wall at different initial energies?

Question is pretty much the title. If I take a system of two gases and allow them to exchange heat I can write the total entropy as $$S_{total}=S_A+S_B=k_b(\ln{\Omega_A+\ln{\Omega_B})}.$$ Will ths ...
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Does entropy depend on reversibility?

When going through a cycle of a process $A \rightarrow B \rightarrow A$, is the change in the entropy of the system always equal to $0$? Does the reversibility of the process change anything (done ...
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Does the wave function decay? [closed]

Does the wave function decay? Is the wave function subject to entropy? Does a particle decay while it's in superposition or does decay start when a measurement occurs?
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Contradiction in definition of entropy?

I'm studying for my thermodynamics exam and I came across something which really confuses me. An infinitesimal change in entropy $ dS_{sys}$ of a system at temperature $T_{sys}$ during a reversible ...
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How does entropy help decide the spontaneity of a reaction?

Consider the endothermic reaction: $$2\ CH_3COOH\ (l)+(NH_4)_2CO_3\ (s) \to CH_3COONH_4\ (aq)+CO_2\ (g)+H_2O\ (l)$$ This reaction is spontaneous despite being endothermic because the entropy change ...
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Is the arrow of time only given from initial conditions?

I am not a physicist, but I have tried to sort out where the arrow of time comes from or how it fits into our physical models. Harvey Brown, a philosopher, physicist, and professor emeritus at ...
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How does the distribution of entropy in the expanding universe evolve? [duplicate]

Also, Is the entropy divided by the volume of the (observable) universe increasing with respect to time or is that number decreasing, unstable, or constant, or infinite?
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If all energy in the universe originally occupied the same point in space [closed]

How can it not be entangled? What function of physics can allow everything that comes after to be completely separate? Do we have any known laws of physics that can make such a definition? Thank you ...
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Harmonic Oscillators - Statistical Mechanics [closed]

"Consider a system with L states of discrete energy. Assume that the fundamental level energy, E0, has a degeneracy of M: (a) Show that for high temperatures, the average energy is equal to the ...
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What is the actual entropy of the Universe [closed]

I know that it depends on scale, but for example, for an experimenting coissing a coin, What was the maximum run, 20 , 30, that doesn´t influiate taking account that the velociy of the information is ...
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For what type of process, we can use $dq=Tds$?

For what type of process, we can use $dq =Tds$? Reversible or irreversible? If only reversible, how do we replace $dq$ in $dq=dU+ PdV$ by $Tds$?
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Does entropy depend on what we can measure?

This idea has been bouncing around in my mind for a few days. The modern definition of entropy is "the number of microstates corresponding to a given macrostate": $S = k \log W$. In a thermodynamic ...
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Ideal Reversible Heat Engine Entropy

For an ideal reversible heat engine, what is the entropy change of the system (heat engine) after 100 cycles? What contribution does the heat engine make to the entropy change of the universe?
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Finding entropy of Nitrogen at low pressures

I'm trying to calculate the entropy of gaseous Nitrogen (assumed to be ideal) at a particular state in a thermodynamic cycle. I know the pressure, temperature, and specific volume, but all property ...
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A good **modern** introduction to the information theoretic view of entropy? [duplicate]

Jaynes wrote a paper called information theory and statistical mechanics (1957). I tried to read this but found it somewhat hard to follow, and I suspect it's because it's one of the earlier works, ...
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A good modern introduction to the information theoretic view of entropy? [duplicate]

Jaynes wrote a paper called information theory and statistical mechanics (1957). I tried to read this but found it somewhat hard to follow, and I suspect it's because it's one of the earlier works, ...
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Calculating the change of entropy for non equilibrium states

In "Heat and Thermodynamics" by Dittman and Zemansky, section 8.10 (7th ed.) it's explained how to calculate the change in entropy in a system going from a non equilibrium state to an equilibrium ...
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What is maximal entropy?

I am confused about the meaning of maximal entropy. Is it maximal when all particles have same velocity or when there is a gaussian distribution of velocities? In simple words does the system tend to ...
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Microscopic definition of heat in the grand canonical ensemble

For a general ensemble, we define the entropy $S = k_B\left\langle -\ln p_i\right\rangle = -k_B \sum_i p_i \ln p_i$ and the internal energy $U = \left\langle \varepsilon_i \right\rangle = \sum_i p_i \...
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Carnot engine efficiency and entropy

I think I am not understanding a key concept about thermodynamics. I have worked out the heat and work changes for a particular Carnot cycle. In fact, there is no heat change as we have 2 isothermal ...
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Example for negative entropy change in an Open thermodynamic System (Practical Scenario)

Can any one cite an example for a practical scenario (preferably not involving chemical reactions) wherein entropy change is negative. Viz. heat flows from a "Thing" to a second 'thing' at equal or ...
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Positivity of $dt$?

Background I had an idea to write time $dt$ in the first law of thermodynamics. So let us proceed with the $1$'st law in differential form: $$ dw = T dS - d U $$ where $w$ is the work, $T$ is ...
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Connecting Heat and Statistical definitions of Entropy

My Question: Thanks for reading. I understand that when entropy was first defined, in an attempt to explain which processes happened and which didn't, it was defined as: $$\Delta S=\frac{Q}{T}$$ ...
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Entanglement between what?

According to the standard definition of "Entropy of Entanglement" https://en.wikipedia.org/wiki/Entropy_of_entanglement one starts from the density matrix of a pure state $$ \rho=|\psi\rangle\...
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Entropy change at constant temperature is amount of lost heat?

The thernodynamic definition for.entropy change is only valid for constant temperature. But when we heat up something and its temperature does not rise what happens then to the added heat. If we ...

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