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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In reality, spontaneous entropy reduction can occur, but spontaneous entropy reversal is impossible? [closed]

In reality, spontaneous entropy reduction can occur, but spontaneous entropy reversal is impossible? Can time never go backwards?
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How are topological entanglement and quantum entanglement related?

There are recurring articles about the relation between quantum entanglement and topological entanglement: https://scholar.google.com/scholar?hl=en&as_sdt=0%2C5&q=topological+quantum+...
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What does it mean for a brain to "have more information" or be "more complex," than a volume of gas? [closed]

My big question is: are there set definitions for the concepts of "information," or "complexity?" Before the background, here are my basic sub-questions: Can a brain or any other ...
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Entropy increase while in equilibrium paradox

Suppose that we have two containers containing an ideal gas and both have energy $E_1 = E_2 = E$, $V_1 = V_2 = V$ and $n_1 = n_2 = n$ which implies that they also have the same temperature (assuming ...
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In real life, can entropy decreases bring the dead back to life, make the old ones young, or make the born ones unborn, like in the movie Tenet? [closed]

In real life, can entropy reduction bring the dead back to life, make the old ones young, or make the born ones unborn, like in the movie Tenet? Is that likely? Does the existence of a probability of ...
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Is inflation an entropic process?

I've looked for this specific question and haven't found it so I'm posting it here. What I am asking is whether the process of inflation itself is an entropy raising process? The reason I am asking ...
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What is the entropy associated with a diffusion process?

Is it possible to calculate entropy from the solution of a diffusion equation(with natural boundary conditions) by using the formula of Shanon entropy? Could anyone help me to understand the entropic ...
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Entropy vs dimension of the Hilbert space

In the definition of thermodynamic entropy $S=k\ln\Omega$ where $\Omega$ is the number of possible microstates of a given macrostate, we can also associate $\Omega$ with the dimension of the Hilbert ...
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What is the information content of a single-particle system?

I'm trying to better understand how information is quantified in the case of a closed system containing a single (fundamental) particle located at position $\vec{r}$ and traveling with a velocity $\...
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Is there a difference between a pattern's results and its processes? [closed]

Is there a difference between a pattern's results and its processes? The following link will send you to Wikipedia site where they define Pattern
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Is this definition of information valid?

First following, "that entropy, is information: indeed,in the micro-canonical language entropy is determined by the number of microstates compatible with a given macrostate." Carlo Rovelli;...
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Thermodynamics entropy physics [closed]

At 1C temperature, for ice to change in liquid the change in entropy for system is less negative, then the change in entropy for sorrounding which is more positive, so why is that? Although the bond ...
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Example of entropy and information

I was trying to write up a basic, intuitive explanation of entropy, and I wanted to see if this example I made up makes sense. Imagine a cell membrane separating our two compartments. It can contain ...
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Isn't energy absolute according to Thermodynamics?

I was taught that Internal Energy $U$ is a relative quantity: only changes in $U$ are meaningful. It doesn't have an absolute value, since it always comes with an arbitrary constant (for example $U = ...
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Why do we need an explanation for the arrow of time?

I'm reading Sabine Hossenfelder's new book Existential Physics, where she explains that because fundamental laws are time-reversible, we need an explanation for the arrow of time. Why is that exactly? ...
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Entropy change during adiabatic expansion of ideal gas

I was told that the entropy change is $0$ during adiabatic expansion. However, according to $\mathrm dS=\frac{C}{T}\,\mathrm dT$, $\delta S$ is not zero because temperature is not constant during ...
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Vapor Compression Refrigeration Cycle

My question here is, why do we need point 2 to be on the saturated liquid line, i.e. why do we need a saturated liquid for the throttling process? Why can we not use it in the liquid region or ...
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Maximum Efficiency of Thermodynamic Cycle [closed]

I am a non-engineering student about to start an MSc on Sustainable Energy and I'm trying to get a head start so I don't fall behind. I would really appreciate some guidance on the following past ...
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Is metaphysics a subject that should replace physics and philosophy? [closed]

I'm really seeking some insight and the following may seem opinionated, but it's really my observations and I could be wrong and I'm completely open to hear thoughts and correction from anyone. If ...
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What does the no-hair theorem state about the entropy of black holes?

So does the no hair theorem say that all classical black holes will have zero entropy? If yes, why?
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Boltzmann or Gibbs entropy for the canonical ensemble?

For the microcanonical ensemble the entropy, is given by the Boltzmann entropy which equals: $$S = k_\mathrm{B} \ln(\Omega(E))$$ where $k_\mathrm{B}$ is Boltzmann's constant and $\Omega(E)$ the number ...
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Can an actual physical system have zero entropy? [duplicate]

Obviously, a pure quantum state has zero entropy. It appears that in theory, this is correct; but in practice, it is not, because there is always some mixing with the environment. So, zero entropy is ...
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What are some examples of microscopic quantities?

Mass, volume, energy, entropy, temperature, pressure are some macroscopic quantities. Which means we can think of them even without considering the molecular nature of matter. What are some examples ...
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If in principle all processes are $TPC$ symmetric then what causes the direction of time?

Let's assume all processes are TPC symmetric. Be it the breaking of an egg (just reverse all momenta of all particles involved), the evolution or collapse of the wavefunction (a big if but let's ...
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What's wrong with my argument about entanglement entropy in QFT being time-independent?

Let's say we need to compute the entanglement entropy (EE) of a subsystem $A$ ($A=[0,L]$, $L>0$) in a 2D CFT. The density matrix of the total system (i.e., the real axis) is given by $$ \rho(t)=\...
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Do irreversible thermodynamic processes CONSTITUTE time or do they MOVE IN time? [closed]

Time can be associated with irreversibility. A broken egg can't reassemble. Most, if not all, processes are irreversible and this is associated with time going in one direction. Ŕemarkably, living ...
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Are complexity and disorder correlated in entropy?

I am coming from the musical field, but I am looking into the topic of entropy. In many articles from the field of physics, I keep finding what I consider a sort of misunderstanding, but I may be ...
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Isolation vs the Minimum Energy Principle

The Second Law of Thermodynamics says, that in equilibrium the Entropy S of an isolated system is maximized. The First Law of Thermodynamics says that an isolated system has fixed internal energy U. ...
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It seems that enthalpy is maximized at equilibrium

For a closed system at constant pressure $dH=TdS+VdP=TdS$. On the other side we have that $dS \ge \delta Q/T$ that is $TdS \ge \delta Q$. So we have $dH \ge \delta Q$ and if the transformation is ...
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Conservation of information in expanding universe

As the observable universe expands the amount of information is increasing, at least locally. How is this compatible with the conservation of information in quantum mechanics?
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Would Maxwell's demon having infinite memory storage break the second law of thermodynamics?

Apologies if my understanding is wrong, I am literally a child. Maxwell's demon is meant to break the second law of thermodynamics by making a disorderly system orderly (see image below). But the ...
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Entropy of a deterministic reversible system

Suppose a deterministic reversible system evolving from state A of gas located in a small bottle in an otherwise empty room, to state B where the gas is dispersed throughout the room. Why is the ...
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Iterative calculation of Entropy increase when Bottle A charges Bottle B [closed]

I’m doing a classical problem in an iterative manner on a spreadsheet. This is a trial for a more complicated study. As shown in Figure 1, at each opening of the valve, 0.0784 Kg of air (denoted as ...
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Computation of two-site entanglement entropy of the critical transverse-field Ising chain

The paper Osborne and Nielsen, Phys. Rev. A 66, 032110 gives an exact solution for the two-site reduced density matrix for the transverse-field Ising model with periodic boundary conditions (Eq. 26): $...
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Could the passage of time be sinusoidal? [closed]

As we know the universe is moving towards an equilibrium, or high state of entropy. From what I understand, we call this the flow of time. When google announced their time crystal, they call it "...
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Weinberg's proof of Gibbs' $H$-theorem

I'm trying to understand Weinberg's explanation of a general $H$-theorem he attributes to Gibbs (Foundations of Modern Physics, p. 35), but I'm having trouble with the mathematical modeling. The goal ...
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Entropy of a non isolated system [closed]

I'm trying to self study thermodynamics. I've stumbled upon a problem on my textbook (which is italian by the way): a real thermal machine based on a Carnot's cycle works between two sources of ...
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Interpretation of thermodynamics applied to whole universe gets me confused… [closed]

While thinking about thermodynamics, I was confused about the interpretation of its fundamental concept. If we assume the whole universe as a thermal system, and describe all energy transfer as a ...
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Conceptually, why is the entropy of black hole related to Planck length?

I was watching a lecture on the holographic principle, and it presented the equation for the entropy of a black hole as $$S_{BH} = \frac{A}{4l_p^2}$$ My question is why, conceptually, the entropy of a ...
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How much information can be stored in a system with synthetic dimensions?

Okay this is a completely serious question and keep in mind I have a PhD in theoretical condensed matter physics, in which I have somewhat of a specialization in Floquet physics. So as the title says, ...
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How can Entropy be maximal when it is undefined everywhere else?

This question is about classical thermodynamics. I learned that when an isolated system is not in equilibrium, its thermodynamic variables such as Entropy are undefined. I also learned that when an ...
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Entanglement entropy of the infinite transverse field Ising chain at the critical point

Consider the $1$D transverse-field Ising model, $$H = -\sum_i \sigma_i^z \sigma_{i+1}^z-h\sum_i \sigma_{i}^x$$ at the critical point $h=1$ with periodic boundary conditions. Question: What is the (von ...
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Entropy density and field theory

How does Entropy density depend on Temperature in the $d+1$ dimensional Field theory? Does it always vary as the space power of Temperature, i.e. $s(T) \propto T^{d}$? If so, why?
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Why is rapid expansion/compression reversible?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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Why is rapid expansion/compression considered a reversible/isentropic process?

I am looking over the Otto Cycle on this MIT website and it says at one point "the processes from 1 to 2 and from 3 to 4 are isentropic" in reference to the expansion and compression of the ...
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Given infinite inflation would all combinations of particles be likely to occur?

My question is, in the eternal inflation model of the universe, some theories predict that random thermal fluctuations would be likely to form most combinations of matter over infinite time. This is ...
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Quantum extremal surface and black hole evaporation inquiry

Recently there has been progress made in the black hole information paradox by using the tools of AdS-CFT correspondance. Specifically, the Page curve for an evaporating black hole has been ...
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Derive the Gibbs Entropy from Boltzmann Statistics

It is a known fact that we can derive the Boltzmann distribution if we apply the maximum entropy principle at thermal equilibrium. In this post, I am going to work reversely: I want to first assume ...
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Time's Arrow, or Why does time seem to be flowing in one direction? [duplicate]

I have been working on this topic for the past 6 months, and I Understand what is time, but why does it have a direction? Why was the Entropy low in the Early Universe? I have got success in some ...
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1 vote
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Phase Transition in 2D Hard Rods

Consider $N$ rods in a plane with length $2l$ restricted to rotate by an angle $\theta$ leading to excluded volume $\Omega (\theta) = l^2(\theta + \sin\theta)$. Under the assumption that the phase ...
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