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.

Filter by
Sorted by
Tagged with
0
votes
0answers
27 views

Why do particles have only one bit of information in the Derivation of the Bekenstein bound

Bekenstein derived the formula for the maximum energy content of a given volume of space by considering forming a black hole from particles each containing one bit of information. Actually what is ...
0
votes
0answers
16 views

Entropy in a system constitute by an atom and a photon

Suppose that we have an atom $A$ in an excited state. This atom has a probability of emitting a photon $\gamma$. If we are in a finite space there is a probability that the atom $A$ absorbs the ...
0
votes
2answers
58 views

Is it possible to localize entropy creation?

When two obects $A$ and $B$ exchange heat irreversibly ($T_A\neq T_B$), the entropy of $A+B$ increases. My question is where: in $A$, in $B$, on the boundary? Is there some entropy exchange between $A$...
1
vote
0answers
40 views

Is a reversible path for entropy calculations always physically feasible?

Alright, so now I understand that entropy is a state function and we can easily calculate it by devising a reversible path between the two states of an irreversible path. For calculating the entropy ...
1
vote
1answer
56 views

Is there a meaning to $\mathrm{e}^{H(p_{i})}$ or $2^{H(p_{i})}$?

In my research I find an equation featuring the "exponential entropy" term $\mathrm{e}^{H(p_{i})}$ and I wonder if it has a specific meaning. I have only found rare references to that term (...
1
vote
1answer
61 views

If entropy only increases, at what point was it at its lowest value?

Non-physicist asking. Assuming the origin of the universe of your choice: If entropy only increases, at what point was it at its lowest value? Why? Was this value ever zero?
0
votes
3answers
56 views

Definition of reversibility for a non-adiabatic process

I would like to find a clear definition for the following expression: System A undergoes a reversible transformation when the transformation is not adiabatic (when system $A$ is not thermally ...
1
vote
1answer
79 views

Child Universes

I was watching a program on the future of the Universe and it got into the eventual heat death resulting from Hawking Radiation as the last hurdle till nothingness (assuming the unproven theory of ...
1
vote
2answers
61 views

Maximizing entropy with Lagrange multipliers

This is a problem I saw in a stat mech textbook, and I think it is a fairly common problem. Given the entropy function: $$S = - \sum_{i=1}^N p_i \log p_i$$ Maximize $S$ subject to constraints: $$ \...
1
vote
1answer
70 views

What features do reversible work have over the irreversible kind?

At 6:47 of this video lecture, the professor defines enthalpy for a constant pressure process as $$ q_{p}= \Delta U + p \Delta V$$ but, I can not understand why the work he implicitly starts referring ...
0
votes
1answer
87 views

Matrix Exponential [closed]

i'm working on a paper about quantum entropy and i'm stuck on an analytical step about computing a matrix exponential. I have the following Hamiltonian $$H=\frac{1}{2}\sum_ip_i^2+\frac{1}{2}\sum_{i,j}...
2
votes
3answers
132 views

Statistical mechanics definition of temperature as the average kinetic energy

In most text books of statistical physics, temperature is defined as : $$T=\left(\frac{\partial E}{\partial S}\right)_V$$ where $V$ stands for any external variable(s) the system's Hamiltonian depends ...
1
vote
2answers
52 views

Is Gibbs free energy not zero always? [duplicate]

The heat q we provide is change in enthalpy. Also we measure entropy by the heat we provide with respect to Temperature(S=Q/T). In gibbs equation, dG= dH-TdS dH is the energy we supply. Also TdS is ...
0
votes
1answer
46 views

Temperature of air coming out of a tyre due to a burst

I saw several questions where I had to calculate the temperature of the air coming out of a tyre due to a burst, given the external atmospheric pressure and the initial state of the gas present in the ...
1
vote
1answer
59 views

Is the entropy model fundamentally wrong? [closed]

By a popular definition, "entropy quantifies the number Ω of microscopic configurations (known as microstates) that are consistent with the macroscopic quantities that characterize the system (...
0
votes
0answers
19 views

Is there a tabulated reference for CO$_2$ reactions showing entropy and free energy?

With all the climate change attention I am hoping to find a CO$_2$ reference that can help me find a $\text{CO}_2$ reaction with $\Delta \text{S}^{\circ}$ less than zero, and ideally $\Delta \text{G}^{...
4
votes
1answer
144 views

Introductory References for the Black Hole Information Paradox

I am looking for introductory references for the Black Hole Information Paradox and trying to compile a sequential list through which someone familiar with the basics of QFT and GR can go to ...
0
votes
2answers
116 views

How does String Theory calculate the entropy of a black hole in a background-dependent way?

How does string theory get an agreement to the Hawking-Bekenstein equations to calculate the quantum entropy of a black hole in a background-dependent way? Is there any sort of area parameter in ...
0
votes
0answers
47 views

Given a random distribution of matter in the universe, what's the frequency of permutations of ordered matter?

I know matter isn't purely randomly distributed since it clumps together from various forces acting on it constantly, but I just want to discuss randomly distributed matter. Unless, there is a way to ...
0
votes
1answer
48 views

Does entropy change with Reynolds number?

It seems like, as a flow becomes more turbulent, there should be more possible states in the fluid. Shouldn't that correspond to an increase in entropy? Steam tables seem to only depend on temperature ...
0
votes
2answers
60 views

Question about thermal radiation and the 2nd Law

I am studying thermal radiation and considering two radiating black bodies. The book describes the net heat flux as the difference between the flux from object 1 to object 2, and the flux from object ...
4
votes
1answer
32 views

Max-relative entropy between a state and its marginals

Background The quantum relative entropy is defined for any quantum states $\rho, \sigma$ as $$D(\rho\|\sigma) = tr(\rho\log\rho) - tr(\rho\log\sigma)$$ For arbitrary choice of $\rho,\sigma$, the ...
0
votes
2answers
41 views

Interpolation in a Mollier diagram

I'm currently going a little more in depth with thermodynamics and I'm trying to familiarise myself with Mollier's diagram. What I don't understand is how to read precise values given the initial ...
1
vote
2answers
87 views

Is Carnot cycle the only “most efficient” cycle? [duplicate]

In all the books, that I have studied so far, they say that Carnot cycle is the most efficient cycle. But why isn't any other reversible process as efficient as Carnot cycle? Can somebody please ...
0
votes
1answer
48 views

Boltzmann entropy of Gaussian distribution

Recently I have been looking into different definitions of entropy and came across Boltzmann (unconditional) entropy: $S=-\int_{R} dx \;p(x) \ln p(x)$ I have tried to calculate entropy of regular ...
0
votes
1answer
34 views

How can you determine if a process is possible or impossible by using the 1st and the 2nd Laws of Thermodynamics? [closed]

How can you determine if a process is possible or impossible by using the 1st and the 2nd Laws of Thermodynamics?
0
votes
0answers
30 views

What is the physical meaning of ΔG = q(irr) - q(rev)?

Why is change in enthalpy ΔH equal to heat exchanged following whether reversible or irreversible path whereas TΔS is equal to the heat that would be exchanged if the process was reversible? What is ...
0
votes
2answers
73 views

Can entropy ever decrease in an isolated system? [duplicate]

Consider the simplest such system: a gas-filled chamber. I understand that, were all the gas particles concentrated in one corner, the entropy of the chamber will be lower than the entropy of the same ...
1
vote
0answers
37 views

Discrete Gibbs free energy

Is it possible to define discrete (informational) Gibbs free energy by analogy with Shannon entropy? This is about cellular automata, in particular on a network. We can easily calculate entropy of ...
0
votes
1answer
47 views

A form of entropy for pure states?

A previous question that I asked made me realize I had some major misconceptions about entropy. If I now understand this correctly, given the density matrix of a system, we can calculate Von Neumann ...
3
votes
1answer
59 views

In the theory of open quantum systems, what is really meant by *information backflow* from the environment to the system?

In the context of an Open Quantum System (OQS) i.e. a quantum system coupled to a quantum environment, what is really meant by information backflow from the environment to the system? I'm newly ...
1
vote
1answer
34 views

Maxwell Coexistence from Entropy Considerations

As explained by Maxwell, (1875), a realistic thermodynamical system will, at low temperature, have pressure vs. volume curve that is non-monotonic. In practice, though, the observable states of the ...
0
votes
2answers
54 views

Variation of entropy in a transference of heat

When we put two bodies with different temperatures in contact, there will be a heat transference between them. The variation of the entropy of the system is well known (this is computed in most ...
0
votes
1answer
40 views

2D Ising model entropy as a function of external field

I am trying to figure out what is the entropy expression as a function of the external field in a 2D Ising model with nearest neighbour interaction. My Hamiltonian is the following: $\mathcal{H}=-\...
0
votes
1answer
52 views

Is it possible to have a negative density matrix, and how would you calculate entropy?

I am trying to calculate the Von Neumann Entropy of a quantum state. Given a state $ | \psi \rangle$, I am calculating the Von Neumann entropy by doing the following: $$ S = -\mathrm{tr}(\rho \ln(\rho)...
0
votes
0answers
21 views

Entanglement Measure for 4 qubit?

Given a 4 qubit (pure) state, $|\psi\rangle \in \mathbb{C}^2 \otimes \mathbb{C}^2 \otimes \mathbb{C}^2 \otimes \mathbb{C}^2 $, is there an entanglement measure to determine how much these four qubit ...
1
vote
1answer
54 views

Could a cloud of hydrogen-1 or helium-4 turn into Bose–Einstein condensate when the universe reaches maximum entropy?

Laboratories can cool clouds of hydrogen-1 and helium-4 respectively into Bose–Einstein condensate (BEC), while hydrogen-1 makes up 75% of all atomic matter in the observable universe and helium-4 ...
0
votes
1answer
46 views

Wouldn't Maxwell's demon violate the first law of thermodynamics and if so, is Landauer's principle even needed in this case?

If Maxwell's demon were able to separate a gas into hot and cold regions without adding energy to the system, we would be able to move a piston between the two chambers until the temperatures equalize ...
1
vote
0answers
82 views

Is the entropy change due to particle insertion/deletion the same as increasing/decreasing the volume (or pressure) for an ideal gas?

Background: Consider a pure monatomic ideal gas within a closed system undergoing a reversible, isothermal compression/expansion. The fundamental thermodynamic relation is $$d U = T d S - P d V + \mu ...
1
vote
0answers
33 views

What is the entropy difference between $n$ free-floating amino acids and $n$ amino acids that have been translated into a protein?

Is there any known calculation for the (~ average) change in entropy between $n$ free-floating amino acids in a cell, at typical physiological concentrations, versus those same $n$ amino acids after ...
1
vote
2answers
92 views

Trying to intuitively understand how temperature relates to entropy

Background I was looking into the definition of temperature and how it relates to entropy and internal energy and I came across this answer on StackExchange. According to the answer: [Temperature is] ...
0
votes
0answers
25 views

Does Universe have an overall Entropy? [duplicate]

I am just curious to know whether Physicists have given any measurable Entropy to the Universe? If yes then please tell me whether its value is increasing or decreasing overall?
8
votes
4answers
2k views

Why did the apple fall from the tree, vis-à-vis the second law of thermodynamics?

Newton came up with gravity to explain apple falling from the tree, what would Gibbs have thought? The second law states that entropy of the universe, in general increases. This is relatively easy to ...
0
votes
0answers
23 views

What kind of Entropy is considered here for a single bosonic Oscillator?

In thermofield dynamics, which constitutes an algebraic formulation of thermal quantum field theory, an entropy operator $\hat{S}_\beta$ for a single bosonic oscillator is introduced as $$\hat{S}_\...
14
votes
7answers
3k views

Is the second law of thermodynamics even a law? [duplicate]

I am a high school student trying to wrap my head around the second law of thermodynamics for the past few days to no avail. Having only a cursory knowledge of calculus, and chemistry and physics in ...
0
votes
1answer
133 views

Do irreversibilites change the final temperatures of two bodies?

When two identical bodies are brought into thermal contact, and both are surrounded by an isolation, does the fact that they have a finite temperature difference, which generates entropy, change their ...
3
votes
4answers
195 views

What is the difference between entropy generation and entropy transfer?

When I want to calculate the entropy change of a system with two bodies with finite difference in temperature in an isolated system in thermal contact, do I calculate the whole difference in entropy ...
2
votes
2answers
54 views

Is the entropy of a rotating body largest when the axis of rotation passes through it's centre of mass? [closed]

I am looking for an answer to the observation that a body always rotates about its centre of mass when freely tossed. It can be explained if the entropy is highest in the case when the axis passes ...
5
votes
2answers
2k views

In Maxwell's demon, why are all the cold gas molecules on the same side?

In the Maxwell's demon thought experiment, initially, the gases in both boxes have the same temperature. The devil uses the door in the middle to allow the fast (hot) molecules on the left to pass to ...
0
votes
1answer
58 views

What are some examples of systems which have non-zero entropy at zero temperature?

At zero temperature, the entropy of generic systems need not vanish, but often seems to in practice. I would like to know some concrete examples where $S\neq 0$ at $T=0$. A very high-energy flavored ...

1
2
3 4 5
42