# 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 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 ...
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### 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 ...
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### 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 $A$...
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### 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 ...
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### 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 (...
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### 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?
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 (...
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### 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 ...
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### 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] ...
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### 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?
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### 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 ...
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### 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}_\...
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### 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 ...
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### 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 ...
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### 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 ...
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### 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 ...
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 ...