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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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Is this Article About Possible Mirrored Universe Junk Science?

The article can be found here, entitled "Big Bang May Have Created a Mirror Universe Where Time Runs Backwards". I know any notion of backwards time is probably a dead horse in this site, but given ...
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Physics of time running backwards

Although it would seem weird to analyze physical phenomena when time runs backwards, it seems to have a logical sense, at least for me: Entropy would tend to decrease: two balls having energy ...
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Determine the change in the entropy of the cube

Suppose that a uniform-density cube of volume $l^3$ and mass $m$ is in the room and is under pressure $P$ and at temperature $T$ . Gravitational acceleration is of magnitude $g$ and its direction is ...
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Change in the entropy of the cube [on hold]

Suppose that a uniform-density cube of volume l³ and mass m is in the room and is under pressure P and at temperature T . Gravitational acceleration is of magnitude g and its direction is downward. ...
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How do we quantify and measure the net entropy of today's universe?

We know that the Universe evolved from a very low entropy state in the early universe to very high entropy state of today's universe. What is the quantitative definition of the net entropy of the ...
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Question on Partial Differentiation in Thermodynamics

For energetic fundamental relation $U=U(S,X_1,\ldots)$ where $X_k$ represent extensive parameters $V$ or $N_j$, let \begin{equation}P_k=\frac{\partial U}{\partial X_k}.\end{equation} For entropic ...
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tautologies in phys: “speed of light is c” as “informational” [closed]

Context: https://en.wikipedia.org/wiki/Tautology_(logic) https://en.wikipedia.org/wiki/Metre#Speed_of_light_definition https://en.wikipedia.org/wiki/Second#%22Atomic%22_second https://en.wikipedia....
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What does it mean for thermodynamic entropy to be defined only up to a constant?

I'm reading the Wikipedia article on thermodynamic definition of entropy. Because the energy of a particle in a classical thermodynamic system is a continuous variable, the number possible states is ...
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How looks the “overarching” wavefunction of a number of electrons in an insulating sphere?

I changed my question after reading the comment of Anna. If we put a huge number of electrons inside a non-conducting sphere, what will the total wavefunction describing all electrons look like? I ...
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Time reversal in case of adsorption

We know that the entropy of gas molecules being adsorbed at the surface of a catalyst decreases. Also, the arrow of time is accounted for by an increase in entropy. Then can we say that if we fit a ...
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35 views

Entropy of the big bang

At the moment of big bang, all the matter was in perfect order, that is entropy 0 so what force or disturbance would occur to begin the chaos and the entropy start to increase?
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E. T. Jaynes' subjectivism vs measurement of distributions

In his paper, E. T. Jaynes argues that entropy is a measure of our ignorance about a system. As such, the probability distribution of states $\{p_k\}$ has to be chosen in the most unbiased way, thus ...
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Finding parameters by principle of maximal entropies of two independent systems sharing parameters

I have $n$ observations of system $A$, and $m$ observations of system $B$. $n \ne m$ Behavior of system $A$ and $B$ are independent, given the knowledge of the parameters. However, the two systems ...
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Why is it that the multiplicity function of two subsystems reaches a maximum if the $$\frac{\partial E_{1,2}}{\partial T_{1,2}}_{N,V} > 0$$

Intuitively it's clear to me and I understand why but when I try to break it down rigorously in a way that deals with the equations and their dependencies and derivatives I'm not sure that I can. ...
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Are the Renyi entropies decreasing in the family parameter? [closed]

Are the Renyi entropies: $$S_\alpha=\frac{1}{1-\alpha}\log(\text{tr}[\rho^\alpha])$$ decreasing in alpha? Can I have a formal proof of this?
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Change of entropy in irreversible process

When calculating entropy change for a irreversible process,do I assume a reversible path and then integrated it?
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How large does a system have to be for $\Omega$ to be the multiplicity of the most probable macrostate?

Generally speaking, how large does a system have to be for the total multiplicity of the system to be (100.000000000000000000000000001 percent of) the multiplicity of the most probable macrostate? I ...
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Entropy production, local thermodynamic equilibrium and adiabatic process

It is said that for local thermodynamic equilibrium the local entropy production needs to be 0. Now, I am reading the following from the book by de Groot and Mazur "Non-Equilibrium Thermodynamics". ...
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Is there a correlation between aging and the increase of organisms entropy?

This question is a restatement of Death by entropy. Question: Does aging, as we understand it nowadays (shortening of telomeres etc.) goes hand in hand with the increase of entropy? If so and an ...
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Better understanding the Clausius Inequality

My conceptually understanding draws on the section on the Clausius Inequality from Finn's Thermal Physics. Attached is the graphic used for the derivation in the textbook. If I'm to understand ...
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Energy required for computation [closed]

Is there a way to quantify a theoretical value for the minimum amount of energy required for arbitrary computation? Can an infinite amount of computation occur in a finite amount of time?
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Blackhole Entropy

What happens if substance with zero entropy falls into a Scharzschild blackhole? Since $$S=\frac{k_b A}{4L^2_p},$$ increase in mass should be accompanied by an increase in entropy. Its area can not ...
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Entropy, time reversibility, and the uncertainty principle

I had a coworker bring up time reversibility during a lunchtime conversation the other day and how physical systems would behave. Sparing the unimportant details of the conversation, his position was ...
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Are the net microstates of the universe increasing?

In physics and chemistry we learn that entropy is given by $$S=k\ln\Omega$$ where $S$ is entropy, $k$ is Boltzmann's constant, and $\Omega$ is the number of microstates in the system. We also learn ...
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Photon encoding and computational limit of the universe

The amount of information or entropy that can be contained in a region of space is given by the Bekenstein Bound: $I \leq \frac{2\pi RE} {hc \ln2}$ However, recent publications have shown ...
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Interpreting heat using information entropy

In an answer to the post about Microscopic Definition of Heat and Work, Ronan says, $$<dE> = \sum \epsilon_idp_i + p_id\epsilon_i$$ We can see that the change in average energy is partly ...
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Is there an upper limit on entropy density?

I would like to sell you a perpetual motion machine that works by making the insides of a box continually more messy. The engine comes packaged with a physicist who will continually discover new ...
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Quantum Optics: entropy doesn't change!

I'm reading a paper and without any justification, the author said: Consider a single-mode cavity field initially prepared in a coherent state $|\alpha_0 \rangle$. It leaks out of the cavity through ...
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Is this enough to show that entropy is a state function?

The way I prove that entropy is a state function is that I consider a carnot cycle which consists of an isothermal expansion followed by adiabatic expansion and then isothermal and adiabatic ...
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Boltzmann distribution as an explanation for the 2nd law of thermodynamics

The Wikipedia page for Boltzmann distribution describes it as a distribution of microstates as a function of energy and temperature. From my understanding, the 2nd law of thermodynamics is based on ...
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Entropy and its Differential Treatment in the System vs Surroundings

I have had this question for years, and despite posting in chemistry stack exchange about it, have never received a response which closes the issue for me. My confusion arises from the differential ...
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on diffusion process in semiconductor devices

Consider a PN junction. Say that the P and the N sides are just brought into contact and the diffusion process has started. We say that as the diffusion occurs, the charge carriers leave behind ...
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Derivation of entropy for ideal vs. photon gas

Here's the standard way of deriving the entropy of the ideal gas (see e.g. here): $$ dQ=dU+PdV=C_VdT+\dfrac{NkT}{V}dV $$ $$ dS = \dfrac{dQ}{T} $$ Integration of the latter gives the correct result. ...
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What goes wrong, theoretically, when we reverse time?

(Please bear with me if this is a stupid question; I'm not a physicist, just a curious student.) I know that Noether's Theorem links symmetries to conserved quantities: the fact that the laws of ...
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Is entropy change always zero after a quasi-static evolution?

If I am thinking in terms of a idealized, perfect carnot cycle I know that in sum $$\Delta S_{\mathrm{total}} = 0.\tag{1}$$ But that does not mean that there is no entropy generated during the ...
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Does entropy increase with heat flow?

In an exam, I had a scenario where 2 bodies with different temperatures were put together and over time their temperatures mixed and eventually became uniform. My intuition tells me that as a result, ...
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Deriving the second law of thermodynamics from an irreversible carnot process

I have studied the ideal carnot cycle extensively where we assume that $$\Delta S_{\mathrm{total}}=\sum_i \frac{Q_i}{T_i} =0$$ Now I was wondering whether it is possible to derive basic properties ...
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what has the higher entropy: tap water or hot coffee?

I can't get this simple question out of my head. Does tap water have higher entropy since its temperature is almost in equilibrium with the surrounding? Or does hot coffee have higher entropy since ...
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Information Density of Spacetime [closed]

How much information is required to completely describe a given volume in spacetime?
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Thermal expansion and change in enthalpy

I came across the following equation for differential change in enthalpy: $$ dh = c_p dT + \frac{1-\beta T}{\rho}dP$$ where $\beta = -\frac{1}{\rho}(\partial \rho / \partial T)_P$ is the thermal ...
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Entropy of superposition state vs collapse

Imagine 2 similar atoms one is in superposition state while another is collapse into 1 of the possible States fall into the black hole at the same time, do the 2 atoms lost equal amount of entropy? I ...
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Is Entropy a monotonically increasing function of Gibbs Free Energy/ Helmholtz free energy/ Enthalpy?

Entropy can be axiomatically taken as a monotonically increasing function of internal energy $(E) ,$ from where "energy minimum principle" can be deduced, and this can be stated using variational ...
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Example of time-dependent factorization of a Hilbert space

In these notes on entanglement in QFT it is pointed out that in the Heisenberg picture the factorization of a Hilbert space is time-dependent (pages 18 and 19): In the Schrödinger picture, it is ...
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Is entropy quantized in Loop Quantum Gravity?

From the Beckenstein-Hawking formula, we know that entropy is proportional to the area of the event horizon of a black-hole: $S\propto A$. From Loop Quantum Gravity, we know that length, area and ...
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Relationship between physical and information entropy [duplicate]

This question is inspired by the following example given in Barnett's book on quantum information: (PDF here, starting at the bottom of page 5) I am not a physicist, but I'll accept that the ...
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Why do energy transfers always result some heat loss?

explain that energy transfers and transformations in mechanical systems always result in some heat loss to the environment. Like why is it necessary for a heat loss?
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Why does less knowledge imply more correlations?

Given two systems, correlations quantify how much information we can gain about system 1 by measuring system 2. Entanglement is a type of correlations which only occurs in quantum mechanics. There ...
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Relations derived from ist law of thermodynamics

In the 5th point given in the image, it is mentioned that this relation is applicable for both reversible and irreversible processes, since the parameters involved are state functions i.e independent ...
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Entropy of non-relativistic species in local thermal equilibrium

What happens to the entropy of a species in local thermal equilibrium with itself, after it becomes non relativistic? Although its entropy should be conserved separately, it appears as if entropy ...
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Thermodynamic Entropy seems to be contradictory

For an ideal gas the entropy change with energy is inversely proportional to temperature: This must yield: $$S=\frac 3 2 k_B \ N ln(T)$$ For various reasons, this equation is hard to find. ...