A 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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Where is the flaw in this machine that decreases the entropy of a closed system?

I was thinking about a completely unrelated problem (Quantum Field Theory Peskin & Schroeder kind of unrelated!) when the diagram below sprang into my mind for no apparent reason. After some ...
0
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1answer
29 views

is it possible to get energy by lowering temperature

Is it true that I have a pressure meter that is precise enough and measures fast enough, if I use it to measure the pressure of atmosphere, the measure will vary because gas molecules hit my pressure ...
9
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2answers
316 views

Information Preservation and Burning Books

I recently read an article in the NY Times called A Black Hole Mystery Wrapped in a Firewall Paradox. I really liked the article, but reading one quote immediately made me think of asking Physics.SE a ...
4
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0answers
78 views

What determines time flow? (arrow of time) [closed]

I've been reading up on the arrow of time and there is one thing that is being omitted from every explanation that I've found: time flow. I am rewording this question to make it clearer. From the ...
1
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2answers
50 views

Fundamentals of atomic bonding [closed]

Are these basic statements about atoms and bonding correct: atoms are at their lowest energy state when they have no bonds, existing as single atoms it always requires energy to form any ...
0
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0answers
29 views

Calculating Microcanonical Entropy in Molecular Dynamics

As a beginning, I am simulating Argon liquid at 94 K and characterising as it is done by the Rahman's first paper on Molecular Dynamics. After going through the first two chapters of Art of Molecular ...
4
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1answer
63 views

Is it a law of physics that all machines will break?

The question sounds kinda dumb when I say it out loud but at the same time I'm very curious. When things break, is it solely due to an intrinsic design flaw or is it due to entropy? And is the ...
1
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0answers
35 views

Is there a relation between complexity of a system and entropy?

Disclamer: I'm not a physics professional, so pardon me if the question is stupid/incomperhensible/generally doesn't make sense. And I've googled it, but didn't find an answer. Getting to the point, ...
2
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1answer
206 views

Reference paper to support information — energy relation $\left(kT \ln2 \rm\frac{J}{bit}\right)\;.$

In answer to Maxwell's Demon Constant (Information-Energy equivalence) there is stated that one bit of information allows to perform $kT \cdot \ln2$ Joules of work. Which paper supports the ...
6
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3answers
574 views

Confusion regarding entropy, reference papers request

1.a In paragraph at Wikipedia/Entropy it is stated: This is because energy supplied at a high temperature (i.e. with low entropy) tends to be more useful than the same amount of energy ...
4
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1answer
249 views

Confusions regarding entropy

Help, I am terribly confused about entropy. On the one hand, I am taught at school that a substance such is an ice/solid has a lower entropy than its gaseous equivalent and that a process such as ...
7
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3answers
490 views

Axioms behind entropy!

The concept of entropy is very ubiquitous, we learn about its uses starting from Information Theory (Shannon entropy) up to its basic definition in statistical mechanics in terms of number of ...
0
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2answers
76 views

Entropy of ideal gas with finite volume

I know that the entropy of an ideal gas is given by the Sackur-Tetrode equation, but is there also a way to take into account that even the ideal gas will acquire some volume $v_0$? Or is it then just ...
0
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1answer
23 views

If $\Delta Q/ T$ approximates the entropy change of some transition, is it inclusive of the entropy from volume change?

At the point of a transition where latent heat must be added to some substance, entropy change can be approximated by $\Delta Q/ T$. At these points, the volume of the substance also increases, which ...
0
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0answers
52 views

In an equilibrium of two systems, why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$?

Why is not true that $\frac{\delta S_{1}}{\delta N_{1}} = \frac{\delta S_{2}}{\delta N_{2}}$ across two systems that exchange particles? It is true, instead, that $\frac{\delta F_{1}}{\delta N_{1}} = ...
3
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1answer
55 views

Does the Entropy of the Visible Universe Decrease?

My understanding is that the entropy in a closed system increases. However, I would also assume that the number of particles in the open system of a visible universe decreases because of accelerated ...
0
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1answer
657 views

What is physics behind States of matter?

States of matter in physics are the distinct forms that different phases of matter take on. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. What is physics ...
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0answers
38 views

Is there any relation between the entropy of a system and the kinetic energy of molecules in the system?

The kinetic energy of the molecules in the system increases when we provide heat to the system,thereby increasing its temperature under certain conditions. Similarly providing heat to a liquid ...
0
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1answer
40 views

Energy/entropy in transport of molecules across cell membranes

I'm asking a "Maxwell's Demon" question. I've read statements that sorting molecules and sending them to one side or the other of a barrier requires work, but none of these statements have explained ...
0
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1answer
32 views

Could one, practically or hypothetically, capture energy from heat using magnetic fields? [closed]

I have had this idea, and I'm not sure if it would work. Heat is a form of chaotic kinetic energy, right?. Would it be possible to create a magnetic field within a gas or liquid so that when the ...
4
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2answers
477 views

Quantum entropy in term of density matrix

Why in von Neumann expression of quantum entropy we have trace of density matrix expression? Why don't off diagonal term play a role?
30
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7answers
2k views

How is $\frac{dQ}{T}$ measure of randomness of system?

I am studying entropy and its hard for me to catch up what exactly is entropy. Many articles and books write that entropy is the measure of randomness or disorder of the system. They say when a gas ...
22
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4answers
2k views

How do you prove $S=-\sum p\ln p$?

How does one prove the formula for entropy $S=-\sum p\ln p$? Obviously systems on the microscopic level are fully determined by the microscopic equations of motion. So if you want to introduce a law ...
15
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5answers
3k views

Can a single classical particle have any entropy?

recently I have had some exchanges with @Marek regarding entropy of a single classical particle. I always believed that to define entropy one must have some distribution. In Quantum theory, a single ...
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2answers
902 views

Derive the Sackur-Tetrode equation

How do you derive the Sackur-Tetrode equation? I know that you must start off with the multiplicity of a mono-atomic ideal gas: ...
2
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1answer
286 views

Death by entropy

An idea struck me as I was walking to class today. According to Wikipedia, entropy is defined as the number of specific ways in which a thermodynamic system may be arranged, commonly understood as a ...
3
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2answers
73 views

Entropy reversal in magnets

Entropy is an irreversible phenomenon without any energy supplied to reverse it. I was reading about paramagnetic substances and how dipoles align inside them on application of magnetic field. My ...
0
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0answers
107 views

Change in statistical Entropy negative?

I'm currently stuck with a particular problem: The total energy of a set of molecules in an "isolated" container does not change when the container volume expands by a factor of 2, ...
0
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0answers
15 views

Does 'Entropy-Sated' mean that no 'Order' can be produced from a black hole?

I believe I have a misconception somewhere that I need help to clear up. No-Hair indicates that a black hole created from highly ordered matter with low entropy reaches the same final state as ...
1
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1answer
48 views

Calculation of Entropy of Debye Solid at High T

I am calculating the kmolar entropy of a Debye solid at low temperature ($T << \theta_D$) and high temperature ($T >> \theta_D$). For the low temperature, I use $U = U_0 + \frac{9 k_B ...
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0answers
57 views

Current status of nonextensive statistical mechanics

A version of the maximum entropy principle is the following. $$\max_{P}~~~ -\sum_i p_i\log p_i$$ subject to all probability distributions $P=\{p_i\}$ satisfying $$\sum_i p_i \epsilon_i = U.$$ ...
1
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1answer
103 views

Quantum mechanics and second law of thermodynamics

Recently I came across this idea of Gibbs that, it is the coarse-grained entropy that always increases, whereas the fine-grained remains a constant. So classically, coarse graining refuses us some ...
3
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2answers
133 views

Does the second law of thermodynamics imply a spacetime beginning of the universe?

Recently I have been studying thermodynamics and I noticed a article by a religious person which says that the second law of thermodynamics proves that the universe had a beginning. A spacetime one. ...
1
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0answers
77 views

entropy and dispersion

If I know the positions and the speeds of each particle in a box over the time, how can I compute the entropy ? (I`m making a simulation where I want to show that the disperion of the particles over ...
0
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1answer
92 views

Can entropy be regarded as energy dispersal?

In several answers here the claim has been made that thermodynamic entropy can be regarded as energy dispersion. See, in particular here, and here and here. This is apparently the pet theory of a ...
1
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1answer
77 views

Is entropy increase in disorder or 'energy-dispersal'? [duplicate]

My teacher explained entropy like this: It is increase in disorderliness. Take a glass jar put three layers of blue marbles in it then put three further layer of red marbles, now shake the ...
11
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2answers
388 views

Will entropy continue to increase even if the universe begins to contract?

If the universe is heading for a big crunch, when the universe starts to collapse will entropy decrease and the arrow of time consequently reverse or not? I'm interested in the explanations, not just ...
2
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1answer
411 views

Calculation of entropy change in irreversible cycles, meaning of $\delta Q/T$ in irreversible processes

Let's take the two cycles in the pictures working with an ideal gas. We perform one, and then perform the other. The cycle is made reversible by making the gas exchange heat with a heat bath having ...
0
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0answers
29 views

Entropy changes of water

I have a few questions regarding entropy and water. Suppose you cool down water so that it freezes at $273.15K$. How is entropy positive in this case? I have a feeling it may have to do with the ...
0
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0answers
108 views

Entropy: Disorder or energy dispersal?

The first definition of entropy given by Clausius is I believe this $$S=Q/T$$ It is as I understand a common fact to understand entropy and maybe often teach it as a measure of disorder through the ...
6
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1answer
1k views

Clear up confusion about the meaning of entropy

So I though, and was told, that entropy is the amount of disorder in a system. Specifically the example of heat flow and it flows to maximize entropy. To me this seemed odd. This seemed more ordered ...
1
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0answers
51 views

Calculate the entropy using microcanonical ensemble

$$Ω=\sum_{n=0}^{N-\frac{E}{\epsilon}} \frac{Ν!}{\left(\frac{N-n-\frac{E}{\epsilon}}{2}\right)!\left(\frac{N-n+\frac{E}{\epsilon}}{2}\right)!n!}$$ I am supposed to calculate the above sum using first ...
14
votes
5answers
967 views

Why doesn't the entropy increase when two similar gases mix with each other?

Entropy increases when two substances mix with each other. For example, the entropy of mixing of two different gases are given by $$\Delta S= 2Nk\ln\frac{V_f}{V_i}\;.$$ But, the entropy doesn't ...
1
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0answers
56 views

Is the law of maximum entropy production the same as principle of least action?

I just have read about the law of maximum entropy production. Someone has idolized it enough to make an whole website just for it: http://www.lawofmaximumentropyproduction.com/ A system will ...
2
votes
1answer
78 views

What is the physical implication of Clausius inequality?

Clausius inequality is given as: $$\oint \frac{\delta Q_\text{res}}{T_\text{res}} \le 0\;.$$ From Carnot cycle, we get the equality relation as the entropy lost by the hot reservoir is the same as ...
5
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1answer
364 views

Why does slow compression of a gas doesn't change its entropy to increase?

This is quoted from Daniel V Schroeder's Thermal Physics: It's interesting to think about why the slow compression of a gas doesn't change its entropy to increase. One way to think about it is to ...
0
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2answers
63 views

Why is there no change in internal energy for an isothermal reversible process?

This concept is used for deriving the relation : Change in Entropy = $2.303 \,\ nR \,\ log_{10} (\frac{V_2}{V_1})$ But I don't understand why change in Internal energy = $0$.
4
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1answer
2k views

Isentropic processes

I'm having trouble understanding why reversible adiabatic processes are isentropic. I understand that in a reversible adiabatic process there is no heat exchange and so $dQ = TdS = 0.$ However, if ...
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2answers
128 views

How does the second law of thermodynamics forbid the possibility of perpetual machine of the second kind?

Fermi in his lecture asserts: The second law of thermodynamics rules out the possibility of constructing a perpetuum mobile of the second kind. So, this means there can be no machine which just ...
2
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3answers
259 views

How is the efficiency of a heat engine related to the entropy produced during the process?

I'm reading Schroeder's An Introduction to Thermal Physics. Regarding heat engines, it is stated: Unfortunately, only part of the energy absorbed as heat can be converted to work by a heat engine. ...