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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Why is heat transfer reversible when temperature difference is infinitesimal?

I don't understand why heat transfer from hot reservoir to the system is considered reversible in this case: $T_{reservoir}$ = $T_{system}$ + dT but it's considered irreversible in this case: $T_{...
3
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1answer
26 views

Is perfectly diffuse reflection entropy maximizing?

Suppose that I shine light on a surface and none of it will be absorbed or transmitted, and the spectrum doesn't change (so that all that's left to determine is the power reflected from the surface as ...
3
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1answer
133 views

Why don't we observe spontaneous symmetry restoration in nature?

Why do we always observe spontaneous symmetry breaking in nature and not restoration? Does there exist some argument with the 2nd law of thermodynamics and the entropy of the universe increasing? If ...
3
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1answer
83 views

If an object has a temperature, does it have to radiate?

I'm reading through a powerpoint presentation about Hawking Radiation (HR). They are explaining all of the reasons that built up to the postulate of HR, and one of the reasons is that if there is a ...
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2answers
44 views

Entropy and vacuums

If I have a vacuum (completely devoid of any particles; Q.M. effects aside), then turn a nozzle and let a gas freely expand into the vacuum, will I have increased the entropy of the vacuum? I get ...
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1answer
40 views

Why can't an ocean liner be powered by an engine that takes heat from the ocean water and eject ice cubes?

The following excerpt comes from the physics textbook Understanding Physics, by David Cassidy, Gerald Holton, and James Rutherford: A ball lying on the floor will not somehow gather energy from ...
5
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1answer
73 views

Holevo Information and Quantum Mutual Information

This question is about the difference between Quantum Mutual Information and Holevo Information of quantum channels. From http://arxiv.org/pdf/1004.2495.pdf equation 7 we know that the sum of quantum ...
5
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4answers
389 views

Why is entropy an extensive quantity?

If we have two identical isolated macroscopic systems both with energy $E$. The number of accessible states of each of them is $\Omega(E)$ and hence the entropy is $\ln\Omega(E)$. Now if we put them ...
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3answers
77 views

A relationship between entropy and temperature

I tried deriving a formula relating entropy (not change in entropy, but entropy itself) to temperature. I’ve only seen two equations really relating to entropy thus far, and only one of them includes ...
4
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1answer
70 views

What are the phenomena responsible for irreversible increase in entropy?

https://www.quantamagazine.org/20140416-times-arrow-traced-to-quantum-source This article says that entanglement drives the arrow of time of increasing entropy towards thermodynamic equilibrium: ...
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0answers
41 views

Is there any useful sense in which entropy fluctuates?

One of the classic distinctions between young Boltzmann and old Boltzmann was his view on entropy. Young Boltzmann had his H-theorem where a mechanical quantity H was supposed to represent entropy. ...
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3answers
832 views

Does electricity have an associated entropy?

One can certainly measure entropy changes associated with the generation of electricity, but does electricity itself have an associated entropy (maybe related to voltage, current etc.)?
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1answer
104 views

Replica trick for calculating Entanglement Entropy?

This is probably a simple question. Von Neumann entropy is defined to be $$S_A=-tr_A\rho_A \log\rho_A$$. And it's said that it can be calculate from the "Replica trick": $$S_A=\lim_{n\to 1}\frac{tr_A \...
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1answer
39 views

About the holographic principle

I read at a book this quote "As the degrees of freedom of a particle are the product of all the degrees of freedom of its sub-particles, were a particle to have infinite subdivisions into lower-...
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0answers
37 views

Estimation of an Entropic Path Integral

I'm trying to reproduce some results from a paper (http://www.alexwg.org/publications/PhysRevLett_110-168702.pdf for reference) and basically I need a way of estimating a particular path integral (...
2
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1answer
60 views

Entropy generation during irreversible adiabatic expansion

During irreversible adiabatic expansion entropy is generated. It means that the gas expands to as greater volume than that during reversible adiabatic expansion for the same change in pressure. How ...
0
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1answer
23 views

entropy changes in common processes?

Can you point me please to a reference that will explain what the entropy undergoes (increase, decrease, etc) in common thermodynamic cycle processes, like adiabatic, isobaric, isochoric, etc?
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1answer
82 views

Would it be possible that a broken glass can return to its original state spontaneous at 0K?

my teacher said that a broken glass can't fix itself spontaneous because of the second law of thermodynamics, entropy won't decrease in a isolated system. But when the temperature is at 0k, then ...
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0answers
31 views

Is entropy decreased in this scenario?

I heard one possible definition of entropy $S$ is the number of possible configurations of microscopic variables that satisfy macroscopic variables such as volume and pressure. Suppose I have a box ...
13
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3answers
3k views

Is this thought experiment violating the the Second Law of Thermodynamics?

There is an adiabatic box, with a board in the middle, which is adiabatic too.The board separates the box into two parts and there is a small hole in it, which is close to a coil and the hole has a ...
3
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1answer
73 views

Entropy and gravity

Entropy, at an intuitive level, is often described as a general level of disorder within a system. For example, I have a gas in a container divided in two areas by a divider, the gas all on one side. ...
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1answer
67 views

What is more important, energy or entropy? [closed]

What decides if something will change or remain the same? Energy or entropy considerations?
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1answer
62 views

Why is entropy of system same for reversible and irreversible processes? [closed]

I read that entropy change of universe is zero in a reversible process but positive in a irreversible process,then doesn't it mean that entropy change of system of both the processes must be ...
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1answer
62 views

Is the pressure-gradient force an entropic force?

A gas flows from an area of high pressure to an area of low pressure when there are no other forces preventing it. From a macrosopic perspective you have to infer that an underlying force is ...
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2answers
99 views

Free expansion of an ideal gas

I am having trouble understanding the transient phase of an ideal gas expanding into vacuum. Firstly, the pressure of any gas is defined only when there is an instrument (barometer/ wall/ piston) ...
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1answer
49 views

What has more randomness? [closed]

Four particles in a line or along a square, which has higher entropy? Just for a minute question. × × × × × × × ×
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0answers
53 views

What is the relation between Clausius and Kelvin-Planck statement?

What is the relation between Clausius and Kelvin-Planck statement? In second law of thermodynamics, it is said that these two statement are equivalent and inverse to each other. Violation of one ...
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0answers
28 views

Ice and water mixed and entropy

In any introductory book, everybody has atleast done these type of questions where water at a high temp is mixed with ice and final temp and mass is asked with the understanding that zeroth law define ...
4
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1answer
125 views

Entropy change in a boiling egg

Yesterday in a rather intuitive Q/A session, by a visiting researcher in my town, this question got my attention.What he said was that if you boil an egg, the entropy inside the egg would increase.Now ...
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1answer
66 views

What is meant by a “change in volume of a system”?

I keep getting confused when my professor talks about the change in volume of a system. Sometimes it seems as though he's talking about the volume of the gas and at other times he might be talking ...
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0answers
27 views

Calculate the change in entropy of superheated water [closed]

1 mole of superheated water at 110 degrees Celsius and 1atm is evaporated to a vapour at the same temperature. Find the change in entropy given that i) In the pressure range from 1atm to 1.4atm the ...
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1answer
94 views

A hypothetical equation of state that violates second law of thermodynamics

Suppose for a gas I guess an equation of state in the form $f(P,V,T)=0$. Is it possible that this hypothetical equation of state turns out to violate the second law of thermodynamics. A simple example ...
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2answers
77 views

If for an isolated system, $\Delta$U is 0, then what is $\Delta$S?

My textbook answers this question as $\Delta$S > 0 but I really don't know why. If system is isolated, then dQ = 0 i.e. S = 0. (S = dQ/T). I don't really get why question has provided an additional ...
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2answers
101 views

Change in entropy of two isolated systems merged into one system

From Statistical Physics, 2nd Edition by F. Mandl: Two vessels contain the same number $N$ molecules of the same perfect gas. Initially the two vessels are isolated from each other, the gases ...
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0answers
44 views

How to understand better this point of view on entropy?

On the book "Applied Differential Geometry" by William Burke we see a discussion about thermodynamics in which the following is said: A thermodynamic system is a homogeneous assembly that includes ...
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1answer
95 views

Can a coffee cup really jump off the table?

I've been reading Nassim Nicholas Taleb's book The Black Swan which largely concerns the uncertainty of social and economic systems (and the futility of predicting outcome); the Black Swan being the ...
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0answers
31 views

Does inflation violate the second law of thermodynamics?

Does inflation violate the second law of thermodynamics? It seems like it would, since quantum fluctuations were scaled up and created the varying density field that lead to Galaxy formation. ...
0
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1answer
47 views

In situations where we have entropy decrease, are we violating second law?

When we heat a material and this heat solidifies it (eg. when we cook an egg), isn't that decrease in entropy? when we have an endothermic reaction that produces larger molecules (synthesis), don't we ...
13
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2answers
2k views

Why is entropy additive?

Although it seems simple, I can't get the derivation correct. Here is my reasoning: $P(S)=P(A)P(B)$ Where P is the probability and S, A, and B denote different systems. $S_A=-P(A)\ln P(A)$ and $...
0
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1answer
41 views

Entropy of environment of pendulum?

I remember reading a statement along the lines of: Suppose our system is a simple pendulum. Then the entropy change in it is overall zero because the system is periodic. However, the entropy ...
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2answers
103 views

Does heat death of the universe necessarily imply an inability to perform computation?

Wikipedia defines the heat death of the universe as follows: the universe has diminished to a state of no thermodynamic free energy and therefore can no longer sustain processes that consume ...
0
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1answer
62 views

Why does the expansion of gas into a vacuum mean that we have less information about the system? (entropy)

I'm reading through Statistical Physics by F. Mandl and in the chapter about the 2nd law of thermodynamics he states that: The basic distinction between the initial and final states in such an ...
6
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1answer
87 views

How to justify the entropy maximum postulate using Statistical Mechanics?

The entropy maximum postulate states that given a thermodynamic system there's a function $S$ of the extensive parameters called entropy which has the property that once a constraint is removed the ...
0
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1answer
47 views

Is there any difference between heat and entropy here?

This screenshot is from the Carnot Cycle page on Wikipedia. In the "Stages" section, it says that: The gas expansion is propelled by absorption of heat energy, $Q_1$, and of entropy, $\Delta S=Q_1/...
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1answer
53 views

Heat, temperature and entropy

I have many questions concerning this topic. I know that temperature measures the tendency of an object to give up its internal energy. The transit of internal energy is called heat. I don't know if ...
4
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2answers
92 views

Living organisms decrease or increase entropy?

Common wisdom seems to suggest that living organisms have lower entropy that their environment. For example, the Wikipedia article on "Entropy and Life" mentions that Schrödinger thought that this was ...
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0answers
59 views

Time Vs Entropy [duplicate]

Entropy is a property of thermodycamical systems. We know that entropy measurement it's determinated by preassure P and temperature T (for simplicity). At the same way we consider that the entropy of ...
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1answer
66 views

Understanding Entropy

I know that entropy in an isolated system only increase, also is a measure of order. But I can't grasp the idea behind it in a fundamental level. When you try to transform energy from one state to ...
0
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1answer
49 views

Entropy in ideal fluids [closed]

Can you derive a conservation law for entropy per unit mass? I know that there is a proof for this conservation. My assumptions are: $(\nabla p)/n = D \vec{v} + \vec{v} \cdot \nabla\vec{v}$ (Euler ...
1
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1answer
80 views

my question is about gibbs energy, entropy and all that [closed]

I learnt that Gibbs energy is a free energy to do work! Tell me, what is this free energy and what is the work done (I mean what kind of work). Please also provide me an example of Gibbs free energy, ...