A important property of all systems in thermodynamics and statistical mechanics. Entropy characterizes the degree to which the energy of the system is *not* available to do useful work

learn more… | top users | synonyms

2
votes
0answers
51 views

What's the domain of usability of these two expressions for entropy

$$dS=\frac{dQ}{T}$$ $$S=k\ln \Omega$$ What assumptions are being made about the system/process that allow for using those expressions?
4
votes
5answers
608 views

Having a problem about entropy, thermodynamics

I am a high school student. So, while studying about thermodynamics, I got a little curious about entropy. As I read, entropy is the rate of change of chaos. So, if the entropy change of a system is ...
2
votes
2answers
122 views

Entropy difference between initial and final states for a spherical photon cell collapsing in a black hole

Consider a spherical symmetric thin cell of photons converging to a point. At some moment, there is a formation of an horizon and a black hole. But each black hole is evaporating,and so, after some ...
6
votes
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 ...
0
votes
2answers
464 views

Minimization of energy and maximization of entropy

Are maximization of entropy and minimization of energy equivalent? Or are they contrary? Why should the thermodynamic potentials such as $G$, $A$, etc, be minimum at equilibrium? I am confused. ...
1
vote
1answer
86 views

Entropy of Black Hole

What is the relation between the entropy of rotating and non rotating Black hole? Which one's entropy is greater?
2
votes
1answer
891 views

Sackur-Tetrode equation - clarification required - problem with units

I'm a 2nd year physics undergraduate and recently I've volunteered to give a short presentation on the Sackur-Tetrode equation derivation and its use at removing the Gibbs paradox. I've looked on the ...
2
votes
0answers
80 views

Entanglement and Black holes

If you have two entangled quantum states, One state falls into a black hole and you measure the other state, What can you say about the state that has fallen into the black hole? If you have billions ...
0
votes
0answers
76 views

The most general entropy

What is the most general (likely non-extensive) entropy allowed/realized in Nature and its symmetry group of transformations? We know Shannon-Gibbs-Von Neumann entropy, Tsallis entropy, ...
7
votes
4answers
560 views

Definition of the entropy

In physics, the word entropy has important physical implications as the amount of "disorder" of a system. In mathematics, a more abstract definition is used. The (Shannon) entropy of a variable $X$ is ...
4
votes
5answers
400 views

If particles can find themselves spontaneously arranged, isn't entropy actually decreasing? [duplicate]

Take a box of gas particles. At $t = 0$, the distribution of particles is homogeneous. There is a small probability that at $t = 1$, all particles go to the left side of the box. In this case, entropy ...
5
votes
2answers
170 views

What is the entropy of a system when its volume tends to zero?

Say that a closed system has $n$ dimensions and is in the shape of a $n$-ball with a radius of 1, it's volume will be $$\frac{\pi^\frac{n}{2}}{\Gamma(\frac{n}{2}+1)}$$ which tends to 0 yet is not ...
1
vote
3answers
377 views

Mathematical proof of non-negative change of entropy $\Delta S\geq0$

I understand that we can prove that for any process that occurs in an isolated and closed system it must hold that $$\Delta S\geq0$$ via Clausius' theorem. My question is, how can I prove this in a ...
-3
votes
1answer
481 views

Could entropy explain dark energy? [closed]

This was 3rd beer idea, so please bear with me. What if the universe was not actually expanding but the speed of light was slowing? Wouldn't that be indistinguishable to our observations? Either way ...
1
vote
2answers
219 views

Calculating the change in entropy in a melting process

I have a homework question that I'm completely stumped on and need help solving it. I have a $50\, \mathrm{g}$ ice cube at $-15\, \mathrm{C}$ that is in a container of $200\, \mathrm{g}$ of water at ...
0
votes
1answer
143 views

Negative temperature and Absolute hot

This video explains that heat at negative temperatures flows from the negative object to the normal object. If the temperature of the normal object is absolute hot, what happens with the heat? The ...
1
vote
1answer
77 views

Would the universe get consumed by blackholes because of entropy?

Since the total entropy of the universe is increasing because of spontaneous processes, black holes form because of entropy (correct me if I'm wrong), and the universe is always expanding, would the ...
1
vote
2answers
139 views

Decrease in entropy in a fluid flow

Let's imagine a section of a pipe through which a fluid, gas for example, flows. When there is no pressure gradient, there is no flow. However, that does not mean that the molecules are at rest. They ...
3
votes
4answers
304 views

Integrating factor $1/T$ in 2nd Law of Thermodynamics

How would you prove that $1/T$ is the most suitable integrating factor to transform $\delta Q$ to an exact differential in the second law of thermodynamics: $$dS = \frac{\delta Q}{T}$$ Where $dS$ is ...
1
vote
1answer
176 views

Basic energy calculation for N identical spin system

We have a system that has N identical spins $n_i$, and each spin can be in state 1 or 0. The overall energy for the system is $\epsilon\sum_{i=1}^{N}n_i$. My understanding: There is only one ...
4
votes
4answers
213 views

Does entropy alter the probability of independent events?

So I have taken an introductory level quantum physics and am currently taking an introductory level probability class. Then this simple scenario came up: Given a fair coin that has been tossed 100 ...
4
votes
1answer
169 views

What happens at the interface between two universes with opposite thermodynamic arrows of time? [closed]

I was trying to think but cannot figure it out. For instance, if the interaction is small, for instance limited to a windows, the observers in each universe will see that the other goes in reverse. ...
1
vote
1answer
140 views

Uncertainty and Thermodynamics

Dilemma The uncertainty principle of energy and the 2nd law of thermodynamics don't add up : the uncertainty principle of energy says that $\Delta \tau \cdot \Delta E \ge \frac{h}{4\pi} = ...
1
vote
1answer
131 views

Why does a temperature increase on a fixed volume increase entropy?

I heard that this statement is correct. However, it seems odd to me. The number of possible microstates is still the same, so isn't the entropy constant?
4
votes
3answers
602 views

Does entropy really always increase (or stay the same)? [duplicate]

Consider this image. If the big (grey) molecules were all to spontaneously move to the left, and the small ones were to move to the right, there would be an increase in order. While unlikely, ...
2
votes
3answers
614 views

Why is Entropy expressed in terms of Enthalpy?

Why does ${\Delta}S_{m(fusion)} = \frac{{\Delta}H_{m(fusion)}}{T}$ ? I always thought ${\Delta}S = \frac{dQ}{T}$ In this case does it mean $dQ = {\Delta}H$ ?? Why is it so?
4
votes
3answers
456 views

Is there a mechanism for time symmetry breaking?

Excluding Thermodynamic's arrow of time, all mathematical descriptions of time are symmetric. We know the arrow of time is real and we know the equations describing physics are real so is there any ...
2
votes
2answers
152 views

Von Neumann Entropy: varying definitions

I have seen different authors define von Neumann entropy in different ways. In particular, some use the natural logarithm and others log to base 2. What is the reasoning for this? Does it make any ...
1
vote
0answers
391 views

Difficulties with understanding total entropy change and unavailabillty

Of course, I know the fact that the entropy of an isolated system never decreases. Neverthless what makes me confused about the entropy(or change of entropy) of an isolated system is the explanation ...
0
votes
1answer
686 views

Why is the equation for Entropy of an ideal gas that undergoes reversible change in T at constant Pressure like this?

Why is the equation for change in Entropy for a reversible change in $T$ at constant $P$ described as $$\Delta S = n C_p \ln\frac{T_f}{T_i}$$
0
votes
1answer
94 views

Is there a relation between supersymmetry and entropy?

Considering that entropy denotes the level of order/disorder in a system, would it be possible for entropy and supersymmetry to exist at the same time? Or, are they entirely unrelated?
0
votes
3answers
600 views

Why isn't the Bekenstein-Hawking Entropy considered the quantum gravitational unification?

Based on the Bekenstein-Hawking Equation for Entropy, hasn't the relationship between quantum mechanics and gravity already been established.
1
vote
0answers
92 views

How to solve state parameters using these givens for an ideal gas?

In a thermodynamic turbine using air as an ideal gas, given that you have a known inlet temperature value $T_i$, a known exit pressure value $P_e$, a known inlet and exit velocity $V_i$ and $V_e$, a ...
0
votes
1answer
79 views

Do gasses always mix because of their Gibbs free energy?

As far as I know there are no two gasses that don't mix (excluding demixing by gravitational effects). For me, as someone working with fluids and surface tensions a lot, this means that the surface ...
1
vote
0answers
79 views

Entropy change relation to the number of lost bits

Can we use entropy change value to define the (perhaps fractional) number of bits of information that are lost by and, or, xor gates?
2
votes
1answer
134 views

How can dQ/T be interpreted as a system's level of disorder?

Long before statistical mechanics, entropy was introduced as: $dS = \frac{dQ}{T}$ At the time when entropy was introduced in this manner, was it known that entropy represents how "disordered" a ...
5
votes
7answers
1k views

Entropy and Crystal Growth

I was reading about growing single crystals and I'm a little confused about this - In most crystal growing processes, a "seed crystal" is used, and the rest of the material crystallizes on the seed ...
1
vote
1answer
60 views

What are the units of the Bekenstein bound?

Working with the Wikipedia definition of the Bekenstein bound: $S \leq \frac{2 \pi R k_bE}{\hbar c}$ $2\pi R \ $ is $m^2$ $k_b$ is $\frac{J}{K}$ $E$ is $J$ $\hbar$ is $J*s$ $c$ is $\frac{m}{s}$ ...
15
votes
4answers
356 views

Comments on entropy and the direction of time in Landau and Lifshitz's Statistical Mechanics

In Landau and Lifshitz's Stat Mech Volume I is the comment: However, despite this symmetry, quantum mechanics does in fact involve an important non-equivalence of the two directions of time. ...
0
votes
2answers
247 views

How to compute configurations (entropy) of a system?

If we have a system $X$ consisting of subsystems $X_1$ and $X_2$. We also know that $X_1$ and $X_2$ have eigenstates $H_1 = 1 \times 10^{20}$ and $H_2 = 1 \times 10 ^{22}$. Can we calculate the ...
1
vote
1answer
267 views

relation between first law of thermodynamics and statistical mechanics definition of entropy

From the definition of entropy as $S= - Tr (\rho\, ln \rho)$ one obtains that $S = \frac{\langle E \rangle}{T} + \log Z.$ The first law of thermodynamics has $dS = {dE \over T}$. Why is there no ...
7
votes
1answer
380 views

Why is (von Neumann) entropy maximized for an ensemble in thermal equilibrium?

Consider a quantum system in thermal equilibrium with a heat bath. In determining the density operator of the system, the usual procedure is to maximize the von Neumann entropy subject to the ...
2
votes
2answers
281 views

Entropy exchange of a free fall

I have a problem in which the tell me that you drop a bag of 50 kg of sand from 10 meters high, and you have to caltulate the entropy difference of the sand, asuming that the speific heat of the sand ...
4
votes
5answers
5k views

For an isolated system, can the entropy decrease or increase?

In any sizable system, the number of equilibrium states are much, much greater then the number of non-equilibrium states. Since each accessible micro state is equally probably, it is overwhelmingly ...
5
votes
2answers
195 views

Order = Energy = Mass?

Here is a following problem I encountered when chatting about physics with my friend: Let us imagine a classical example of ordered state of matter in thermodynamic sense: let's take a cylinder ...
3
votes
2answers
3k views

Can ice have a higher entropy than water?

I've leant that entropy is a state of randomness, and that solids have a more structured form, therefore having less entropy. However, I saw a YouTube comment stating the following: a liquid NOT ...
2
votes
1answer
239 views

The definition of entropy

As history of thermodynamics say, it was a mystery that what is the required condition for a given energy conversion to take place? Like there are two possible events each conserving energy but only ...
3
votes
1answer
113 views

Amount of energy to separate Gases - relationship to concentration

I want to understand the efficiencies of separating mixed gases, and for that I want to understand the thermodynamic limit case. Looking at the wikipedia page for entropy of mixing, I find the ...
2
votes
1answer
685 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 ...
4
votes
1answer
127 views

Relation between Casimir and hydrophobic effects

Background Some years ago I was studying "Fundamentos de biología" (Biology fundamentals) and learned how the lipids create a bilayer due to the water repulsion. Some time later I learned that this ...