26 votes
Accepted

Is thermodynamics only applicable to systems in equilibrium?

It entirely depends on what you think "thermodynamics" is. The traditional idea of thermodynamics dealing with systems whose macrostate can be fully described by e.g. temperature, pressure and volume ...
user avatar
  • 108k
19 votes
Accepted

What is "Dynamical phase transition"?

Different people have different definitions of dynamical phase transition. At present, a widely accepted one is by Heyl et al. See their original paper Dynamical Quantum Phase Transitions in the ...
user avatar
  • 498
11 votes

How is Newton's first law compatible with transport equations?

In order to have a (constant, non-zero) flux you need either no force at all or else a balance of forces. The situations ordinarily under discussion here are where there is either friction or a ...
user avatar
10 votes
Accepted

Local and global detailed balance

In non-eq stat mech the comment above isn't what they mean. We have to establish 3 separate things: Balance This is the condition that all transitions into and out of a state 'balance' ie $$ \...
user avatar
10 votes
Accepted

Diffusion coefficient for asymmetric (biased) random walk

PREFACE After several edits, this answer provides a naive explanation of why your approach failed, how to fix it (naive-ish) and a completely different (but right) approach to solve the problem. ...
user avatar
  • 4,454
10 votes

What is "Dynamical phase transition"?

Of course the name implies that time is involved somehow. People talk about dynamical thermal and quantum phase transitions and in one case you will rapidly change temperature, while in the other ...
user avatar
10 votes

How does radiation become black-body radiation?

Stars can be approximated by a black body, because the star's atmosphere is in local thermodynamic equilibrium. This is because the mean free path length of a photon is shorter than the length scale ...
user avatar
  • 1,520
9 votes

Definition of entropy in nonequilibrium states

Just to give an account of some of the most popular approaches that I have met so far about out of equilibrium thermodynamics and corresponding generalized definitions of entropy and thermodynamic ...
user avatar
  • 6,784
8 votes

What is the use of Schwinger-Keldysh formalism?

In my opinion, the reason to be of the Keldysh formalism is that it is the way to write a path integral for non-equilibrium quantum systems. It provides an action which can be used to sample paths for ...
user avatar
8 votes
Accepted

Keldysh formalism and Kubo formula

Matsubara formalism works for statistical systems in equilibrium, and Kubo formula corresponds to the linear response approximation when the system is weakly perturbed by a time-dependent interaction. ...
user avatar
  • 9,905
8 votes

Is thermodynamics only applicable to systems in equilibrium?

Strictly speaking thermodynamics only describes systems at equilibrium or systems which undergo some change, at the end of which they have time to relax back to an equilibrium state. The signature of ...
user avatar
  • 24.8k
7 votes

How is temperature defined in non-equilibrium?

What the other answers are missing is something that needs to be made explicit -- when the system is not in equilibrium, there is not a single temperature. In other words, for a non-equilibrium system,...
user avatar
  • 16k
7 votes

What is the intuition behind the statement that non-equilibrium systems with static disorder are self-averaging?

I've seen this claim echoed in other references, e.g. in Jordan Rammer's book Quantum Field Theory of Non-Equilibrium States pg. 455 below equation 12.33, however I haven't found a satisfying ...
user avatar
  • 91
7 votes

Is thermodynamics only applicable to systems in equilibrium?

Good question. The study of thermodynamics is usually between eqilibria. But these take many shapes. And they are yours to define - a state of chemical equilibrium is for instance a state where we ...
user avatar
6 votes
Accepted

Are ultracold atoms only created by intelligent life?

Although not a complete answer, one place to start is with the coldest naturally occurring place in the universe, which is the Boomerang Nebula, a planetary nebula that is around 1 K. As best as I can ...
user avatar
  • 7,052
6 votes
Accepted

Physical meaning of the power spectrum: information it gives about the frequency content of a noise

Note: I'm using $$S_F(\omega) \equiv \int_{-\infty}^\infty dt e^{i \omega t} \left \langle F(0)F(t) \right \rangle$$ because I believe it is considerably more standard than the definition given in the ...
user avatar
5 votes
Accepted

Book recommendation for nonequilibrium thermo/stat mech

You may want to check 'Elements of Non-Equilibrium Statistical Mechanics' by V. Balakrishnan. The book does not cover too large a ground but focuses on the basic probabilistic tools of the subject. It ...
5 votes

What is the intuition behind the statement that non-equilibrium systems with static disorder are self-averaging?

I think the response by user kapaw is largely correct; I will try to simply expand on it in relation to the formalism. Indeed, the replica trick can be circumvented provided we ensure that the ...
user avatar
5 votes
Accepted

Can Liouville's theorem describe the passage from nonequilibrium to equilibrium?

The fact that Liouville's Theorem appears to contradict the increase in entropy with time was one of the objections to the statistical mechanical definition of entropy when it was proposed by ...
user avatar
  • 12.7k
5 votes

Why turbulence is non-equilibrium?

I believe that indeed equilibrium/nonequilibrium here refers to thermal equilibrium/nonequilibrium. Informally, a system is in equilibrium if you leave it be and wait long enough, so that all currents ...
user avatar
  • 311
5 votes

What happens to entropy when half the particles are removed?

Let the container be insulated and rigid, and let the initial entropy of the 2N particles be 2$S_0$. If a rigid partition is first inserted to separate the two sets of particles without letting the ...
user avatar
  • 28.4k
5 votes

How does radiation become black-body radiation?

"most radiation described as black body radiation is in strongly non-equilibrium state, being a flux flowing from a hot object (such as a lamp filament or a star) to much colder surroundings"...
user avatar
  • 13.4k
5 votes
Accepted

How does radiation become black-body radiation?

Of your possibilities it is the second one that means that the blackbody approximation can be used in some cases. Ideal blackbodies are really hard to produce in nature because of the interface you ...
user avatar
  • 113k
5 votes
Accepted

Equation of motion of a gas's center of mass due to heating

The natural convection problem you are envisioning can be solved for the time- and spatial variations of the temperature, the velocity, and density using the basic spatially differentiated transport ...
user avatar
  • 28.4k
4 votes

Is Fourier's law of conduction a consequence of the second principle?

When we speak about heat conduction we must use the laws of continuum thermomechanics, where quantities like temperature, internal energy, etc. can vary from place to place. The second law of ...
user avatar
  • 3,245
4 votes

Non equilibrium statistical mechanics

There is no consistent and general formulation of non-equilibrium statistical mechanics because of three problems: (i) the lack of equilibrium constraints, (ii) irreversibility --the time-arrow ...
user avatar
  • 5,224
4 votes

How to prove the Bose enhancement factor $(1+f)$ and the Pauli blocking factor $(1-f)$ in Boltzmann equation?

A proper derivation of the Boltzmann equation from non-equilibrium quantum field theory (which will give the factors $1\pm f$ in the weak coupling, quasi-particle dominated, limit) is a difficult ...
user avatar
  • 41
4 votes

Relationship between lesser Green's function and greater Green's function in Keldysh formalism

TL;DR In general, no. A longer but possibly irrelevant discussion follows. Consulting the classic review RevModPhys.58.323 by Rammer and Smith, the quantities you are considering are defined as (Eq. ...
user avatar
  • 578

Only top scored, non community-wiki answers of a minimum length are eligible