Questions tagged [ergodicity]

A system is said to be ergodic if time averages are, for a sufficient long time, equivalent to phase space averages. This "ergodic hypothesis" is taken by many authors as the foundation of statistical mechanics.

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124 views

Is it possible for a system to be chaotic but not ergodic? If so, how?

In a recent lecture on ergodicity and many-body localization, the presenter, Dmitry Abanin, mentioned that it is possible for a classical dynamical system to be chaotic but still fail to obey the ...
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About FPU non linear problem, in reference to the original article

I'm reading the original article about the Fermi-Pasta-Ulam-Tsingou (FPUT) problem and I have some problems about the conclusion. Here the behavior of the system as was reported in the article: $$x_i=(...
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40 views

Invariant density of Harmonic oscillator

In general, dynamical systems described by a pure Hamiltonian can have an infinite number of invariant densities. In fact, each initial state determines exactly a closed path in phase-space and the ...
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71 views

Ensemble average VS spatial average for a cosmological density field

I'm studying statistical properties of a cosmological density field and I have some doubts, in the following quote and pictures you can see what my problem is: A fundamental limitation arises in ...
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114 views

Ergodic Hypothesis in cosmology

I'm studying primordial fluctuations of the Universe from a statistical point of view and I'am aware of the following problem: A fundamental limitation arises in cosmology – because there is only ...
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1answer
46 views

Violation of Virial theorem as indication to ergodicity breaking

Under which conditions the break of virial theorem implies break of ergodicity? I've seen this question, but it is very limited and not sufficient. To constrain the discussion I'm interested in 1D ...
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25 views

Global Balance and Ergodicity of a Markov Chain

I bagan to study Markov chains applied to non equilibrium statistical physics, after ergodicity global balance was presented, here are the definitions I have been given: Ergodicity: A Markov chain is ...
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2answers
92 views

Derivation of 2nd law of Thermodynamics from ergodicity assumption

In Wikipedia it is claimed that: Assumption of the ergodic hypothesis allows proof that certain types of perpetual motion machines of the second kind are impossible. Since perpetual motion ...
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1answer
60 views

Question about ergodicity and the evolution of the probability distribution under Liouville's theorem

According to Liouville's theorem, the probability distribution function $\rho$ evolve in phase space with $$ \frac{d \rho}{d t} = \frac{\partial \rho}{\partial t}+\left\{\rho,H\right\}_{P.B} =0 $$ ...
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188 views

When is the ergodic hypothesis reasonable?

Consider an Hamiltonian system. In which circumstances is it possible to assume that all the states belonging to the hypersurface $H=E_0$ are equally visited? Is it necessary to have a very high ...
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92 views

Are interactions with the environment unnecessary to attain thermodynamic equilibrium?

First of all I apologize for the lenght of this question. I have some basic statistical mechanics facts that I am confused about, and in this subject it is probably better to be precise. When ...
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104 views

One consequence of the ergodic hypothesis?

this is my first question here, and I'm trying to self-learn physics from Kip Thorne's 2017 textbook "Classical Physics". IF I understand the ergodic hypothesis correctly, it is simply the statement ...
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Does the ergodic hypothesis provide a uniquely determined definition of entropy?

One can distinguish between two schools of thought regarding thermodynamic entropy: (a) Thermodynamic entropy is a measure of the "amount of hidden information" in a system. Therefore, the entropy ...
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193 views

What is the relationship between the integrability of a quantum many-body system and thermalization?

If a quantum many-body system is integrable, does it imply the system would always thermalized or many-body localized?
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734 views

Why does the Coarse-grained Entropy increase?

It is a simple fact the entropy in the exact meaning in dynamical system does not change over time if the system is measure-preserving and ergodic. However, it is often said that the coarse-grained ...
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420 views

Two Independent Harmonic Oscillators is NOT Ergodic!

I read on a book that the system of two or more independent harmonic oscillators in classical mechanics is not ergodic. I want to know why a harmonic oscillator is actually ergodic but two or more ...
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304 views

Relation between ergodic hypothesis and fundamental postulate of statistical mechanics?

The fundamental postulate states, roughly, that each microstate of a system consistent with certain known constraints (e.g. on the total energy of the system), is equally likely to occur. The ...
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1answer
112 views

Thermalization in Classical Mechanics: A Paradox

I was wondering to know whether there is any argument shows how a classical system (a system with a Hamiltonian and Poisson bracket) approaches its equilibrium and how the entropy increases. Newton's ...
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277 views

Necessary vs sufficient condition for thermodynamic equilibrium in statistical mechanics

This question came to me after a discussion on another post on the site, which you can find here. I will restrict the following discussion to Hamiltonian systems. Also, I will use the abbreviated ...
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5answers
724 views

Microcanonical ensemble, ergodicity and symmetry breaking

In a brief introduction to statistical mechanics, that is a part of a wider course on Solid State Physics I am taking, the teacher introduced the concept of microcanonical ensemble and the ergodic ...
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344 views

Are there necessary and sufficient conditions for ergodicity?

What are the necessary and sufficient conditions (if any) for ergodicity (or non-ergodicity)? I see for instance that some integrable systems are not ergodic. For instance a linear chain of harmonic ...
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150 views

Questions on ergodicity

The "definition" of an ergodic system is that the average of its states in phase space is the same as its average over time. So I was thinking to myself Is a pendulum an ergodic system? In this case,...
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972 views

Is ergodic hypothesis in contradiction with the notion of equilibrium?

From wikipedia: In physics and thermodynamics, the ergodic hypothesis1 says that, over long periods of time, the time spent by a system in some region of the phase space of microstates with the ...
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Why is the Virial Theorem not a Special Case of the Ergodic Theorem? What is their Relationship?

The virial theorem involves the time-averages of the potential and kinetic energies if the motion of the system is bounded to a finite region of space. An ergodic theorem relates the time and space ...
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Extending the ergodic theorem to non-equilibrium systems

I try to make this as short and concise as possible. For equilibrium systems in statistical mechanics, we have the Liouville's theorem which says that the volume in phase space is conserved when the ...
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4answers
868 views

What is the cause for the inclusion of 'thermal equilibrium' in the statement of Ergodic hypothesis?

This is the fundamental assumption of statistical mechanics: In an isolated system in thermal equilibrium $^1$, all accessible microstates are equally probable. But why does it mention the ...
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186 views

Can binary sequences generated from ergodic maps be chaotic?

Briefly, the way symbols are generated is: Consider a one-dimensional chaotic map $T: [0,1]→[0,1]$ and a time series $\{x_n\}_{n=1}^N$ generated with this map. Define a threshold $A$ and a ...
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369 views

Can an Ergodic dynamical system approach equilibrium?

An ergodic dynamical system $(\Omega,\phi^t,\mu)$ is such that the time average $\bar{f}$ of every function $f\in L_1(\Omega,\mu)$ equal the space average $\langle f \rangle_\mu$, i.e. the system ...
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Ergodic Hypothesis; canonical ensemble

I'm currently studying for an exam in thermodynamics/classic statistical mechanics and 2 things came up which are confusing me. First the Ergodic Hypothesis states that it is equal to take the mean ...
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What would be non-ergodic physics processes? [closed]

As the title says, what would be non-ergodic processes that occur in statistical physics? Many textbooks do not really cover ergodicity really well so I ask this question. I can't suddenly remember ...
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85 views

Which quantum models violate the third law of thermodynamics and have an ergodic ground state?

Which any condensed matter quantum spin models over a finite lattice of size N which violates the third law of thermodynamics with ergodic mixings for the ground state?
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What are the justifying foundations of statistical mechanics without appealing to the ergodic hypothesis?

This question was listed as one of the questions in the proposal (see here), and I didn't know the answer. I don't know the ethics on blatantly stealing such a question, so if it should be deleted or ...