Does the Hamilton-Jacobi equation exist for chaotic systems?

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Discussion Overview

The discussion revolves around the existence of the Hamilton-Jacobi equation in the context of chaotic systems, exploring the implications of Hamiltonian mechanics and the nature of dynamical chaos. Participants examine the conditions under which canonical transformations can be applied and how these relate to the integrability of systems.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Conceptual clarification

Main Points Raised

  • One participant suggests that for a Hamiltonian H(q,p), a canonical transformation must exist for the Hamilton-Jacobi equation to be applicable, but questions arise regarding the implications for chaotic systems lacking sufficient constants of motion.
  • Another participant notes that such transformations may exist locally outside of equilibrium, but the regions where they are defined are not invariant, leading to complications in chaotic dynamics.
  • A further contribution emphasizes the need to clarify what is meant by "dynamical chaos," pointing out that it encompasses various effects, including ergodicity and separatrix splitting, and that real-life examples are complex to identify.
  • One participant expresses frustration and fascination with the topic, referencing literature on perturbation theory and noting that traditional texts in analytical mechanics may not address these issues adequately.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the existence of the Hamilton-Jacobi equation for chaotic systems, with multiple competing views on the nature of canonical transformations and the definition of dynamical chaos remaining unresolved.

Contextual Notes

Participants highlight limitations in the definitions of chaos and the applicability of canonical transformations, as well as the challenges in identifying real-world examples of chaotic behavior.

andresB
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TL;DR
Does the Hamilton-Jacobi equation exist for chaotic systems?
Given a Hamiltonian ##H(\mathbf{q},\mathbf{p})##, in the time-independent Hamilton-Jacobi approach we look for a canonical transformation ##(\mathbf{q},\mathbf{p})\rightarrow(\mathbf{Q},\mathbf{P})## such that the new Hamiltonian is one of the new momenta $$H(\mathbf{q},\mathbf{p})=K(\mathbf{Q},\mathbf{P})=P_{1}=E.$$
If such transformation exists, all the momenta ##\mathbf{P}## are constant of the motion. And, since the transformation is canonical, we will have n constant of the motion in involution, i.e., ##\left\{ P_{i},P_{j}\right\} =0.## But this seems to be the requirement of the Liouville theorem for integrability. Chaotic systems don't have that many constants of motion in involution.
This seems to imply that the Hamilton-Jacobi equations cannot be even written for chaotic systems, so my reasoning has to be wrong somewhere. Where?
 
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andresB said:
TL;DR Summary: Does the Hamilton-Jacobi equation exist for chaotic systems?

Given a Hamiltonian H(q,p), in the time-independent Hamilton-Jacobi approach we look for a canonical transformation (q,p)→(Q,P) such that the new Hamiltonian is one of the new momenta H(q,p)=K(Q,P)=P1=E.
If such transformation exists, all the momenta P are constant o
Such a transformation exists locally outside an equilibrium. The set where this transformation is defined is not invariant. The system comes and goes away from there, while a dynamical chaos appears in invariant sets.
 
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wrobel said:
Such a transformation exists locally outside an equilibrium. The set where this transformation is defined is not invariant. The system comes and goes away from there, while a dynamical chaos appears in invariant sets.

Ok, I suspected the issue had to do with the new momenta not being defined globally.

Yet, I'm not sure I understand your answer. Can you give more details or point to a source with an example?
 
A dynamical chaos is an informal concept which expresses a complex of very different effects. The common feature for all these effects is a complicated behavior of trajectories of a dynamical system. Every time, one should specify what he means by saying “dynamical chaos”. For example, in Hamiltonian systems, ergodicity or separatrix splitting are commonly considered as a dynamical chaos, but there are a lot of other chaotic effects. Real life examples are really hard.
See for example this https://link.springer.com/book/10.1007/978-3-642-03028-4
or start from this https://www.mat.univie.ac.at/~gerald/ftp/book-ode/ode.pdf

UPD

Dissipative systems commonly have attractors. If an attractor is of complicated geometry, say has a fractional dimension, then trajectories which wind up on the attractor replicate its geometry and become complicated. That is another chaotic effect.
 
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Fascinating and frustrating at the same time.

wrobel said:

My doubts started by studyng perturbation theory. In the book Canonical Perturbation Theories Degenerate Systems and Resonance, I find the following
1691594084323.png


The usual books in analytical mechanics don't deal with this.
 

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