Where does Hamilton's Principle come from?

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Discussion Overview

The discussion revolves around the origins and implications of Hamilton's Principle in physics, particularly its relationship to the formulation of action and the existence of a Lagrangian for a system. Participants explore theoretical foundations and seek to understand the reasoning behind the principle's application across various physical theories.

Discussion Character

  • Exploratory
  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant questions the ability to always find a Lagrangian for a system and seeks to understand why the action is stationary.
  • Another participant expresses familiarity with classical mechanics, quantum field theory, and electromagnetism but struggles to grasp the foundational reasoning behind the action principle.
  • A link to a related discussion is provided as a potential starting point for further exploration of why the action integral should be stationary.
  • One participant proposes that the deepest origin of Hamiltonian formalism is linked to the symmetry associated with the principle of relativity, referencing the Poincare group and its representation in quantum mechanics.
  • This participant suggests that the generators of the Poincare group lead to the relativistic Hamiltonian dynamics as discussed by Wigner and Dirac.

Areas of Agreement / Disagreement

Participants express varying levels of understanding and perspectives on the origins of Hamilton's Principle, with no consensus reached on the foundational reasoning or the necessity of a Lagrangian in all systems.

Contextual Notes

Some assumptions regarding the applicability of Hamilton's Principle and the existence of a Lagrangian for all systems remain unaddressed, and the discussion does not resolve the underlying mathematical or conceptual questions raised.

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TL;DR
Hamiltons Principle
Hamiltons Principle and the physcial entity action are the terms in which modern physics is formulated. How do you know that you can always find a Lagrangian for a System which is then used for Hamitlons Principle and the formulation of Action? Why is the action stationary?
 
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What have you found so far on this question?
 
Thanks! Pretty much nothing, I know classical mechanics, quantum field theory, electromagnetism can formulated this way by I don't see why (I understand the math, I don't see where it comes from).
 
In my opinion, the deepest origin of the Hamiltonian formalism is the symmetry associated with the principle of relativity.

As all inertial observers are equivalent, there has to be a Lie group of transformations connecting different observers. In relativistic physics this is the Poincare group. According to Wigner, transformations from this group are represented by unitary operators in the Hilbert space of any isolated physical system. Generators of this representation form a 10-dimensional Lie algebra of Hermitian operators. The generator of time translations is the Hamiltonian.

This path will lead you to the relativistic Hamiltonian dynamics of Wigner and Dirac.

Eugene.
 

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