Motion equation in quantum mechanics?

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Discussion Overview

The discussion revolves around the motion equation in quantum mechanics, specifically the equation dA/dt=[H,A], where H is the Hamiltonian and A is an operator representing an observable. Participants explore the implications of this equation, its derivation, and its relationship to classical mechanics and various quantum equations.

Discussion Character

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

Main Points Raised

  • One participant requests clarification on why the motion equation is dA/dt=[H,A], linking it to the Lie derivative in the context of a manifold.
  • Another participant argues that this equation describes the time evolution of an observable rather than being a traditional equation of motion, suggesting a study of mathematical foundations in quantum mechanics.
  • A third participant asserts that the derivation of this equation is straightforward and commonly found in quantum mechanics textbooks, questioning the original poster's understanding.
  • Some participants express interest in deriving various quantum equations (Schrödinger, Klein-Gordon, Dirac) from the motion equation, proposing that time dynamics relate to energy and translation symmetry.
  • One participant emphasizes that dA/dt=[H,A] is valid in different quantum contexts when transitioning between the Schrödinger and Heisenberg pictures.
  • Another participant advises gaining more practice in standard quantum mechanics before pursuing personal conjectures about the structure of the material.

Areas of Agreement / Disagreement

Participants express differing views on the interpretation and implications of the motion equation, with no consensus reached on its foundational aspects or its derivation from classical mechanics.

Contextual Notes

Some discussions reference the need for a deeper understanding of mathematical concepts in quantum mechanics, and there are indications of varying levels of familiarity with the subject matter among participants.

ndung200790
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Please teach me this:
Why the motion equation must be:dA/dt=[H,A] where H-Hamintonian,A-operator of any observation,because with a local flow t(time) of vector X in a manifold we can write the Lie derivative:dA/dt=[X,A].(Where we consider time t as one-parameter group and as local flow of some operator X)
Thank you very much in advanced.
 
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It is not equation of motion it states time evolution of a state under operator A. After studying it, it comes out to be analogus(or same) to classical equations of motion (Ehernfest theorem).
You need to thoroughly study foundations of mathematical aspects applied to quantum mechanics. von Neumann's work might help.
 
ndung200790 said:
Why the motion equation must be:dA/dt=[H,A] where H-Hamintonian,A-operator of any observation

An essentially trivial derivation is in any decent textbook on quantum mechanics.
What is it that you don't get?
 
I would like to derive all equations:Schrödinger,Klein-Gordon,Dirac equation from this"motion" equation.It seem to me that dynamics of time is energy,the translation symmetry in time relate with Hamintonian.So if time t is local flow of vector H,then following Lie derivative we have the motion equation dA/dt=[H,A].
 
ndung200790 said:
I would like to derive all equations:Schrödinger,Klein-Gordon,Dirac equation from this"motion" equation.It seem to me that dynamics of time is energy,the translation symmetry in time relate with Hamintonian.So if time t is local flow of vector H,then following Lie derivative we have the motion equation dA/dt=[H,A].

For these equation, the relevant dynamics is i hbar psidot = H psi.
H = p^2/2m +V(x) gives Schroedinger,
H=sqrt(p^2+m^2) gives the physical (positive energy) part of Klein-Gordon,
H=gamma_0(gamma dot p + m) gives Dirac (with both physical and unphysical part; the physical part is obtained by multiplying with a projector to E>=0).

dA/dt=[H,A] holds in each of these cases for arbitrary A if one changes from the Schroedinger picture to the Heisenberg picture according to the standard recipe.

I'd like to suggest that you get more practice in standard QM before you explore your own conjectures about how to structure the standard material.
 
Thank you very much for your kind helping and kind advice
 

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