Poisson brackets commutator vs. quantum commtation relation

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Discussion Overview

The discussion centers on the relationship between Poisson brackets in classical mechanics and commutation relations in quantum mechanics. Participants explore the pedagogical transfer between these two frameworks, examining the differences in their formulations and implications for understanding dynamics in both classical and quantum contexts.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the pedagogical transfer from Poisson brackets to quantum mechanics, noting the differences in their mathematical formulations, such as partial derivatives in classical mechanics versus matrix multiplication in quantum mechanics.
  • Another participant suggests that there is no straightforward pedagogical transfer, referencing the axiomatic Dirac quantization scheme and its limitations as shown by Groenewold and van Hove, while also mentioning contributions from Weyl, Wigner, and Moyal related to deformation quantization.
  • A later reply proposes that one can express the classical dynamical Lie algebra in terms of Poisson brackets and re-express it using quantum commutators, suggesting that ambiguities can sometimes be resolved by symmetrizing products of operators.
  • It is noted that in the Schrödinger picture of quantum mechanics, commutators can also involve differential operators, drawing a parallel to classical Poisson brackets.

Areas of Agreement / Disagreement

Participants express differing views on the nature of the transfer between Poisson brackets and quantum commutation relations. Some argue for a lack of a clear pedagogical transfer, while others suggest methods for relating the two concepts, indicating that the discussion remains unresolved.

Contextual Notes

The discussion highlights the complexities and limitations of transferring concepts between classical and quantum mechanics, including the dependence on specific mathematical formulations and the potential need for deformation of the Lie algebra in quantum contexts.

exponent137
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If we have Poisson bracket for two dynamical variables u and v, we can write as it is known ...

This is for classical mechanics. If we write commutation relation, for instance, for location and momentum, we obtain Heisenberg uncertainty relation.

But, what is a pedagogical transfer from Poisson bracket to quantum mechanics. Because formulae are very different, Classical one has partial derivations, quantum one has only multiplication of matrices.

What is transfer to quantum mechanics, or in the opposite direction?

One example of this question:
http://physics.stackexchange.com/qu...tion-between-poisson-brackets-and-commutators
But; i think, that it can be answered more clearly.
 
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exponent137 said:
If we have Poisson bracket for two dynamical variables u and v, we can write as it is known ...

This is for classical mechanics. If we write commutation relation, for instance, for location and momentum, we obtain Heisenberg uncertainty relation.

But, what is a pedagogical transfer from Poisson bracket to quantum mechanics. Because formulae are very different, Classical one has partial derivations, quantum one has only multiplication of matrices.

What is transfer to quantum mechanics, or in the opposite direction?
[...]

There's no pedagogical transfer. It's only the axiomatic Dirac quantization (PB/DB --> 1/ihbar x commutator) scheme (shown by Groenewold and van Hove to be severely limited) which is standard textbook material then the further contributions of Weyl, Wigner and Moyal which are only presented in advanced texts (they form the basis for the so-called deformation quantization). The link you gave contains more detailed answers. In the Schrödinger picture of QM, commutators also contain differential operators, quite similarly to the classical PB.
 
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One can go a surprisingly long way by simply taking the (classical) dynamical Lie algebra (expressed in terms of Poisson brackets), and re-expressing it by quantum commutators (possibly inserting factors of ##\hbar## to make the dimensions correct). The ambiguities Dex mentioned above, where quadratic and higher products of operators are involved, can often be resolved in practical cases by to simply symmetrizing them. (Indeed this is necessary to obtain a satisfactory Hermitian quantum operator corresponding to the LRL vector in the H-atom problem.) In other cases, one must deform the Lie algebra to obtain a satisfactory quantum version.
 
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