Can Quantum Mechanics Have 'Elegant' Trajectories in Hilbert Space?

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Discussion Overview

The discussion explores the concept of representing time evolution in quantum mechanics through trajectories in Hilbert space, particularly in relation to the quantum harmonic oscillator. Participants examine whether such representations can be considered 'elegant' and how they compare to classical mechanics.

Discussion Character

  • Exploratory
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • One participant notes that classical mechanics allows for elegant state-space trajectories, such as ellipses for the harmonic oscillator, and questions how this translates to quantum mechanics.
  • Another participant suggests that for a spin 1/2 system, the trajectory in Hilbert space is represented by the rotation of a unit vector, which they describe as elegant.
  • A different viewpoint introduces the idea of trajectories in projective Hilbert space and discusses their Hamiltonian dynamics and Poisson brackets.
  • One participant reiterates the initial question about the representation of quantum harmonic oscillator trajectories in Hilbert space, expressing skepticism about the elegance of such representations.

Areas of Agreement / Disagreement

Participants express differing views on the nature of trajectories in Hilbert space, with some finding elegance in certain representations while others remain skeptical about their applicability to quantum systems. The discussion does not reach a consensus.

Contextual Notes

Some assumptions about the nature of trajectories and their representations in quantum mechanics remain unexamined, and there are unresolved questions regarding the complexity of the mathematical frameworks involved.

Logic Cloud
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State-space trajectories in classical mechanics can be used to nicely represent the time evolution of a given system. In the case of the harmonic oscillator, for instance, we get ellipses. How does this situation carry over to quantum mechanics? Can the time evolution of, say, the quantum harmonic oscillator be represented by some 'trajectory' in Hilbert space? The obtained wave functions do not seem to lend themselves for such 'elegant' representations.
 
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If you choose a unit vector, say for spin 1/2, the trajectory in Hilbert space is just rotation of a unit vector. It's very elegant.
 
There is also the trajectories in the projective hilbert space and their hamiltonian dynamics and poisson brackets.
 
Logic Cloud said:
State-space trajectories in classical mechanics can be used to nicely represent the time evolution of a given system. In the case of the harmonic oscillator, for instance, we get ellipses. How does this situation carry over to quantum mechanics? Can the time evolution of, say, the quantum harmonic oscillator be represented by some 'trajectory' in Hilbert space? The obtained wave functions do not seem to lend themselves for such 'elegant' representations.

If that sort of thing interests you here is the book to get:
https://www.amazon.com/dp/0387493859/?tag=pfamazon01-20

Be warned - its what mathematicians call decidedly non-trivial - meaning it's hard.

Said with a German accent - We have ways and means of stopping you asking certain questions :-p:-p:-p:-p:-p:-p:-p:-p:-p

Thanks
Bill
 
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