Very basic questions about operators in QM

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    Operators Qm
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Discussion Overview

The discussion revolves around the understanding and application of operators in quantum mechanics (QM), particularly in relation to wavefunctions, probability densities, and momentum measurements. Participants explore theoretical concepts, mathematical formulations, and implications of these operators in various scenarios.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant describes the wavefunction of a system with a proton and electron as a function of time and spatial coordinates, emphasizing the role of generalized coordinates.
  • Another participant notes that the operator applied to a wavefunction yields a value that the operator measures, but this holds true only if the wavefunction is an eigenfunction of the operator.
  • Concerns are raised about how to find momentum information if the wavefunction is not an eigenfunction, questioning the implications of the Heisenberg uncertainty principle.
  • Participants discuss the nature of probability densities, stating that they should be integrated over all possible coordinates, and that the probability of finding a particle at a specific coordinate is zero due to the infinite possibilities.
  • There is a discussion about the expectation value of momentum and how it can be calculated using integrals of the wavefunction, with questions about whether these integrals include time as an argument.
  • One participant mentions the transformation of the coordinate wavefunction to a momentum wavefunction via Fourier transform, highlighting the convenience of this approach for understanding superposition of momentum eigenstates.
  • Another participant raises the possibility that in some systems, the expectation value of momentum may depend on the coordinates of the particle, prompting further inquiry into how to derive such probability densities.

Areas of Agreement / Disagreement

Participants express differing views on the implications of operators acting on wavefunctions, particularly regarding eigenfunctions and the nature of probability densities. There is no consensus on how to approach certain calculations or the interpretations of results, indicating ongoing debate and exploration of the topic.

Contextual Notes

Some participants highlight limitations in understanding related to the dependence on definitions and the need for integration over multiple variables, while others question the treatment of time in calculations.

Who May Find This Useful

This discussion may be useful for students and researchers interested in quantum mechanics, particularly those exploring the mathematical foundations of operators and wavefunctions.

  • #31
vanhees71 said:
My recommendation as the introductory QM textbook is

J. J. Sakurai and S. Tuan, Modern Quantum Mechanics,
Addison Wesley (1993).
I took "David J. Griffith, Introduction to Quantum Mechanics". Also tried to read "J. J. Sakurai and S. Tuan, Modern Quantum Mechanics", but "David J. Griffith, Introduction to Quantum Mechanics" seems more easily understandable.
 
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  • #32
PeroK said:
Who needs a textbook when you have @vanhees71 !
True, but sometimes having @vanhees71, makes you realize you should have read your textbook.
 
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