Momentum eigenfunctions in an infinite well

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Discussion Overview

The discussion revolves around the nature of momentum eigenfunctions in the context of a particle confined in an infinite potential well. Participants explore the implications of the Schrödinger equation solutions, the relationship between momentum and energy eigenstates, and the mathematical properties of the momentum operator.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants note that the wavefunctions for an infinite well, sin(nπx/L), are not eigenfunctions of the momentum operator, leading to questions about the measurability of momentum.
  • Others argue that the wavefunctions represent a superposition of various momentum eigenstates, suggesting that momentum can still be observed through probability distributions.
  • It is mentioned that the momentum operator is not self-adjoint in the context of the infinite well, which raises questions about the existence of a momentum observable.
  • Some participants propose examining finite potential wells as a way to understand the behavior of momentum in the limit as the potential approaches infinity.
  • There is a discussion about the implications of momentum eigenstates in free space versus those in a confined system, with some asserting that momentum eigenstates should correspond to energy eigenstates.
  • Participants explore the concept of infinite momentum in quantum mechanics and its compatibility with special relativity, leading to a debate about the limits of momentum in both frameworks.
  • Some participants express confusion about the relationship between velocity, momentum, and their limits in classical and relativistic mechanics.

Areas of Agreement / Disagreement

The discussion contains multiple competing views regarding the nature of momentum in quantum mechanics, particularly in relation to the infinite well scenario. There is no consensus on whether momentum can be measured or the implications of infinite momentum in quantum mechanics versus special relativity.

Contextual Notes

Participants highlight the mathematical complexities involved, such as the self-adjointness of operators and the implications of boundary conditions in quantum systems. There are unresolved questions about the definitions and interpretations of momentum in different physical contexts.

  • #31
dyn said:
Are you telling me that in QM , CM and SR there is no limit on how big momentum can be ?
Yes, that's what they have told you.

dyn said:
Surely v not being able to reach c places a limit on momentum in SR
Instead of waving your hands, do the math. If you have questions about the math, you can start a new thread in the appropriate forum. This thread is closed as the question you asked in your OP has been answered.
 
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  • #32
dyn said:
Are you telling me that in QM , CM and SR there is no limit on how big momentum can be ? Surely v not being able to reach c places a limit on momentum in SR
It does not.
The momentum of a particle moving at speed ##v## is ##p=mv/\sqrt{1-(v^2/c^2)}##.

That value can be made as large as we please by choosing a value of ##v## sufficiently close to but still less than ##c##.
 
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