Question about the hermiticity of the momentum operator

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Discussion Overview

The discussion centers on the hermiticity of the momentum operator in quantum mechanics, specifically whether it is dependent on the normalization of the wave function. Participants explore implications for box normalization and the mathematical foundations of operator theory.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions if the momentum operator \(\frac{\hbar}{i}\frac{\partial}{\partial x}\) is Hermitian only for normalized wave functions, particularly in the context of box normalization for free particles.
  • Another participant references an external source, suggesting that the hermiticity can be demonstrated using any wave function, implying independence from normalization.
  • A participant asserts that the hermiticity of the momentum operator does not depend on wave function normalization, citing a university question that prompted their inquiry.
  • Another response emphasizes that the equations referenced do not require normalization, arguing that constants do not affect the operator's action on the wave function.
  • A later reply reiterates the initial question about normalization and introduces the idea that the analysis of the momentum operator's hermiticity depends on its domain, suggesting that the couple \((A,D(A))\) is crucial for understanding the operator's spectrum.
  • This participant also argues that normalization does not significantly impact the analysis, providing an example of a function scaled by a constant.

Areas of Agreement / Disagreement

Participants express differing views on the relationship between the hermiticity of the momentum operator and the normalization of wave functions. No consensus is reached, and multiple competing perspectives remain.

Contextual Notes

Some participants highlight the importance of the operator's domain in analyzing its properties, indicating that the discussion may involve complex mathematical considerations that are not fully resolved.

neelakash
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Is momentum operator [tex]\frac{\hbar}{i}\frac{\partial}{\partial\ x }[/tex] is Hermitian only for a normalized wave function?What is the case for the box normalization as done for a free particle?

Actually when we prove the Hermiticity of the momentum operator, we do simple by parts integartion and use the scalar products.I never bothered about whether the wave function is normalized or not.

Can anyone suggest anything?
 
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So, hermiticity of the momentum operator is independent of whether the wave function is normalized or not----right?

I faced this question in university question book and got astonished.They asked to prove this and also asked what would it be if the wave function is box-normalized.
 
It should not matter.

Look at eq (13) and below, never is it stated that the wave function is normalized. Normalized means that <psi |psi > = 1, so it is just some multiplicatible constants that is added. And constants never affects what your operator does with the wave function.

A is an operator, b is constant:

[A,b] = 0, they commute. etc.
 
neelakash said:
Is momentum operator [tex]\frac{\hbar}{i}\frac{\partial}{\partial\ x }[/tex] is Hermitian only for a normalized wave function?What is the case for the box normalization as done for a free particle?

Actually when we prove the Hermiticity of the momentum operator, we do simple by parts integartion and use the scalar products.I never bothered about whether the wave function is normalized or not.

Can anyone suggest anything?

Actually the analysis on P must be carry out in the differnet configurations scheme. I mean that its hermitianity depend upon its domain D(P).
In fact mathematically speaking what is really important is the couple (A,D(A))
to analize all the spectrum of an operator. In some circumstances can happen that P does posses residue spectrum.
Obviously they have no physical meaning.

Normalization on a function doesn't mean anything. f(x)=100g(x) its ok either.
regards
marco
 

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