Why Can't Free-Particle Wave Functions Be Normalized Over Their Entire Range?

In summary, the conversation discusses the impossibility of normalizing free-particle wave functions over the entire range of motion, as well as the use of arbitrary wave packets constructed from plane waves and the difference between being a free particle and being an eigenstate of the free Hamiltonian. The conversation also touches on the issue of wave functions being zero at infinity and whether this is observable in the cases of free particles and particles in a square potential barrier.
  • #1
alimehrani
6
0
why it is not possible to normalize the free-particle wawe functions over the whole range of motion of the particles?
 
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  • #2
The whole range of motion is from minus infinity to plus infinity (no restricted range, otherwise the particle would not be free).
The free particle is described by a plane wave u(x) = exp(ikx).
The normalization means to integrate |u(x)|² = 1; the integral will certainly divergy
 
  • #3
One should add that exp(ikx) is obviously not the only possible form for the wavefunction of a free particle. Rather the wavefunction may have almost any form, especially normalizable.
However, there are no normalizable wavefunctions which are eigenfunctions of the Hamiltonian.
 
  • #4
Let me see if I understood you correctly.

You propose to use (nearly) arbitrary wave packets constructed from plane waves (Fourier modes) and let these wave packets evolve in time using the free Hamiltonian. That means you construct normalizable wave functions, but they are no longer eigenstates of the free Hamiltonian.

Yes, of course you are right. I assumed that "free particle" means "eigenstate of the free Hamiltonian H", but that need not be the case.

@alimehrani: what was your intention?
 
  • #5
tom.stoer said:
Let me see if I understood you correctly.

You propose to use (nearly) arbitrary wave packets constructed from plane waves (Fourier modes) and let these wave packets evolve in time using the free Hamiltonian. That means you construct normalizable wave functions, but they are no longer eigenstates of the free Hamiltonian.

Yes, of course you are right. I assumed that "free particle" means "eigenstate of the free Hamiltonian H", but that need not be the case.

@alimehrani: what was your intention?

yes
yes
exactly
thank you very much
i think you are very good teacher
 
  • #6
thank tom.stoer and others
you greatly help me
 
  • #7
this problem exist also about a particle in a square potential barrier!?
what is the justification here?

another question:
we assume that wave function is zero at infinity while we couldn't observe such a thing in the cases of free particle and particle in a square potential barrier?
 

Related to Why Can't Free-Particle Wave Functions Be Normalized Over Their Entire Range?

1. What is a free particle?

A free particle is a theoretical concept in physics that refers to a particle that is not influenced by any external forces or interactions. In other words, it moves freely in space without any constraints or obstacles.

2. What is normalization in the context of free particles?

Normalization is a mathematical procedure used to ensure that the total probability of finding a free particle at any point in space is equal to 1. This allows for the calculation of the probability of finding the particle within a specific region of space.

3. Why is normalization important in quantum mechanics?

Normalization is important in quantum mechanics because it ensures that the wave function, which describes the behavior of a free particle, is physically meaningful. It also allows for the calculation of measurable quantities, such as the probability of finding the particle in a specific location.

4. How is free particle normalization calculated?

The normalization of a free particle is calculated by integrating the square of the wave function over all space and equating it to 1. This involves using mathematical techniques, such as the Fourier transform, to solve the Schrödinger equation and obtain the wave function.

5. What are the units of free particle normalization?

The units of free particle normalization depend on the specific system being studied. In general, it has the units of inverse length squared, such as meters-2 or angstroms-2. This is because the wave function, which is squared in the normalization integral, has units of inverse length.

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