Zero momentum distribution and consequences on uncertainty principle

Click For Summary

Discussion Overview

The discussion revolves around the implications of a zero momentum distribution in the context of the uncertainty principle in quantum mechanics. Participants explore the conditions under which momentum and position uncertainties can be zero, and the theoretical consequences of such scenarios.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions the possibility of having a momentum distribution (sigma p) equal to zero, suggesting that this leads to contradictions with the uncertainty principle.
  • Another participant asserts that as momentum measurement accuracy increases (sigma p approaches zero), position uncertainty (sigma x) must approach infinity, reinforcing the uncertainty principle.
  • A claim is made that a zero expectation value for momentum does not imply zero uncertainty, indicating a distinction between expectation values and uncertainties.
  • It is noted that if both the expectation value for momentum and the expectation value for the square of momentum are zero, the uncertainty could also be zero, but this situation is argued to be unattainable in solutions to the Schrödinger equation.
  • A new learner expresses confusion about the implications of a wave function being a constant and questions whether this could lead to zero fluctuation in momentum.
  • Another participant responds to the new learner, stating that a constant wave function would not satisfy the Schrödinger equation, implying that such a scenario is not physically realizable.

Areas of Agreement / Disagreement

Participants do not reach a consensus on the implications of a zero momentum distribution. There are competing views on the feasibility of such conditions and their compatibility with quantum mechanics principles.

Contextual Notes

Participants highlight limitations in understanding the implications of zero momentum distribution and its relation to the uncertainty principle, as well as the conditions under which wave functions can exist in quantum mechanics.

hoju
Messages
3
Reaction score
0
What happens if the momentum distribution (sigma p) equals zero. Say the expectation value for the momentum (<p>) and <p^2> are zero. Then you will get 0>or=h/4Pi. How can this be possible? Or vice versa, what if sigma x equals zero?
 
Last edited:
Physics news on Phys.org
That's not possible, indeed.
So the more accurately one measures the momentum, the less accurately one knows the position. When \sigma p \to 0, therefore, \sigma x \to \infty and vice versa.
You can interpret this as saying that not only is it impossible to measure position or momentum with infinite precision, but even that the theory tells you so!
Or you can interpret this as saying that at some very small scale \sigma x &lt; L quantum mechanics breaks down and the uncertainty relation cannot be applied anymore anyway.
 
A zero expectation value doesn't imply a zero uncertainty.
 
No but if in addition <p^2> = 0 then the uncertainty \sqrt{\langle p \rangle^2 - \langle p^2 \rangle} is zero.
 
CompuChip said:
No but if in addition <p^2> = 0 .

It never is for a solution to the Schrödinger equation.
 
I appologize for my ignorance. I am a new learner as well, and just trying to figure out the meaning of quantum mechanics rather than just doing some algebra. However, what if a wave function is just a real constant? Will not we get a zero fluctuation in momentum?
 
caduceus said:
However, what if a wave function is just a real constant?

I believe that's impossible, a real wavefunction couldn't satisfy the Schrödinger equation.
 

Similar threads

  • · Replies 7 ·
Replies
7
Views
856
  • · Replies 32 ·
2
Replies
32
Views
4K
  • · Replies 20 ·
Replies
20
Views
2K
  • · Replies 12 ·
Replies
12
Views
2K
  • · Replies 17 ·
Replies
17
Views
3K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 2 ·
Replies
2
Views
2K
  • · Replies 10 ·
Replies
10
Views
3K
  • · Replies 8 ·
Replies
8
Views
2K