If you shoot an electron at a wall....

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    Electron Wall
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SUMMARY

This discussion centers on the behavior of electrons fired from a gun towards a wall, specifically addressing the implications of momentum and position uncertainty. It is established that if the momentum of an electron is well-defined in the x-direction, the transverse momenta (p_y and p_z) lead to an undefined position in the y-z plane, resulting in a probability distribution of impact points on the wall. The conversation emphasizes that in practical scenarios, electron guns cannot achieve perfectly defined momentum due to inherent uncertainties, as described by quantum mechanics. The conclusion drawn is that while idealized models suggest infinite uncertainty in position with precise momentum, real-world applications yield a narrow distribution of impacts based on the gun's design.

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  • #31
This contradicts the best theory we have about particles, which is QT, according to which there are no determined trajectories in the sense of classical physics.
 
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  • #32
vanhees71 said:
This contradicts the best theory we have about particles, which is QT, according to which there are no determined trajectories in the sense of classical physics.

Does this imply that a trajectory could reverse direction and take a different path before reaching its final destination? If so, is this one way to explain interference patterns?
 
  • #33
mike1000 said:
It cannot be a fact

Well, then all QM books and physicists lie to the world.
 
  • #34
mike1000 said:
Does this imply that a trajectory could reverse direction and take a different path before reaching its final destination? If so, is this one way to explain interference patterns?
There are no trajectories, and QT explains interference patterns (of probability distributions) as observed.
 
  • #35
weirdoguy said:
Well, then all QM books and physicists lie to the world.

Well, unfortuantely, that can be true. The wave-particle duality comes to mind.
 
  • #36
mike1000 said:
The wave-particle duality comes to mind.

In that sense, that is true:biggrin: That is why one should learn science from textbooks, not pop-sci books.
 
  • #37
weirdoguy said:
In that sense, that is true:biggrin: That is why one should learn science from textbooks, not pop-sci books.

Textbooks have their own unique set of problems.(no pun intended).
 
  • #38
Maybe, but none of them textbooks will tell you that particle takes any trajectory. That is not intuitive, but you really have to gice up most of your classical thinking.

Btw, am I the only one who didn't have any problem in giving up my classical intuitions? I was always like "oh, ok", and most of my collegues got into looong discussions during QM lectures...
 
  • #39
mike1000 said:
As far as I know, interference has never been observed for a single particle. It always takes a system of at least two or more particles to observe interference patterns.

This is obviously false, since as DrClaude pointed out, the double slit experiment can be run with only one particle at a time, and you still get an interference pattern.

mike1000 said:
I think what you are implying is that QM really cannot say anything about a single particle.

This is obviously false as well. QM does not say a single particle has a definite path, but that's a long way from not saying anything at all about a single particle.

mike1000 said:
This suggests to me that the single particle does indeed follow some path.

Garbage in, garbage out.

mike1000 said:
If you say that is false, please provide a link.

Any QM textbook will do.

mike1000 said:
Textbooks have their own unique set of problems

You can always go directly to the original peer-reviewed papers if you have questions about what a textbook is telling you. What you can't do is just decide not to believe the textbooks because "they have problems".
 
  • #40
The OP's question has been more than sufficiently addressed. Thread closed.
 
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