- #31
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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.
If you shoot an electron at a wall....
Click For Summary
Discussion Overview
The discussion revolves around the behavior of an electron fired at a wall from a hypothetical electron gun. Participants explore the implications of momentum and position uncertainties in quantum mechanics, questioning where the electron will hit the wall and the effects of the gun's design on this outcome. The scope includes theoretical considerations of quantum mechanics and the practical aspects of electron guns.
Discussion Character
- Exploratory
- Technical explanation
- Debate/contested
Main Points Raised
- Some participants propose that if the electron has well-defined momenta in the x, y, and z directions, it could hit anywhere on the wall due to the wave function's nature.
- Others argue that achieving well-defined momenta in all three directions is an idealization and not practically realizable, as it would imply infinite uncertainty in position.
- A later reply questions the construction of the gun, suggesting that the state of the electron as it exits the gun must be specified to understand its behavior upon hitting the wall.
- Some participants assert that a precise momentum would determine the impact point on the wall, while others counter that this would require a precise starting position, which is not possible in practice.
- There is a discussion about the implications of a Gaussian distribution of momentum and how it relates to the distribution of hits on the wall.
- One participant highlights that the gun's design, particularly its barrel length, affects the momentum distribution of the emitted electrons.
Areas of Agreement / Disagreement
Participants express multiple competing views regarding the relationship between momentum, position, and the design of the electron gun. The discussion remains unresolved, with no consensus on the implications of idealized versus practical scenarios.
Contextual Notes
Limitations include assumptions about the electron gun's design, the idealization of momentum and position, and the practical realizability of these conditions. The discussion touches on the complexities of quantum mechanics without reaching definitive conclusions.
- #32
mike1000
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vanhees71 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?
- #33
weirdoguy
- 1,339
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mike1000 said:
Well, then all QM books and physicists lie to the world.
- #34
- 24,488
- 15,057
There are no trajectories, and QT explains interference patterns (of probability distributions) as observed.mike1000 said:
- #35
mike1000
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weirdoguy said:
Well, unfortuantely, that can be true. The wave-particle duality comes to mind.
- #36
weirdoguy
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mike1000 said:
In that sense, that is true
That is why one should learn science from textbooks, not pop-sci books.- #37
mike1000
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weirdoguy said:In that sense, that is true
Textbooks have their own unique set of problems.(no pun intended).
- #38
weirdoguy
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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...
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
PeterDonis
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mike1000 said:
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:
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:
Garbage in, garbage out.
mike1000 said:
Any QM textbook will do.
mike1000 said:
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
PeterDonis
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The OP's question has been more than sufficiently addressed. Thread closed.
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