Klein-Gordon Operator: Creating Particles at Position x

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Discussion Overview

The discussion centers around the interpretation of the Klein-Gordon operator in quantum field theory, specifically regarding the creation of particles at a specific position in space and the implications of the uncertainty principle on this concept. Participants explore the physical meaning of creating a localized particle and the constraints imposed by relativistic principles.

Discussion Character

  • Exploratory, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant questions the physical meaning of creating a particle at position x, noting the implications of the uncertainty principle which suggests that a particle cannot be perfectly localized.
  • Another participant asserts that it is possible to localize a particle, stating that the uncertainty principle only affects knowledge of the particle's momentum, not its position.
  • A further reply challenges the idea of perfect localization by arguing that knowing a particle's position with zero error implies infinite uncertainty in momentum, which raises concerns about the particle's ability to travel faster than light.
  • Another participant responds by clarifying that while momentum can be very large for a relativistic particle, its velocity remains less than the speed of light, referencing the relativistic momentum formula.

Areas of Agreement / Disagreement

Participants express differing views on the implications of the uncertainty principle for localized particles, with some arguing for the feasibility of localization and others highlighting the contradictions that arise from it. The discussion remains unresolved regarding the interpretation of the Klein-Gordon operator and the physical implications of particle localization.

Contextual Notes

Participants reference the uncertainty principle and relativistic momentum, but the discussion does not resolve the mathematical implications or the assumptions underlying the definitions of localization and momentum.

Silviu
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Hello! I read that the Klein-Gordon field can be viewed as an operator that in position space, when acted upon vacuum at position x creates a particle at position x: ##\phi(x) |0 \rangle \propto |x \rangle##. It make sense intuitively and the mathematical derivation is fine too, but I was wondering what does it physically means, as according to uncertainty principle, you can't have a localized particle. So what exactly does it mean to create a particle at position x?
 
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You can localise a particle as much as you like. Uncertainity principle only tells you that your knowledge about the momentum of the particle will decrease the more you localise it.
 
DrDu said:
You can localise a particle as much as you like. Uncertainity principle only tells you that your knowledge about the momentum of the particle will decrease the more you localise it.
I know this. But based on this definition of Klein-Gordon operator, you know the position of particle with 0 error, which means that you should know the momentum with infinite error, which is, the particle can have any momentum from 0 to infinity. But this is not possible, as the particle can't travel faster than light and you know the mass of the particle as you know what particle you create, and the particle is not virtual, so its mass is known (of course with a certain uncertainty, but again a finite one). Is this logic wrong?
 
The momentum of a relativistic particle can get as large as you like, yet it's velocity is always smaller than c.
Namely ## p=\frac{mv}{\sqrt{1-v^2/c^2}}##.
 
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