Particle antiparticle creation

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Discussion Overview

The discussion revolves around the creation of particle-antiparticle pairs, specifically addressing whether these pairs are created at the same position in space and the implications for energy conservation. The conversation touches on quantum mechanics, the nature of fermions, and the concept of position in particle physics.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Technical explanation

Main Points Raised

  • One participant questions whether particle-antiparticle pairs are created at the same position, suggesting that if they were not, it could lead to issues with energy conservation.
  • Another participant argues that the particles are distinguishable, implying they can exist at different positions.
  • A different perspective emphasizes that the concept of position is problematic in quantum mechanics until a measurement localizes the particles, using the example of a gamma photon creating an electron-positron pair to illustrate energy conservation in interactions.
  • Another participant reiterates the initial question about position and adds that fermions typically cannot occupy the same position due to differing quantum numbers, while also noting that the concept of position becomes less meaningful at very short distances.

Areas of Agreement / Disagreement

Participants express differing views on the position of particle-antiparticle pairs at creation, with no consensus reached on whether they can occupy the same position or the implications for energy conservation.

Contextual Notes

The discussion highlights the limitations of classical intuitions about position in the context of quantum mechanics and the complexities involved in defining particle interactions at very short distances.

Michel Raskin
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When a particle and antiparticle pair is created are they created on the same position?
If they weren't in the same position it would lead a problem on energy conservation, but they are fermions so they shouldn't be on the same position in space.
 
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No, they are distinguishable so that is not the the case.
 
Michel Raskin said:
If they weren't in the same position it would lead a problem on energy conservation
You may thinking in classical terms here.

Quantum mechanically, the "position" of a particle is a rather dubious concept unless and until you've interacted with it in a way that localizes it (informally, "measured its position"). So consider an example of an interaction that produces a pair of fermions: an energetic gamma photon interacts with a heavy nucleus and produces a positron/electron pair: all energy conservation (and similarly for momentum) requires is that when the dust settles the sum of the energies of the nucleus, electron, and positron coming out is equal to the energy of the photon and the nucleus going in. The interaction itself should be thought of as a black box: some particles went in, some other particles came out, the energy coming out is equal to energy going in.
 
Michel Raskin said:
When a particle and antiparticle pair is created are they created on the same position?
If they weren't in the same position it would lead a problem on energy conservation, but they are fermions so they shouldn't be on the same position in space.
Usually a particle and an antiparticle cannot have the same quantum number, and hence can occupy the same position.
When two photons (which are their own antiparticles) are created one cannot talk about their position and the question is moot.

In any case, the particle concept becomes meaningless at distances that are too short, and ''the same place'' becomes a nonrelativistic fiction.
 
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Thank you A.Neumaier Nugatory andJilang for your answers they were really helpful
 

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